PREGNATED FIBROUS MATERIALS

m

REPORT f » OF A STUDY GROUP, BANGKOK, 20-24 N O V E M B E R 1967

IMPREGNATED FIBROUS MATERIALS The following States are Members of the International Atomic Energy Agency:

AFGHANISTAN GERMANY, FEDERAL NORWAY ALBANIA REPUBLIC OF PAKISTAN ALGERIA GHANA PANAMA ARGENTINA GREECE PARAGUAY AUSTRALIA GUATEMALA PERU AUSTRIA HAITI PHILIPPINES BELGIUM H O L Y SEE POLAND BOLIVIA HUNGARY PORTUGAL BRAZIL ICELAND ROMANIA BULGARIA INDIA SAUDI ARABIA BURMA INDONESIA SENEGAL BYELORUSSIAN SOVIET IRAN SIERRA LEONE SOCIALIST REPUBLIC IRAQ SINGAPORE CAMBODIA ISRAEL SOUTH AFRICA CAMEROON ITALY SPAIN CANADA IVORY COAST SUDAN CEYLON JAMAICA SWEDEN CHILE JAPAN SWITZERLAND CHINA JORDAN SYRIAN ARAB REPUBLIC COLOMBIA KENYA THAILAND CONGO, DEMOCRATIC KOREA, REPUBLIC OF TUNISIA REPUBLIC OF KUWAIT TURKEY C O S T A R IC A LEBANON UGANDA CUBA LIBERIA UKRAINIAN SOVIET SOCIALIST CYPRUS LIBYA REPUBLIC CZECHOSLOVAK SOCIALIST LUXEMBOURG UNION OF SOVIET SOCIALIST REPUBLIC MADAGASCAR REPUBLICS DENMARK MALI UNITED ARAB REPUBLIC DOMINICAN REPUBLIC MEXICO UNITED KINGDOM OF GREAT ECUADOR MONACO BRITAIN AND NORTHERN EL SALVADOR MOROCCO IRELAND ETHIOPIA NETHERLANDS UNITED STATES OF AMERICA FINLAND NEW ZEALAND URUGUAY FRANCE NICARAGUA VENEZUELA GABON NIGERIA VIET-NAM YUGOSLAVIA

The Agency’s Statute was approved on 23 October 1956 by the Conference on the Statute of the IAEA held at United Nations Headquarters, New York; it entered into force on 29 July 1957. The Headquarters of the Agency are situated in Vienna. Its principal objective is "to accelerate and enlarge the contribution of atomic energy to peace, health and prosperity throughout the world".

Printed by the IAEA in Austria

October 1968 PANEL PROCEEDINGS SERIES

IMPREGNATED FIBROUS MATERIALS

REPORT OP A STUDY GROUP ON IMPREGNATED FIBROUS MATERIALS ORGANIZED BY THE INTERNATIONAL ATOMIC ENERGY AGENCY AND HELD IN BANGKOK, 20-24 NOVEMBER 1967

INTERNATIONAL ATOMIC ENERGY AGENCY VIENNA, 1968 IMPREGNATED FIBROUS MATERIALS (Panel Proceedings Series)

ABSTRACT. Proceedings of a Study Group convened by the IAEA and held in Bangkok, 20-24 November 1968. The m eeting was attended by 39 participants from 13 countries and from international organizations. The publication contains 13 technical papers by various experts and status reports covering work and technology in polymer-containing fibrous materials in the Western and Eastern Hemispheres. Statements prepared by the Study Group are also included. Each technical paper is preceded by an abstract. Entirely in English.

(376 pp., 16 X 24 cm, paper-bound, 122 figures; 1968) Price: US$9,50; £3.19.2

♦ The front cover shows two hand-carved figurines from the Republic of China (Taiw an). The material is soft wood which, after carving, was impregnated with a monomer that was subsequently polymerized by gamma ra d ia tio n .

IMPREGNATED FIBROUS MATERIALS IA E A , V IE N N A , 1968 STI/PUB/209 FOREWORD

There has recently been renewed interest in the use of radiation from radioisotopes or particle accelerators to initiate and sustain chemical re­ actions. Particular attention is being paid to the production of wood-plastic composites, a process which is now a commercial reality with radiation competing against chemical methods to enhance the properties of wood. It has been reported that water repellancy, hardness, weathering, insect and chemical resistance, compressive, bending and shear strength can be signi­ ficantly improved by the process, but so far there has been a limited com­ m ercial outlet for the product. Papers on this subject were presented at the International Atom ic Energy Agency1 s Symposium on Industrial Uses of Large Radiation Sources, Salz­ burg, May 1963, and since then the Agency has been aware of the interest of developing countries in conducting research on wood and other fibrous materials as a means of further exploiting natural resources. It was felt that some attempt should be made to co-ordinate, on a regional basis, the work being done in this field and at the same time review the world status, including the associated technology in such areas as monomer-polymer chemistry and impregnation techniques where they are directly related to this w ork. Because of the wide range of fibrous materials being studied there, Asia and the Far East was chosen as the most representative area and 39 participants from 13 countries, and from international organizations, met in Bangkok from 20 to 24 November 1967 to assess the potential of im­ pregnated fibrous materials. This report is a record of the meeting and is based not only on work performed both inside and outside the region but also on details of the resources and industries in the area. The Agency gratefully acknowledges the help of the Thai Office of Atomic Energy for Peace which made facilities available for the meeting and wishes to thank all the authors, including those not present in Bangkok, who contributed papers.

CONTENTS

INTRODUCTORY PAPER

History of impregnation techniques' with fibrous materials ...... 3 H. T a г к o w

SUPPORTING TECHNOLOGY

Permeability of wood in relation to its structure and penetrability by fluids ...... 19 E.L. Ellwood and R.C. Thomas Factors affecting the impregnation of bagasse and other Far-Eastern fibrous materials ...... 35 Ung-Ping Wang Monomer-polymer chemistry and the impregnation process ...... 45 V. Stannett Radiation engineering in the polymerization of monomers in fibrous materials: accelerators ...... 57 F.L. Dalton and J.D. McCann Radiation engineering in the polymerization of monomers in fibrous materials: radioisotopes ...... 71 A.J. Felice Impregnation and polymerization methods and systems used in the production of wood-polymer materials ...... 83 W.E. Mott and G.J. Rotariu Degradation of polymers by ultra-violet light...... 93 D.T. Turner Emulsion graft-polymerization in wood by means of gamma irradiation ...... 107 M. G o t o d а Wood impregnation with polyethyleneglycol...... 115 P .-О. К in ell

STATEMENTS PREPARED BY THE STUDY GROUP

Monomers and monomer mixtures used in impregnation of fibrous materials ...... 121 Comparison of thermal, gamma and electron initiation...... 124

STATUS REPORTS

Status and Technology of Polymer-Containing Fibrous Materials in the Western Hemisphere ...... 129

Western Europe, with particular reference to Sweden...... 129 Contributed by P .-О. K i n e 11 and P. Aagaard Finland ...... 152 Contributed by J.К. Miettinen Europe...... 169 Contributed by T. Czvikovszky and J. Dobó United States of America ...... 190 Contributed by G.J. Rotariu and W.E. Mott Europe: a summary ...... 209 Contributed by A. Burmester

Status and Technology of Polymer-Containing Fibrous Materials in the Eastern Hemisphere ...... 217

Australia...... 217 Contributed by J .G. Clouston India...... 231 Contributed by V.K. Iya Japan...... 250 Wood-plastic composites ...... 250 Contributed by T. Hirayama Radiation grafting of vinyl comonomers to wood ...... 262 Contributed by T. Murayama Republic of Korea ...... 264 Contributed by Chwa-Kung Sung Pakistan ...... 267 Graft-polymerization under irradiation and its effect on water repellency and resistance to certain micro-organisms ... 267 Contributed by М.H. Awan and Ather Husain Effect of percentage graft on the breaking strength of jute yarn ...... 278 Contributed by M.H. Awan, Din Mohammed and Quazi Abdul Qadir The Philippines ...... 286 Contributed byLetitica Bonoan Republic of China (Taiwan) ...... 293 Contributed by Ung-Ping Wang Thailand ...... 303 Radiation polymerization in Thailand ...... 303 Contributed by M.L. Anong Nilubol and Somkiart Greethong Wood resources of Thailand ...... 305 Contributed by PongSono Viet Nam...... 310 Contributed by Le-Van-Thoi

TECHNICAL PAPERS

Fibrous material resources in Asia and the Far East ...... 315 D.L. Stacey Production economics of impregnated fibrous materials ...... 327 E. Rotkirch Potential markets for wood-plastic composites in Japan...... 349 T. Hirayama STATEMENTS PREPARED BY THE STUDY GROUP

Wood-plastic composites in the wood-carving industry in the Far East (Japan, the Republic of Korea, the Philippines, the Republic of China (Taiwan), Thailand and Viet Nam) ...... 367 Fibre- and particle-board in Asia and the Far East ...... 370

Conclusions ...... 371

List of Participants and Secretariat 373

INTRODUCTORY PAPER

HISTORY OF IMPREGNATION TECHNIQUES WITH FIBROUS MATERIALS

H. TARKOW FOREST PRODUCTS LABORATORY, * FOREST SERVICE, UNITED STATES DEPARTMENT OF AGRICULTURE, MADISON, WIS., UNITED STATES OF AMERICA

Abstract

HISTORY OF IMPREGNATION TECHNIQUES WITH FIBROUS MATERIALS. The importance of wood as a raw material is described and its deficiencies are listed. The history of the development of some impregnatio processes for fibrous materials is outlined and a hopeful prognosis for the future utilization of improved wood is m a d e .

The land area of the world provides man with much of his food and an array of products with which he clothes and shelters himself. These products include natural fibres such as cotton, jute, flax, hemp, and various tree crops, the most important of which is wood. The culti­ vated land area devoted to growing vegetable fibres is about 100 million acres (40 million hectares). The land area devoted to cereal grain pro­ duction is about 1500 million acres (600 million hectares). By far the largest crop harvested by man is wood [1] . From 10 billion acres (4 billion hectares) (billion = 109) of forest land, 1300 million tons of wood are consumed yearly - half for fuel and half for construction, pulp, plywood, mine props, furniture, and other uses. Thus wood serves man very well. One wonders how houses would have looked in temperate climates without this material. What would man have sat on, slept on, eaten off, or trod upon? Yet wood has its deficiencies. In former days, these were accepted with equanimity. More recently, with the coming of competitive materials, man has been forced to recognize these deficiencies; he has had to de­ velop procedures for correcting them and even for improving properties previously regarded as adequate. Unlike a man-made metal with predictable and uniform properties, wood has the variability to be expected from several hundred commercial species grown under extremes of climatic conditions and in soils of varying composition. Yet one of the main problems of use, common to all species, results from the reactivity or inherent instability of wood substance. It burns and decays; it is acted on by light, and it reacts reversibly with moisture under varying conditions of relative humidity. It is tempting to conjecture that this is nature's way of assuring a full cycle of production and destruction of wood tissue, thus preventing the choking off of con­ tinuous growth of wood.

* Maintained in co-operation with the University of Wisconsin.

3 4 TARKOW

F IG .l. Joints shown at left are properly designed, whereas joints at right are not and show an accumulation of water that produces a decay potential.

The formation of wood substance is not spontaneous; it occurs with considerable molecular ordering and with the absorption of considerable energy. The energy, of course, comes from the sun. In only three days, the earth's surface can receive as much solar energy as could be obtained by burning all reserves of coal, petroleum, natural gas, and all the forests [l] . Not all of the solar energy is used for photosynthesis. Yet, if we assume an annual growth increment of 1 cord per acre, the total energy that could be derived by burning the total annual increment from the 10 billion acres of forested land would be equivalent to that obtained from burning 5 billion tons of coal - twice the world's annual consumption ■ of energy. Plant tissues, then, are storehouses, of chemical energy. Yet the release of this energy, like that from an equally unstable explosive, requires triggering. In other words, under certain conditions, wood possesses a pseudostability. Air-dry wood, for example, is inert to decay organisms. Many religious temples, constructed with wood, have withstood the ravages of time. Triggering may come through the action of organisms on wet wood. The decay organisms use wood both as a source of carbon and as a source of energy to build their own unstable body components. As they do this, a portion of the wood substance is oxidized to carbon dioxide. This is the 'dust to dust' allegory enunciated by many religious groups. One detects transformations such as these in wet or dank forests. One HISTORY OF TECHNIQUES 5

О Ю 20 30 40 50 60 70 60 90 tOO RELATIVE HUMIDITY (PERCENT)

FIG.2. Moisture adsorption isotherm for wood, rayon, and cotton. observes it when wood is improperly used, for example when kept moist in poorly ventilated regions or at improperly protected joints. Figure 1 shows sections of two wall panels. One (on the left) had been treated with a water repellent; the other (on the right) had not. On exposure to liquid water, the joints in the section on the right collected water and presented a serious decay potential. Triggering of the deterioration may come by photo-oxidation [2] . Wood substance absorbs all wavelengths of light; the shorter wavelengths, although the least penetrating, are the most harmful because they contain sufficient energy to break bonds or create free radicals. These free radicals in turn readily react with atmospheric oxygen. The net result is the eventual conversion of the wood substance involved to carbon dioxide and the liberation of the heat of oxidation. Wood substance is hygroscopic; as a consequence it swells and shrinks with variation in relative humidity. Figure 2 gives the adsorption iso­ therms for different cellulosic materials. Between the oven-dry and water-swollen condition it swells 45% in volume. The tendency for wood substance in equilibrium with 30% relative humidity to swell when trans­ ferred to 100% relative humidity is measured by a force of about 11 000 lb/in2 [3] . If the swelling or shrinking is restrained, as can happen outdoors if sharp moisture gradients develop, the wood is subjected to severe stresses. These may open up or develop checks from the surface inwards. This 6 TARKOW facilitates more rapid penetration of decay organisms or of liquid water. Even if checking is avoided by eliminating sharp moisture gradients, swelling or shrinking can occur. Many people have encountered doors swollen shut, windows that refused to open, or hammer handles that had come loose from the tool head. These weathering characteristics are undesirable. Some are mere annoyances, others are serious and cause considerable dissatisfaction with wood in use. Their control is desirable, by means that do not alter any of the many valuable characteristics of wood. This can be done to a large degree by impregnating wood with certain resins. In fact, the use of wood in combination with resins goes back to the very early days of resin technology. The Genesis of the modern Resin Era is 7 December 1909, when Leo Baekeland was granted a patent describing the composition of a mixture of phenol and formaldehyde that could be transformed from a fusible to a non-fusible state by heat and pressure. The early uses of the mixture were disappointing because the final product underwent considerable shrinkage during cure and was very brittle. Some improvement was found when 10 - 40% of wood flour was added to the original mixture. Moulded objects (Bakelite) now had improved mechanical properties. They under­ went considerably less shrinkage during cure. The first use of these compositions coincided with the infancy of the electronics industry; in fact the early growth of this industry owed much to the peculiar properties of the moulding composition of the phenolic resin- wood flour. By 1940, 6 million pounds of composition material were made annually and used in radios, telephones and products requiring good strength and electrical properties. Considerable improvements were also made in the basic resin. Other formulations based on urea and melamine were developed. Nevertheless, phenolics remained the 'workhorse' - a term that reflects America's rural beginnings. With the approach of World War II, considerable interest was dis­ played in reversing the purpose of incorporating wood flour into resin. Instead of using wood to improve the properties of the resin, could the resin be used to improve the properties of the whole wood? Could some of the deficiencies of wood be controlled? The answers were sought in a work program at the US Forest Products Laboratory. This program continued throughout the war and for several years afterwards. During this period, several principles for stabilizing wood were de­ veloped [4] . To achieve permanent improved dimensional stability, it is necessary to modify the wood substance. This can be done by chemical modification, for example by acétylation, or by infusing certain resins into the wood substance. Chemical modification is an excellent but very cumbersome procedure; infusing with resins is also good and more practical. As mentioned, wood substance (cell walls) swells 45% in volume when placed in water. If the water within the cell walls is replaced with a non­ volatile, insoluble or potentially insoluble material, collapse of the cell walls is prevented as moisture is removed from the wood. The cell wall remains permanently swollen. With changes in relative humidity, no further swelling occurs. The wood is said to have 100% anti-shrink efficiency. Actually, this situation is impossible to achieve because of m s TORY OF TECHNIQUES 7

FIG.3. Lower panel is control ; upper panel, with marked increase in dimension, shows bulking action resulting from dimensional stabilization of the wood. the great difficulty in completely replacing the water in the cell walls with the resin. Seventy per cent replacement is about the maximum; the anti-shrink efficiency is 70% [4], that is, the swelling and shrinking tendency is reduced by 70%. Suitably chosen phenolic resins are ideal for this. The requirements are that they be water soluble and that the aqueous solution be infinitely dilutable with water. Penetration of the cell wall is dependent on the relative sizes of the sub-microscopic voids within the swollen cell walls and the molecular size of the solute. Experience has shown that if the phenolic resin meets the requirements of water compatibility, its molecular size is sufficiently small to allow penetration into the wood substance. In recent years, the relationship between molecular size and penetrability has been studied in detail. The importance of a low molecular weight cannot be over­ emphasized. If the phenolic resin is so advanced in cure that it requires alcohol or acetone for solubilization, poor dimensional stability is im­ parted to the wood. A greater proportion of the resin now resides within the lumens and a smaller amount within the cell wall. After impregnation the water is cautiously removed. If this is properly performed, additional resin diffuses into the cell walls from the lumens. On heating to about 300°F for 30 min to 1 hour, the resin is converted to an insoluble, infusible material. This is revealed by a bulking or an enlargement of the wood; the air-dry dimensions are close to those of the green dimensions (Fig. 3). 8 TARKOW

The upper panel shown in this figure, originally of the same di­ mensions as the lower, was treated with phenolic resin. The resin content of the cured board was 30%. The tangential dimension had in­ creased by about 8% and the radial dimension by about 4%; thus the volume had increased by 12%. The lower, untreated panel swelled by about 16% in volume when placed in water. The treated panel swelled by only 5-1/2%. Thus the treatment had reduced the swelling tendency by 70%. This is true for most species. It must be emphasized, how­ ever, that this holds only for resins meeting the requirements of water compatibility. If these requirements are not met, the degree of bulking, which is a good index of stabilization, decreases. Thus, with yellow birch, at a phenolic resin content of 28%, the volumetric bulking is 12.8% with proper resin, and only 9.3% with a resin so advanced as to be in­ soluble in water. What advantages do we lose in gaining this improvement in dimensional stability?

(1) Weight increase of 30% is accompanied by a volume increase of 12%. The specific gravity is thus increased by 18%, from 0.60 to 0.71 g/cm3. (2) Material is severely embrittled.

What is gained?

(1) Equilibrium moisture content is reduced at all relative humidities. Within different relative humidity ranges, the swelling tendency is reduced by 60 to 70%. (2) Decay resistance is increased. Because of the reduction in moisture content within the cell walls or wood substance, the resistance to decay and to termite attack is considerably increased. A group of panels of Douglas-fir plywood that contained 30% properly introduced phenolic resin was 80% unattacked after four years in termite-infested ground. With 15% resin, 50% was unattacked. With no resin, all panels were completely destroyed within two years. The relationship between dimensional stability and resistance to decay is shown in Fig. 4. (3) Resistance to weathering is increased. Douglas-fir plywood was faced with 1/16-in. veneer, some of which was treated with 30% phenolic resin. These panels were weathered outdoors for two years (Fig. 5). Resin treatment markedly enhanced the weathering resistance of the face veneers. This is due to the increased dimensional stability of the face veneer and to the protective action of the phenolic resin against photo-oxidation of the wood. Phenolic resins are excellent absorbers of ultra-violet light; thus, they filter the light striking the wood. Un­ fortunately, this leads to severe discoloration of the resin. The wood, however, remains intact. (4) Most mechanical properties are not adversely affected (Table I). In impregnated, resin-treated, uncompressed wood, the only property adversely affected is toughness. Despite the 35% resin content, the other mechanical properties are not appreciably affected. These mechanical properties depend mainly on the relative volume of wood substance, or the density of the wood. Because the density of impregnated wood is only about 35% greater than that of untreated wood, one would not expect an appreciable increase in its density-dependent properties. HISTORY OF TECHNIQUES 9

FIG.4. Relationship of dimensional stability, produced by impregnation with phenolic resin, to resistance to d e c a y .

FIG.5. Douglas-fir plywood after two years of outdoor weathering. A: untreated face; B: phenolic- resin-treated face. 10 TABLE I. EFFECT OF WOOD MODIFICATION ON MECHANICAL PROPERTIES OF BIRCH TARKOW

(a) Resin-treated» uncompressed wood.

(b) R esin -treated, compressed w o o d .

(c) No resin treatment, compressed wood. HIS" ^s 11

FIG. 6. Drawing of cube of softwood. Permeability depends on the communication between the cells.

Thus, following proper treatment of wood with 30 to 35% phenolic resin, there is a marked reduction in swelling and shrinking capacity and a marked increase in decay resistance and stability to photo-oxidation. The loss in toughness is serious. Similar results are obtained with water-soluble urea and melamine resins. Although we have discussed the properties of resin-treated wood, wç have yet to discuss the problems in making it. These, as we shall see, are responsible for the poor acceptance of the material. The most serious problem is that of the low permeability of wood (Fig. 6). Wood is a very porous material; about 70% of the volume is made up of air- filled cells. The remaining 30% is wood substance, or cell walls. Communication from cell to cell is generally very poor, so that despite high porosity, wood has little permeability. This creates problems for introducing the phenolic resin. Two procedures have been thoroughly studied:

(1) Permeation of aqueous solutions into air-dry wood. Permeation can occur through the cell cavities in series with the pit systems [4] (Fig. 6). The cell walls are ineffective for flow of solution. Thus, the condition of the pit systems is critical for liquid flow. For example, Douglas fir grown in mountainous areas of the United States of America 12 TARKOW has aspirated, or blocked, pits. Permeability is very poor. The same species grown in the coastal regions has clear pit systems and permeability is very good. The permeability of hardwoods is further influenced by the condition of the vessels, which may constitute up to 25% of the volume of the wood. The vessels in red oak are clear, and this wood is very perme­ able. The vessels in white oak are plugged with tyloses, this wood being highly impermeable. Among different species, liquid permeability can vary by a factor of many thousand. The most highly permeable species can be readily treated with 30% aqueous phenolic resin under a pressure of 100 to 200 lb/in2. The sapwood, especially, is permeable. However, because of the greater usage of heartwood, impregnation with aqueous solutions must be made on veneers 1/16 inch or less thick. There is an additional reason for preferring thin sections. After impregnation the water must be cautiously removed. The only way to accelerate this removal is to use very moderatetemperatures(to prevent premature curing of resin) and to use thin sections of wood. This may take 24 hours at about 150°F. After the removal of water, the veneers are heated at about 300°F for 15 to 20 minutes to cure the resin within the cell walls. Adhesives are then applied to the faces and laminates of the desired thickness are made in a 'plywood1 press. (2) Diffusion into green wood. The movement of solutes into wood can occur by diffusion, that is, by molecular motion. A water-saturated condition is desirable to provide continuous pathways for diffusion (Fig.6). Here diffusion may occur continuously through the lumen-pit system as well as through the lumen-cell wall system. Continuous diffusion through the cell wall probably occurs to a very small extent. The object is again to get the resin into the lumen whence it can diffuse into the cell walls and be cured later. With flat panels, diffusion occurs mainly'in the trans­ verse direction. Diffusion constants, however, are small; that is, about 0.03 of that through a similar volume of pure water. For the reasons cited, adequate diffusion is achieved in a reason­ able time only with thin veneers. Green softwood veneer 1/16 inch thick with 100% moisture content takes up the desired 30% of resin from an external 35 to 40% solution in about 15 hours. With veneers containing only 6% moisture, the time is 80 to 100 hours, reflecting-the absence of continuous water-filled pathways for diffusion. With 1/8-inch green veneers, times for adequate resin uptake (by diffusion) are prohibitively long. Solid wood cannot be satisfactorily treated by diffusion means. As with pressure-treated veneers, the moisture in diffusion-treated veneers is cautiously removed to optimize further diffusion of resin into the cell walls. The veneers are then heated at 300°F for 30 minutes and lami­ nated. The composite is called impreg. Three companies in the United States of America make about one- half million board feet annually of impreg. It is sold for about US$2 to $3 per board foot or about 50 to 75 cents per pound. It is now being used commercially to make pattern and die models for the automobile industry (Fig. 7). Here dimensional stability and ease of carving are out­ standing attributes. Because of its high heat resistance, it is used to some extent for making forms for shell moulding (Fig. 8). Because of cost, how­ ever, impreg is not widely used. ECHNIQUES

P F ^ ^ - T ^

» 4 . • * ы ЯЁШЯШЯШ

Pattern of car-top made from phenolic-resin-stabilized mahogany (impreg).

FIG. 8. Pattern made from impreg for shell moulding. 1 4 TARKOW

It should be mentioned that the treatment of wood with solutions of thermoplastic resins, such as polymethyl methacrylate in acetone or polystyrene in benzene is extremely difficult because of the high viscosity of these solutions. Viscosities such as these may be several thousand times greater than that of 30% aqueous phenolic resin. Furthermore, the resin would not penetrate the cell walls and permanent dimensional sta­ bility would not be imparted to the wood. It should be pointed out again that the treatment has only a small beneficial effect on compressive or elastic properties of wood. This is so because there is little change in void volume (or density). During early development it was noted that if the phenolic resin was cured during lamination and at pressures of about 1000 lb/in2, the wood showed remarkable plasticity. It was readily compressed, yielding a laminate with a density of 1. 35 g/ml. This material is called compreg [4] . Since void volume is reduced, mechanical properties are increased substantially (Table I). Hardness is increased by several hundred per cent. Again because of the resin in the cell walls, the toughness is still inferior to that of the original wood. The use of compreg for making gears, (water-lubricated) patterns, electrical-insulating blocks, (high- tension) handles for cutlery, cutting boards, and in other applications, is very limited. Attempts to use compreg for flooring were not successful because of a lack of resilience and the high costs (about US$4 per board foot). The compression of phenolic-resin-treated wood can be looked on as a procedure whereby the void volume of wood is 'impregnated' with wood substance. The proper treatment of the cell walls with phenolic resin merely imparts sufficient plasticity to the wood so that compression or 'impregnation with wood substance' can be made at 1000 to 1200 lb/in2. If the resin treatment is omitted, compression or filling the void volume with 'wood substance' can still be made at a higher pressure, about 2000 lb/in2, andat 300°F. The resulting mechanical properties of the material, called staypak [4], are excellent (Table I). Modulus of elasti­ city in tension exceeds 4 million pounds per square inch and the tough­ ness is greater than that of the original wood. Furthermore, since more than 90% of moisture movement in normal wood occurs through the air- filled channels, the water vapour transmission rate through staypak, with practically zero void volume, is very small - so much so that thick sections have effective and very good dimensional stability, unless exposed for very long periods of time at relative humidities in excess of 90%. Moisture vapour movement from atmospheres of 80% relative humidity into staypak is extremely slow. Interior uses were considered because of the stability and excellent mechanical properties when properly made. Costs, how­ ever, are very high and staypak is not made commercially. Staypak is mentioned since with it we have the first tie between an early modified wood and a currently investigated, monomer-treated, radiation-cured wood. Neither process produces a truly dimensional stabilized wood because the wood substance is intact unless, with the newer treatment, some penetration of monomer can occur. In both, how­ ever, the access of moisture to wood substance is extremely difficult be­ cause the void volume has been reduced or eliminated - in staypak by 'impregnation' with wood substance and in the wood-plastic combination with polymerized methyl methacrylate. Both have improved mechanical ras TORY OF TECHNIQUES 15 properties only because the void volume of the wood has been substantially reduced. These modified woods have very limited use in the United States of America because of high costs and also because of the development of still another resin-impregnated fibrous material, or resin-impregnated paper. The development of resin-impregnated papers began shortly after Baekeland's discovery of phenolic resins. The early modifications were dark coloured and were used for radio and electronic forms and panels. Interest continued to grow because of the ease of treating paper, 3 to 10 mil thick, and because of the growing demands for aircraft, ordnance, and electronic equipment. The greatest growth occurred shortly after the Second World War with the development of melamine resins; this produced more naturally coloured resin-treated paper panels. Further­ more, with the development of procedures for printing figured patterns or patterns simulating wood grain onto paper, an appreciable 'decorative laminate' industry grew up. Patterned papers such as these (generally kraft paper) are saturated with melamine resins and surfaced with a thin sheet of melamine-resin- saturated alpha-cellulose paper. This pack in turn is placed in contact with several sheets of phenolic-resin-impregnated kraft paper and cured in a press at 300° to 325°F under pressures exceeding 500 lb/in2. The result is a 'decorative laminate', generally l/32-inch thick, with a sur­ face remarkably resembling a wood-grain pattern or other pattern and having a very high resistance to abrasion and wear. Such decorative laminates are readily bonded to plywood, hardboard or particle boards to give flat panels that have found wide use in tabletops, cabinets and vertical panelling. Their outstanding properties are appearance, colour and design, and wear resistance (including resistance to solvents such as alcohol and acetone). Overall resin contents average about 40 to 50%, although the top sheets may contain 70% resin. Because of this, water vapour transmission to the underlying untreated base cores is extremely slow. A balanced construction is necessary to prevent warping; that is, the back of the overall panel must be faced with a water-vapour barrier. It should be emphasized that, as with the staypak and compreg, the increased hardness is due to the elimination of voids within the paper by thorough resin impregnation. Dimensional stability is excellent. About 1 billion ( 109) square feet of decorative laminates are made annually in the United States of America. They sell for about 30 cents per square foot. In addition, treated paper is produced for panel backing. The pattern on decorative laminates is that printed on the paper. The art of this printing on laminates is so advanced that it takes a skilled eye to distinguish it from another type of real wood surface made by bonding a thin sheet of transparent thermoplastic film (polyvinyl chloride or poly­ methyl methacrylate) directly to a well-prepared wood surface. In addition to decorative laminates, there is a growing use of 'industrial laminates' where aesthetic appearance is not important (for example making reusable concrete forms). It is estimated that about 100 million square feet of industrial laminates are made annually. Several years ago, studies were made at the Forest Products Laboratory on the durability of paints applied to wood siding faced with resin-impregnated papers. After 15 years of outdoor weathering, the finishes look very good. There has been no acceptance of this treatment for siding, because of high initial costs. 16 TARKOW

One problem in the manufacture of various laminates is the long time required for cure, followed, generally, by a period for cooling the press before removing the panels, generally true for thermosetting resins. De­ velopments are now occurring in the United States of America that will permit the manufacture of these items in a continuous manner without the need for opening the press. These will produce flat panels having a surface hardness, scratch resistance, solvent resistance, and appearance resulting from the presence of a very dense, resin-impregnated surface layer, 10 to 30 mil thick. We have sketched here the history of the development of some impreg­ nation processes for fibrous materials. These began in the early nineteen- twenties with the discovery of thermosetting phenolic resins. Numerous additional resins are becoming available. The growing list reads like a pharmacopoeia of impregnation resins with distinctive properties. The most prominent fibrous material being impregnated is paper, because treating problems encountered with wood are minimized. There is every reason to believe that the use of these processes and their products will grow and expand.

REFERENCES

[1] BROWN, H ., The Challenge of Man’s Future, Viking Press, New York (1958). [2] BROWNE, F.L.. SIMONSON. H .C., Forest Prod. J. 7 (1957) 308-14. [3] TARKOW, H., TURNER. H .D ., Forest Prod. J. 8 (1958) 193-97. [4] STAMM, A. J., Wood and Cellulose Science, Ronald Press, New York (1964). SUPPORTING TECHNOLOGY

PERMEABILITY OF WOOD IN RELATION TO ITS STRUCTURE AND PENETRABILITY BY FLUIDS

E.L. ELLWOOD AND R.C. THOMAS SCHOOL OF FOREST RESOURCES, NORTH CAROLINA STATE UNIVERSITY, RALEIGH, N .C ., UNITED STATES OF AMERICA

Abstract

PERMEABILITY OF WOOD IN RELATION TO ITS STRUCTURE AND PENETRABILITY BY FLUIDS. The salient features o f wood structure, as they determine the nature of fluid pathways in wood, are discussed. Attention is directed towards pressure (hydrodynamic) flow as the mechanism of fluid movement which is of most importance in practical impregnation treatments of bulk wood. The permeability of wood to inert fluids can be described reasonably by em pirical fluid-flow equations such as Darcy's and Poiseuille's Laws. It is pointed out that permeability, and hence penetrability, of wood under fluid flow conditions is limited primarily by the nature of the pit membranes. Penetrability o f wood by fluid flow depends not only upon the characteristic permeability of wood but also upon the nature o f the fluid system and presence or absence of air in the system. Treatments which have been shown to improve the permeability of wood are also discussed.

1. STRUCTURE OF WOOD

Although wood is considered to be a highly porous material, it is not always highly permeable and shows great variability in permeability both within and between species. Important existing processes that are strongly influenced by wood permeability are seasoning, wood preservative and fire retardant treatments, and pulping. The efficiency of the above treatments, which in turn is related to cost, is largely controlled by the anatomical structure of the wood. The influence of anatomical structure on perme­ ability has been reported in numerous publications [ 1-9]. An understanding of the structure of wood is essential for a full understanding and appreci­ ation of wood permeability and associated problems. Distinct anatomical differences exist between the gymnosperms (softwoods) and the angiosperme (hardwoods). The softwoods are fairly homogeneous as they consist basically of only two cell types, the longitudi­ nal tracheids and ray cells. Hardwoods, on the other hand, are composed of mixtures of four or five cell forms and are thus relatively heterogeneous in their structure. Although definite structural differences exist between species within both the softwoods and hardwoods, they will not be discussed here as they are beyond the scope of this paper. These differences are reported in detail elsewhere [10, 11].

* Paper No. 2512 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh, N .C ., United States of America.

19 20 ELLW OOD and THOMAS

FIG. 1. Electron micrograph of a longitudinal tracheid -bordered pit membrane from the inner sapwood of Pinus palustris M ill, in the non-aspirated condition. Note the relatively large openings between the radiating m icrofibrillar strands.

2. ANATOMY OF THE GYMNOSPERMS

The longitudinal tracheid, which constitutes more than 90% of the volume of a softwood, is an elongated, hollow, cylindrical type cell from 100 to 250 times longer than it is wide. The longitudinal tracheid is a general purpose element and performs the dual functions of translocation and support. The ends of longitudinal tracheids are closed and appear rounded in the radial view and pointed in a tangential view. Access between the longitudinal tracheids is provided through openings in the membrane of bordered pit pairs. A bordered pit is a gap or recess in the secondary wall of the cell in which the pit membrane is overarched by the secondary cell wall. A bordered pit pair is an intercellular pairing of two bordered pits, thus connecting contiguous tracheids. The pit membrane consists of a central thickened area called the torus and an unthickened perforated area designated as the margo. The torus is sup­ ported by the cellulosic strands of the margo radiating from the torus to the edge of the pit, much like the spokes of a wheel (Fig. 1). Openings in the margo reportedly range from less than 0.1 jum to greater than 1.0 мт [8, 12]. In some species the torus is not substantially thickened; thus by strict definition this structure is lacking and the dense area in the centre of the pit membrane is the region where the cellulosic strands overlap [8, 13 ]. PERMEABILITY OF WOOD 21

FIG. 2. Electron micrograph of a longitudinal tracheid-bordered pit membrane from the heartwood of Pinus serótina Michx. in the aspirated condition.

Figure 1 depicts a bordered pit membrane in the non-aspirated state. That is, the membrane is centrally located and therefore allows liquid flow between the cells. However, when a pit membrane is in the aspirated condition (Fig. 2) the aperture is effectively sealed and liquid flow is completely prevented or substantially reduced, depending upon the tightness of the seal between the torus and overarching border [2, 6, 7, 14]. A complete discussion of the mechanism of pit aspiration has been prepared [15]. In most species the heartwood permeability is lower than sapwood permeability. The incrustations of the pit membrane [8, 16] and the fact that most of the bordered pits in the heartwood are in the aspirated state [12] appear to be the major factors causing a reduction in heartwood permeability. For some species extraction of the heartwood with hot water and organic solvents significantly improves permeability [8, 17]. The effect of rays on the permeability of softwoods appears to be quite variable. In the pines, and to a lesser degree in a few other softwoods, the rays consist of ray parenchyma and ray tracheids. The ray parenchyma cells, when secondary thickening occurs, possess simple pit pairs. These simple pits do not reveal an overarching border, a torus, or openings in the membrane. On the other hand, the ray tracheids possess bordered pit pairs similar to the bordered pit pairs of longitudinal tracheids (Fig. 3). The most obvious differences are the smaller overall diameter and denser pit membranes found in the ray tracheid border pit [12]. On the basis of structure it would appear that the ray tracheids are more permeable than 22 ELLVÍOOD and THOM AS

FIG.3. Electron micrograph ot a ray-tracheid to longitudinal-tracheid bordered pit membrane from the sapwood of Pinus palustris. Note the very dense margo m icrofibrillar network.

: ¡¡¡¡¡ВНЩШ 1L

■ ■ ■ ■ I g g g g

■ н и ш

FIG.4. Electron micrograph of a ray-parenchyma to longitudinal tracheid pit membranes from the outer sapwood of Pinus serótina as viewed from the ray parenchyma. Note the continuity of the pit membranes and the ray parenchyma wall as well as the incrustations which mask the m icrofibrillar network. PERMEABILITY OF WOOD 23 the ray parenchyma. However, one study [6 ] revealed a greater penetration of Coppick and Fowler reagents in the ray parenchyma than in ray tracheids of Pinus radiata. Another study [18] showed that a monomeric styrene moved mainly in the ray tracheids. It was also noted that in longitudinal impregnation the liquid moved into many of the ray tracheids, spread radially, then often re-entered longitudinal tracheids. However, the ray- tracheid-bordered pit membranes connecting the longitudinal tracheids in southern yellow pine are heavily incrusted and therefore do not appear to be very effective. Also, since the half-bordered pits which interconnect the ray parenchyma and longitudinal tracheids are apparently imperforate [12, 16, 19], movement across this membrane may be by diffusion only (Fig. 4). On the whole, the rays apparentlyrplay only a minor role in the impregnation of softwoods. The presence of resin canals oriented in both the longitudinal and radial directions appear to have a variable effect on permeability. Their effectiveness depends upon the size, number and distribution and upon whether or not they are plugged with resin or tylosoids [3]. In the sapwood of Pinus they are effective, while in Picea, Pseudotsuga and Larix, where fewer resin canals exist, they do not appear to be effective [3].

3. ANATOMY OF THE ANGIOSPERMS

In hardwoods the vertical elements are more varied than in softwoods. The general purpose element of softwoods, the longitudinal tracheid, responsible for support and conduction, is replaced by several cells each of which has a specialized function. In general, all of the cell types found in hardwoods can be classified as either vessel elements, fibres or parenchyma. In the living tree, the primary and perhaps only function of vessels is conduction. Since the structure of the vessels facilitates longitudinal liquid movement in the living tree, it is not surprising that vessels play a primary role in the fluid impregnation of hardwoods. Lateral movement proceeds from the vessels to adjacent fibres, rays or longitudinal parenchyma through bordered or half-bordered pit pairs [6]. The role of the different fibre types in the conduction of liquids is not clearly understood, mostly due to the complex arrangements found throughout the wood [20]. Vasicentric tracheids, which are heavily pitted and possess a large lumen, and vascular tracheids, which are identical to vessel elements except for the lack of a perforation plate, appear to be structurally suited for conduction. On the other hand, fibres with thick cell walls and narrow lumen do not substantially contribute to longitudinal movement. In fact, the longitudinal parenchyma cells have been reported to be more permeable than fibres [6]. The influence of rays on lateral flow appears to be more variable in hardwoods than in softwoods. For example, the uniserate rays of oak (Quercus) are permeable in both the sapwood and heartwood, while the rays of sycamore (Platanus occidentalis) do not permit radial movement [20]. The lack of ray permeability in sycamore has been attributed to a lack of pitting between the vessel elements and the ray parenchyma [20]. Since the lateral movement of liquids is controlled by the pitting between the vessels and surrounding cell types, a description of the hardwood bordered pit pairs is appropriate. The hardwood bordered pit membrane differs considerably from the softwood bordered pit membrane as it lacks 24 ELLWOOD and THOMAS

a torus and does not present any detectable openings (Fig. 5). The random arrangement of the microfibrils suggests that the membrane is actually the primary wall which suggests that the permeability of hardwood pit membranes is considerably less than that for softwoods. Pressure flow of liquid in the lateral direction has been detected in the drying of oak [21]. This raises the question as to whether or not the hardwood pit membrane is perforated in the green condition. The use of solvent exchange drying techniques with liquids of low surface tension lowers drying stresses and would presumably reduce alteration of pit membrane structure. However, the application of this technique to hardwoods reveals a non-perforated membrane similar to that obtained in hardwoods dried from water. Additional effort to resolve this apparent discrepancy is needed. The transformation of hardwood sapwood to heartwood generally causes a reduction in permeability. The bordered pit membranes become incrusted to such an extent that it is difficult to detect the microfibril structure with the electron microscope. This increase in thickness of the pit membrane causes a reduction in the effective movement of liquids from cell to cell. In many species the vessels become blocked due to the formation of tyloses, thus preventing significant longitudinal fluid flow [11, 22]. In a number of hardwoods, particularly diffuse porous woods, tyloses are lacking but the vessels may be obstructed by gum. Thus, in most cases the reduction in heartwood permeability can be explained on the basis of structural alter­ ations . PERMEABILITY OF WOOD 25

4. GENERALIZED MODEL OF WOOD

From the viewpoint of fluid movement a simplified model of wood can be considered as an aggregate of parallel tubes (tracheids, fibres and vessels) with a determinate length. These tubes constitute the coarse capillary structure with effective diameters ranging from 20 to 200 ц т . Liquid movement in the transverse direction (to adjacent tubes) as well as beyond the determinate length of the tubes occurs through pit membranes. These communicating structures have effective diameters ranging from less than 0.01 /um to 2 or more цm. The tube walls may also provide a passageway in the case of polar liquids, which swell the cell walls and thereby provide transient capillaries. Effective diameters for transient capillaries have been reported on the order of 0.0008 ium [23]. Thus the impregnation of wood with liquids involves liquid penetration and flow-through capillaries. The size and arrangement of the capillaries, upon which liquid penetration and flow are largely dependent, is directly related to the structure of wood.

5. PENETRATION OF WOOD BY FLUIDS

As can be observed from the description of wood as a porous medium, complexities of fluid pathways, variability in physiological processes and in pathway closure mechanisms, which vary both within and between wood species, have created difficulties in the development of a universal model to predict penetrability of fluids accurately. The fact that wood is a material of generally low and variable permeability has severely limited the appli­ cation of chemical treatments, which depend upon deep and uniform pene­ tration, to modify its properties. The penetration of wood with fluids can be attained by the use of one of three mechanisms, namely, (1) diffusion, (2) capillary flow, and (3) pressure flow.

5.1. Diffusion

Diffusion processes involving wood-swelling liquids are not strongly dependent upon permeability throughout the range found in wood, but are primarily dependent upon the density of the wood (or percentage of voids) in the approximate relationship

diffusion « ---;— -- wood density——9

This is because the transient capillaries of the swollen cell wall provide more numerous and effective diffusion pathways between wood fibres than do the openings in the pit membranes. In the case of non-polar fluids, diffusion rates are determined by the size and number of the pit membrane openings and hence are correlated with permeability. Diffusion of fluids through wood can be shown to approximate Fickian diffusion, i.e. t-, „ dc 26 ELLWOOD and THOMAS

Where F = rate of transfer, D = diffusion coefficient, ^ = concentration gradient, с = concentration of moisture, and x = distance in direction of diffusion

Diffusion mechanisms have been extensively studied, particularly by Stamm and Hart, and Refs [24-30] elaborate further on the nature of diffusion in wood. Although the diffusion mechanism is utilized in certain waterborne preservative treatments of lumber [31], penetration is very slow. When non-polar or non-swelling liquids are used as the penetrant, then diffusion is impractically slow (except for wood in thin sections such as veneer) as the dried fibre walls (other than pit openings) offer no pathways to the pene­ trating fluid. Consequently, diffusion processes will not be discussed furthe in this paper. It should be noted, however, that diffusion treatments in­ volving polar liquids such as water can provide deep penetration of wood provided the long time necessary is not a limitation. Further, diffusion of polar liquids into the cell wall would naturally follow pressure impregnation of the liquids into the coarse capillary structure.

5.2. Pressure flow

The mechanism of pressure or hydrodynamic flow is a mass flow phenomenon as a result of a pressure differential applied, or existing, across the fluid as opposed to the random molecular movement of fluid molecules occurring in Fickian diffusion. This mechanism can be much more rapid than diffusion processes and provides more opportunity for control of depth of penetration and retention of the penetrant. It is the mechanism which is most prevalently used by the wood preserving industry to penetrate wood to specified depths and loadings of preservative or fire-retardant chemicals [3] Recommended practical procedures for pressure impregnation treatment of wood, involving manipulation of both vacuum and pressure to control fluid penetration and retention, are discussed in several texts [3, 32]. Capillary flow is a special case of liquid pressure flow, in which the pressure differential is produced by surface tension forces at the gas-liquid interface. In pressure treating processes, capillary generated flow is generally of secondary importance to flow generated by pressure applied to the system. In contrast to diffusion mechanisms, pressure flow in wood is largely determined by permeability and is largely independent of density. The transient cell-wall capillaries of the swollen cell wall are not effective in pressure flow, even in the case of wood-swelling penetrants. The pene­ trating fluid must pass from fibre or vessel cavities through the constrictions of the pit membrane which, at least in softwoods, have radii of only 0.01 to 2 ц т . The sizes of the pit membrane openings are generally independent of the density of the wood. Wood shows a vastly greater range in pressure flow than in diffusion rates. For example, experimental data obtained on longitudinal permeability on over 100 species showed a range of over PERMEABILITY OF WOOD 2 7

2 million to 1 in hardwoods and over 440 thousand to 1 in softwoods [32]. By comparison, diffusion rates do not vary more than approximately 10-fold in commercially used woods. Wood structure, and in particular the number and size of pit membrane pores, is therefore far more a determinant on the effectiveness of pressure flow than it is on diffusion rate of fluids through it. In the general case, the permeability of wood to a fluid (which does not react with the wood) can be stated in the modified form of Darcy's Law which includes the effect of fluid viscosity [34].

Q = k i £ Др

Where

Q = the rate of flow, A = area of cross-section of specimen, L = length of specimen, Др = pressure drop across length, 77 = viscosity of fluid, and к = permeability constant

Permeability can also be stated in terms of Poiseuille's equation, which introduces capillary dimensions

Where

V = rate of flow, p = applied pressure, r = equivalent radius of capillary, L = equivalent length of capillary, and rj = viscosity of fluid

Both of the above expressions assume streamline flow through the capillaries. In the simplified case, pressure flow of fluids through wood occurs through fibre cavities (lumen) that are in parallel but also in series with pit membrane openings in the fibre walls. Applying Poiseuille's equation to this simplified model for softwoods, it has been shown that pressure flow through the unpitted cell wall is negligible in comparison with parallel flow through the pit membrane openings, and that the pressure drop through the fibre cavities (lumen) is negligible compared with that through the pit membranes [23]. It can thus be stated that in softwoods the permeability of pit membranes almost completely determines fluid pressure flow. However, data obtained by Sebastian et al. [35] indicate that the resistance of the fibre cavity (lumen) to pressure flow can account for up to 25 percent of the total re­ sistance for wood in which pit membrane permeability is relatively high. It is apparent from Poiseuille's equation that the effect of capillary radii on pressure flow is considerable. This, in large part, accounts for 28 ELLWOOD and THOMAS the high variability in permeability found even within wood cut from the same tree as the effective sizes of membrane pores vary considerably. Although both Darcy's and Poiseuille's Laws also hold for hardwoods [33, 36], the pathway system of fluid flow through hardwoods is more complex than that for softwoods because of the presence of vessels, greater amounts of parenchyma and the fact that the pit membranes in hardwoods show no visible openings and may be less permeable than softwood membranes. Evidence on the nature of pressure flow through hardwoods suggests that vessels play a major role in penetration, the penetrant first permeating the wood via vessels and then penetrating adjacent fibres via the pit membrane structure [4, 6 ]. If the vessels are plugged by tyloses or deposits, the permeability of hardwoods can fall to extremely low values.

5.3. Relative permeability in the longitudinal, radial and transverse directions

As can be predicted from applying Poiseuille's equation to flow through wood, longitudinal permeability is considerably higher than transverse permeability. Because wood fibres'are approximately 100-250 times longer than they are wide, fluids must of necessity traverse many more pits per unit length of flow in the transverse direction as compared with longitudinal flow. The longitudinal/transverse permeability ratio has been found to vary from 20 to 65 000 [3, 33], which in turn can be interpreted in terms of variation of effective capillary dimensions of different species. With some exceptions, radial and tangential permeability in wood are of the same general magnitude. However, in certain wood transverse movement of fluids is aided by ray penetration [3].

5.4. Comparison of gaseous and liquid flow through wood

Gas flow through wood can be described with reasonable accuracy by means of either Darcy's or Poiseuille's equation. A slightly more accurate description of gas flow may be obtained by combining the Knudsen equation with Poiseuille's equation to account for molecular slip in situations where the mean free path of the penetrant molecules approaches the size of the capillary dimensions [37]. Liquid flow and penetration, however, introduce additional hindrances which are not encountered in gas-flow mechanisms. Three major influences predominate:

(a) Effect of air-liquid menisci In the normal situation of impregnating dried or semi-dried wood with chemicals, air-liquid menisci can superimpose a major blockage to the flow of the penetrant. This has been ascribed to the fact that condensable vapours will condense in the fine capillaries of the pit membrane structure, thus preventing escape of trapped air from fibre cavities [23]. To obtain flow under these conditions it is necessary to apply sufficient pressure to overcome the effect of surface tension between air and the liquid before the trapped air can escape. PERMEABILITY OF WOOD 29

The pressure P required to overcome the surface tension is determined by the air-liquid surface tension and the radius of the capillary as follows:

r

Where p = surface tension and r = capillary radius. The necessary pressures may range over several hundred pounds per square inch. This phenomenon, depending upon the size of the pit membrane openings, accounts for much of the practical difficulty encountered in the impregnation of wood with liquids. In practice, the hindrance to penetration and flow by air-liquid menisci can be largely overcome in freshly cut green sapwood by applying external pressure to a water miscible penetrant, so that the water in the wood is displaced by the penetrant, e.g. the Boucherie preservative type process involves this principle.

(b) Time-dependent diminishing rate of flow

A frequently encountered phenomenon is a decreasing rate of flow, under constant pressure, through wood. Causes have been variously ascribed to pit closure through aspiration and blockage of pit pores by transported debris. More recently Kelso et al. [38] have shown that diminishing rate of flow is primarily due to air blockage resulting from the evolution of air bubbles from the penetrating liquid as it passes through the wood. The effect would then be similar to that described under (a). Only under the most stringent laboratory preparative conditions could the air blockage be overcome when water was used as the penetrant. (c) Chemical reactions between penetrant and wood

Polar or swelling fluids cause changes in capillary dimensions. However unless severe degrading or solution of wood components is involved, changes in pressure flow rate resulting from the use of polar fluids would be less pronounced than effects listed under (a) and (b). Although there is some evidence that the flow of organic liquids through wood decreases with in­ creasing polarity, experimental evidence has shown that wood-swelling liquids penetrate refractory wood more effectively than non-polar liquids of the same viscosity [32]. This is most probably due to added influence of diffusion of the swelling liquids through the transient capillaries of the cell walls. In summary, it can be stated that both liquid- and gas-phase pressure flow through wood can be reasonably well described by application of known pressure-flow equations. This has been recently demonstrated experi­ mentally [33, 39] for the case of the pressure flow of inert gases and non­ swelling liquids. However, liquid flow can introduce factors involving menisci effects, transportation of debris, and movement of tori which diminish flow and penetration in comparison with that of gases. Thus, in some instances, liquid flow and penetration into wood may deviate consider­ ably from that predicted from gas-flow permeability studies. Because of the influence of penetrant viscosity, gaseous pressure flow is more rapid than liquid flow, but penetration with gases markedly limits 3 0 ELLWOOD and THOMAS the total mass of penetrant that can be deposited in the wood, in comparison with that from liquid penetration.

5. 5. Pretreatments that influence wood permeability

As fluid penetrability into wood is limited by permeability, it is of interest to consider possible means of improving permeability.

(a) Moisture removal

Except for penetration processes involving diffusion or water re­ placement (e. g. Boucherie type), wood is normally treated with chemicals in the dry or near dry condition (25%-5% moisture content) both to improve its performance properties in use and to provide space for the penetrant. The moisture content at which wood is penetrated would be more likely determined by end use requirements of the product rather than by determi­ nation of the optimum moisture content for penetration. Enough is not known to identify precisely the optimum wood moisture content for pressure impregnation by fluids. However, there is agreement that penetrability is reduced at wood moisture contents considerably above 30%. In softwoods, pit aspiration develops on drying which tends to reduce permeability but, on the other hand, the pit membrane pores enlarge [24], which increases permeability. Undoubtedly the nature of the drying procedure itself modifies perme­ ability to the extent that it enlarges or reduces pit pores, and in softwoods prevents pit closure by aspiration. For example, it has been shown that by using liquids of low surface tension, such as acetone and toluene, to replace the water in wood and then drying, pit closure is markedly reduced in softwoods [40]. This is a field in need of further investigation.

(b) Presteaming of green wood

It has been shown by various investigators [17, 41 ] that steaming fresh- cut green wood at 100° С or heating the wood by other means under non­ drying conditions increases the permeability of the wood to air or vapours. The mechanism involved is imperfectly known. In softwoods there is some indication that the pit membrane structure may be affected by the process [42] and in hardwoods the treatment prevents the growth of tyloses in the vessels of beech [43]. The effect of presteaming on improving liquid-pressure flow has not yet been clearly demonstrated.

(c) Removal of extractives

Several investigators [17, 34, 41 ] have shown that removal of both water and organic solvent soluble extractives, particularly from heartwood, increases the permeability of both hardwoods and softwoods. Permeability increases from 2- to 10 000-fold have been observed. Removal of encrusting extractives from the pit membrane is the most probable mechanism involved. The effect of solvent extraction on permeability is more pronounced than that caused by heat treatment. PERMEABILITY OF WOOD 3 1

(d) Chemical pretreatments Vapour phase pretreatments may offer a means of increasing wood permeability. It has been shown, for example by Lantigen et al. [44], that ozone gas increased the permeability of western red cedar heartwood almost 100-fold. The ozone preferentially attacked the polyphenolic incrustations on the heartwood pit membranes.

(e) Biological pretreatments Infestation with the mould fungi, Trichoderma viride, substantially increases the sapwood permeability of softwoods through breakdown of parenchyma cells [45]. Certain bacteria can also rapidly increase the permeability of pine sapwood to almost the degree of blotting paper [46]. The bacterial attack resulted particularly in breakdown of the ray parenchyma. It has been demonstrated that selected enzyme preparations are highly effective in preferentially attacking and opening up the pit structure in certain softwoods, resulting in increased permeability [42].

On lumber or logs, both mould fungi and bacteria have only proved effective in sapwood. Their lack of effectiveness in heartwood may be due to lack of readily assimilable nutrients, the presence of toxic extractives, and inaccessibility due to the generally low permeability of heartwood. In summary, it is apparent that comparatively few pretreatments are known which can substantially enhance the permeability of wood without involving the problem of penetrability of the permeability-improving agent itself, or seriously affecting mechanical properties.

6. CONCLUSIONS AND SUMMARY

The penetration of wood by fluids still remains a problem area that is in need of further investigation. From the aspect of industrial feasibility, achievement of wood penetration by pressure processes, rather than by diffusion, has decided advantages. Notwithstanding the fact that a large wood preservative industry exists, which is based upon the pressure impregnation of wood, severe constraints are imposed by the nature of wood itself. Thus, with some exceptions, uniform and consistent penetration by rapid (pressure) methods can only be attained in sapwood. The heartwood of comparatively few commercial species can be readily and uniformly penetrated by known pressure impregnation methods. In addition, there is considerable variation in penetrability of species which are considered to be amenable to impreg­ nation treatments. The complex and varying structure of the capillary systems in wood determines its characteristic permeability. The capillary structures most limiting permeability are the openings in pit membranes. While penetra­ bility of wood with fluids depends upon its characteristic permeability, it also depends upon the nature of the penetrating fluid system itself. Thus penetrability may not achieve the level expected from the characteristic wood permeability in the case of liquid flow, primarily as a result of menisci blockage effects. Because of the influence of fluid viscosity in pressure flow, penetrability of wood with gaseous state fluids is very much faster than penetrability with liquids. 3 2 ELLWOOD and THOMAS

Comparatively few treatments are known which improve the permeability of bulk wood without drastically degrading its strength or structure. This is a field of research which is deserving of more attention, in view of the practical limitations to chemical modification treatments of wood, which are imposed by its generally low and variable penetrability.

REFERENCES

[1] BAILEY, I.W ., The preservative treatment of wood. II. The structure of the pit membranes in the tracheids of conifers and their relation to the penetration o f gases, liquids and finely divided solids into green and seasoned wood, For. Q. 11^(1913) 12. [2] PHILLIPS, E .W .J., Movement of the pit membrane in coniferous woods, with special reference to preservative treatment, Forestry 7 (1933) 109. [3] HUNT, C .M ., GARRETT, G .A ., Wood Preservation, McGraw-Hill, New York (3rd edn) (1967). [4] CRONSHAW, j. , The fine structure of the pits of Eucalyptus regnans and their relation to the movement of liquids into the wood, Aust. J. Bot. £ (1960) 51. [5] KRAHMER, R .L,, Anatomical features of permeable and refractory Douglas-fir, Forest Prod. J, 11 (1962) 439. [6] WARDROP, A .B ., DAVIES, G. W ., Morphological factors relating to the penetration of liquids into wood, Holzforschung 15 (1961) 129. [7] COTE, W .A ., Jr., KRAHMER, R .L., The permeability of coniferous pits demonstrated by electron microscopy, Tappi 45 2 (1962) 119. [8] KRAHMER, R .L ., CÔTE , W .A ., Jr., Changes in coniferous wood cells associated with heartwood formation, Tappi 46 1 (1963) 42. [9] LIESE, W ., BAUCH, ]., On the closure of bordered pits in conifers, Wood Sci. and Tech. 1^ (1967) 1. [10] JANE, F.W ., The Structure of Wood, Macmillan Co. New York (1956). [11] PANSHIN, A.J., DeZEEUW, C ., BROWN, H.P., Textbook of Wood Technology, McGraw-Hill New York (1964). [12] THOMAS, R .j., The development and ultrastructure of the pits of two southern yellow pine species, Unpublished D. F. dissertation, Duke University, Durham, N.C. (1967). [13] LIESE, W ., "Fine structure of bordered pits in softwoods", Cellular Ultrastiucture of Woody Plants (COTE , W. A ., Jr., Ed.), Syracuse University Press, Syracuse, N .Y . (1965). [14] GRIFFIN, G ., Further note on the position of the tori in bordered pits in relation to penetration of preservatives, J. For. 22 (1924) 82. [15] HART, C .A ., THOMAS R.J., A theory of the mechanism of bordered pit aspiration as caused by capillarity, Forest Prod. J. (in press). [16] COTE , W .A ., Jr., Electron microscopic studies of pit membrane structure. Implications in seasoning and preservation of wood, Forest Prod. J. 8 (1958) 296. * [17] BENVENUTI, R .R ., An investigation of methods of increasing the permeability of loblolly pine, unpublished M .S. thesis, North Carolina State University, Raleigh, N .C . (1963). [18] ERICKSON, H .D ., BALATINECZ, J.J., Liquid flow paths into wood using polymerization techniques — Douglas-fir and styrene, Forest Prod. J. 14 (1964) 293. [19] HARADA, H ., The electron microscopic observation of xylary ray cells of conifer woods, J. jap. For. Soc. 35 (1953) 194. [20] COTE , W .A ., Jr., Structural factors affecting the permeability of wood, J. Polym. Science: Part C, N o.2 (1963) 231. [21] HART, C .A ., Personal communication (1967). [22] KOR'AN, Z., COTE , W .A ., Jr., "The ultrastructure of tyloses", Cellular Ultrastructure of Woody Plants (W .A. COTE , Jr., Ed.), Syracuse University Press, Syracuse, N .Y . (1965). [23] STAMM, A .J ., The movement of fluids in wood. Part 1: Flow of fluids in wood, Wood Sci. and Tech. 1 (1967) 122. [24] STAMM, A.J., Wood and Cellulose Science, The Ronald Press C o ., New York (1964). [25] STAMM, A .J ., The movement of fluids in wood. Part II: Diffusion, Wood Sci. and Tech. 1 (1967) 205. [26] HART, C .A ., Principles of moisture movement in wood, Forest Prod. J. 14 (1964) 207. [27] HART, C .A ., The Drying of Wood, Technical Report N o.27, N.C. State University School of Forestry (1965). PERMEABILITY OF WOOD 33

[28] CHOONG, E .T ., Movement of moisture through a softwood in the hygroscopic range, Forest Prod. J. 13 (1963) 489. [29] CHRISTENSEN, G .N ., Diffusion in wood, C .S.I.R .O . Division of Forest Products (Australia), Reprint No. 152 (1951). [30] STAMM, A .J., Passage of liquids, vapors and dissolved materials through softwoods, U .S.D .A . Technical Bull. No. 929 (1946). [31] TAMBLYN, N .. "Penetration of chemicals into wood", Proc. Fifth World Forestry Congress, Seattle, Washington, £(1960) 1510. [32] MacLEAN, J.D ., Preservative Treatment of Wood and Pressure Methods, U .S.D .A. Agrie. Handbook No. 40 (1952).

[33] SMITH, D .N ., "The permeability of wood", Proc. Fifth World Forestry Congress, Seattle, Washington, 3 (1960) 1546. [34] RESCH, H., ECKLUND, B.A., Permeability of wood as exemplified by measurements on redwood, Forest Prod. J. 5 (1964) 199. [35] SEBASTIAN, L.P., COTE , W .A., Jr., SKAAR, C ., Relationship of gas phase permeability to ultrastructure of white spruce wood, Forest Prod. J. 9 (1965) 394. [36] ELLWOOD, E .L., Longitudinal How through vessels and sapwood, C .S.I.R .O . Division of Forest Products (Australia), Proj. 7-8, Report 1 (1958). [37] ADZUMI, H ., On the flow of gases through a porous wall, Bull. chem. Soc. Japan (1937) 304. [38] KELSO, W .C ., Jr., GERTJEJANSEN, R.O., HOSSFELD, R .L., The effect of air blockage upon the permeability of wood to liquids, Univ. of M inn., Agrie. Expt. Station Technical Bull. 242 (1963). [39] COMSTOCK, G .L ., Longitudinal permeability of wood to gases and non-swelling liquids. Forest Prod. J. 10 (1967) 41. [40] ERICKSON, H .D ., CRAWFORD, R .J., The effects of several seasoning methods on the permeability of wood to liquids, Proc. Am . Wood-Preserv. Ass. 55 (1959) 210. [41] ELLWOOD, E .L ., ECKLUND B .A ., Treatments to improve wood permeability as an approach to the drying problem, Proc. Annual Meeting of West Coast Kiln Clubs, Oregon (1961). [42] NICHOLAS, D .D ., Structure and chemical composition of the pit membrane in relation to the permeability of loblolly pine, unpublished Ph. D. thesis, N .C . State University, Raleigh, N .C . (1966). [43] SCHMIDT, J ., Press drying of beechwood, Forest Prod. J. 17 (1967) 107. [44] LANTIGEN, D .M ., COTE , W .A ., Jr., SKAAR, C ., The effect of ozone treatment on the hygroscopicity, permeability and ultrastructure of the heartwood o f western red cedar, I and EC Product Res. and Dev. 4 (1 9 6 5 ) 66. [45] LINDGREN, R .M ., Permeability of southern pine as affected by mould and other fungus infection, Proc. Am. Wood-Preserv. Ass. 48 (1952) 158. [46] ELLWOOD, E .L., ECKLUND, B .A ., Bacterial attack on pine logs in pond storage, Forest Prod. J.9 (1959) 283.

FACTORS AFFECTING THE IMPREGNATION OF BAGASSE AND OTHER FAR-EASTERN FIBROUS MATERIALS

UNG-PING WANG RADIOISOTOPE LABORATORY, UNION INDUSTRIAL RESEARCH INSTITUTE, MINISTRY OF ECONOMIC AFFAIRS, REPUBLIC OF CHINA (TAIWAN)

Abstract

FACTORS AFFECTING THE IMPREGNATION OF BAGASSE AND OTHER FAR-EASTERN FIBROUS MATERIALS. Natural fibrous materials contain a variety of natural oils or resinous compounds which partly retard the copolymerization of impregnated fibrous materials. Impregnation and gamma irradiation tech­ niques are discussed with particular reference to bamboo and bagasse.

1. INTRODUCTION

Natural fibrous materials produced in Taiwan, such as bagasse, bamboo, wood, etc., contain a variety of essential oils or resinous compounds which partly retard the copolymerization of impregnated monomer compounds. This paper treats the impregnation of fibrous materials followed by gamma irradiation as an improved method of obtaining useful construction materials. Impregnation of fibrous materials with suitable vinyl monomers can be performed without difficulty, except when the raw materials have a high water content. The water-content limit is 15% for bamboo and wood and 5% for bagasse. Higher water content entails problems which could lead to inhomogeneous distribution of the plastic material and uneven mechanical strength of the final products. Low water content can enhance the grafting reaction of monomers to the cellulose of fibrous materials. Impregnated fibrous materials have induction periods of varying length after being irradiated with gamma rays. This is obviously attributable to the presence of free radical scavengers included in the essential oils and resinous compounds, since the gamma- ray induced monomer reaction at room tempera­ ture follows the mechanism of radical polymerization. Air included in the pores of the material is also a good scavenger of free radicals resulting from exposure to gamma radiation. A longer induction period means that more scavenging agents are contained in the raw materials and a higher total gamma dose is accordingly required. Thus the method of removing or destroying these free radical scavengers is considered to be the most funda­ mental factor affecting the impregnation of fibrous materials. Economic evaluation of irradiated bagasse-plastic, bamboo-plastic and wood-plastic combinations recommends selecting the monomer for im­ pregnation from the viewpoints of both commercial utility and production cost. The lowest-priced monomer is vinyl chloride (US $0. 176/kg), while vinyl acetate (US $0.253/kg), styrene (US $0. 274/kg) methyl methacrylate

35 36 UNG-PING WANG

(US $0. 55/kg), etc. entail a much higher monomer cost. Although vinyl chloride is the cheapest monomer for impregnation and is readily polymerized in fibrous materials by exposure to gamma radiation, it must be copolymerized with vinyl acetate or plasticizers because of its non-homogeneous powdery polymer (PVC) which does not enhance mechanical strength. Styrene is considered to be an unfavourable monomer on account of its long induction period and the ready inflammability of the polymer. Although methyl metha­ crylate is a suitable monomer displaying ready polymerization by gamma radiation and the final product is hard, its high price is a limiting factor in its application to the impregnation of fibrous materials for manufacture of products of bagasse-plastic, bamboo-plastic and wood-plastic combination products.

2. IMPREGNATION OF BAGASSE-BOARD

A wide variation of the induction period was found in our laboratory among several kinds of bagasse-board which were impregnated with vinyl acetate and styrene in atmospheric pressure or in vacuo and exposed to gamma radiation. Bagasse-board, which is prepared by combining bagasse with urea-formaldehyde resin, is readily impregnated by soaking monomer into the board on account of its porosity. However, any excess formaldehyde in the resin prolongs the induction period during the gamma-ray induced polymerization of vinyl monomers. This is demonstrated by the experi­ mental results shown in Figs 1 and 2. It was also found that ammonia does not influence the induction period after neutralization of formaldehyde in the bagasse material. Since oxygen inhibits the polymerization of some vinyl monomers, such as vinyl acetate, methyl methacrylate and styrene, it is better to replace air with nitrogen before impregnating bagasse board (Figs 1 and 2). This ia easily performed by evacuating the air (10 mmHg) and pumping nitrogen gas into the closed vessel. The application of a solvent such as carbon tetrachloride accelerates the polymerization of vinyl monomers and reduces the induction period. Replacing air with nitrogen before impregnation is, however, more effective than the solvent effect of carbon tetrachloride. When crude bagasse, which has been completely washed with water (bagasse board B), is partly hydrolyzed with sodium hydroxide solution (bagasse board A), the partially hydrolyzed cellulose compounds acting as radical scavengers retard considerably the polymerization of vinyl monomers. The time of impregnation is shorter for bagasse than for bamboo and wood; for example one hour is sufficient for one-inch-thick board. The monomer content in the impregnated bagasse board reaches 60% by weight as the highest value.

3. IMPREGNATION OF BAMBOO

Bamboo is readily impregnated with vinyl monomers (vinyl acetate and methyl methacrylate). The impregnation is effectively accelerated in vacuo, while the saturated impregnation (25 - 35% monomer content) requires two to four hours. Before impregnation, it is not necessary to replace the evacu­ ated air in the impregnation vessel with nitrogen gas since no worthwhile IMPREGNATION OF BAGASSE 37

------X------BAGASSE BOARD A ------О ------BAGASSE BOARD 8 (T> O R IG IN A L S A G A S .S E B O A R D

(•TREATED BY HEAT (105 *Cj S 4 hri. ) ® BAGASSE BOARD < IMPREGNATED AT AIR PHASE ( t ATM ) I IRRADIATED AT AIR PHASE t DOSE RATE 4.5 XIO f/hf ) (■TREATED BY HEAT AND EVACUATED flO S’C , I Ù * m H j,6 hr*. ) ® BAGASSE BOARD < IMPREGNATED AT AIR PHASE ( IO ™.«Hj ) A , llP.RADIATED AT NITROGEN GAS PH ASE ( DOSE RATE 4.5X10 Г/ЛГ.> Г TR E ATE D BY HEAT ANO EVACU ATED ( 1 0 5 'C . I O m m H j,6 hrt .) @ BAGASSE BOARD J IMPREGNATED AT NITROGEN GAS PHASE( IO »i»H j) I IRRADIATED AT NITROGEN GAS PHASEtDOSE RATE 4.5 X Ю Г/hr.) ("TREATED BY HEAT AND EVACUATEDdOS 'C , 10 "> m-H } , 6 hti. ) ® BAGASSE BOARD J IMPREGNATED AT AIR PHASE ( Ю mm. H . ) I WITH THE MIXTURE OF 10 %COt<. 9 0 % V. A. (b y W j t ) IRRADIATED AT NITROGEN GAS PHASE! OOSE RATE 4.SX 10* l/ЛГ )

FIG .l. Polymerization of vinyl acetate in bagasse board. advantage results during the gamma-ray induced polymerization of soaked monomers. Among the five principal bamboo products in Taiwan, the thorny bamboo (Bambusa stenostachya Hackel) evidences the longest induction period (3 Mrad) resulting from the retardatory effect of its essential oils. In our experiments bamboo material over one year old proved to be better for the manufacture of bamboo-plastic combinations (BPC). Figures 3 and 4 show the results of induction period experiments with five kinds of bamboo material. It is worth mentioning that four kinds of bamboo (excluding thorny bamboo) show little difference in their induction periods, which are almost fixed within the range of 0. 5 - 1 Mrad. Good penetration of the monomer soaked into bamboo can be achieved as longitudinal capillaries extend to the surface of the cutting section and are directly exposed to the monomer. However, penetration is recognized to be slight in the bamboo knot regions, the texture of which is much more dense than other part's of bamboo. The mixture of vinyl acetate and vinyl chloride (30:70 by weight) is also readily impregnated into bamboo under a pressure of 3 kg/cm2 (saturated monomer content, 20- 30%), and the succeeding polymerization has proved to be similar to that of methyl methacrylate. 38 UNG-PING WANG

I 1 S ? “ 5 3 = ô ' ° ? 3 8 Л * g ОС

*.¿¡Sis 2 э « о « - о ? *« J 3 w*5 S i - o S з 3 £ Ж p

8 g £ S з

f i ï ï î S « a a « 8 О О о О О о I О О а « i S3 Î332 < 4 < w

33VlN3DH3d N0HU3AN03 FIG.2. Polymerization of styrene in bagasse board. FIG.3. Polymerization of vinyl acetate in bamboo material. IMPREGNATION OF BAGASSE 39

------О ------TAIWAN GIANT BAMBOO < DENOROCALAMUb LATIF4.0RUS MUNRO ) ------X ------G R E E N B A M B O O ( B A M e u S A o l d h a m i M U N f lO > — д — m o s o b a m b o o ( phvllostachys e d u l i s h d e L i H . ) — # — m a r i n o B a m b o o < phyllostachys m a k i n o i m a y . ) — o — THORNY BAMBOO < BAMBUSA STENASTACHYA HACKED

D O S E R A T E : 4 5 X ( O 4 Г/ h r. IMPREGNATION : Ю «"VH» . 2h

FIG.4. Polymerization of methyl methacrylate in bamboo materials.

4. IMPREGNATION OF WOOD The impregnation of many kinds of wood produced in Taiwan presents no unusual problems, showing that they can be treated satisfactorily as already mentioned in the section on bamboo. Replacing the evacuated air with nitrogen gas is necessary for woods, since their impregnation volume is greater than that of b'amboo. However, some woods (teak, stout camphor tree, Taiwan cypress, etc. ) are more intractable than others because of the longer induction period required for the polymerization of vinyl monomers, as shown in Fig. 5. For such woods, pretreatments such as extraction of the retardatory essential oils or resinous compounds or their destruction by gamma pre­ irradiation (1.5 Mrad) are applied to reduce the induction period. Figures 6 and 7 show examples of pretreated Taiwan cypress wood. It is evident that the shortening of the induction period achieved with both extraction and pre-irradiation methods confirms the presence of retardants in wood which act as radical scavengers. The period required for impregnation depends on such factors as the type of wood and its density, and the size and viscosity of the monomer; for example, with vinyl acetate and methyl methacrylate, soft wood such as common schefflera 10 cm in diameter and 30 cm in length requires 4 hours, while dense wood, such as teak and stout camphor, of the same dimensions requires 8 hours for satur­ ation with monomer. The maximum monomer content in the impregnated common schefflera reaches 60% while the intractable teak wood attains only about 30%. In the case of very long or thick wood samples, pressure should be applied during the soaking period. Unlike bagasse, impregnated wood has 40

! I 5CHCFFLCRA OCTOPHYLLA HAPMS. < COMMON &CHEFPL£AA) О < ALeuaiTCSMONTANA >с ;ff У [< 5 < i 2 < ¡¿ i t-О t- О * 2 S 2 * г * S i l * 2 < n s ; s g ^ I1 Ul j S Hs s aH ô Í 2 Œ 2 2 2 - x 5 лyj э û “ й й “ û э 20 О ш • • □ \ a Z 2 О \ Ï N-IG WANG UNG-PING

FIG. 6. Polymerization of vinyl acetate and methyl methacrylate in natural and FIG.5. Polymerization of vinyl acetate in natural wood. treated wood (Taiwan cypress). IMPREGNATION OF BAGASSE 41

FIG.7. Polymerization of styrene in natural and treated wood (Taiwan cypress). a large monomer concentration gradient between the longitudinal and the transverse directions of the wood. This indicates that monomer penetrates from the end of the grain, where the longitudinal capillary ends are exposed to the monomer, at a faster rate than from the transverse direction of the grain. Graft reaction between non-crystalline cellulose in wood cells and vinyl monomer is promoted by the polar solvents such as alcohols, acetone, chloroform, chlorobenzene, etc., which act as the swelling agents toward the wood fibrous cell walls. However, the graft percentage is recognized to be lower than that of pure cellulose (cotton or paper). Carbon tetrachloride, which is a non-polar solvent, also promotes the homopolymerization of vinyl monomers. These solvents exert a strong activation effect on graft or homo­ polymerization. Although the swelling agents would be available both for reducing the irradiation times and for controlling the heat of polymerization, their use may sometimes weaken the wood to some extent. The apparent compatibility of fibrous materials with plastics and the methods of treatment for impregnation are summarized in Table I.

4. CONCLUSIONS

Impregnation of fibrous materials, although easy to perform, is dependent to a large extent on the polymerization of vinyl monomers. The fundamental procedure is to remove the possible radical scavengers as well as to prevent them from encountering the polymerization. The water-content limitation (below 15% by weight), the size and density of the wood, and the viscosity of monomer are also leading factors to be considered. 42 UNG-PING WANG TABLE I. (cont. MRGAINO BGSE 43 BAGASSE OF IMPREGNATION 44 UNG-PING WANG

BIBLIOGRAPHY

[1] Chem. Engng News 42 31 (1964) 69-88. [2] RAMALINGAM, K.V., J. Polym.Sci., Part С No.2 (1963) 153-67. [3] KARPOV, V.L. et al., Nucleonics¿8 3 (1960) 88-90. [4] KENT, J.A. eta l., "Manufacture of wood-plastic combinations by use of gamma radiation". Industrial Uses of Large Radiation Sources (Proc.Conf-. Salzburg, 1963) 1_, IAEA, Vienna (1963) 377. MONOMER-POLYMER CHEMISTRY AND THE IMPREGNATION PROCESS

V. STANNETT CHEMICAL ENGINEERING DEPARTMENT, NORTH CAROLINA STATE UNIVERSITY, RALEIGH, N .C ., UNITED STATES OF AMERICA

Abstract

MONOMER-POLYMER CHEMISTRY AND THE IMPREGNATION PROCESS. A brief outline of early polymerization techniques is followed by a description of polymerization process chemistry, impregnation and polymerization methods and criteria for the choice of monomer. General considerations, including the effects of polymerization inhibitors, swelling agents, radiation dose rate and sample thickness, are enumerated.

Introduction Since the first early work on polymerization chemists have been study­ ing the modification of natural and synthetic fibers by polymerizing monomers inside their structure. The desire to change their properties by building into the fibers the properties of a second polymer is the basic driving force behind this kind of research. In principle a second polymer could be allowed to diffuse into the swollen fiber structure and the swelling agent, such as water, removed by evaporation. This is the way, for example, that wood can be modified to improve its dimensional stability by sorbing polyethylene oxide into it in a water swollen state. The technique is virtually impossible, however, in most cases, because of the extremely slow rate of diffusion of high polymers even into highly swollen fibers. This is overcome, however, if the polymer is actually grown inside the fiber since only the small monomer molecules need to diffuse in to feed the growing chains. Early work was carried on in this way in the case of wool fibers by the use of a redox catalyst system. With the growing interest and use of high energy radiation for initiating polymerization reactions, it was natural that this method would also be used for polymerizing inside fibrous structures of various kinds. Since the first papers were published in this field in 1955 or so, radiation has become the favored method for the formation of polymers in fibrous ma­ terials and several hundred papers have been published on this subject [1]. A clear distinction has been drawn between the simple case of in situ polymerization and of so-called graft polymerization. The former process only involves the formation of homopolymer inside the fibrous matrix. Once fomed, the polymer is essentially impossible to remove without destroying the fiber because of its size and shape and numerous entanglements. The latter process, however, involves actual chemical linkages between the new polymer and the polymeric compound of the fiber itself. Fbr a number of reasons the polymer chains, as produced inside the fiber,are extremely large and the number of chemical links are, therefore, very few. It is doubtful, therefore, whether the properties of the polymer treated fibers will be greatly different between the two different types of polymer deposition. It could be, however, that properties such as fatigue to flexing, for example, might lead to migration of non-anchored polymer. Further work is clearly

4 5 46 STANNETT necessary to study the difference in behaviour between grafted and non-grafted polymer treated fibers in order to be able to answer such a basic question. In the case of open fibrous structures such as wood the polymer can be fomed under non-swelling conditions in which case it would be mainly located in the lumen and other capillary openings. Alternatively, with adequate swelling, polymer could be formed inside the cell wall structure itself. The latter situation should lead to different properties but up to this time only limited comparative studies have been reported. When simple fibers such as cotton are involved changes in the swelling and other conditions of polymer formation can also lead to changes in the location of the polymer such as near the surfaces or throughout the fibers. It is clear that there must be considerable variations in the impregnation and polymerization procedure itself. In addition, the choice of the polymer to be fomed is of obvious importance. The properties of the various polymers can vary from hard glassy material to soft rubbery types. The behaviour and method of treatment also may vary with the different types of monomer due to changes in their chemical behaviour. The various facets of the impregnation and polymerization processes will now be discussed in more detail.

Chemistry of the Polymerization Process [21- The polymerization reaction, in general, involve three components, viz. the fibrous substrate F, the monomer M, and sometimes a swelling agent, such as water, S. Although radiation has been studied in the greatest detail, it must be pointed out that chemical methods have also been studied. Thus, the fibrous structure can be treated with monomer containing a free radical initiator such as benzoyl peroxide or azo(isobutyro) nitrile. The monomer in the structure is then polymerized by heating by oven heat or using radio-frequency heating. The heat can cause degradation of the fibers and in this way radiation might have an advantage. There are other methods such as treating the fibrous ma­ terial with part of a redox catalyst system and later with the monomer con­ taining the other half of the redox fomulation. This type of treatment has the advantage that it does not require heat. A good example is to treat the fibrous material with ferrous ammonium sulfate solution, dry and then slurry the fibers with monomer solution containing hydrogen peroxide. This method has been used extensively for studies with both wool and cellulose. The OH free radicals generated by the reaction,

Fe++ + H202 ------► HO • + OH" + Fe+++ initiate the polymerization. All the chemical methods involving the presence of free radical initiators mainly generate polymer inside the fibrous struc­ ture. There is some grafting caused by chain transfer reactions of the type,

P. + fibrous polymer F ----- ► PH + F.

R. + fibrous polymer F ----- * BH + F. F. + monomer ------FM, etc. (graft polymer) where P. is the growing polymer chain, R. the primaiy radicals arising from the decomposition of the initiator and F. a macroradical formed by the abstraction of a hydrogen atom from the fibrous polymer. However, these reactions are rather minor compared with the main initiation reaction. They are maximized, MONOMER-POLYMER CHEMISTRY 47 however, with well swollen systems. Radiation, as discussed below, in addition to the above reactions, forms radicals directly on the fiber and, thus, increases the proportion of graft to straight homopolymer. Meyer et al.C3] conducted some interesting comparative experiments between polymethyl methacrylate treated birch wood in which the polymerization was initiated with benzoyl peroxide at 6S°C and radiation at room temperature. No significant property differences could be observed except a 25% increase in abrasion resistance in the case of the radiation product. When the monomer treated fibrous material is irradiated with high energy radiation free radicals are fomed from each component. Although positive and negatively charged ionic species are also fomed, these only participate in polymerization reactions under special circumstances such as extreme dryness, low temperatures, and so on. All the work on polymerization in fibrous materials up to this time have only involved free radical reactions due to the conditions used. Thus F —JW—> F.

M -JUtf—• 2M

s -тЛАР—• 2S

F. is the polymer radical formed and X. a small molecular weight fragment radical usually but not necessarily a hydrogen atom, M. 1 and S. 1 are radicals arising from the monomer and swelling agent, respectively. Kinetically both radicals from M and from S will behave similarly and are, therefore, designated on 2M.1 and 2S. 1 for simplicity. However, chemically, two different radicals such as a hydrogen atom or methyl radical and a larger monomer or solvent frag­ ment will result. e.g. CH2 = CH -JW—* CK2 = CH + CH3 - COO. i O-COCH3

M(vinyl acetate) -WU^ M1- + МП’ toth designated M1.

Each radical can, and probably will, add monomer leading to the formation of polymer in the' fibrous structure. Only F., however, will generate grafted polymer, the other five radicals will generate homopolymer in situ. The rate of generation of radicals will depend on the concentration of the three components and the G (radical) value of each, times the radiation intensity. It is clear that to maximize the production of graft polymer rather than homo­ polymer the concentration of the fiber must be maximized and that of the other two components minimized consistent with other requirements of the process such as adequate yields and molecular weights. In addition it would be useful to use monomers and swelling agents which have low G (radical) values, i.e., are com­ paratively insensitive to radiation but will carry out their other functions efficiently. The rate of formation of polymer will depend, at a given radical concen­ tration, on the propagation rate constant, at the temperature used for the process, times the monomer concentration. The propagation rate constants vary widely, thus two monomers which lead to rubbery polymers are isoprene and ethyl acrylate. The latter, however, propagates forty times faster than the former, i.e., if all other conditions were equal the treatment would take forty times 48 STANNETT

as long to complete and could become quite impractical. The radical concentra­ tion depends also on the rate at which the kinetic chains terminate themselves which will also vary somewhat with different monomers although in the liquid state across a narrower range than the propagation rate constants. The dis­ cussion given above on the rate of formation of polymer is highly simplified and only applies to liquid systems. Even in highly swollen or capillary systems the situation becomes highly complex because of the role of diffusion in the whole process. The initial phase, i.e., the rate of formation of radicals is not itself complicated by diffusion. The chain growth, and in particular the chain termination processes are, however, highly affected. Thus, in a liquid system the basic polymerization steps are: 1) generation of radicals ccG(R. ), Cone., 2) propagation of chain cck^ÍM) (M. ) 3) chain termination мк^(М. ) 2 kp and k^ are the propagation and termination rate constants, respectively. Step 1 is essentially the same in fibrous matrices as in liquids. Step 2. however, is controlled frequently by the rate of diffusion of monomer to the free radicals produced in Step 1. Step 3 is highly delayed due to the slow rate of diffusion of the growing chains in the fibrous matrix, i.e., k^. is much smaller than in the liquid state. This leads to very long chain lengths of the polymer. In general the rate of radical build up under both sets of conditions

^ d P - = This leads on integration to

— ’ = tanh (2k1ktI)2t

where (R.)œ is the steady state concentration of radicals k, the initiation constant and I the radiation intensity (dose rate).

With a dose rate of 100,000 rads per hour and a G (radical) value of

_ g unity k,I becomes equal to 3 x 10 m l secs . A typical value for k^ in a liquid system is 10 +7-1-1 1 m sec which leads to )( R-4 ) = tanh (0.8t). ( . K . ¡CO Thus when (R.)/(R.)a> = 0.99, i.e., when 99% of the steady state value is reached then 0.8t = 2.65 or t = 3-3 seconds. It can be seen, therefore, that such polymerization reactions essentially all take place in the steady state. The situation with polymerization in fibrous materials is quite different. We have determined[4], for example, к for styrene in water swollen cotton fibers using electron spin resonance and obtained a value of 0.017 1 1m secs \ i.e., about one billion times less than the same rate constant in liquid styrene. MONOMER-POLYMER CHEMISTRY 49

In this case

4 1 4 - = tanh (3.2 x 10_5)t 4-ft* /00 Thus when (R.)/(R. )co= 0.99, i.e., when 99% of the steady state value is reached then (3.2 x 10 )t = 2.65 or t = 83000 seconds, or about 23 hours. It can be seen, therefore, that such polymerization reactions essentially all take place in the non-steady state.

Methods of Impregnation and Polymerization

The discussion presented above tacitly assumes that the fibrous structure is immersed in the monomer solution and irradiated directly. This is indeed the most popular method but it has, however, one disadvantage. The liquid monomer on the outside of the fibers will not only act as a reservoir to feed the fiber as the monomer inside is used up but will also polymerize itself. This wastes monomer and may pose a problem of cleaning up the deposited polymer or sticky monomer-polymer mixture. Two modifications largely overcome this difficulty but have attendant limitations. One method uses monomer vapor to feed the growing polymer chains. With volatile monomer this can work very well but with styrene, for example, the vapor pressure is too low to provide an adequate supply of monomer at ambient temperatures. If the temperature is raised, there may be some thermal polymerization and other difficulties. The second method which is much used for the preparation of so-called wood plastics is to soak the material in the monomer solution and irradiate it in the absence of excess monomer. This method limits the total amount of polymerization to the equilibrium monomer con­ tent of the fibrous structure. Furthermore, as the monomer polymerizes there is about a 15% shrinkage so the surfaces are deprived of monomer and the product may have to be trimmed down in size.

A different method of polymer fomation in fibers is the so-called pre­ irradiation method. The fiber is irradiated dry and the monomer solution added afterwards, i.e., the fiber is pre-irradiated. If the fiber is irradiated in air some peroxides are also formed and these will also initiate polymerization in the fiber on heating in the monomer solution. The bulk of the polymer, however, is formed by initiation by trapped radicals. The rate of termination of the radicals in dry fibrous structures is so slow that they remain essen­ tially trapped and can be used for subsequent polymerization reactions.

The pre-irradiation method has a number of advantages compared with the direct method. There is little or no polymerization of the monomer outside of the fibers and the radiation can Ъе carried out separately from the impregna­ tion which can be advantageous from a manufacturing standpoint. Also, most of the polymer is actually grafted in the case of the pre-irradiation method. In the case of monomers which polymerize rapidly with radiation, the pre-irradiatior method peimits polymerization which may be initiated by the fibrous material itself. There are disadvantages, however. In general, the pre-irradiation method is less reproducible than the direct method. Furthermore there is, in general, more degradation with this method. It is clear that the method and technique must be chosen carefully in each individual case in order to select the best possible process.

Choice of Monomer

The discussion on the fundamentals of the impregnation and polymerization process presented above mentions a number of characteristics of the monomers and 50 STANNETT

the way in which they affect the reaction. In particular the radical yield, polymerization rate constant and the vapor pressure of the monomer were dis­ cussed. In addition to these properties each monomer gives rise to a polymer with different properties. In Table I the common monomers are listed together with their characteristics and the type of polymer formed. Expensive monomers with limited availability have not been included. In addition to the single monome mixtures of monomers are often useful. This increases the range of polymer properties and may have other advantages. For example, styrene-acrylonitrile polymerises much faster than either monomer alone and leads to polymers with greater solvent and oil resistance.

TABLE I. MONOMERS AND THEIR PROPERTIES

b .p t . kP T y p e o f M on om er G (ra d ) C °C ) (3 0 cC ) p o ly m er

Vinyl, chloride - 14 - Hard, tough

S tyren e 145 0 .7 55 Hard, brittle

Methyl methacrylate 100 6. 7 143 Hard, tough

Ethyl acrylate 9 9 .5 6 .0 700 Soft, rubbery

Acrylonitrile 7 7 .3 2 .5 - Hard

Vinyl acetate 7 2 .5 12 1240 W eak

B u tadiene - 3 .0 - 3 26 Soft, rubbery

Isoprene 34 ~ 3 11 Soft, rubbery

There has been remarkably little work done where different monomers were compared from the point of view of the properties of the treated material under otherwise similar conditions. There is a very broad correlation between the properties! in the sense that soft rubbery polymers give rather lower modulus filled fibers than hard glassy ones. In the case of wood, also, there is some correlation between the properties of the polymer and the wood-polymer combination particularly in the case of hardness and overall toughness and, for example, abrasion resistance. To repeat, however, there is almost no systematic work along these lines of any extent. It should be borne in mind that the rather rigid fibrous structure governs the overall properties of the types of material under consideration. Whether the structure is filled, so to speak, with soft or hard polymer often only exerts a secondary effect on the strength properties. The presence of the polymer does, however, change many other properties, abrasion resistance being a particularly good example. Again the water resistance, as opposed to equilibrium water content, is greatly improved if the polymer is hydrophobic in nature. MONOMER-POLYMER CHEMISTRY 5 1

General Considerations

There are a number of general observations which are important with regard to the impregnation and polymerization processes. Most of these relate equally to both chemical and radiation methods of initiation but considerations of such effects as dose rate are obviously unique to radiation.

1. Effect of Air and Other Polymerization Inhibitors. Free radical poly­ merizations are greatly inhibited by oxygen (air) and various chemical compounds such as phenolic compounds. However, the oxygen has to reach the growing polymer chains and often, in the case of fibrous structures, the diffusion is sufficiently slow to minimize the inhibiting effect. A typical example of the effect of air is shown in figure 1 for the polymerization of vinyl acetate in white pine wood [5]. Even when the effect of air is minimal, such polymerizations are often less re­ producible than under nitrogen, for example, and experiments should be conducted with each system to check such behaviour before proceeding on a larger scale.

Similarly certain natural components in the fibrous materials can also cause inhibitions. Thus, the natural resins present in most woods inhibit poly­ merization, vinyl acetate monomer is particularly susceptible to inhibitions by these components. Similarly, lignin itself can exhibit an inhibiting effect. Recent work with the polymerization of styrene in wood pulp, for example, showed values of 200, 130, and 89% polymerization under similar conditions for pulps containing 0, 4, and 8% of lignin, respectively. Again, it is well to be aware of these considerations when studying polymer-fiber systems and in particular when extending such studies from one fiber system to another.

2. Effect of Swelling Agents. The importance of diffusion in the graft­ ing and in situ polymerization process has been mentioned repeatedly in this report. It is clear, therefore, that changing the rate of diffusion of monomer into the fiber will have a great effect on the process. Diffusion constants into fibers increase greatly as the fiber swells and in general exponentially with the concentration of the swelling agent in the fiber. In the case of the natural fibrous materials water is an ideal swelling agent although other polar solvents are also effective. In Figure 2 the effect of swelling on grafting plus in situ polymerization to cotton fiber is presentedUl. It is highly in­ teresting that an actual threshold of water content exists, i.e¿, up to about 10% water little grafting occurred and after that value there was a short in­ crease until the yield began to level off at 25-30% water content, a similar type of curve was found later for the grafting of styrene to polyvinyl alcohol by direct (mutual) irradiation in monomer. No explanation for threshold effect can be given at this time.

In the case of grafting and polymerization in wood, a similar dependence of the percent polymerization on swelling was found. A good illustration of this effect may be found in the data presented in Figure 3- The percent poly­ merization can be seen to vary greatly with the swelling agent present in the monomer solution,in this case styrene. It is significant that the order of in­ creasing yield is the same as the swelling power of the solvents used in these experiments ethanol > dioxane > acetone. The use of swelling agents other than water for cellulose based fibrous materials is probably mainly of interest for help in understanding the problem as economics would be against their choice, all other things being equal. As more solvent is used there is ob­ viously less monomer present which acts in an opposite direction as can be seen from Figure 3. Thus going from 25% styrene to 33-1/3% increases the yield in roughly similar proportions. This is a simple kinetic effect and illustrate the need for small quantities of highly effective swelling agents such as water to optimize the yield. The dioxane and acetone experiments were each conducted with about 5% of water added whereas the ethanol was water free. 52 STANNETT

HOURS

F IG .Î. Effect of air on polymerization of vinyl acetate in birch wood. Dose rate about 110 000 rad per hour.

FIG. 2. Effect of water on the pre-irradiation grafting of styrene to cotton.

FIG.3. Effect of swelling agents on the polymerization of styrene in pine wood. All 3:1 solvent to styrene ratio except where noted. Dose rate 50 000 rad per hour except 2:1 dioxane (25 000 rad per hour). MONOMER-POLYMER CHEMISTRY 53

The appearance of the specimens showed that considerably more homopolymeriza- tion occurred with the latter solvent.

3. Effect of Radiation Dose Rate. The effect of dose rate in the pre- irradiation method is almost negligible at the same radical concentration. However, the rate of build-up of radicals in the dry fibers increases with dose rate so that at a given total dose a greater dose rate leads to a greater yield of polymer. In the case of the direct (mutual) method the dose rate exerts a strong effect on the yield, particularly as before with the pre-irradiation on the yield per dose. As the dose rate increases the number of free radicals in the fiber increases and the supply of monomer to them by diffusion becomes more and more difficult to maintain. In addition the probability of growing chains and primary radicals terminating each other increases. The consequence is a rather sharp decrease of yield per megarad with increasing dose rate. A good illustration of this is found, for example, in the case of the radiation poly­ merization of styrene in pine wood wafers. These results are shown in Figure Д. Gamma radiation tended to give higher values in this case compared with machine produced electrons because of penetration limitations with the latter. The same data is presented in Figure 5 but this time the yield per hour is plotted against dose rate. It can be seen that in spite of the lower yields per total dose the rate of polymerization increases with increasing dose rate showing that advantages in time can be obtained by increasing the dose rate of the irra­ diation. This behaviour is quite typical also with natural fibers themselves such as wool or cotton.

о

FIG.4. Polymerization per megarad versus radiation dose rate of styrene in dioxane (1:3 ratio plus water) in p in e w o o d .

The lower yields in the case of machine irradiation are not always found in the case of thin specimens such as fibers, paper and textiles where there are no radiation penetration problems. A study in the case of wool fiber showed that the immediate yield was often low with machine irradiation because of the kinetic effects discussed earlier. However, there was considerably more post-irradiation polymerization due to the simultaneously rapid build up of 54 STANNETT radicals which continued to initiate polymerization for a long time after removal from the radiation source. This effect tends to increase the yield per megarad greatly above that expected from dose rate considerations alone and should be borne in mind when considering alternative methods of radiation.

FIG. 5. Data from Fig.4 but plotted on the basis of rate of polymerization versus dose rate.

* , 0 .05 Mcgarad i p«r hr. о » 3

2

CC 0.10 ri.garad ; per hr. Ш Q. О >____ 2 » О У CL20 H.garad p .r hr. н z UJ b LJ ОС о О 0.05 0.10 0.15 0 2 0 0 .2 5 Q3C THICKNESS - Inch**

FIG. 6. Effect of longitudinal thickness of pine-wood wafers on polymerization per megarad irradiated at given dose rates in styrene:dioxane 1:3 solution.

4. The Effect of Thickness. In the case of polymerization in wood, the thickness of the specimens can be varied and the effect studied. In Figure 6 the results of such a study are presented again using pine wood wafers. It can be seen that between 0.06 and 0.25 inches thick the yields were independent of thickness. However, at these thicknesses in the longitudinal direction almost every cell lumen would be exposed and the governing rate would be detemined by MONOMER-POLYMER CHEMISTRY 55 the rate of diffusion into the cell walls which, of course, would not change with thickness. No doubt at greater thicknesses the yield would tend to drop off somewhat.

Again in the case of wood, the direct radiation technique only works well with the simple contact plus soaking in monomer solution technique in the case of very thin wafers. For thicker specimens, it is best to pump out the air from the wood and allow the monomer solution to be sucked in or alternatively to impregnate under pressure. These techniques are familiar for many wood treat­ ment operations and are beyond the scope of this report. The only point to emphasize is that the method of impregnation with the monomer solution should also maximize the removal of oxygen from the wood in order to give the highest yields of polymer.

REFERENCES

[1] GILBERT, R. D ., STANNETT, V., Isotopes radiat. Techn. 4(1967) 403. [2] KRASSIG, A ., STANNETT, V ., Fortschr. HochpolymForsch. 4(1965) 111. [3] SIAU, J. F., MEYER, J.A., Forest Prod. J. 16 (1966)47. [4] RESTING, R. E., STANNETT, V ., Makromolek. Chem. 55 (1962) 1. [5] KENT, I.A ., WINSTON, A ., BOYLE. W.R., USAEC Rep. OR0612, Sept. 1, 1963. [6] KENAGA, D .L ., FENNESSEY, J.P., STANNETT, V ., Forest Prod. J. 12 (1962) 161.

RADIATION ENGINEERING IN THE POLYMERIZATION OF MONOMERS IN FIBROUS MATERIALS: ACCELERATORS

F.L. DALTON AND J.D. McCANN WANTAGE RESEARCH LABORATORY, AERE, GROVE, WANTAGE, BERKS, UNITED KINGDOM

Abstract

RADIATION ENGINEERING IN THE POLYMERIZATION OF MONOMERS IN FIBROUS MATERIALS: ACCELERATORS. Little consideration has been given to the possibility of using accelerators for the pro­ duction of plastic composites because the classical kinetics of polymerization are unfavourable to high initiation rates and the thickness of materials which can be treated by electron beams is lim ited. Recent developments in the surface coatings field have indicated that several monomers w ill polym erize rapidly in an electron beam of high intensity even in the presence of air, and it is suggested that a detailed study of the behaviour of a wide range of systems in such beams is necessary to determine the practical possibilities and limitations of the method. On the assumption that suitable chem ical systems can be found, the requirements of accelerators for throughputs o f about 10 000 ft2/h are discussed and the processing advantages over heat of gamma radiation mentioned. A more detailed description of the most appropriate accelerators for processing various thicknesses o f board up to i in. thick is given, with some indication of desirable development work where appropriate. Finally, the longer term possibility of using high-power linear accelerators operating at 1000 MHz or below to process extremely large quantities of 1 in. thick board is mentioned. Approximate capital and running costs of various types of accelerator are given, but because of the dependence of plant design on .the curing method a comparison of overall plant costs at a specified throughput w ill be necessary if a realistic assess­ ment of the relative merits of heat, gamma and electron initiation is to be obtained.

1. INTRODUCTION

To date, little consideration has been given to the use of accelerators for the production of wood plastic composites, and this neglect has been due to two main causes. Firstly, much of the early work on wood plastics was aimed at the treatment of bulk timber and the much higher penetrations available with gamma radiation were essential. Secondly, the classical free radical kinetics of vinyl polymerization suggest that the high intensity radiation produced by an accelerator will at best be used inefficiently and at worst will not produce any polymerization at all. The first point is clearly not relevant to the treatment of relatively thin sheets of impreg­ nated fibreboard. The second objection is more significant because it can be shown that the rate of a radiation-initiated free radical polymerization is proportional to (intensity)^, while the molecular weight is proportional to (intensity)"^: it follows that if the intensity is sufficiently high the mole­ cular weight will fall to a level at which the product can no longer be con­ sidered a high polymer. Although relatively few systems follow such kinetics accurately, intensity exponents are usually found to be less than unity and it has therefore been thought that the above considerations would apply. In recent years a considerable amount of work has been done on the

57 58 DALTON and McCANN curing of total forming paint films with electrons from low-energy (125 - 500 kV) accelerators, and it has become clear that if intensities are sufficiently increased, classical kinetics do not hold for a number of systems. The unsaturated polyester/styrene system has been widely studied [1-4], and high reaction rates have been achieved with intensities above 1000 Mrad/min. Although this system is not of interest for the production of composites, workers in both the United States of America and the United Kingdom have found that a number of acrylic formulations will polymerize readily, and these could be modified for use in wood-plastic composites. Furthermore, a number of acrylic monomers, notably acrylic acid, have been shown to polymerize completely in an accelerator beam at relatively low doses when impregnated into veneer [5] . It would therefore seem fruitful to investigate such systems further, particularly the de­ pendence of polymerization rate on intensity, since thin film work has shown that it is not feasible to predict the behaviour of materials at high intensities from their behaviour at low or even intermediate (20 - 150 Mrad/min) intensities. Until such work has been done it will not be possible to make an objective assessment of the usefulness of ac­ celerators in composite production. If suitable monomer systems are established, electron accelerators will offer a number of technical advantages over competitive initiation methods if large production volumes of plastic-filled fibreboard are re­ quired. There are two alternative initiation systems: heat, which re­ quires the addition of a suitable catalyst to the monomer, and gamma radiation from either 60Co or 137Cs. The introduction of a catalyst into the monomer in the thermal process means that the life of the monomer in the impregnation tank is limited, and this necessitates periodic cleaning down and may involve a waste of monomer. The transfer of boards from the impregnation tank to the oven involves monomer loss from the surface of the board by evaporation, and this loss will increase during the initial period in the oven. These problems, together with that of inhibition of the cure by atmospheric oxygen, can be overcome by wrapping the boards in heat-resistant foil, but this involves additional expense and the risk of the wrapping sticking to the boards. Gamma-ray processing avoids the use of a catalyst in the monomer but still suffers from monomer loss and oxygen retardation unless the boards are wrapped. Since both methods involve a fairly long curing time the physical movement of monomer within the board has to be considered, and this may well preclude stacking ma­ terial in the vertical plane. If accelerators are used, boards can go from the impregnation tank to the radiation beam in a matter of seconds, thus effectively avoiding monomer loss or movement of monomer in the board. It has been shown in surface coating work that oxygen inhibition effects disappear at sufficiently high intensity in many cases, and therefore this problem may well be avoided: if it is important a light metal cover above the conveyor running from the impregnation tank to the accelerator would be cheap and require only a small amount of inert gas to maintain a 'blanket' above the surface of the boards. The method lends itself readily to con­ tinuous processing: one can envisage boards being loaded onto a conveyor, carried to a dip tank where monomer uptake is controlled by the time of immersion (in contrast to timber, vacuum impregnation may well not be necessary for the more open structured fibreboard), over a speed adjusting conveyor section to the accelerator head or heads. RADIATION ENGINEERING: ACCELERATORS 59

It must be emphasized that these considerations are for large volume production: if only small amounts of material are needed then a con­ ventional thermal cure is the economic choice since small ovens are cheap and already possessed by many potential producers; both accelerators and gamma plants are prohibitively expensive to install to treat small quantities and would only be considered if service facilities were available. At large throughputs the economics are significantly different: the capital cost, space requirements and power consumption of an oven treating 10 000 ft2/h or more increase rapidly with throughput and need to be carefully costed in any specific case. We have so far attempted to show the desirability of developing im preg­ nation systems suitable for electron-beam curing and we shall now turn to the basic requirements of an accelerator to process impregnated fibre­ board. These are :

(1) Sufficient electron energy to irradiate the board uniformly, the thickness of which may be between 1/8 in. and 1 in. (2) The energy of the electrons must not be high enough to induce any residual activity in the board. (3) The conveyor and accelerator system must be capable of handling products up to at least 4 ft wide. (4) The accelerator should have sufficient power available in the beam to treat at least 1000 ft2/h with a dose between 5 and 20 Mrad. (5) The installation must be operable by process workers. (6) The equipment must be very reliable indeed since unscheduled breakdowns would be extremely costly. (7) The installation must be capable of maintenance by competent but not necessarily expert maintenance staff. (8) The installation must be economic in its demands on electric power, spares and associated services.

These eight requirements will now be considered in more detail.

2. ENERGY REQUIRED

The bulk density of the monomer-impregnated board is between 1. 0 and 1.3 which means that 0.125 in. of board is equivalent to between 0.125 in. and 0.163 in. of water, and 1 in. of board to between 1.0 in. and 1.3 in. of water. Assuming that an acceptable surface-to-sample interior dose ratio is about 2 : 1, reference to a suitably scaled Trump curve [6] shows that the electron energy required to keep within this ratio is 1 : 1.3 MeV for l/8-in. samples, and 6. 1 : 9 MeV for 1-in. boards. If losses in the window and air gap are taken into consideration, then the figures become 1. 08 to 1.37 MeV and 6.15 to 9.05 MeV, respectively. The above figures apply to radiation from one side of the sample only. Single­ sided operation, although convenient from the point of view of accelerator and associated beam-scanning equipment, is most inefficient in the use of the electron beam, since the tail of the depth-dose curve is not used. If the boards are irradiated from both sides, the useful board thickness (assuming 2: 1 surface-to-interior dose ratio) is increased 2.4 times over that of a single-sided operation. The electron energy for satisfactory ac- 60 DALTON and McCANN complishment of double-sided irradiation of the board thicknesses quoted above would therefore be 0.42 to 0.54 MeV for 1/8-in. boards, and 3.95 to 5.15 MeV for 1-in. boards: after allowance for window losses, these figures become 0.52 to 0. 64 MeV and 4. 0 to 5. 20 MeV, respectively.

3. INDUCED ACTIVITY

If the product is to be made available to the public the process must not induce any long-lived radioactivity; since product storage and handling must be as simple as possible for economic reasons, even short-lived activity must be avoided. If the upper lim it of energy is restricted to 5 MeV, induced activity does not present any problem. For reasons to be discussed later, 5 MeV would also appear to be the upper lim it of particle energy on a commercially viable installation. This necessitates double­ sided irradiation for all boards thicker than about 3/8 in.

4. BOARD WIDTH

The installation should be capable of uniformly irradiating standard production boards of which the most common width is 4 ft. The acceler­ ated beam of electrons from all accelerators in the voltage class being considered have circular cross-sections and generally are about 1/2 in. in diameter. In order to cover the 4-ft-wide board, the beam must be scanned or fanned by a magnetic field so that the 1/2-in. diameter spot can be made to cover the entire length of a 4-ft window. This window, through which the electrons emerge from the accelerator into the air above the conveyor, must be thin enough to transmit as much of the electron beam as possible, and yet be strong enough to complete the vacuum chamber, withstanding 15 lb/in2. The most common method of making the beam cover the 4 ft is the use of a transverse magnetic field which causes the electrons to be deflected at right angles to the field. By varying the strength of the field in a periodic way, the beam can be made to sweep back and forth along the window. The angle through which the electrons are deflected is generally only ±10° to ±20°, so that beam and dose distortion can be kept to a reasonable level. Movement of the beam within the magnetic field is only about an inch on either side of the centre line, but this is magnified in the geometry of the beam path within the scanner horn (a section of the vacuum system) to give full conveyor width coverage. The electron beam of only 1/2-in. diameter (0.2 in2) when scanned along a 4-ft window produces a difference in the peak spot intensity to mean product intensity of over 100 times. As mentioned earlier, this higher peak electron intensity (hence dose rate) may increase the dose to cure and thus reduce plant throughput. An alternative beam-spreading system is based on the use of one section or, preferably, a pair of quadruple lenses. A single quadruple lens will produce focus in one plane and defocus in the other and if a second lens section is added, such that the focus/defocus action is cumulative instead of complementary, a fan-shaped beam can be produced. The system has the advantage of having equal peak and mean intensities and the magnetic fields required are steady. The disadvantages of the system are that: RADIATION ENGINEERING: ACCELERATORS 61

(a) good uniformity is difficult to obtain at reasonable defocusing angles; (b) greater geometric magnification is necessary, thus involving an even larger beam handling chamber; (c) non-uniformities in the emission of the cathode appear in the final output, since the lens gives a defocused image of the source; (d) it is much more difficult to set up for different particle energies and sample widths than an installation equipped with scanning.

Since both types of beam-spreading device detailed above use a primary accelerated beam of high intensity, a failure of the spreading system must immediately cut off the incoming beam or window destruction will occur. Reliance on the quick operation of the supply contactors is generally not good enough on a high-power installation, and systems with electron gun gating and off-set incident beam bias have been devised to cope with the vital few milliseconds before the contactors can come into operation and remove the accelerating voltage completely.

5. POWER REQUIREMENTS

If single-sided irradiation is used and a generated beam of 1 mA is spread out over 48 in. X 1 in. of sample, then the dose at the 50% remote surface of the board will be approximately 7.2X 105 rad/s. If the dose requirement at the minimum point is assumed to be 5 Mrad, then the conveyor speed would be 1 in./7 s or 43 ft/h. On 4-ft-wide board this gives a production of 172 ft2/h. The desired throughput is at about 10 000 ft2/h and this would require a beam current of about 60 mA. The current required for the 20-Mrad dose would of course be 240 mA. Double-sided irradiation would reduce the current required per side enormously due to the better utilization factor and lower overdose ratio. A current of 1 mA per side spread over 48 in. X 1 in. of board would give an average dose rate of 1. 6 Mrad/s. Since the minimum, all important dose, is only about 10% below that of the average value if the correct energy/thickness relationship is used, the effective dose rate will be­ come 1.45 Mrad/s. To deliver a dose of 5 Mrad at the minimum dose rate point, the con­ veyor belt must move 1 in. in 3.5 s. This rate amounts to 85.8 ft/h on boards 4-ft w ide, i . e . 343 f t 2/h. T o attain a throughput o f 10 000 f t 2/h, 29 mA would be required on each side of the board for a 5-Mrad dose; 116 mA per side would be needed for a 20-Mrad dose. The above figures are based on the uniform 'illum ination' of a 48 in. X 1 in. strip of board. In practice, due to deflection distortion and non-linearity in the scanning system at or near the ends, the beam must be scanned over a length greater than that of the sample to be irradiated. This over-scanning means, as far as a finished product is concerned, wasted beam. The over-scanned sections of the beam would be used, how­ ever, for current or energy monitoring. The loss of throughput due to over-scanning is usually about 10%, but if uniformity is very important it may be as high as 20%. Table I shows beam currents and power requirements for single-sided operation on boards up to 3/8 in. thick and for double-sided irradiation from 1/8 in. to 1 in. thick. In all cases the dose quoted is the minimum 62 DALTON and McCANN

TABLE I. POWER REQUIREMENTS

Single-sided

T h ickn ess Energy Current D ose Power per 1000 ft2/h ( i n . ) (M e V ) (m A ) (M ra d ) (k W )

1/8 1.08 to 1.37 6 .6 5 7.13 to 9.03

3/8 3.06 to 3.95 6 .6 5 2 0 .2 to 26

1/8 1.08 to 1.37 2 6 .4 20 28.5 to 36.2

3/8 3.06 to 3.95 2 6 .4 20 80.4 to 104

Double-sided

Current Total machine power per Th ick n ess Energy D ose per side 1000 ft 2/ h ( i n . ) (M e V ) (M ra d ) (m A ) (k W )

1/8 0.52 to 0.64 3 .2 5 3 .3 3 to (2 x 1.67) 4 .0 8 (2 x 2 .0 4 )

3/8 1.55 to 2.0 3 .2 5 9 .9 0 to ( 2 x 4 . 9 5 ) 1 2 .8 ( 2 x 6 . 4 )

1 4.0 to 5.20 3 .2 5 25 to 32 (2 x 12.6) (2 x 16)

1/8 0.52 to 0.64 1 2 .8 20 1 3 .3 to ( 2 x 6 . 6 5 ) 1 6 .3 (2 X 8 .1 5 )

3/8 1.55 to 2.0 1 2 .8 20 3 9 .6 to ( 2 x 6 . 6 5 ) 5 1 .2 ( 2 x 2 5 . 6 )

1 4 .0 to 5 .2 1 2 .8 20 100 to 128 (2 x 50) (2 x 64) RADIATION ENGINEERING: ACCELERATORS 63 value on or within the board. Accelerator window and air gap keV losses have been added to the energy required, and 10% has also been added to the beam current to allow for over-scanning.

6. SIMPLICITY OF OPERATION

The accelerator, conveyor and impregnation plant must be operable by available staff with the minimum of special training, and it is therefore desirable to control the conveyor speed by a suitable feedback loop from an intensity monitor, which in turn may be linked to a program unit into which required dose information is fed. The particle energy could also be 'called up' for thickness of board going through and its correct function­ ing determined automatically by an energy monitor. Normal minor devi­ ations from the programmed parameters should be capable of automatic correction by the above feedback loops. Major deviations likely to lead to a complete breakdown and damage, such as jamming of the conveyor, failure of scanning, etc., should immediately shut down the accelerator high-tension system and any other supplies considered necessary. Interlocks would be designed such that no process worker could get near the radiation, high voltage or inner conveyor area. Access to such areas would be available only to maintenance staff, but process workers should be on hand to take corrective action should the feedback loops momentarily fail to hold the process within prescribed limits.

7. RELIABILITY

This is of utmost importance when considering a factory process handling 10 000 ft2 or more of board per hour. Failure in any one part of the system means either a complete shutdown, transferof workto standby equipment or storage of the partly finished product until the necessary repairs have been completed. Storage could provide an answer during a short break of a few minutes. Momentary failure of the accelerator due to a mains surge need not stop production provided the low dose boards could be rejected from the stream before stacking. Due to the high capital cost of accelerators the use of standby equipment would not be possible. With special designs of the accelerator beam transfer system it is possible to carry out load sharing and allow the plant to carry on at a re­ duced speed. The reduction in throughput may not be serious if each indi­ vidual accelerator in a double-sided system is designed for short-period operation at more than normal beam power. This is far cheaper than a complete standby system, which, in any case, would take time to bring into operation.

8. MAINTENANCE OF THE ACCELERATOR

Planned maintenance should be performed scheduled with the rest of the process plant. The accelerator should be so designed that this can be carried out by regular maintenance staff, after a training course at the manufacturers' works. The staff should also have sufficient knowledge 64 DALTON and McCANN and skill to rectify emergency breakdowns on a unit or tube replacement b a s is . The accelerator manufacturer should be able to provide expert help at short notice to correct obscure defects. He should also be able to get any necessary unusual spares to the plant rapidly. Without such backing, the plant user may have to employ unnecessarily highly qualified staff to advise on difficult repairs, and tie up large sums of capital in the form of spares, many of which may never be used. Some types of accelerators use high pressure gas to provide insulation in the high-voltage section. This gas must be kept clean and dry as well as at the correct pressure. This entails high-pressure gas-handling equipment. If the gas is expensive, such as SFg , it must be collected when any maintenance involving opening of the high-voltage equipment tank is carried out. This gas must be stored during maintenance and, after undergoing some repurification process, be used to refill the tank when required. Less expensive gases such as nitrogen and C02 are usually allowed to go to waste on a pressure release for maintenance. Sufficient high-pressure storage has to be provided to cater for a refill after maintenance and also the possibility of an unscheduled pressure release being necessary a few hours later to correct some newly developed fault. Some accelerators use expensive finite life components; these include accelerator (beam) tubes, high voltage rectifiers, high-power radio frequency valves and high-power klystrons. Replacement of such items would be required every 1000-4000 hours of operation, and adequate component testing would reduce unscheduled replacement to a minimum.

9. ECONOMY IN THE USE OF MAINS SERVICES

The power requirements given in Table I show the beam power re­ quired atthebo'ards being processed. Accelerators vary in their efficiency of conversion of electric supply input to useful output beam. This can range from over 90% for a simple transformer/rectifier system to as little as 15% for some types of linear accelerator. These figures refer only to high tension to beam conversion efficiency, but when cathode power, vacuum systems and cooling circuits are considered, the overall efficiencies are even lower. Although the sheer cost of the electric power must be considered when assessing the merits of an installation, a much more significant cost is that of getting rid of the heat generated in an inefficient accelerator. Having considered the basic requirements of accelerator systems, we shall now discuss the types of accelerator which are available or could be developed from known designs. In all cases straight accelerator tubes are used, and in them the electrons only make one transit from the emitter in the electron gun through to the exit window. The systems may be divided into two groups: those using the full direct voltage to provide the acceler­ ation and those using radio frequency fields in a series of resonant cavities placed along the beam path, each of which adds energy to the electron beam. A machine using the RF cavity principle is usually known as a linear ac­ celerator and, if operating at frequencies above 1000 MHz, a microwave linear accelerator. In machines using a direct accelerating voltage, the RADIATION ENGINEERING: ACCELERATORS 65 accelerator tubes have a series of intermediate shaped electrodes between the electron gun and exit window. These electrodes are arranged both to focus the beam and to control the voltage gradient along it; this is achieved by supplying them from a voltage dividing network.

10. CONVENTIONAL TRANSFORMER/RECTIFIER HIGH-VOLTAGE SUPPLIES

Conventional transform er/rectifier high-voltage systems are straight­ forward, efficient, reliable and cheap, but at present operate at voltages well below the normal limits of power transformer technology. Since power transmission systems are now operating at over 500 kV, there seems no reason why this technology should not be used to raise the commonly ac­ cepted lim it of 2*50/300 kV on transformer rectifier sets to about 500 kV. Reference to Table I shows that even if this were done the transformer/ rectifier power unit would only be suitable for treating the thinnest sheets mentioned, though for such sheets it would be the simplest and cheapest s y s te m . To enter the 3- or 4-MV class, different methods of obtaining high potential must be employed.

11. VAN-DE-GRAAFF ELECTROSTATIC SYSTEM

Although the Van-de-Graaff type accelerator is now regarded as al­ most the classical radiation research tool of high precision, it does not have the power output capabilities to conduct large-scale radiation processing.

12. OTHER TYPES OF ELECTROSTATIC GENERATORS

With other machines attempts have been made to increase the charge transfer rate (current) of the devices. The moving belt of the Van-de-Graaff, although convenient, has many mechanical disadvantages. A well tried substitute for the belt is an insulated cylinder. This can be made rigid, accurately balanced and made to run at very high speeds of rotation. In addition, the surface area can be increased by increasing the length of the cylinder. Since the path length between the input spray comb and out­ put terminal is in general only a quarter of the circumference of the cylinder, high output voltages are not possible without resort to large-diam eter cylinders. Mechanical features, such as centrifugal stress, set a practical lim it to the size and speed of the insulating cylinders. Voltage ratings of 600 kV are usual, although values of 800 kV can be obtained at currents of 12 to 14 mA. At 500 kV, currents available can be as high as 50 mA. It is possible to couple mechanically two or more cylindrical gener­ ations in cascade. In this way higher final voltages can be obtained without the use of a large rotor, the penalty paid being in the form of a more complex construction. 66 DALTON and McCANN

13. CASCADE RECTIFIER POWER SUPPLIES

In cascade rectifier circuits the rectifiers and capacitors are arranged to give a stage-by-stage multiplication of the input voltage but at no "time are the ratings of individual components exceeded. Standard high-voltage com­ ponents can therefore be used to obtain very high final voltages. The voltages appearing at each multiplier stage can also be used to supply the inter­ mediate beam-tube electrodes. The first multiplier circuit capable of extension to a reasonable number of stages was the Cockcroft/Walton system, and air insulated versions operating at 50 Hz input supply were built at the Cavendish Laboratory, C a m b rid g e . Until recent years, these accelerators had advanced little, but, since the late nineteen-fifties, totally enclosed versions using oil or pressurized gas insulation, modern rectifiers and high-frequency drive have appeared on the market. 10-kc/s valve-driven versions are available to 600 kV at 200 mA with extension to at least 1 MV [7] . Another important form of cascade rectifier circuit is that using a parallel input feed and capacitors connected from the feed lines to each multiplying stage. In this system the series impedance is very low, but the feed capacitors have to stand the full high voltage appearing at that point in the system. Since the feed capacitor in the last stages must with­ stand 3 or 4 MV, the only practical values of capacitors at this voltage are in the pico-farad range. This size of capacitor immediately dictates operation at input frequencies of 100 kHz or more to keep the individual stage supply impedances down to a workable value. Such machines (known as Dynamitrons [8] are currently available in the 1.0- to 3.0-MV range with beam currents of 10 mA. Gperation of 4.0-MV stacks has been carried out and with engineering improvements 5 MV should be possible. Beam currents above 10 mA should also be possible but this would involve more than making more 130-kHz radio frequency power available. The thermionic valve rectifiers would have to be increased in their current capability and this would bring with it the usual troubles of departing from a well tried type. Their heater powers would also probably be greater, giving problems in supply and then the removal of waste heat. The feed capacitors would also have to be increased to keep the regulation acceptable. Even in its present form, this type of accelerator does have sufficient power to form the basis of a plant capable of processing about 3000 ft2/h to 5 M rad.

14. INSULATING CORE TRANSFORMER

In the insulating core transformer system (also invented by Van-de- Graaff), the rectifiers, capacitors and associated transformer windings are kept down to 25 kV. A secondary winding, together with rectifiers and capacitors, is built as an assembly on an insulated section of ferrite core. If sections are now stacked up with suitable insulation between them, and the output voltages connected in series, a high final voltage can be produced without resort to any special very high voltage components. One feature of a practical design does, however, reduce the usefulness of the system. The magnetic flux in the segmented core must have a return RADIATION ENGINEERING: ACCELERATORS 67

path and this must be made without shorting out the high voltage existing on the core. Flux return is usually made through a large gap at the high- voltage end. The shape of this end is designed to reduce the reluctance, and the transform er system is pressurized so the gaps may be kept to a minimum. Even so, this gap in the flux path does produce a very high leakage of flux in systems designed for operation at above 2 MV and conse­ quently a high kVA input is required. The system can be designed for single- or three-phase operation from the public electricity supply. The three- phase mode opens up the possibility of very high power operation. 500-kV units at 30 mA are in use in various parts of the world. 500 kV at 200 mA (100 kW) has been proposed for power accelerators used to cure surface coatings by electron irradiation. Insulating core transformer units are available to operate at 1. 5, 2.5 and 4 MV, the currents being 30 mA at 1. 5 MV, 20 mA at 2.5 MV and 10 to 15 mA at 4.0 MV. If the customer requirement developed sufficiently for 5 MV at 50 mA the engineering and technology should be able to fulfil the demand.

15. RESONANT TRANSFORMER

The resonant transformer is the last type of directly applied voltage accelerator system to be mentioned in this paper and dates from 1937-39 [9] . In its earliest form it was used as an X-ray generator, but later the internal structure was rearranged to enable electrons to be accelerated and extracted [10] . A great deal of further development would be neces­ sary before outputs of interest for board processing could be obtained.

16. LINEAR ACCELERATORS

The microwave linear accelerator, using a travelling electromagnetic wave within an evacuated waveguide, has been known since the early nineteen-forties. Electrons are launched onto the travelling wave by an electron gun and once bunched up on the wave move along with it, taking energy from it as they ride. Electrons can easily gain 10 MV per metre of such a guide when the 3000-MHz power to excite the guide comes from a large klystron. Microwave linear accelerators are usually used for research purposes and as such designed for maximum energy gain rather than maximum efficiency. In a machine used for irradiation processing the aim would be for maximum conversion of RF power to accelerated electron power. A 20-MW peak/20-kW mean power, 3000-MHz klystron would be best employed driving two accelerator waveguides each capable of producing 5-MeV beams of electrons at 6-kW average power. This means power is in­ sufficient for required processing speeds, and to obtain useful power levels it is necessary to operate at or below 1000 MHz. Klystrons of this type can only produce this high power in short pulses. The on-to-off time (duty cycle) is usually about 0.001. In this frequency range high power valves are available that can be operated at high duty cycles, some even under continuous wave conditions. It is in this class that real possi­ bilities exist for 4- and 5-MV machines of average powers of 250 kW (50 mA at 5 MV). 68 DALTON and McCANN

Continuous wave operation produces a steady beam as distinct from a pulsed beam from the 3000-MHz klystron accelerators. The higher average beam does not involve enormous peak currents. The beam of electrons is not, however, a continuous stream, but is in the form of electron bunches, one per cycle of the radio frequency input. These bunches, known as the fine structure, occupy between 2% and 5% of the cycle, depend­ ing on waveguide design. This leads to a peak current between 50 and 20 times the average value and this should be taken into account when assessing dose-rate effects in the board. The accelerating structure could either be a set of cavities operating on a travelling wave system, or, at frequencies of 400 to 600 MHz, could take the form of a set of separate cavities and drift spaces. The first system would be designed to give a particular energy and would require a fixed valve of peak RF input, while the second system could be made more versatile since the phase progression along the set of cavities would be capable of variation to suit different energies and peak inputs. Such a machine should be capable of efficient operation over the range 1 to 5 MeV at beam currents of greater than 50 mA. In order to keep the number of cavities (acceleration stages) and hence the overall size of the system down to reasonable dimensions, the peak value of the RF input power should be at least 500 kW, preferably 1 MW in a 5-MeV accelerator. If the acceler­ ator is to be operated under continuous wave conditions and assuming 50% conversion efficiency, then the smallest practical system would have 250 kW of electron beam output. A processing installation with two such accelerators (one per side) would have a production capability of about 20 000 ft2/h at a 5-Mrad dose le v e l. We shall now consider the most practical installations for a given thickness of board, and give some estimate of the costs involved. Since accelerator processing of board is not at present carried out, such figures must necessarily be approximate but will indicate the relative costs of alternative systems and serve as a guide to the magnitude of the investment required.

17. 1/8-INCH BOARD

As suggested previously, a simple transformer rectifier system could be extended to 500 kV and this would be just sufficient to treat l/8-in. board of low density if double-sided irradiation were used. Further ex­ tension to 650 kV, which may well be possible, would cover the full density range encountered. At 500 kV, using two heads (one on each side of the board) and each giving 32 mA, a complete accelerator system, with shielding, would cost approximately £70 000 and would treat 10 000 ft2/h to 5 Mrad. Running costs of the accelerator would be about £5.10. 0/h whether one- or two-shift working were employed. This gives an overall cost based on a 5-year amortization and 10% interest on capital of about 0. 2 d/ft2 on a 5000-h year and 0. 3 d/ft2 on a 2000-h year. Insulating core transformers operating at 500 kV and up to 200 mA are at present being developed and higher voltages are also available. This suggests that in the short term larger throughput plants could be built using this system . A t 500 kV and 200 m A (100 m A / sid e) capital cost would be RADIATION ENGINEERING: ACCELERATORS 69 about £140 000 and running cost about £7/h. Such a plant would treat 30 000 f t 2/h to 5 M rad and with a 5 -y e a r a m ortiza tion and 10% in terest on capital this gives a cost of 0. 2 d/ft2 for a 2000-h year and 0.1 d/ft2 for a 5000-h year.

18. 1/4-INCH AND 3/8-INCH BOARD

These thicknesses would best be treated by an insulating core trans­ form er of appropriate energy. Some idea of cost may be obtained by con­ sidering an existing 1.5-MeV machine of 30-mA output. Two such machines would be needed to treat board up to 5/16 in., and their cost would be about £65 000 each (a single unit made to deliver 50 mA would presumably cost somewhat less), and would treat 10 000 ft2/h to 5 Mrad. Overall costs would be about 0. 5 d/ft2 of board on a 2000-h year and 0. 3 d/ft2 on a 5000-h year.

19. 1/2-INCH BOARD

A pair of 2.5-MeV insulating core transformers of existing design delivering 20 mA each could treat 6300 ft2/h. Capital cost would be around £100 000 p e r unit and o v e r a ll costs 1 d/ft2 fo r a 2000-h y e a r o r 0. 55 d fo r a 5000-h year. At all-thicknesses up to 1/2 in. (2.5 MeV) cascade rectifier systems could be engineered to compete with insulating core transformers, but this requires a considerable scale-up of existing equipment.

20. 1-INCH BOARD

T h e treatm en t o f boards 1 in. thick at throughputs o f 10 000 f t 2/h and above is not economically feasible with existing equipment. The develop­ ment of a linear accelerator operating at 1000 MHz or less would offer a possible method of treating very high throughputs (above 20 000 ft2/h), but the capital cost involved would be about £500 000 and overall costs in the region of 1 - 1 1/2 d/ft2 . In view of the development necessary, capital cost and power requirements (~ 2000 kW from the mains for the accelerator and its ancillaries), it does not seem likely that such a system could be considered in practice for a considerable period and it is mentioned here m erely to give an indication of the problems of treating thick boards. In all, the above data costs have related only to the accelerator, but any realistic appraisal of a practical process must involve the whole technology, and the relatively simple board-handling equipment needed by accelerators may well be a great advantage at processing speeds above about 30 linear ft/min. In summary, it seems that relatively little development of existing accelerator technology would enable boards of 1/2 in. thickness and below to be conveniently processed at high speed and if a large market for a plastic impregnated board (at realistic cost) can be found, then an investi­ gation of monomer systems suitable for electron curing should be under­ taken at an early date. 70 DALTON and McCANN

REFERENCES

[ 1 ] CALLINAN, T .D ., Proc. ONR Symposium ACR-2 (1954) 24; Electl Engng, Lond. 74 (1955) 510; Electl Equip. (July, 1956); Insulation (August, 1956). [2] CHARLESBY, A ., WHYCHERLEY, V ., J. appl. Radiat. Isotopes 2 (1957) 26; CHARLESBY, A., WHYCHERLEY, V ., GREENWOOD, T .T ., Proc. R. Soc. A244 (1958) 54. [3] BURLANT, W ., HINSCH, J., J.Polym.Sci. A3 (1965) 3587. [4] HOFFMAN, H.S., SMITH, D. E., Mod. Plast. 43 (1966) 111. [5] BARTLETT, J. A., DALTON, F. L., unpublished results. [6] TRUMP, J.G., VANDEGRAAFF, J., J. appl. Phys. 19 (1948) 599. [7 ] REINHOLD, G ., TRUEMPY, K ., Future high voltage dc power supplies, IEEE Trans. Nucl. Sci. 14 3 (1 9 6 7 ) 139. [8] MASON, C. F ., Mechanical design concepts of dynamitron accelerator, IEEE Trans. Nucl. Sci. 14 3 (1967) 157. [9] CHARLTON, E. E.. WESTENDORP, W .F., DEMPSTER, L.E., HOTALING, G ., A new million volt X-ray outfit, Radiology 10 6 (1939). [10] KNOWLTON, J.A ., MANN, G .R ., RANFTL, J. W ., The resonant transformer, a source of high energy electrons, Nucleonics 12 (1953) 64. RADIATION ENGINEERING IN THE POLYMERIZATION OF MONOMERS IN FIBROUS MATERIALS: RADIOISOTOPES

A.J. FELICE COMMERCIAL PRODUCTS, ATOMIC ENERGY OF CANADA LIMITED, OTTAWA, ONT., CANADA

Abstract

RADIATION ENGINEERING IN THE POLYMERIZATION OF MONOMERS IN FIBROUS MATERIALS: RADIOISOTOPES. The choice of radiation source and plant design for polym erizing monomers in fibrous materials has been studied. A comparison is made with m edical product sterilization to provide useful in­ sight and perspective. Alternative features of irradiation plant design are considered and some general conclusions drawn.

1. CHOICE OF RADIOISOTOPE SOURCE

A survey of the possible types of radiation source has been made in a study for the United States Atomic Energy Commission regarding wood- plastic composites fl] . The findings are summarized below:

Type of source Com m ents

S od iu m -24 Short 15-h half-life requires use of a loop at a nuclear reactor. Sodium must be kept above its melting point of 208° F. Source output dependent on reactor power level.

Caesium-137 Has long 30-yr half-life. Potentially competitive with cobalt-60 but cost is not firm and has not as yet been used extensively to demonstrate long­ term performance.

Spent fuel elements Cost not established; variable source output; requires proximity to reactor site. Gross fission products Requires piping a diluted liquid stream from a fuel processing plant. Requires further explor­ ation.

Nuclear reactor Cost of radiation, per se, is competitive but requires cadmium shield for neutrons, more complex and costly conveyor system and biological shield. Needs further engineering study.

X - r a y m achines and (Outside scope of this paper). accelerators

C o b a lt - 60 Now extensively used; technology is well devel­ oped and price structure is firm.

71 72 FELICE

Cobalt-60 was selected for use in the pilot and production facilities under study. Similarly, cobalt-60 will be singled out for further consider­ ation in this paper. It should be borne in mind that many of the consider­ ations entailed are common to all types of sources; in the case of caesium- 137, close sim ilarities in design are to be expected.

2. CHARACTERISTICS OF MEDICAL PRODUCTS STERILIZATION PLANTS

A review of some of the existing commercial irradiation plants will provide a useful background and will set the stage for the design consider­ ations of an irradiation plant for polymerizing monomers in fibrous m a te ria ls . Medical products have been sterilized commercially with cobalt-60 since 1960; these plants now number thirteen. Many improvements and refinements have been introduced over this period of time so that now the- cobalt-60 plant provides an ideal high performance. One of the highest capacity plants is that of Ethicon Inc., Somer­ ville, New Jersey, illustrated in Fig. 1 [2] .

FIG .l. The l-M C i cobalt-60 plant used for sterilizing medical supplies by Ethicon Inc., Somerville, N. I.-. United States of Am erica. RADIATION ENGINEERING: RADIOISOTOPES 73

The conveyor system consists of a load-unload station, a maze con­ veyor and a cell conveyor. The irradiation boxes are moved through the system in a metal frame, or carrier, which has four open compartments on top of one another. At the load-unload station, which is outside the radiation cell, the boxes are handled with an elevator mechanism. In each cycle, two irradiated boxes coming from the cell are removed from the lower compartments of the carrier. The boxes from the two top compart­ ments are transferred to the two lower ones, and two irradiated boxes are placed in the top compartments. The top of the carrier is attached to a trolley head which is taken, by an overhead chain conveyor from the load-unload station, through the maze and deposited in front of the cell conveyor system. Here it is picked up and taken through the cell and then back to the load-unload station. The carriers are advanced and transferred from one pass to the next by pneumatic push and transfer devices located at both ends of the cell conveyor system. Motion is intermittent, and the stops are in predeter­ mined sequence. Failure of completion of one cycle automatically shuts down the plant.

FIG.2. Ethicon's Edinburgh Plant showing the vertical cell conveyor.

One variation from the foregoing design is a vertical cell conveyor which is used in Ethicon's Edinburgh plant illustrated in Fig. 2. This plant uses a 'dry' storage for the source, whereas the foregoing uses 'wet'. Another Ethicon plant at Hamburg, Germany, illustrated in Fig. 3, has two very narrow mazes — one for conveying the product into the ir ­ radiation chamber, the other out. A separate 'plug' type door provides access for maintenance personnel. In contrast, the plant of Fig. 1 uses a single maze for all three purposes. 74 FELICE

FIG.3. Ethicon's Hamburg Plant showing the double m aze arrangement and personnel access door.

FIG.4. Ethicon's Rome Batch Plant. Each box is irradiated from all four sides as it circulates around the central source.

At the other end of the scale is the small batch plant shown in Fig. 4. In this design the product boxes are automatically circulated around the source to expose all four sides, but are manually indexed from one level to the next and are manually loaded and unloaded. The lower capital costs made possible by this small plant are accompanied by a lower radiation efficiency and by a higher per-unit irradiation cost. Medical products sterilization is, in general, characterized by the following features:

(a) Excellent irradiation plant utilization has been realized; opera­ tion virtually 24 hours per day throughout the year is commonplace. (b) Completely safe operation has been proven concerning the radi­ ation hazard, source integrity and ozone hazard. (c) The virtual absence of a limit on product inventory permits excellent radiation efficiencies of 25 to 3 5% to be attained in the larger plants. RADIATION ENGINEERING: RADIOISOTOPES 75

(d) The wide latitude in size and proportions of irradiation con­ tainer permits good uniformity of radiation; the overdosing ratio, i.e. the ratio of maximum to minimum dose, normally falls in the range of 1. 2 to 1. 5. (e) The sterilization process is independent of dose rate. (f ) High dose rates can be used; in the larger plants, most of the dose is delivered at dose rates up to 2 Mrad/h. (g) Irradiation can be dealt with quite separately from the balance of the manufacturing process aside from meeting the dose requirements. Questions of toxicity or explosion hazards do not a ris e . In many respects, the properties of cobalt-60 are ideally suited to the irradiation of medical products. The foregoing review conveys, in terms of practical reality, some appreciation of the latitude open to the designer and of the interplay of the various requirements. The considerations in the design of cobalt-60 irradiation plant for polymerizing monomers in fibrous materials can now be examined by focusing attention on the requirements which are 'unusual' relative to those of medical products sterilization. Considerations that follow are based predominantly on the methyl methacrylate system about which more technical data are available.

3. 'UNUSUAL' REQUIREMENTS OF AN IRRADIATION PLANT FOR POLYMERIZING MONOMERS IN FIBROUS MATERIALS

Although further development work is needed on some aspects of this polymerization process, the 'unusual' requirements are sufficiently well known to permit fruitful consideration of the various aspects of irradiation- plant design. These 'unusual' requirements are:

(a) The dose for complete polymerization is a function of the dose rate to the 0. 3 power over the range 0. 01 to 0. 82 Mrad/h (3] . This relationship applies to several monomer systems and varieties of wood, as shown in Fig. 5. This relationship favours the use of a low dose rate so as to economize on radiation; however, to do so requires a physically larger plant with attendant higher capital cost. Where higher dose rates are concerned, it is noted that the pre-gel region of polymerization is relatively insensitive to dose rate. It appears worthwhile to use a high dose rate during the pre-gel period followed by a lower one for the re­ mainder of the irradiation. Current data leads to the belief that when the ratio of the high to the low dose rate is small, say, three or four, the total dose required is that usually necessary with only the lower dose ra te [4]. (b) Heat of polymerization is released [1] . The resultant temper­ ature rise must be limited to prevent product deterioration. Control can be achieved by heat removal and by limiting the rate of polymerization. For a given monomer system the latter factor is controlled by the dose ra te. (c) The required dose being dependent upon the type of monomer, as shown in Fig. 5, requires that the irradiation plant be capable of deliver­ ing a total dose which is variable by a factor of, say, three if more than one monomer system is to be used. 76 FELICE

FIG. 5. Effect of dose rate on the total dose requirements for complete polymerization of various systems.

FIG. 6. Effect of dose rates on the total dose requirements for complete polymerization of methyl methacrylate systems in various wood species. RADIATION ENGINEERING: RADIOISOTOPES 77

(d) The required dose is also dependent upon the type of wood, as shown in Fig. 6 [3] ; however, this factor is of little importance for pur­ poses of this paper. (e) The hazards associated with handling and processing monomers are fire, toxicity, and uncontrolled polymerization [1] . The first two re­ quirements, though demanding, can be met. The polymerization rate must be kept in check by appropriate controls on the monomer system, given that a specified maximum dose rate will be involved.

4. IRRADIATION PLANT DESIGNS FOR POLYMERIZING MONOMERS IN FIBROUS MATERIALS

It would be useful to have complete information on the pilot plant owned by American Novawood Corporation, which has been operating since May 1966 with an initial source of 63 kCi of cobalt-60 [5] . For reasons of commercial security, little may be reported. The plant capacity is five million lb/yr at one Mrad dose with 400 kCi cobalt-60. Irradiation is per­ formed underwater on a batch basis with gas-tight containers. Containers can accommodate product to maximum dimensions of 4 ft wide, 8 ft long, and 1 ft thick. The total capital cost, including the impregnation and irradiation facilities, was $500 000. A production-sc ale irradiation plant design, developed by Vitro Engineering Company for the USAEC [1] , is shown in Figs 7 and 8 and entails the following features:

Processing capacity: 24 million lb/yr (3000 lb/h for 8000 h) Product load per carrier: 3000 lb Space in carrier for product: 8 ft high X 8 ft long X 17 in. thick Size of three source racks: 70 ft, 35 ft and 100 ft long, each 9 ft high Source storage: Water-filled trenches 24 ft deep Cobalt-60 capacity: 1. 28 million Ci cobalt-60 Total dose: 1. 0 Mrad Dose rate at 3 source segments: Each independently adjustable to maximum o f 0. 11 M rad/h Overdosing ratio: 1. 40 Capital cost - Sitework and yard improvements: $100 000. - Administration building: $ 45 000. - Process building and equipment: $450 000. - Irradiation facility: $365 000. - Source: $704 000. -Engineering: $200 000.

Total: $ 1 864 000. Annual operating cost: $830 650 'C o n v e rs io n ' cost: 3. 46

SECTION "B-B" (TYPICAL SECTION AT SOURCE)

FIG. 7. Conceptual design of a 3000-lM i cobait-60 irradiation plant for wood-plastic composites. RADIATION ENGINEERING: RADIOISOTOPES 79

<

СО 6 the the 3000-lb/h production plant. 80 FELICE

lb (ê z i >4f9= ( g t =

SOURCE > j4 0 =

'>•0 : * •,.

■•.P FIG.9. 500-kCi cobalt~60 irradiation plant for wood-plastic composites.

Another design which presents alternative features for consideration is shown in Fig. 9. It entails batch operation with half of the thirty-six product carriers, or containers, flanking each side of the vertical source RADIATION ENGINEERING: RADIOISOTOPES 81

plaque. The input-output conveyor removes simultaneously one container from each side as the source-pass conveyor is lowered into the pool. The procedure is reversed to load a new batch of thirty-six containers. The input-output conveyor, as depicted, operates through a vertical maze which shields against radiation while the source is exposed. An alternative is a plug door which is quickly opened together with a quick means of connecting the input-output conveyor. The product container is a circular cylinder having a space for the product which is 17f in. in diameter and 98 in. long. Filled with one-inch pine boards spaced one inch apart, 271 lb of product are accommodated. Work done at AECL suggests that pressurization during impregnation is not necessary, thus permitting thinner walls. At the same time a gas- tight seal is possible, resulting in the reduced likelihood of an explosion hazard. A combination of frequent air changes, ducted air flow and mono­ mer detection could obviate the use of a nitrogen blanket or burning off the oxygen in the irradiation chamber. Maintenance and routine inspection is thus facilitated. Such a product container could also serve as its own impregnation vessel. It can be rotated to attain better uniformity. As depicted, the design entails only one dose rate: approximately 0. 08 Mrad/h, at the axes of the containers, with a 500 kCi source. If varying dose rates were to be used some simplicity would have to be sacrificed. The required dose at this dose rate is approximately 0. 97 Mrad thus requiring a 12. 1-h irradiation. Batch interchange would re­ quire about I h; hence, the cycle time is 12.8 h and correspondingly longer for a lower source strength or higher dose. Work done at AECL indicates that vertical orientation of grain during irradiation is feasible as monomer loss is not great. If so, design can be further simplified by arraying the product containers vertically with the source plaque 28 ft high and 10 ft wide. Either way, the entire batch of 36 containers could be quickly lowered into the water with the source-pass conveyor in case of serious leakage or hazard.

5. SOME GENERAL CONCLUSIONS

A few conclusions concerning plant design can now be drawn:

(1) Whereas radiation efficiencies of 25 to 35% are realized in steriliz­ ing medical products, that attainable in this application w ill be more like 15%. A given amount of radiation energy will, therefore, cost roughly twice as much. (2) The capital cost of the irradiation facility excluding source will also be much higher. (3) It costs 1.6^/lb, i.e. 0.64^/Mrad-lb, to sterilize medical supplies in a 700-kCi plant [6] . The cost of irradiating fibrous materials would be at least double, or, say, 2^/Mrad-lb. (4) In relation to the dose rates apparently needed for this applica­ tion, the dose rates entailed in medical product sterilization are 'too high'. However, because medical product irradiation plants are 'ideal' in practical terms, it is desirable to explore all opportunities for raising the usable dose rate — even if the dose rate may be higher only momentarily though repetitively. 82 FELICE

REFERENCES

[1] FRANKFORT, J. H., BLACK, К. М., Engineering and Evaluation Study for the Manufacture of Wood- Plastic Composites, KLX - 1976, Clearing House for Federal Scientific and Technical Information, US Department of Commerce, Springfield, Virginia (1966). [2] ARTANDI, C., Ethicon worldwide complex of cobalt-60 sterilization units, Isotopes and Radiat. Technol. 4 4 (1967) 399. [3] KENT, J. A., WINSTON, A., BOYLE, W.R,, TAYLOR, G. B., Preparation of Wood-Plastic Combina­ tions Using Gamma Radiation to Induce Polymerization, ORO-2945-7 (1967). [4] BOYLE, W.R., private communication. [5] BARRETT, L. G., private communication. [6] BROWN, M. G., "The relation of design parameters, plant capacity and processing costs in cobalt-60 sterilization plants” , Radiosterilization of Medical Products (Proc. Symp. Budapest, 1967) IAEA, Vienna (1967) 381. IMPREGNATION AND POLYMERIZATION METHODS AND SYSTEMS USED IN THE PRODUCTION OF WOOD-POLYMER MATERIALS

W.E. MOTT AND G.J. ROTARIU DIVISION OF ISOTOPES DEVELOPMENT, UNITED STATES ATOMIC ENERGY COMMISSION, WASHINGTON, D.C. 20545, UNITED STATES OF AMERICA

Abstract

IMPREGNATION AND POLYMERIZATION METHODS AND SYSTEMS USED IN THE PRODUCTION OF WOOD-POLYMER MATERIALS. Studies on the radiation production of wood-polymer materials began in the United States in 1961 at West Virginia University and have continued until today. In this paper the impregnation and polymerization methods and systems that have evolved from these studies are reviewed. Included is a description of the procedures developed at the College of Forestry, Syracuse University, for producing wood-polymers via a thermal-catalytic process.

1. INTRODUCTION

In the United States three commercial companies, The American Novawood Corporation, Lockheed-Georgia Company and Atlantic Richfield Company, and one university, West Virginia University, have facilities for the radiation production of wood-polymer materials. In addition, Syracuse University and American Machine and Foundry Company each have units for producing wood-polymers by a thermal-catalytic process. By and large, the impregnation and polymerization methods and systems employed have evolved from the initial development work performed at West Virginia University beginning in 1961. Even so, for a broad understanding of present-day wood- polymer production technology, it is worthwhile to review the specific approaches taken by the different organizations.

2. MONOMERIC IMPREGNATION OF WOOD

Most of the information on the impregnation of wood with monomers has been generated during the last six years. Extensive studies have been directed at the identification of monomers and mixtures of monomers and of suitable impregnation procedures and systems for a broad range of applica­ tions. Of the many easily identifiable possible imprégnants, methyl methacrylate, although costly, appears to have the most interesting proper­ ties. And of the great variety of ways to vary the impregnation parameters, and hence the properties and costs of the final wood-polymer product, those leading to uniform maximum loading appear to have the greatest range of applicability. Other imprégnants, such as styrene-acrylonitrile and vinyl chloride, and impregnation procedures that give uniform partial loadings and shell loadings could offer property and cost advantages in a number of areas once the technology has been refined.

The impregnation procedures in general use today have essentially the same overall features. Basically, they involve an evacuation step, a monomer addition step, and a curing preparation step. Major differences in impregnation systems relate to size of equipment and innovations in handling imprégnants and wood.

83 84 MOTT and ROTARIU

2.1. West Virginia University

The program to determine the basic parameters associated with the impregnation of wood with a suitable monomer and the subsequent radiation polymerization of this monomer within the wood to give a wood polymer began at West Virginia University in 1961 and has continued until the present time (1-7). During this six-year period, over 150 monomer and monomer mixtures have been evaluated as imprégnants with methyl methacrylate emerging as the overall favorite. The impregnation system and procedures developed for this monomer are described below. They are equally acceptable for other monomers having about the same viscosity as methyl methacrylate.

The West Virginia University impregnation system is shown schematically in'Fig. 1. The impregnation chamber is 60 inches long and was constructed from a 3-inch diameter, %-inch thick, stainless steel tube. It is welded closed at one end and is provided with a flange and bolted cover at the other. The monomer supply reservoir was made by welding %-inch thick steel plates to each end of a 60-inch long, 3-inch diameter double standard black iron pipe. The impregnation chamber and reservoir are connected with %-inch double standard black iron pipe; standard %-inch valves are used throughout. Pressures as low as one Torr are achieved with a standard laboratory-type mechanical vacuum pump connected to the apparatus through a cold trap.

Manometer

Experience has taught that best results are obtained by precondition­ ing the wood to a constant moisture content. At West Virginia, the wood is conditioned to a TL moisture content by storing in a constant humidity room kept at 367o relative humidity and 22°C.

The impregnation procedure that has been found to be optimal for uniform maximum loading with methyl methacrylate (containing 35 ppm of butylated hydroxytoluene inhibitor) involves the following steps: METHODS AND SYSTEMS 85

1. With the wood in the treating chamber, evacuate to minimum pressure and hold for 30 minutes.

2. Introduce the monomer into the treating chamber while maintaining the vacuum as close as possible to the vapor pressure of the monomer.

3. Increase the pressure on the liquid (using nitrogen) to 125 lb/in2 gauge and hold for 18 hours.

4. Release the pressure slowly and drain the monomer.

This procedure will yield consistently good results with adequately- sized equipment. Care must be taken to insure that the volume of the system is large enough to handle the dissolved air released from the monomer as it is introduced into the evacuated impregnation chamber. Also, the monomer reservoir must contain sufficient monomer to keep the wood covered at all times during the loading phase. And every attempt should be made to minimize the amount of oxygen in the wood pores because the presence of oxygen greatly reduces the efficiency of the radiation-induced polymeriza­ tion reaction. Good vacuum practices must be observed if sufficiently low vacuums are to be produced.

To obtain a uniform partial loaded material, the recommended impreg­ nation procedure is to:

1. Evacuate to minimum pressure, add nitrogen to establish the pressure required to give the desired polymer loading, and hold for 20 minutes. (The impregnation pressure depends upon the wood and monomer in the system; for example, with maple and methyl methacrylate a pressure of about 380 Torr will give a final product with 0.35 lbs. of polymer per lb. of original wood. With pine and methyl methacrylate, the same pressure will give a product having 0.8 lbs. of polymer per lb. of wood).

2. Introduce the monomer into the impregnation chamber, while maintaining the pressure constant.

3. Introduce nitrogen to return system to atmospheric pressure and hold for 4 hours.

4. Drain the monomer, increase the nitrogen pressure to 125 lb/in2 gauge and hold for 18 hours

5. Reduce the system pressure to atmospheric pressure over a period of 1% hours.

In addition to developing the two procedures described above, West Virginia University performed a set of experiments aimed at producing controlled shell loading. The thickness of the wood used was 12 mm. Their procedure was to:

1. Evacuate the impregnation chamber and hold the vacuum for 15 minutes.

2. Add nitrogen gas to a pressure of 10 lb/in2 gauge, and maintain for 30 minutes.

3. Introduce monomer, pressure with nitrogen to 160 lb/in2 gauge, and hold for 18 hours. 86 MOTT and ROTARIU

4. Drain the monomer while the system is at 160 lb/in2 gauge, and then reduce the pressure to atmospheric, over a two-hour period.

The final wood-polymer product contained a high concentration of polymer (about 90 per cent of theoretical maximum) in a 4 mm-thick outer shell. The average concentration of polymer inside this shell was about 20 per cent of theoretical maximum.

After excess monomer is drained from the wood samples (in each of the three impregnation procedures described above), and prior to irradiation, the samples are wrapped in aluminum foil, and the edges are taped closed with masking tape. This procedure is best carried out in an oxygen-free atmosphere -- again, to eliminate oxygen effects during polymerization. The wrapping step is very important, since it prevents the evaporation of the monomer from the wood surfaces. Otherwise, depleted or non-uniform distribution of the monomer is evident after polymerization.

2.2. Lockheed-Georgia Company

In early 1964, the Lockheed-Georgia Company began a company-sponsored program to develop equipment and procedures for processing wood-polymer materials in sizes and quantities that would permit evaluation for com­ mercial uses. Although this continuing program (8) was built on the results of the early West Virginia University work, the scale-up of the processing techniques to allow standard sizes of lumber up to 8-feet long to be processed in batches up to 2500 pounds required many modifications to the basic impregnation procedures. Specific process and equipment details are still proprietary information of Lockheed-Georgia Company.

Fig. 2. shows lumber being loaded into one of the Lockheed-Georgia impregnation chambers at the beginning of the process. When the chamber is fully loaded with lumber the end cover is positioned, with an elastomeric gasket between the cover and flange, and bolted to effect a seal. After the chamber is sealed, it is evacuated and liquid plastic monomer, from the upright monomer storage tank shown on the left side of the figure, is pumped into the impregnation chamber until it is filled. After a soak period under a pressure of about 501b/in2 gauge, the excess monomer is pumped back into the storage tank and the impregnation chamber opened. The impregnated wood is then removed from the chamber and placed in an irradiation container (shown loaded in Fig. 3.). After closing, this container is purged with nitrogen at atmospheric pressure to remove the air prior to irradiation.

2.3. American Novawood Company

The American Novawood Company was the first company organized in the USA to produce wood-polymer materials commercially. Initial products were made in 1965, and full commercial capability was reached in 1966, with the acquisition of a 60,000 curie cobalt-60 source. The facility is licensed to hold up to 400,000 curies. Wood-polymer parquet flooring is offered under the trade name of "Gammapar." The company has facilities for handling pieces of wood up to 4 feet x 8 feet x 1 foot in size (9).

The American Novawood production procedure is unique in that once the wood is loaded into cannisters for impregnation, it is not handled again until after the monomer is polymerized. The impregnation cycle varies, of course, with the type of loading, i.e., full, partial, or shell. For full loading, the cannisters are evacuated, after which nitrogen is allowed to flow in to bring the pressure up to one atmosphere. Following a reevacua­ tion, the monomer is pumped into the system with a high capacity pump. This METHODS AND SYSTEMS 87

1

FIG. 2. Lockheed-Georgia Company impregnation chamber.

is done to obtain a rather fast, uniform loading. After the cannisters are filled, nitrgoen gas is used to pressure the system to 401b/in2 . The soaking time varies from 1 to 12 hours, depending upon the type of wood and the desired degree of impregnation. At the end of the soaking period, the excess monomer is drained off, and the cannisters again flooded with nitrogen. The impregnation system is so designed that a series of cannisters can be handled simultaneously.

2.4. Atlantic Richfield Company

Very recently, the Atlantic Richfield Company announced its entry into the wood-polymers commercial field and the availability of "Permagrain," a pre-finished parquet-panel plastic-impregnated flooring. The flooring is being produced by Nuclear Materials and Equipment Corporation, a wholly- owned subsidiary of the Atlantic Richfield Company. No details are avail­ able concerning the method of impregnation.

2.5. College of Forestry, Syracuse University

The impregnation procedure developed at the College of Forestry, Syracuse University, for making wood-polymer materials via the thermal- catalyst method again resembles the basic West Virginia approach (10). The major equipment needed includes an impregnation chamber (or treating cylinder) made of metal or glass, an oven capable of maintaining a 88 MOTT and ROTARIU temperature of about 120°F, a vacuum pump, a surge tank, standard valves, and associated piping. In normal practice:

1. The total system containing the wood samples is evacuated to the normal operating limit of the vacuum pump.

2. The monomer-catalyst solution is introduced into the treating cylinder via a separatory funnel. The solution is prepared by dissolving 0.2% of benzoyl peroxide or azobisisobutyronitrile in methyl méthacrylate or some other vinyl monomer. Sufficient monomer-catalyst solution is added to cover the wood or fill the impregnation chamber.

3. The monomer-catalyst solution is held in contact with the wood samples for a sufficient time to attain a maximum loading. A suitable contact time for birch, maple, basswood and most sapwoods is about 30 minutes.

4. The monomer is drained, the wood samples are removed, and wrapped in aluminum foil.

A surge tank five to ten times the volume of the treating cylinder is advisable in a system like that at the College of Forestry at Syracuse University. As mentioned earlier, this allows the dissolved air in the monomer to expand without increasing the pressure substantially. If an expansion tank is not used, the loading of the wood will be uneven due to the build-up of pressure from the dissolved gases released under vacuum.

FIG.3. Lockheed-Georgia Company irradiation container. METHODS AND SYSTEMS 89

All catalyzed monomers should be stored in a refrigerator or cold room to stop or retard the decomposition of the catalyst. Usually, monomers contain 30 to 100 ppm of inhibitor which will prevent the uncata­ lyzed monomer from polymerizing during shipment and storage at room temperature. Eventually, the inhibitor is used up due to the spontaneous formation of free radicals from thermal and radiation energy sources. Refrigerated catalyzed monomer at freezing temperatures can be stored for more than a year without danger. Once the inhibitor is used up, the monomer will begin to polymerize and release heat. Since the catalysts are auto- catalytic, their decomposition will be accelerated by the exothermic polymerization reaction. Care must be exercised in the storage and use of catalyzed monomers.

Most vinyl monomers can be used with free-radical catalysts to make wood-polymer materials. The most used monomer at present is methyl methacrylate; but, the College of Forestry has also used styrene, t-butyl styrene, chlorostyrene, many of the different acrylates, acrylonitrile, polyesters and others.

3. POLYMERIZATION OF MONOMERS IN WOOD

3.1. Radiation-Induced Polymerization

3.1.1. West Virginia University

After impregnation and wrapping in aluminum foil, wood samples are placed in gasketed aluminum boxes, nitrogen gas is introduced, and the boxes are lowered underwater next to a 50,000 curie cobalt-60 source. The total gamma-ray dose to produce the required degree of polymerization varies with the wood species, monomer, and dose rate. For example, for maple impregnated with methyl methacrylate at the optimum dose rate of about 40,000 rad/hr, the curing dose is about 0.6 Megarads; for maple impregnated with a 607= styrene-40% acrylonitrile mixture at 1.1 x 10 rad/hr, the dose is 2.6 Megarads (3) (6).

It should be pointed out that the use of proper dose rate is very important in achieving complete polymerization while at the same time, minimizing the temperature effect within the wood. The polymerization process is exothermic, and the temperature build-up is related to the heat of polymerization plus rate of release of heat. In the case of methyl methacrylate, with a molar heat of polymerization of 13 kcal/mole, the temperature can build up in a pine sample to almost 200°F under the worst conditions. Since wood is degraded by prolonged exposure to temperatures much in excess of 250°F, the choice of proper dose rate becomes obvious. Much dose rate information has been accumulated on methyl methacrylate, vinyl chloride and styrene-acrylonitrile (3). Also, dose rate information on methyl methacrylate in various woods, suitable and necessary for pilot plant design, has been obtained within the last year (6). Fig. 4. summarizes this information.

3.1.2. Lockheed-Georgia Company

Two radiation sources, a nuclear reactor and a cobalt-60 gamma facility, have been used by Lockheed for irradiating monomer-containing materials. In the effort prior to April 1967, the filled irradiation containers were transported via railroad car to the reactor for irradiation. The temperatures of the exotherm from the polymerization reaction were monitored during irradiation by thermocouples placed at appropriate positions within the stacks of wood. These temperatures are utilized in 90 MOTT and ROTARIU controlling the irradiation rate and total dose to provide the desired polymerization of the plastic without damage to the wood fiber. During processing, there is some depletion of plastic concentration in the surfaces and ends of the wood pieces which must be removed prior to use. Radioactivation of wood irradiated by the reactor was slight and within a few days decayed to levels less than the maximum permissible concentration specified by the Code of Federal Regulations for unlicensed use by the public. In April 1967, the reactor facility was replaced by a 200,000 Ci cobalt-60 facility (8).

5.0 1— I l Г I I I г 1 I I I I IT 4.0

3.0

S 2.0

1.0 0.9 0.8 0.7 0.6 0 0.5 □ MMA in yellow poplar, sugar maple and birch O MMA In white pine 1 0.4 о 12% Phosgard-88% MMA in white pine 0.3 a 12% Phosgard-88% MMA in yellow poplar, red oak and loblolly pine —

0.2 i i i 11 I I I I I I I 0.01 0.02 0.03 0.05 0.07 0.1 0.2 0. 3 0. 4 0. 5 0.7 1. 0 DOSE RATE, Megarad/hour

FIG.4. Effect of dose rates on the total dose requirements for complete polymerization of methyl methacrylate systems in various wood species.

3.1.3. American Novawood Company

After the cannisters are drained of monomer and nitrogen introduced over the wood samples, they are moved into the vicinity of the cobalt-60 source and revolved automatically about the source to produce a uniform dose. Total dose varies from 1.1 to 2.0 Megarads.

The facility has special devices for handling a wide variety of configurations of specialty products. Most of the work has been with methyl methacrylate with styrene-acrylonitrile as second choice. The total annual capacity of this facility is several million pounds of final wood-plastic product. Five pounds of WPC product is equivalent to one board foot (9).

3.1.4. Atlantic Richfield Company

No details are known about the polymerization procedures used by Atlantic Richfield Company in the production of its parquet-flooring except that the radiation source is cobalt-60. METHODS AND SYSTEMS 91

3.2. Thermal-Catalyzed Polymerization N

The only effort going on in the USA on non-radiation polymerization is at the College of Forestry and at American Machine and Foundry Company. The systems and procedures are essentially the same for each (10).

After the wood samples are covered with aluminum foil and closed with tape, they are introduced by hand into an oven and kept at 120°F for approximately six hours. (The unwrapped monomer-containing samples can also be placed in pipe capsules and cured in a drykiln.) For the production of billiard cues at American Machine and Foundry Company, a steam heated chamber of the same size as the impregnation cylinder is used for curing. AMF has not found it necessary to wrap the impregnated cues in aluminum foil prior to insertion in the curing chamber.

REFERENCES

(1) KENT, J., WINSTON, A. and BOYLE, W . , "Preparation of wood-plastic combinations using gamma radiation to induce polymerization; effects of gamma radiation on wood," US AEC Report OR0-600 (March 1, 1963), available from the Clearinghouse for Federal Scientific and Tech­ nical Information, National Bureau of Standards, U. S. Department of Commerce, Springfield, Virginia 22151.

(2) KENT, J., WINSTON, A. and BOYLE, W., "Preparation of wood-plastic combinations using gamma radiation," US AEC Report 0R0-612 (September 1, 1963), ibid.

(3) KENT, J., et. al., "Preparation of wood-plastic combinations using gamma radiation to induce polymerization," US AEC Report 0R0-628 (May 14, 1965), ibid.

(4) KENT, J., et. al., "Preparation of wood-plastic combinations using gamma radiation to induce polymerization: impregnation of wood with acrylic monomers," US AEC Report ORO-2945-4 (April 1, 1966), ibid.

(5) KENT, J., et. al., "Studies of radiation polymerization of vinyl monomer in relation to wood-plastic combinations," US AEC Report 0R0-2945-6 (September 21, 1966), ibid.

(6) KENT, J., WINSTON, A., BOYLE, W., and TAYLOR, G., "Preparation of wood-plastic combinations using gamma radiation to induce polymeri­ zation," ORO-2945-7 (March 17, 1967), ibid.

(7) LOOS, W. E. and KENT, J., "Topical report on fastening of wood- plastic combinations," US AEC Report ORO-2945-9 (September 1, 1967), ibid.

(8) BURFORD, A. 0., Lockheed-Georgia Company, Dawsonville, Georgia; personal communication.

(9) BARRETT, L. G., The American Novawood Company, Lynchburg, Virginia; personal communication.

(10) MEYER, J. A., Chemistry Department, State University College of Forestry, Syracuse University, Syracuse, New York; personal communication. See also: MEYER, J. A., "Treatment of wood-polymer systems using catalyst-heat techniques," Forest Products Journal, 15 (1965) 362.

DEGRADATION OF POLYMERS BY ULTRA-VIOLET LIGHT

D .T. TURNER CAMILLE DREYFUS LABORATORY, RESEARCH TRIANGLE INSTITUTE, RESEARCH TRIANGLE PARK, N .C ., UNITED STATES OF AMERICA

Abstract

DEGRADATION OF POLYMERS BY ULTRA-VIOLET LIGHT. To reach an understanding of the complex processes which occur when polymers are degraded by ultra-violet light under service conditions it is first judicious to try to elucidate the photochemistry of relatively simple polymer reactions. For this reason, emphasis is given to studies in which purified polymers, in bulk, were exposed to monochromatic radiations in the absence of oxygen. In respect of product analysis, emphasis is given to methods for estimating quantum yields for fractures and crosslinks. Photochemical mechanisms are illustrated by discussion o f polystyrene, polytethylene terephthalate) and cellulose. Special emphasis is given to the role of free radicals. Attention is drawn to reports that the course of photolysis may be changed by application of an external pressure of a chem ically inert gas, such as nitrogen. The explanation suggested in the literature is that this depends on the ease of escape o f hydrogen atoms which, alternatively, might react with trapped polymer radicals. The course of photolysis may also be affected by polymer radicals acting as strongly absorbing chromophores and consequently undergoing further chem ical reaction. This is illustrated by reference to the conversion of allyl radicals to alkyl radicals in polyethylene and also by changes observed in the ESR spectrum of polymer radicals trapped in poly (ethylene terephthalate) as a result of exposure to light. It is suggested that this effect is primarily responsible for the evolution of hydrocarbon gases on photolysis of polyethylene or natural rubber. In contrast, radiolysis of these polymers yields almost pure hydrogen because, in this case, energy is absorbed by relatively non-selective processes, i.e . free radicals do not absorb high energy radiation much more strongly than does their polymeric environment.

1. INTRODUCTION

It is common experience that many polymers degrade in service be­ cause of exposure to light. Sheets of paper turn yellow and become brittle, lace curtains tear easily, plastics become discoloured and rigid, and elastomers become tacky or develop cracked and crazed surfaces. Then again, there are polymers with otherwise useful properties which cannot be accepted for commercial production because of their poor light stability [1] . To reach an understanding of the complex chemical reactions involved in photodegradation it would seem judicious, in the first instance, to seek an understanding of relatively simple polymeric systems. A suitable ap­ proach was pioneered 20 years ago by Bateman in a study of the photolysis of rubber [2] . A polymer, sample was rigorously purified, exposed in a vacuum to ultra-violet light of known narrow wave-bands and intensities, and then a determined effort made to analyse reaction products. In this review emphasis will be given to kindred work in which investigators took pains to get chemically meaningful data by trying to decrease an other­ wise overwhelming number of experimental variables. An initial simpli­ fication to be desired is to work with monochromatic light but, as will be

93 94 TURNER seen, this desideratum can prove to be inconvenient. After a brief dis­ cussion of ultra-violet absorption spectra, a prerequisite for any informed discussion of photochemistry, attention will be given to methods of product analysis. Emphasis will be given to methods of estimating fractures and crosslinks and brief mention will be made of photo-induced changes of colour. This choice coincides with the two main causes of polymer failure in photodegradation. Fractures and excessive crosslinks lead to a loss of mechanical strength while discolouration may lead to early rejection for aesthetic reasons. Finally, after discussion of three selected polymers, some general comments will be made about the special role of free radicals in the photochemistry of polymers.

2700 3000 3300 3600 ¿000 A

FIG .J. Ultra-violet spectral energy distribution from sunlight and from a xenon arc [3 ].

2. CHOICE OF A L IG H T SOURCE

In most cases, the degradation of polymers exposed to sunlight is due to ultra-violet light of wavelengths in the range 3000-4000 Á. In the labora­ tory this may be simulated by use of a Xenon arc or bracketed by the use of filters (Fig. 1) [3] . The use of such a source can provide a good corre­ lation with 'weathering' tests but, as pointed out by Oster, exposure to polychromatic light may result in complicated interrelated processes and lead to a wide range of reaction products. Even the sequence in which radi­ ations are applied may be of extreme importance [4] . A great sim plifi­ cation is achieved by working with monochromatic light, and Jellinek's authoritative review of 1962 lists 11 studies with 2537 Á and 3 with 3130 Â radiations; there were also 9 significant studies with defined wave-bands [5] . The preference for 2537 Â radiation is one of experimental convenience inasmuch as a reasonably high intensity at this wavelength can be obtained, without resort to filters, from a low-pressure mercury arc. Viewed from DEGRADATION OF POLYMERS 95 the point of view of deterioration in sunlight, however, it would be more apposite to work at a wavelength in the range 3000-4000 Â. The experi­ mental problem here is that useful polymers have very low quantum yields, generally 10'2 to 10"5 [5] , and therefore high light intensities are needed to produce easily measured changes after a reasonably short exposure. One approach has been to isolate the intense 3130 Â line from the emission of a medium pressure mercury arc by use of filters but, unfortunately, these also seriously reduce the intensity of the desired wavelength. In cases where admixture of longer wavelengths can be tolerated, a more transparent filter can be used which cuts out all wavelengths up to and including 3025 Â, i.e. the transmitted light comprises wavelengths § 3130Â [6] . Reasonably high intensities of the 3660 Â line may be isolated but little work has been reported with this wavelength.

3. ULTRA-VIOLET ABSORPTION SPECTRA

An ultra-violet absorption spectrum is necessary to design experi­ ments in which the rate and depth of energy deposition is known. It may also provide information about the nature of the groups in the polymer which initiate photochemical reactions but in many cases is disappointing in this respect. Natural rubber and cellulose, for example, have feature­ less absorption tails at long wavelengths which cause photolysis. Purified natural rubber evolves gas on exposure to wavelengths up to at least 3800 Â. Purified cellulose, as far as is known, has not yet been studied under vacuum at wavelengths > 2537 Â. An extreme example of a lack of a neat correlation of an absorption spectrum with photolytic reactions has been provided by Monahan in a study of the vacuum photolysis of a film of poly-(tert-butyl acrylate) which was prepared under vacuum from a purified monomer with either benzoyl peroxide or azoisobutyronitrile as initiator (Fig. 2). The absorption maxima at 1800, 1925 and 2150 Â correspond satisfactorily to the expected transitions of the carbonyl group: 7т-чг*, o r * 'a * , and n -*^, respectively. In practice this information is not es­ pecially helpful because the polymer is degraded by longer wavelengths. In fact, quantum yields for isobutene elimination were insensitive to wave­ length, Ф (isobutene) = 10"2, at all three wavelengths studied, namely, 1849, 2537, and 3660 Â. It was suggested that the photolysis was due to impurities,

X(AM

FIG. 2. Absorption spectrum of a 1.08 poly(tert-butyl acrylate) film [7 ]. 96 TURNER possibly initiator fragments, which absorb weakly in the long wave absorp­ tion tail [7] . Impurities also play an important role in the photolysis of nylon and polyethylene. Although it is difficult definitely to rule out the possibility that an impurity may play a role in a photochemical reaction with a low quantum yield, it is, nevertheless, believed that the photo­ chemistry of polystyrene [8] and poly(ethylene terephthalate) [6, 9] may be referred solely to their main repeat units.

ESTIMATES OF FRACTURES AND CROSSLINKS

If no crosslinking occurs then the initial quantum yield for fractures, 0(F), may be calculated from E q.(l), in which M 0 and Mt are number average molecular weights at times zero and t, respectively, and where Et is the number of Einsteins of absorbed quanta per gram at time t.

It is the practice to estimate number average molecular weights from conveniently measured solution viscosity data. A detailed analysis of this practice has been made by Jellinek [5] . Results obtained from sheets of poly(ethylene terephthalate) which were exposed in air to a fluorescent sunlamp, are exemplified by Fig.3 [9] . Confidence in the results is given by the approximately linear dependence of the number of fractures on d ose: 4>(F) = 5 X IQ '4 .

TIME (HOURS)

FIG.3. The photolysis of poly(ethylene terephthalate). The effect of intensity [9] . DEGRADATION OF POLYMERS 97

O n e objection to the application of the above procedure is that the assumption of zero crosslinking might not be valid but, as pointed out by Shultz, a small am o u n t of crosslinking would not be expected to affect sensibly the estimate obtained [10] . A second objection concerns the implicit assumption that fractures occur at random throughout the sample. In view of the exponential attenuation of light, in accord with the Beer- Lambert Law, this can at best be only an approximation. A number of authors have devised ways of correcting for an exponentially changing concentration of fractures [11-13] . In the case of a purified sheet of cellulose, which reflected 5 5 % and transmitted 1. 8% of incident 2537 Â radiation, Flynn s h o w e d that this correction increased the estimate of fractures by up to 55%. Presumably, the true value lies somewhere in between this and the uncorrected value because the fracture reaction need not be localized at the site of energy deposition, for example reaction might occur at s o m e distance a w a y via the migration of free radicals. Techniques for measuring fractures and crosslinks during formation of an insoluble crosslinked network have been discussed elsewhere [14, 15] . Examples of the application of such techniques will be found in a paper by Jacobs and Steele on the v a cu u m photolysis of poly(ethyl acrylate) under 2537 Â radiation [16] . At present, the most informative procedure is to follow quantitatively the decrease in solubility of the p o l y m e r with in­ creasing dose. If fractures and crosslinks are formed randomly and at constant rate then, for a p o l y m e r with a r a n d o m molecular weight distri­ bution, the soluble fraction (s) is related to dose (D) by Eq.(2), in which P is the average n u m b e r of repeat units per molecule prior to irradiation and F and X are, respectively, the probabilities that a repeat unit is fractured or crosslinked per unit dose [16]

s +s' - 1 + x 5 d <2>

F r o m experimental plots of S+S^ versus 1/D, estimates m a y be obtained of both fractures and crosslinks. Exceptionally good conformity of ex­ perimental data with Eq.(2) has been reported by M a x i m and Kuist [18] in the case of certain acrylate esters which w e r e exposed in air to a l a m p which simulated sunlight (Fig. 4). Procedures for estimating both fractures and crosslinks in the case w h e r e an allowance is to be m a d e for expo­ nentially changing concentrations have been devised by Shultz [12] and by M a x i m and Kuist.

5. COLOUR CHANGES

It is difficult to identify those chemical reactions which are responsible for colour changes. In the case of vinyl poly m e r s the formation of long sequences of conjugated carbon-carbon or carbon-nitrogen bonds seems to be of general importance. Particularly severe problems of this origin have been encountered in the light aging of polyvinyl chloride [5, 19] . In a few cases s o m e rather m o r e specific changes have been identified as in the case of poly(4, 4'-diphenylopropane isophthalate), which undergoes a photo-induced molecular rearrangement analogous to a Fries reaction of phenolic esters [20] . 98 TURNER

T gcl ¡T

FIG.4. Plot of (S+S^) versus reciprocal of time of exposure X time to reach gel point (this is proportionate to D '1) [18] .

Some surprising and rather general changes of colour on exposure of polymers to visible and ultra-violet light have been discovered byLauner. He terms the effect "spectral conformity" and epitomizes it as follows: "Light in an unknown fundamental effect imparts some of its colour to common objects around us." The most detailed work was done with wool which was found to become greener in green light, bluer in blue light, and more "ultra-violet" in ultra-violet light. Launer's explanation is that ab­ sorbers cease to function as such after absorption of a photon and so sub­ sequently reject other photons of the same energy. These absorbers were not identified [21] .

6. P O L Y S T Y R E N E

Grassie and W eir have given a lucid account of the vacuum photolysis of an exceptionally pure sample of polystyrene under 2537 Â radiation at 28°C [22] . The only gaseous product detected was hydrogen, but comparison with other work suggests that higher molecular weight products might have been collected with more rigorous outgassing [23] . The yield of hydrogen was proportional to the time of irradiation, Ф(Н2) =4.3X 10"2, and the over- DEGRADATION OF POLYMERS 99 all activation energy was 2.9 kcal/mole. An insoluble crosslinked network was formed and carbon-carbon unsaturation developed in the main chain, ultimately resulting in the formation of conjugated sequences and colour. The concentration of a chromophore with an absorption peak at 2400 Â in­ creased linearly with time of irradiation; it was assigned to the structure ~CH2-C (C 6H5) = CH-CH2~. The above results were explained by reference to the following mecha­ nism, in which RH represents polystyrene:

+ RH —;------» H2 + R.

hv + R. RH -» R . + H. -> H2+ unsaturation

+ R.

crosslinking

It was pointed out that as reactions 2, 3, and 4 all depend on the mobility of hydrogen atoms, then the importance of reactions 2 and 3, relative to reaction 4, might be increased by confining hydrogen atoms in the film by means of an inert atmosphere. To test this hypothesis films were irradiated under nitrogen at various pressures. It was shown experimentally that the optical density at 2400 Â, due to the unsaturated structure mentioned earlier, did in fact increase linearly with increase in nitrogen pressure. Thus the simple photolysis mechanism accounted for all the observed experimental features. The above system would appear to promise the best hope of attaining a detailed knowledge of photochemical processes in a polymer. The next step might be to obtain quantum yields for fractures and crosslinks and to investigate free radical formation by ESR spectroscopy under 2537 Â radi­ ation. It could then be decided whether it would be worth accepting the in­ convenience of repeating such work at other wavelengths.

7. POLY(ETHYLENE TEREPHTHALATE)

Quantum yields for products formed in vacuum photolysis under 2537 A and radiations й 3130 A are shown in Table I [6]. Fractures and cross­ links were estimated, by reference to Eq.(2), for films which transmitted about 63% of the incident 3130 Â radiation. An absorption peak which appeared in the infra-red near 12.9 jum was attributed to the structure - О - CO - C6 H4 - X - in which X is not a - CO - О - group. ESR spectra 100 TURNER

TABLE I. QUANTUM YIELDS X 104 FOR POLY(ETHYLENE TEREPHTHALATE)

A CO СО г Crosslinks Fractures Trapped radicals

3130 6 2 5 .5 16 1 .5

2537 6 -9 2-3 Network not characterized Not determined

were not well resolved but were tentatively assigned to the free radical - CgH3- plus a singlet, which was not assigned. Hydrogen gas was not evo lved . The prim ary reactions leading to the formation of CO and C 02 may be as shown:

I

Radicals I, II and III combine disproportionate or abstract hydrogen atoms from neighbouring molecules. Combination would result in groups of the type para - O - CO - CgH4 - X - . Disproportionation and hydrogen abstraction would consummate chain fracture. However, it would appear necessary to invoke additional fracture reactions because of the inequality <î>(F)>(CO) + Ф (С 0 2). In the absence of m o re d etailed an alytical data it seems unprofitable to speculate on their nature. An important consequence of hydrogen atom abstraction would be the formation of free radicals which could account for crosslinking in the absence of hydrogen gas formation. On the basis of the ESR work the following crosslinking reaction might be important: DEGRADATION OF POLYMERS 101

H H H H

Finally, in a rigid m e d i u m such as poly(ethylene terephthalate), with glass transition and melting températures of about 80 and 250°C, respec­ tively, it is to be expected that s o m e of the m o r e stable free radicals would be trapped at room temperature.

8. CELLULOSE

Th e degradation of cellulose by ultra-violet light has recently been reviewed in detail by Phillips and Arthur [24] . Here, attention will be confined to an exemplary and painstaking series of investigations on the v a c uu m photolysis of purified cellulose under 2537 A radiation by Flynn, Morrow and Wilson. As m a y be seen in Fig. 5, the major products are

FIG. 5. Yields of products versus dose in Einsteins o f quanta in the vacuum photolysis of purified cellulose under 2537 A, radiation at 40 °C [25]. 102 TURNER hydrogen gas and aldehyde groups, i.e. groups in the polymer which are oxidized by sodium chlorite. The initial quantum yield for each of these products is 10'2. The two quantum yields decrease in a roughly parallel manner with increasing dose [25] . A detailed analysis provided evidence that hydrogen is formed by a zero-order reaction, but is retarded by a product of irradiation [26] . A deuterated cellulose, of average composition [Cg H70 2(0H)(0D )2 ] x, gave the initial quantum yields for hydrogen isomers shown in Table II [27]. The small amount of deuterium and the relatively small change in the yield of HD with temperature suggest the occurrence of a molecular elimination reaction, rather than one involving free radicals. Thus,

------» C = 0 + H D (H 2)

O D (H ) '

TABLE II. QUANTUM YIELDS OF HYDROGEN ISOMERS FROM THE IRRADIATION OF COTTON LINTERS

Temperature Total hydrogen H 2 HD d 2 (d e g C )

-196 0 .0 0 3 2 8 0 .0 0 0 8 9 0 .0 0 2 3 6 0 .0 0 0 0 3

+ 40 0.0 0503 0 .0 0 2 0 0 .0 0 3 0 0 .0 0 0 0 5

+ 92 0 .0 0 4 1 9 0 .0 0 1 2 7 0 .0 0 2 8 6 0 .0 0 0 0 5

In addition, it would seem likely that part of the hydrogen is formed by free radical reactions involving the fracture of C-H bonds. This would help to account for the temperature dependence of the H2 yield (Table II). In fact, ESR studies do show that polym er-free radicals are formed, under comparable experimental conditions, but their structure and yield have yet to be determined [28] . The quantum yields for CO and C02, which initially are sm aller than that for hydrogen by about one order of magnitude, are much more sensi­ tive to the temperature of irradiation, increasing ten-fold and five-fold, respectively, on raising the temperature from -196°C to +92°C. It was suggested that the low temperature yields can be attributed mainly to secondary photolysis of carbonyl, carboxyl and free radical groups. The increase in yield with temperature was attributed to fragmentation of free radicals [27] . Evidence that free radicals may be photolysed at -196°C was adduced from studies of methanol under 2537 Â radiation in a vacuum. The following free radicals were identified in methanol by ESR spectroscopy: • CH3, • CH2OH, and • CHO [29] . Other evidence indicated that • CHO is a secondary product arising from photolysis of the free radical • CH2OH [30] . Yields of fractures and carboxyl groups were little influenced by the temperature of irradiation. It was suggested that these products were DEGRADATION OF POLYMERS 103 formed during a post-irradiation oxidative reaction of trapped radicals [27] . Post-irradiation degradation of cellulose had been discovered previ­ ously by Launer and Wilson [31] .

9. ROLE OF FREE RADICALS

T w o unusual roles of free radicals have been postulated to explain certain features of the photochemistry of polymers. T h e first of these is based on observations that their reactivity is influenced by an external pressure of an inert gas. In addition to the well d o c umented case of poly­ styrene, extensive and earlier studies have been reported of similar effects in five other polymers. T h e explanation proposed is that this effect m a y be traced to a reaction of trapped radicals with hydrogen atoms [31, 32] . Further studies of this interesting effect would be valuable, especially with cross-reference to findings on the reaction of trapped polymer radicals with gases, which have been accumulated in studies of radiation chemistry [15]. T h e second unusual postulate is that trapped radicals in cellulose contribute to product formation by undergoing secondary photolysis. At least this postulate w a s unusual w h e n it w a s m a d e in 1964 [27] . In the meantime, considerable evidence has accrued which suggests that such reactions are commonplace. By ESR spectroscopy it has been shown that hydrogen transfer reactions can occur as a result of exposure of polymer radicals to visible and ultra-violet light [34, 35] . E x a m p l e s are given for polyethylene [35, 36] and polyethylene terephthalate [37] :

- c h 2 - c h 2 - C H - C H = C H ------* . Сн2 _ ¿H . C h 2 . CH = CH -

h ea t * .H H H

H H H H

A n ex a m p l e of the change of the E S R spectrum, due to conversion of allyl to alkyl radicals in polyethylene, is sh o w n in Fig.6. T h e alkyl radical has been found to have a molecular extinction coefficient Of 5.5X10s mole"1 litre c m ' 1 at its absorption peak near 236 m / u m [35] . T h e alkyl radical is believed to be responsible for a broad band between 200 and 230 m p m which has been detected in у -irradiated polyethylene [38] . It is n o w suggested that the photolysis of trapped radicals might account for a previously puzzling difference in the gaseous products evolved from polyethylene on exposure to high energy as compared with ultra-violet radiations, which was first pointed out by Weiss [39]. Radio­ lysis yields almost pure hydrogen whereas photolysis yields a mixture of hydrogen and hydrocarbons. A comparison of the products formed by the radiolysis and photolysis of purified natural rubber shows a similar difference [14] . Presumably, hydrocarbons are formed following a secondary energy deposition in trapped radicals. Of course, further d a m a g e to trapped radicals is not expected to be important in the case 104 TURNER

FIG. 6. ESR spectra for radicals in an oriented sample of polyethylene, (a) spectrum of allyl radicals; (b) spectrum of alkyl radicals formed by subsequent exposure of same sample to a high-pressure mercury lamp [36] .

of radiolytic reactions because of the relatively non-selective processes of energy absorption. • Trapped radicals may also create some confusion in product analysis, as in the photolysis of cellulose, by participating in post-irradiation oxi­ dation reactions. This general problem has been discussed in some detail by Dole in relation to the radiation chemistry of polymers. One solution is to expose the irradiated sample, while still under vacuum, to a gas such as methyl mercaptan which can eliminate a free radical by donation of a hydrogen atom [15] .

10. CONCLUDING REMARKS

Although attention has been limited to 'sim ple' polymer systems which, it is hoped, can be discussed meaningfully in chemical terms, a number of important topics have been omitted for lack of space, such as the influence of the physical state of a polymer on its photolysis. After consideration of these omitted topics, the present approach would be to consider increasingly complex situations more closely approaching actual service conditions. First, photolysis in the presence of oxygen. Second, the influence of various additives such as photosensitizers, radical scavengers, quenching agents, internal filters and fillers. Possibly, the reader may find an up-to-date coverage of these topics in a review article by R.B. Fox which is currently announced for publication [40] .

ACKNOWLEDGEMENTS

The author wishes to thank Dr. F.B. Marcotte and Dr. L. Monteith for many stimulating discussions. This work was supported, in part, by NASA Contract No. NAS1-7553. DEGRADATION OF POLYMERS 105

REFERENCES

[1] COLEMAN, D. , J. Polym. Sci. 14 (1954) 15. [2] BATEMAN, L., J. Polym. Sci. 2 (1947) 1. [3] HIRT, R.C., SCHMITT, R.G., SEARLE, N.D., SULLIVAN, A.P., J. opt. Soc. Am. 50 (1960) 706. [4] OSTER, G., OSTER, G .K., KRYSZEWSKI, М ., J. Polym.Sci. 57 (1962) 937. [5] JELLINEK, H .H .G ., Pure appl. Chem. 4 (1962)419. [6] MARCOTTE, F.В., CAMPBELL, D., CLEAVELAND, J.A., TURNER, D .T., J. Polym. Sci. A5 (1967) 481. [7] MONAHAN, A.R. , J. Polym. Sci. A4 (1966) 2381. [8] GRASSIE, N., WEIR, N .A., I. appl. Polym. Sci. 9 (1965) 963. [9] OSBORNE, K .R ., I. Polym. Sci. 38 (1959) 357. [10] SHULTZ, A.R., ]. phys. Chem. 65 (1961) 967.

[11] FLYNN, J.H., I. Polym. Sci. 27 (1958) 83. [12] SHULTZ, A .R ., J. chem. Phys. 29 (1958) 200; J. appl. Polym. Sci. 10 (1966) 353. [13] JELLINEK, H .H .G ., J. Polym. Sci. 62 (1962) 281. [14] TURNER, D. T., in The Chemistry and Physicsof Rubber-Like Substances, (BATEMAN, L ., Ed.) John W iley and Sons (1963). [15] DOLE, М ., in Crystalline Olefin Polymers, Parti, (RAFF, R .A .V ., DOAK, K. W ., Eds), Interscience Publishers (1965). [16] JACOBS, H., STEELE, R ., J. appl. Polym. Sci. 3 (1960) 239, 245. [17] CHARLESBY, A ., PINNER, S.H., Pioc. R. Soc. A249 (1959)367. [18] MAXIM, L. D., KUIST, С. H ., The light stability of vinyl polymers and the effect of pigmentation, Western Coatings Society Symposium, 27 Feb. 1964. [19] GOLUB, M .A ., PARKER, J.A., Makromolek. Chem. 85 (1965) 6. [20] MAEROV, S.B., J. Polym. Sci. A3 (1965) 487. [21] LAUNER, H .F., Text. Res. J. 36 (1966) 606. [22] GRASSIE, N.. WEIR, N. A ., J. appl. Polym. Sci. 9 (1965) 975. [23] ACHHAMMER, B.G., REI NY, M.J., WALL, L.A ., REINHART, F. W ., J. Polym. Sci. 8 (1952) 555. [24] PHILLIPS, G .O ., ARTHUR, J.C.,Jr., Text. Res. J. 34 (1964) 497, 572. [25] FLYNN, J.H., WILSON, W. K ., MORROW, W. L ., J. Res. natn Bur. Stand. 60 (1958) 229. [2 6 ] F L Y N N , J .H ., J. phys. C h e m . 60 (1 9 5 6 ) 1332. [27] FLYNN, J.H., MORROW, W .L., J. Polym. Sci. A2 (1964) 81. [28] FLORIN, R.E., WALL, L.A., J. Polym. Sci. A l (1963) 1163. [29] SULLIVAN, P.J., KOSKI. W.S., J. Am. chem. Soc. 84 (1962) 1. [30] ALGER, R.S., ANDERSON, Т.Н ., WEBB, L.A ., J. chem. Phys. 30 (1959) 695. [31] LAUNER, H .F., WILSON, W .K., J. Res. natn Bur. Stand. 30 (1943) 55. [32] STEPHENSON, C .V ., MOSES, B.C., BURKS, R. E., Jr., LACEY, J.C.,Jr., COBURN, W .C.. Jr., WILXOC, W .S., J. Polym. Sci. 55 (1961) 451, 465, 477. [33] STEPHENSON, С. V ., WILCOX, W .S., J. Polym. Sci. A l (1963) 2741. [34] MILINCHUK, V .K ., PSHEZHETSKII, S.Ya., Vysokomolek. Soedin. 5 (1963) 946. [35] OHNISHI, S., SUGIMOTO, S., NITTA, I., J. chem. Phys. 39 (1963) 2647. [36] DEFFNER, U ., Kolloid-Zeitschrift 201 (1964) 65. [37] CAMPBELL, D ., TURNER, D .T., Polym. Lett, (in press). [38] DOLE, М ., BOHM, G .G .A ., Radiat. Res. (1967) 274. [39] WEISS, J., J. Polym. Sci. 29 (1958) 425. [40] FOX, R.B., "Photodegradation of high polymers", Progress in Polymer Science I_ (JENKINS, A. D ,, Ed.) Pergamon Press, Oxford.

EMULSION GRAFT-POLYMERIZATION IN WOOD BY MEANS OF GAMMA IRRADIATION

M. GOTODA TAKASAKI RADIATION CHEMISTRY RESEARCH ESTABLISHMENT, TAMURA-CHO, MINATO-KU, TOKYO, JAPAN

Abstract

EMULSION GRAFT-POLYMERIZATION IN WOOD BY MEANS OF GAMMA IRRADIATION. Experiments to study the extent of graft-polymerization in wood are described and the results discussed. The effects of wood impregnation with methyl methacrylate, styrene and combinations of the two are reported.

1. IN T R O D U C T IO N

Considerable world attention has recently been drawn to so-called wood-plastic combinations achieved by means of the irradiation method, and much research and development has been reported. It now seems to be clear that in the absence of suitable solvents or swelling agents vinyl monomers only fill the voids in the wood and cannot penetrate into the cell walls, so that there will be little or no reaction between these monomers or polymers and the cell-wall components. In this case only homopolymers are formed in the voids. Several researchers have, in fact, already succeeded in forming graft copolymers, which cannot be extracted from the milled product, by adding swelling solvent to the imprégnant [1, 2 ] or by sorption of moisture to the wood before im preg­ nation [3, 4]. It nevertheless seems to be still uncertain to what extent these graft copolymers are really formed and whether their formation favourably affects the physical properties of the wood-plastic combinations. On the other hand, it was reported that with the irradiation method it was possible to achieve 100% conversion in emulsion polymerization [5]. Such emulsions apparently impregnate and swell the wood very well. These facts prompted the present investigation of emulsion graft- polymerization in wood by means of gamma irradiation, the main object of which was to examine the reaction conditions of the emulsion polymerization of MMA and styrene in several native Swedish woods, and also to compare the effects of several kinds of detergent upon them.

2. EXPERIMENTAL

2.1. Materials

2.1.1. Wood

The species examined (sapwood) were Swedish birch (B), pine (F), beech (O), and oak(E) in blocks of 2 X 2 X 2 cm supplied by the Swedish

107 108 GOTODA

Wood Research Institute at Stockholm. All these test pieces were conditioned to about 6% moisture content at 20°C before impregnation.

2. 1.2. M onom er

Stabilizer was removed from commercial grade monomer by washing with 5% aqueous sodium hydroxide solution. The monomer was washed free of alkali and dried over calcium chloride. In the case of styrene, vacuum distillation was applied just before its use, but methyl methacrylate (MMA) was used without distillation.

2.1.3. Detergent

Technical grade detergents, as described below, were used as obtained without further purification. They included non-ionic, anionic and cationic detergents, i.e. alkylbenzensulphonate (Berol Sulfonsyra, made by Berol AB), polyethÿleneglycolmonostearate (D.P. 1000), sorbitan monolaurate (Aracel 20, HLB 8.6), polyoxyethylene sorbitan monolaurate (Tween 20, HLB 16.7), and polyoxyethylene sorbitol fatty-acid esters-alkylarylsulphonate blend (Atlox 3386, HLB 9.6). These five detergents were manufactured by Atlas-Goldschmidt GmbH. Alkylimidazoline (Geigy Amin S), made by Geigy Industrial Chemicals, and n-hexadecylpyridinumchloride, made by Fluka AG, were also used.

2.2. Experimental procedures

2.2. 1. Preparation of monomer emulsion

The emulsions (monomer 50 wt % and 70 wt %) were made by mixing water with monomer in the designated ratio in air.

2.2.2. Impregnation

Wood samples (10-15 pieces in a 500-ml beaker) were placed in an evacuated vacuum desiccator at about 2 mmHg for one hour. Then, without interrupting the vacuum, monomer emulsion was introduced carefully so that the liquid would not overflow from the beaker due to foaming caused by the rapid escape of air from the liquid. After all specimens had been completely covered with liquid, the pressure above the liquid surface was raised to normal by introducing nitrogen. The specimens were kept immersed for six hours. The impregnated samples were then removed, their surfaces were wiped lightly with tissue paper and they were wrapped as tightly as possible in two layers of aluminium foil.

2.2.3. Irradiation

Aluminium-foil-wrapped specimens were irradiated in a 3-kCi60Co irradiator (6 rad/s) at AB Atomenergi, Studsvik, at room temperature.

2. 2.4. Conditioning of irradiated specimens

The irradiated specimens were usually vacuum dried at 50°C over a period of 3 days to remove the unreacted monomers and water. With this EMULSION GRAFT -POLYMERIZATION 109 ordinary drying method the specimens always showed severe cracks. To obtain perfect specimens the blocks were kept for a long time in a humid vessel and the volatiles were allowed to evaporate from the wood as slowly as possible by carefully controlling the evaporation rate. The residual volatiles were finally removed by this method.

2.2, 5. Extraction of homopolymer

The samples were then cut into chips which were extracted with benzene in a Soxhlet extractor for 20 hours. The amount of homopolymer was determined by the weight loss of the chips.

2.2.6. Specimen dimensions

The dimensions of the specimens were measured in three directions by m icrom eter at every stage of the treatments and the swelling effects were compared. Most of these experimental procedures were the same as those adopted by Kinell and Aagaard [4].

3. RESULTS AND DISCUSSION

3.1. MMA graft polymerization in wood

The first procedure was the comparison of the reactivity of the MMA methanol solution with that of the 70% emulsion containing 0.2% alkylbenzene- sulphonate. From the result for pine (F ig.l), it was determined that emulsion is more reactive and the induction period is shorter. The grafting efficiency (per cent of graft polymer versus total polymer formed) was checked and was found tobe very high (e. g. 80-90%) at the early stage but lower at the later stage (e.g. 60-50%). It will be shown by these r’esults that graft polymerization by both emulsion and MeOH solution can be attained with a lower radiation dose. Next, the effects of 70% MMA emulsion, containing 0.2% alkylbenzen- sulphonate, were compared. Impregnation and swelling tendencies are shown in Fig. 2. In this figure the emulsion loading is plotted against void volume to get the linear relation between the two, except for oak, which was rather difficult to impregnate as compared with the other three. The different woods were then compared with regard to their reactivity (Fig. 3). Judging from these results pine is most reactive and oak, which has a low swelling factor, behaves rather irregularly. The volume change of swollen woods was also observed before and just after irradiation (Fig. 4(a)), and also that of dry woods, initially and after grafting (Fig. 4(b)). In the absence of a swelling agent the volume generally does not change in either case [4]. However, in this instance rather large volume changes were observed, that of pine being the smallest among the woods tested. For these reasons, only pine was used as the wood specimen hereafter. Next, the effects of different detergents on grafting to pine were studied with 50% MMA emulsions containing 0.5% detergent. Swelling factors were compared and large variations were observed between the different de- 110 GOTODA

0.80

S'

5 o.to

/ / / 6 . SO 50 to 40 void uo/umf %

FIG .l. Comparison of the reactivity of the MMA MeOH FIG.2. Swelling of woods by MMA emulsion. solu tio n w ith th a t o f the em u lsion (70°7o). W o o d :p in e .

FIG.3. Comparison of woods (symbols as in Fig. 2). FIG.4. Comparison of volume increase. (a) Swollen woods, before and after irradiation; (b) dry woods, initial and after grafting. tergents tested (Fig. 5). Polymerization behaviour depends on the type of detergent (Fig. 6). N o obvious trends were observed, but emulsion, containing alky lbenz ene- sulphonate had the most rapid initial polymerization rate, presumably because of its ability to exclude air by foaming during impregnation under EMULSION GRAFT-POLYMERIZATION 111

M» / / Й°0 о/ ato / - а ? г

Ъ о» / 4 •/ 0.70

/ /

au / 50 éO 70 юл/ vol. %

FIG. 5. Comparison of swelling power of the detergents. ▲ Alkyl benzene sulphonate x Polyethylene glycol monostearate ■ Sorbitan monolaurate Д Polyoxyethylene sorbitan monolarate ; О Polyoxyethylene sorbitol fatty acid esters-alkyl aryl sulphonate blend * Alkylimidazoline • n-Hexadecyl pyridinum chloride

FIG. 6. Comparison of detergents FIG.7. MMA and styrene graft polymerization to pine, (sym b ols as in F ig . 5 ) . vacuum. It also had the highest final percentage conversion. Aracel 20 had the second highest polymerization rate. The effect of concentration of alkylbenz ene sulphonate as the detergent in a 7 0 % M M A emulsion in pine w a s then studied at 0.2, 0.5, 0.8 and 1.1%. Large differences, however, were not observed. 112 GOTODA

3.2. Styrene graft copolymerization in pine

Comparison of MMA and styrene graft polymerization in pine was per­ formed both by bulk and emulsion 70% emulsion, containing 0.2% alkylbenzene- sulphonate). The results showed that styrene can be graft-polymerized more easily by emulsions, but at a slower rate than MMA (Fig. 7)

3. 3. Styrene-MMA graft copolymerization in pine

Graft copolymerization of styrene and MMA in pine was performed with emulsions having the same composition as those mentioned above. The effect of monomer ratio was studied (Figs 8 and 9), It is obvious that styrene

FIG. 8. Graft copolymerization of styrene-MMA to pine MMA styrene Д 100 0 • 80 20 О 60 40 X 40 60 ▲ 0 100

FIG. 9. Effect of the monomer ratio of MMA-styrene graft copolymerization. EMULSION G RAFT-POLYMERIZATION \ 113 polymerization can be accelerated by adding MMA. However, since high percentage conversions were not obtained, the effect of heating the samples after irradiation was studied. The results (Table I) show that percentage conversion increased with heating only at high styrene contents. In this emulsion polymerization method, the wood must be heated to remove vola­ tiles after irradiation. Thus this effect will be helpful during actual processing.

TABLE I. HEATING EFFECTS AFTER IRRADIATION

Monomer comp. Irrad. dose Heating time Percentage conversion MMA styrene (M ra d ) at 50° С (h) I n it ia l After heating

3 .4 4 2 .7 , 6 6 .7 6 1 .8 , 5 4 .2 80 20 w © 2 .1 СЛ СЛ 5 3 .7

3 .4 4 5 8 .0 , 5 3 .5 5 9 .9 , 5 1 .3 60 40 2 .1 5 0 .0 (a) 3 8 .4

40 60 3 .7 4 8 .5 , 4 1 .4 62.7, 65.4, 70.8

2 3 8 .4 , 5 2 .2 3 4 4 .8 , 4 6 .7 4 .5 4 7 .6 , 5 2 .4

1 6 0 .3 , 5 7 .8

6 2 5 8 .1 , 5 4 .8 5 9 .2 , 5 3 .1

3 5 9 .3 , 6 5 .7

(a) Estimated from experimental value.

4. S U M M A R Y

Emulsion graft polymerization in wood by gamma rays was examined together with the factors affecting it, and the results were described. The dimensional stabilities of the wood-plastic combinations obtained by these methods are now being studied.

ACKNOWLEDGEMENTS

The author wishes to express his thanks to Dr. Kinell and Dr. Aagaard for their kind advice and their support of this work. 114 GOTODA

REFERENCES

[1] GIBSON, E.J. et al., J. appl. Chem. 16 (1966) 58. [2] RAMALINGAM, K.V. et a l., J. Polym. Sci. C, Polymer Symposia No.2 (1963) 153. [3] SINGER, K .A.J.. Radiation Chemistry, Proc. Tihany Symposium 2 (1966) 915. [4] KINELL, P.O ., AAGAARD, P., private communication. [5] OKAMURA, S., 1NAGAK1, K ., Rep. 2nd Japan Isotope Conf. (1958) 125, WOOD IMPREGNATION WITH POLYETHYLENEGLYCOL

Р .-Ô. KINELL SWEDISH RESEARCH COUNCIL LABORATORY, STUDSVIK, NYKÔRING, SWEDEN

Abstract

WOOD IMPREGNATION WITH POLYETHYLENEGLYCOL. A description is given of the use of polyethyleneglycol as an exchange agent to replace water in the cell walls of wood and thus improve its dimensional stability. The use of other chemicals to enhance this effect is discussed.

1. G E N E R A L

The dimensional stability of wood can be considerably improved if the water in the cell walls is exchanged for some compound which can be bound to the cellulose molecules in the same way as the water and which has a reduced diffusion ability due to a high molecular weight. One compound that has been tried for this purpose is polyethyleneglycol. This substance pene­ trates the cell walls and also fills part of the lumen. Due to the molecular weight its incorporation is negligible and it is also difficult to extract with w a ter. Polyethyleneglycol is obtained from ethyleneoxide which is built into molecules of diethyleneglycol. It thus contains other groups in the molecular chain and hydroxyles as end groups. The number of ethyleneoxide molecules varies. Polyethyleneglycols that are usually used have molecular weights ranging from 200 to 5000. They have a high solubility in water, a low vapour pressure, a high resistance against chemical agents, and good stability against both high and low temperatures and against fungi. Homologues with a low molecular weight are hygroscopic; both this property and the solubility in water decrease with increasing molecular weight. However, the viscosity of water solutions will then be higher (Table I). Polyethyleneglycol has a low vapour pressure even at elevated tempera­ tures, and when it is used for a wood treatment its incorporation when the wood is dried becomes very small. Within the wood industry polyethyleneglycol is used both as a surface treating agent in connection with drying of wood on storage before use and as a volume impregnation to improve the dimensional stability of wood when it is dried below the fibre saturation point. The surface treatment is carried out to a depth of 2-10% of the thickness with a low molecular weight quality. In this way the surface layer of the wood is kept in a swollen state and the water from the inner parts can freely diffuse out. Formation of cracks in the wood can thus be prevented. Volume impregnation of wood is made either at atmospheric pressure or as a vacuum-pressure procedure. In the form er case the polyethyleneglycol

115 116 KINELL

TABLE I. PHYSICAL PROPERTIES OF POLYETHYLENEGLYCOL

D en sity F re e zin g V isco sity Solubility M o le c u la r (g / c m 3) p oin t (c P ) at in w a ter Hygroscopicity w eig h t 2 0 °/ 2 0 °C CC) at 20° С (glycerol = 100) 9 9 °C (by weight)

190 - 210 1 .1 2 6 - 15 4 .3 100 80

285 - 315 1 .1 2 6 - 10 5 .8 100 70

380 - 420 1 .1 2 6 + 6 7 .3 100 60

570 - 630 1 .1 2 6 + 20 1 0 .5 100 45

950 - 1050 1 .1 4 0 + 38 1 7 .4 70 5

3000 - 3700 1 .2 0 4 + 52 78 60 -

6000 - 7500 - + 58 800 50 -

diffuses into the wood. When the original wood contains more than 80% water (e. g. in preservation of waterlogged archaeological discoveries), the im ­ pregnation solution must contain only about 10% glycol, but as the im preg­ nation proceeds the amount can be increased. The temperature of the bath, its pH and density should be checked regularly. For wood with a moisture content less than 80% a 30% polyethyleneglycol solution from the beginning of the process is recommended. By using the pressure procedure even wood with large dimensions can be stabilized within a few hours. With this technique it is also possible to add fungicides, insecticides or fire-proofing agents. The pressure im ­ pregnation increases the volume of the treated material. The absorption of polyethyleneglycol depends upon the concentration of the impregnation so­ lution, the molecular weight and the type of wood. The penetration occurs most easily in the sapwood. On spruce the pressure method does not work, but a fairly good penetration is obtained at atmospheric pressure and with a long soaking time. The amount of moisture in the wood should be 15-30%. The time for the pressure treatment depends upon the dimensions of the wood and varies from less than one hour up to several hours. A low molecular weight polyethyleneglycol needs a shorter time. Experiments have shown that a content of 5-40% glycol in the impregnation solution is suitable at reasonable wood dimensions. The time for vacuum can vary from 5-60 minutes. A final vacuum treatment of 15-30 minutes is beneficial. Wood impregnated with polyethyleneglycol has been treated in several aspects. Thus its resistance to severe weather conditions is remarkably improved. The wood has a lower swelling in water and a higher gloss. The anti-shrinking efficiency can be as high as 85%. The behaviour of poly- ethyleneglycol-treated wood, painted with oil and alkyd paints, is very good with respect to adhesion of the paints on the wood surface. The blister formation is considerably reduced. When wood is treated with polyethylene­ glycol its stability decreases. IMPREGNATION WITH POLYETHYLENEGLYCOL 117

2. WARPING IN COMPRESSED WOOD

Under very wet conditions the polyglycols can to some extent be leached out, especially when a substance having a low molecular weight has been used. If fresh ash wood is to be treated, a 10-50% solution of polyethylene­ glycol is recommended. The cell walls will gradually absorb a sufficient amount of glycol to reduce or practically prevent shrinkage and swelling. This would, of course, otherwise result in cracking. In a few cases woods treated with polyethyleneglycol have been irradi­ ated with or without other additives. Some improvements can be observed in combination with polyester-styrene. The addition of diethyleneglycol and subsequent irradiation has also improved the stability. As mentioned at the beginning, the starting material for producing polyethyleneglycol is ethyleneoxide. This is made from ethylene. Industrial processes for impregnation of wood with polyethyleneglycol have been formulated. The polyglycol is compatible with most of the agents commonly used for wood preservation. No estimations of the costs of treatment are available.

STATEMENTS PREPARED BY THE STUDY GROUP

MONOMERS AND MONOMER MIXTURES USED IN IMPREGNATION OF FIBROUS MATERIALS

Some important properties of monomers and polymers in relation to their use for reinforcement of fibrous materials are listed in Table I. In Table II some monomers and their properties important in im ­ pregnation of fibrous materials are listed. In general it is not advantageous to use a pure monomer for impregnation but rather a mixture of monomers or a mixture of a monomer and a low molecular weight polymer such as un­ saturated polyester. Some of these mixtures which have been well studied in connection with WPC are listed in Table III together with some of their properties when used in WPC. Other monomer mixtures may well come in question and other monomers can probably be used. For instance, it is reported from Japan that the cheap monomer ethyleneoxide, which cannot be polymerized by gamma radiation as such, can be polymerized (in bulk) as a mixture with methylmethacrylate. Good results with WPC have generally been obtained without swelling agents but more is grafted if some swelling agent is used, and it is possible that a swelling agent might be useful in the case of fibre-boards. Solvents, plasticizers, crosslinkable natural resins, aromatic chlorinated hydrocarbons, and retardants can be added, and with their use the properties of WPC can be widely modified. For example, a chlorinated wax can act as retardant, can reduce the total dose of radiation and can increase the flame resistance simultaneously.

TABLE I. PROPERTIES OF MONOMERS AND POLYMERS IMPORTANT FOR THE IMPREGNATION OF FIBROUS MATERIALS

Properties of monomers Properties o f polymers

P ric e Toughness

Availability Hardness

Dose (or catalyst) requirement E la sticity

Heat of polymerization Weather resistance (including u. v.-resistance)

Volume contraction in polymerization Rot resistance

T o x ic it y Insect resistance

V o la t ilit y Flame resistance

Viscosity and surface tension Water resistance

Aging resistance

Solubility in monomers

Insolubility in organic solvent

Chem ical resistance

121 122 MONOMERS AND MONOMER MIXTURES MONOMER AND MONOMERS 122

TABLE II. MONOMERS AND THEIR P R O P E R T IE S S £ D CO < D C/5 < o ' S to CQ ? E u £ >G L S •й 5 •-H -S5 2 . a e g, E о

TABLE III. SOME MIXTURES USED FOR IMPREGNATION OF FIBROUS MATERIALS AND' THEIR PROPERTIES (APPROXIMATE COMPOSITION; APPROXIMATE PRICE IN BULK)

Total dose required World market price M ix tu re P rop erties (M r a d ) (U S í/ k g )

1. Vinylchloride- H ard, 1 .5 0 .2 1 vinylacetate tou gh , (8 0 :2 0 ) s o lven t resistant

2. Acrylonitrile-styrene H ard, ~ 2 . 5 ( ? ) 0 .2 6 (4 0 :6 0 ) tough

3. Polyester-styrene H ard, 1 .2 0 .3 5 (5 0 :5 0 ) tough in so lu b le

4. Methylmethacrylate- H ard, 1 .2 0 .3 5 styren e tough (5 0 :5 0 )

Most of the monomers in Table II can be mixed with each other; how­ ever vinyl chloride or vinyl acetate does not mix with styrene, butadiene or isop ren e. Monomers have been used in emulsion for preparing WPC and these may be useful also in impregnation of fibre-board. COMPARISON OF THERMAL, GAMMA AND ELECTRON INITIATION

No important differences in the physical properties of wood-plastic combinations initiated by the different methods have yet been demonstrated. The choice of the appropriate initiator system will thus be determined by technical feasibility, capital cost and running costs of the plant, although it is necessary to consider these parameters for the whole plant rather than m erely for the initiation step since the choice of initiator will affect overall plant design. European experience would suggest than when a specific project is considered in detail a clear advantage for one initia­ tion system will be apparent, and the following comparisons are therefore aimed at informing the reader rather than suggesting an overall superiority for one method. Electron irradiation is not suitable for the treatment of thick timber sections, and a comparison of gamma and thermal initiation for treatment of impregnated solid wood will now be made.

Gamma radiation Thermal

High capital investment: Very low capital investment treatment of small production or, in factories having ovens, zero volumes is not feasible unless capital investment. Ideal for pilot a facility has been installed for scale studies and low-volume pro­ other reasons. duction. Transport of material to a Ovens and kilns are widely central gamma irradiation facility available. would add greatly to the cost if products to be treated are made in a large number of small factories. No catalyst is required: A suitable catalyst is neces­ this saves actual cost of catalyst sary and at large production volumes and prolongs the usable life of its cost may be prohibitive. the monomer. If too high a radiation dose H ighly a cid ic catalysts and is used, the timber itself will be excessively high initiation tempera­ weakened; at doses usually pro­ tures should be avoided. This is not posed for WPC manufacture difficult to achieve in practice. this factor will not be important.

It should be added that while both systems involve safety factors (radiation hazards and the explosive nature of peroxides), present indus­ trial practice deals with these problems adequately. In view of the rela­ tively low cost of styrene monomer, the high radiation dose needed to polym erize this monomer is an additional disadvantage to the radiation method. If fibre-board and bagasse board are to be combined with monomer, then the use of electron accelerators must be considered. The boards are made in factories having a large individual throughput and the capital cost of the accelerator would be largely offset by the difficulties of handling

124 THERMAL, GAMMA AND ELECTRON IN ITIATIO N 125 the boards in a conventional curing cycle. Detailed discussion of electron beam curing is given elsewhere in these Proceedings, but the possibility of microwave heating techniques being developed for the rapid treatment of large areas of board should not be overlooked, though catalyst cost would be considerable. Should subsequent work reveal major differences in the properties of wood-plastic combinations initiated by different methods, this would, of course, greatly influence the choice of initiation system. Since research is continuing on all the initiation methods discussed, the relative standing of the various techniques may change significantly in the future.

STATÜS REPORTS

STATUS AND TECHNOLOGY OF POLYMER-CONTAINING FIBROUS MATERIALS IN THE WESTERN HEMISPHERE

Abstract

STATUS AND TECHNOLOGY OF POLYMER-CONTAINING FIBROUS MATERIALS IN THE WESTERN HEMISPHERE. A series of reports by well-known experts from Sweden, Finland, Hungary, the United States of America and the Federal Republic of Germany is presented. These reports cover work carried out in Western Europe, Eastern Europe and the United States of Am erica.

WESTERN EUROPE, WITH PARTICULAR REFERENCE TO SWEDEN

CONTRIBUTED BY Р .-Ô. KINELL SWEDISH RESEARCH COUNCIL LABORATORY AND P. AAGAARD SECTION OF NUCLEAR CHEMISTRY, AB ATOMENERGI, STUDSVIK, NYKÔPING, SWEDEN

1. INTRODUCTION

A short survey is given here of the work done in Western Europe, ex­ cluding Finland, on wood-polymer composites and some related treatments of wood and wood products. It should first be pointed out that the subject cannot be completely covered because of the difficulty of obtaining reliable and up-to-date information. A more detailed report is presented on the work done in Sweden. Materials such as 'compreg', 'impreg', uralloy and arboneeld are not discussed.

2. WORK IN WESTERN EUROPE (EXCLUDING FINLAND)

The application of polymer loading to wood to improve its properties has been studied in most Western European countries, mainly in connection with research work at atomic energy establishments. In several cases these establishments collaborated with institutes for wood research and wood technology. Industrial firm s representing various kinds of wood manufactur­ ing have taken part in development work only to a limited extent.

129 130 KINELL and AAGAARD

In 1966 two symposia were arranged to discuss wood-polymer compo­ sites: one in Brussels, Belgium, organized in October by Euratom for the EEC countries, and one in Studsvik, Sweden, arranged in November by the Swedish Atomic Energy Company for the Scandinavian countries. In September 1967 a symposium on Applications of Ionizing Radiations in the Chemical and Allied Industries was organized in the United Kingdom by the British Nuclear Energy Society, at which the status of wood-polymer combi­ nations was briefly mentioned.

2. 1. A u stria

The institute of chemistry of the Reactor Centre in Seibersdorf outside Vienna has been working with the combination spruce-methylmethacrylate [1]. Spruce is of special interest to Austria. The hardness of the material has been studied.

2.2. Belgium

Polymerization of methylmethacrylate in spruce and poplar has been studied at the Centre d'Etudes Nucléaires in Mol [2].

2.3. Denmark

Work is being performed at the chemistry department of the Danish Atomic Energy Commission, Research Establishment Ris^, Roskilde, in co-operation with the Danish wood manufacturing industry and the Danish Wood Research Laboratory. Very important work has been done on the wood species pine, spruce, beech, teak and palisander and on the monomers methylmethacrylate, vinylacetate, styrene and acrylonitrile. Included in the work is a comparison between the use of an 10-MeV electron accelerator (5 Mrad/s) and a 60Co gamma-source (55 rad/s) which is of special in­ terest with respect to the impregnation of veneer [3]. Some industrial applications have been studied.

2.4. France

A group for applied radiation chemistry at the Centre d' Etudes Nuclé­ aires in Saclay is working with beech and styrene in co-operation with Centre Technique de Bois in Paris. Collaboration has been established with the corresponding organization in Japan. Saint-Gobain Techniques Nouvelles in Courbevoie is working with beech, poplar and oak and methylmethacrylate, styrene and acrylonitrile [2]. Manufacturing of knife handles is under way at Conservatome Industrie in Courbevoie [5].

2.5. Germany, Federal Republic of

At the Bundesanstalt für Materialprüfung in Berlin some work on the action of ionizing radiation on wood has been performed [6]. The possibility of forming space networks by the coupling of diisocyanates to cellulose has been studied. The use of polyesters in combination with styrene and of formaldehyde has been tried. At the Farbwerke Hoechst AG in Frankfurt am Main spruce has been combined with acrylonitrile and vinylacetate [2]. WESTERN EUROPE 131

2.6. Holland

The polymerization of methylmethacrylate in pine, spruce (hemlock) and beech by means of high frequency heating and ordinary catalysts has been studied at the Wood Research Institute in Delft [2]. Heat evolution during irradiation has been measured.

2 .7 . Ita ly

Research is planned at the Societa Ricerche Impianti Nucleari in Saluggia-Vercelli in co-operation with the wood manufacturing industry on the use of methylmethacrylate and spruce, beech, poplar, birch and larch. At the Centro Nazionale del Legno in Florence a process with prepoly­ m erized ethylene is under investigation [2].

2.8. Norway

At the Central Institute for Industrial Research in Norway some work has started [7].

2. 9. United Kingdom

At the Forest Products Research Laboratory (under the Ministry of Technology), Aylesbery, pine sapwood, birch and podo have been impreg­ nated with methylmethacrylate [4]. Attention has been paid to the problem of graft-copolymerization to carbohydrates and lignin in the wood.

3. W O R K IN SW EDEN

One of the most vital points on which research and development work on wood has to be concentrated in the near future is the improvement of the properties of wood in ordinary use. This means that the problem of finding protective agents against fungi and rot is still very current. Surface treatment in various forms is necessary as well as the improve­ ment of dimensional stability. These are all old and well-known questions, but their importance for the development of the wood manufacturing industry within the next ten years has recently been stressed by wood specialists in Sweden [8]. Even in a wood producing country like Sweden it has not been possible to find solutions to all of the problems involved in the use of wood and other fibrous materials. A considerable amount of research and de­ velopment work is being done at various institutions in Sweden. Here only two of the activities are reported: firstly, the treatment of wood with polyethyleneglycol and, secondly, the formation of wood-polymer combina­ tions by means of radiation-induced polymerization in situ.

3. 1. Polyethyleneglycol impregnation of wood

The use of polyethyleneglycol to impregnate wood for better dimensional stability was first studied in Sweden by Moren in 1952 [9]. The idea is to reduce the moisture content in the wood and at the same timé to replace the water, either partially or completely, with a substance which prevents 132 KINELL and AAGAARD the damp from spreading [10, 11]. The most suitable substance is poly­ ethyleneglycol (PEG) which has molecular weights in the range 200 - 6000. At the same time it is possible and even advisable to incorporate insecticides, fungicides and fire-proofing chemicals. The impregnating water solution should contain about 10% PEG when the original wood contains more than 80% water (waterlogged wood, e. g. in preservation of archaeologi­ cal discoveries). As the impregnation proceeds the amount of PEG can be increased. The temperature of the bath, its pH and density should be checked regularly. For wood with a moisture content less than 80%, a 30% PEG solution from the beginning of the process is recommended. Dry wood has to be treated with regard to the character of the object. For certain purposes it is possible to apply PEG in a continuous in­ dustrial process to obtain a thorough wood impregnation. For the treat­ ment of green wood, e. g. green veneer, a continuous method exists that employs concentrated PEG with which not only the properties of the veneer are improved but an increased wood yield is also obtained. This has been tried on pine and birch. Surface treatment of freshly cut wood with con­ centrated PEG can reduce or eliminate face checking. Under certain con­ ditions it is even possible to obtain a better yield and better appearance of the wood after drying. The impregnation of wood with PEG by the application of alternating pressure has been developed. Wood impregnated with PEG has been tested in several aspects. Thus its resistance to severe weather conditions is remarkably improved. The wood has a lower swelling in water and a higher gloss. The behaviour of PEG-treated wood, painted with oil and alkyde paints, has been investigated for blister formation and for adhesion of the paints on the wood surface.

3.2. Research on wood-polymer combinations

Research work on the radiation-induced polymerization of vinyl mono­ mers in various types of woods has been performed since 1964 by the Swedish Research Council Laboratory in co-operation with the Section of Nuclear Chemistry, AB Atomenergi. Financial support was obtained from the Swedish Technical Research Council. The majority of the wood ma­ terial was delivered by the Swedish Forest Products Laboratory, Wood Technology Department (Dr. B. Thunell), Stockholm. The same laboratory has also evaluated the mechanical properties of the wood-polymer samples according to a slight modification of their standard test procedure. During the work some industrial firm s showed great interest in possible uses of this new material and, as will be mentioned later, the various objects have been produced and their properties checked. At present there are no definite plans for introducing the wood-polymer material on the market. A review is given below of the research work done in Sweden, but a more detailed report is available [12].

3.2.1. Materials

The materials used include different kinds of wood, monomers and solvents used as additives in monomer solutions or as extractants and précip­ itants for polymers

3.2. 1.1. Wood m aterials: Four main species of native wood were used. These included two softwoods, Scotch pine (Pinus silvestris) and spruce WESTERN EUROPE 133

TABLE I. WEIGHT STATISTICS OF WOOD SAMPLES (dimensions: 2 cm X 2 cm X 2 cm)

W ood N u m ber o f Mean number in Weight range W e ig h t at Num ber

p ie c e s e a c h group ■ ( g ) m a x im u m average weight 6 ° ) ( g ) eg)

P in e 580 4 .6 3 .1 - 5 .4 3 .4 4 .7 3.92 ± 0.51

584 5 .6 3 .6 - 5 .3 3 .9 5 .1 4. 37 ± 0.52

Spruce 251 10 3 .3 - 4 .2 3 .5 3 .5 9 ± 0 .1 7

B irch 599 5 .6 4 .2 - 6 .0 4 .6 5 .5 5 .1 2 ± 0 .3 9

318 4. 5 4. 2 - 6. 5 4 .9 5 .6 5.21 ± 0.40

B eech 203 1 4 .3 5 .5 - 6 .1 5 .8 5.80 ± 0.14

508 10 5 .2 - 6 .1 5 .7 5.70 ± 0.17

(Picea excelsa), and two hardwoods, birch (Betula verrucosa) and beech (Fagus silvatica). Most of the experiments were performed on wood blocks measuring 2 cm X 2 cm X 2 cm; some blocks with dimensions of 2 cm X 2 cm X 4 cm and 2 cm X 2 cm X 20 cm, the large dimensions being along the fibre direction, were also used. The wood material consisted of both sapwood and heartwood of Scotch pine (selected from species with a high heartwood content grown in southern Sweden). Due to the method of selection the m aterial had a very small variation in volume. However, for some woods there was a rather large variation in the density of the samples. Table I gives the weight statistics of some consignments of wood as received, divided into weight classes of 0. 1 g. The distributions for pine and birch are especially wide, showing a standard d eviation o f 12. 5% and 7. 5%, r e s p e c tiv e ly . The deviation fo r spru ce is near 5% but that for beech only 2. 5%, which shows a rather high degree of homogeneity. An estimation of the variation in density within some specimens, 20. cm in length, of pine, birch and beech gave standard deviations from the mean of 1.4, 1. 1 and 0. 3%. The two higher values are outside the limits inherent in the experimental technique. The basic variation in density arises from such factors as the springwood-summerwood ratio, the width of annular rings, the thickness of the cell walls, and the formation of heartwood.

3.2. 1.2. Monomers: The monomers us^d were methylmethacrylate, butylmethacrylate, styrene and acrylonitrile. They were specified to a minimum monomer amount of 99. 5%. Added inhibitor was removed by repeated extractions with alkaline solutions, washing with distilled water and drying.

3.2. 1.3. Other m aterials: Organic liquids and other chemical agents used in various stages of the experiments were generally of pro analysi grade or equivalent purity. 134 KINELL and AAGAARD

3.2.2. Impregnation

The low density of wood, about 0. 5 g/cm3, indicates a very porous structure. The fibrous substance has more or less continuous and inter­ connected pores. In the experiments performed the wood was impregnated with monomer in a reduced pressure procedure, then the air in the pore volumes was partly exchanged for the monomers. The uptake of monomer in the cell walls is limited for non-polar liquids due to the strong hydrogen bonding between the constituents in the fibre structure. An addition of a polar agent swells the cell walls and makes them more accessible even to non-polar monomers. The pore volume utilization was used as a measure of the impregnation efficiency [3]. This is defined as the ratio of the sorbed volume of monomer to the pore volume of the wood. The uptake of monomer in pine sapwood is given in Fig. 1 as a function of the density of the wood. The same behaviour is characteristic also of birch, which is as easily impregnated as pine sapwood. Pore volume utilization as a function of the impregnating pressure is shown in Fig. 2. For woods which are difficult to impregnate the soaking time has to be prolonged as shown in Fig. 3 for pine heartwood and spruce.

0.40

FIG. 1. Pore volume utilization (Im .eff. ) of pine sapwood of different initial densities (p). 91% pressure red u ctio n .

The distribution of monomer in the wood matrix was studied by m icro­ photography of wood sections after completed polymerization [4]. There is clear evidence that a large part of the monomer is located within the lumens of the cells. By adding dye stuffs to the monomer before impregnation it can be shown that some types of cells are closed and can often never be filled with monomer. This is the case for medullary strings. The results obtained so far support the view that the monomer-wood system contains the liquid in small, homogeneous volumes distributed in the wood structure. Generally only a small amount of monomer can diffuse into the fibrous structure and be molecularly dispersed among the con­ stituents of the cell walls. In experiments with low-boiling-point monomers it is advantageous to impregnate and polymerize at low temperatures. Preliminary work on the impregnation of pine sapwood with trichloroethene at -10°C and with a p ressu re reduction o f 90% and a soaking tim e o f 160 m in gave a pore volum e u tiliza tio n o f 0. 91 ± 0. 02. WESTERN EUROPE 135

Impregnation of woods of differing moisture content has shown that within the standard deviation there is no correlation between water content and impregnation efficiency.

FIG.2. Pore volume utilization (Im .eff.) as a function of impregnation pressure: (a) 30 min soaking time, (b) 20 h soaking tim e for different woods, pine sapwood (O), pine heartwood (♦), spruce (X), beech ( □) and birch (V).

FIG.3. Pore volume utilization (Im .eff.) as a function of soaking time for pine heartwood (O ) and spruce (X). 98% pressure reduction.

In a series of experiments polar organic solvents were added to the monomer before impregnation to study the effect of concomitant swelling. With excessive swelling the free volume model for impregnation will not apply. As an example of this behaviour the areal swelling (tangential X radical) of birch was found to exceed 20% when the wood was impregnated with a 1: 1 methanol-monomer solution at a pressure reduction of 90%. An overloading with monomer of 17. 5 ± 1.1% is then obtained. 136 KINELL and AAGAARD

3.2.3. Irradiation

After the impregnated specimens had been wrapped in aluminium foil irradiation was carried out in an AECL Gammacell 220 loaded with a 60Co gamma source. Most of the experiments were performed with a dose rate of 70 - 80 rad/s and the remainder with 7 rad/s. The temperature in the radiation cell was about 30°C.

3.2.4. Polymerization experiments

The relation between the degree of conversion and the radiation dose was determined for the following monomer-wood combinations:

Methylmethacrylate-pine sapwood, pine heartwood, spruce, birch and beech; Methylmethacrylate/butylmethacrylate-pine sapwood; Butylmethacrylate-pine sapwood; Styrene-pine sapwood; Styrene (7)/acrylonitrile (3)-pine sapwood.

FIG.4(a). Moisture effects on conversion of methylmethacrylate in pine sapwood as a function of dose (Mrad). Moisture contents: 19.5% (V), 6% (O). dry (X). Dose rate: ~80 rad/s. The full lines at 19.5% and the dry wood do not represent the true course of the polymerization.

FIG .4(b). Conversion of methylmethacrylate. as a function of dose (Mrad) for pine heartwood. Moisture contents: ~12% (0), dry (X). Dose rate: ~ 75 rad/s. Maximum dose: 5.2 Mrad. The full line does not represent the true course of the polym erization. WESTERN EUROPE 137

These experiments were performed at various moisture contents in the wood. Complete conversion of methylmethacrylate at a moisture content of about 6% was obtained after a dose of 1. 3 Mrad in pine sapwood (Fig. 4(a)), 1. 8 Mrad in pine heartwood and beech (Fig. 4(b)), about 2 Mrad in spruce and more than 2 Mrad in birch. The dependence of the moisture content is as follows : in pine sapwood and spruce there is an increase in the degree of conversion with increased moisture content, pine heartwood and beech do not show any effect, and birch behaves rather irregularly. Butylmetha- crylate in pine sapwood requires a dose of 4 Mrad for complete conversion, styrene shows at 4. 5 Mrad a conversion of only 10% but copolymerization with acrylonitrile gives complete conversion after 3. 7 Mrad. Dilution of the monomer has been studied in the following systems :

Methylmethacrylate/benzene-pine sapwood; Methylmethacrylate/tetrachloromethane-pine sapwood, birch and spruce; Methylmethacrylate/methanol-pine sapwood, spruce and birch; Styrene/methanol-pine sapwood.

The addition of benzene lowers the rate of polymerization of methylmetha­ crylate and thus increases the dose necessary for complete conversion. The dependence of the conversion on the monomer content in the impregna­ tion mixture at a constant dose is rather complicated in a wood matrix compared with a pure system. At about 25% monomer a minimum in the degree of conversion is obtained at all dose values. Complete conversion can only be reached at_2 Mrad and a monomer content of 90%, Tetrachloromethane increases the rate of polymerization, but the dose for complete conversion is only slightly affected. The gel effect is less pronounced. The dependence of the degree of conversion on the monomer content at a constant dose shows to a great extent the same behaviour in both wood and a pure system. Nearly complete conversion is obtained at 1. 2 Mrad when the monomer content exceeds 90%. The addition of methanol to the monomer gives a rather complicated picture. Thus in wood complete conversion at 1. 2 Mrad is obtained at monomer contents of less than 25% and near 100%. In a pure system complete conversion is rëached at 2 Mrad when the' monomer content is more than 25% and at 1. 2 Mrad at a content of more than 90%. This probably depends upon the swelling action of the methanol on the wood, which may make initiation centra in the cell walie accessible for initiation of poly­ merization. The conversion decreases in the order birch > pine sapwood > spruce over the whole dose range 0. 2 - 2. 5 Mrad. The rate of polymerization of styrene increases with decreasing mono­ mer content in the methanol. At 75% a saturation effect is observed. Further studies of the dependence of the degree of conversion on swelling have been made in the following systems with 5 and 15% swelling agent; Methylmethacrylate/dioxane-pine sapwood, spruce, birch; Methylmethacrylate/dimethylformamide-pine sapwood, birch; Methylmethacrylate/dimethylsulphoxide-pine sapwood, spruce, birch; Methylmethacrylate/diethyleneglycol-pine sapwood, birch.

All conversion versus dose relations show a transition dose, at which the degree of conversion changes order among the types of wood (15% swelling agent): 138 KINELL and AAGAARD

D ioxan e: Spruce > birch > pine sapwood/1. 2 - 1. 5 Mrad/spruce ~ pine sapwood > b irch . Dimethylform amide : Birch > pine sapwood/O. 5 Mrad/pine sapwood > birch. Dimethylsulphoxide : Birch > spruce - pine sapwood/O. 6 Mrad/spruce > pine sapwood > birch. Diethyleneglycol : Birch > pine sapwood/O. 4 - 0. 9 Mrad/pine sapwood > birch.

A simple explanation of this behaviour is difficult to find. It has been observed that the swelling of the wood in itself gives a certain degree of conversion. Thus at 5% dimethylsulphoxide the conversion in birch is 13% compared with 9% in pine sapwood. In birch about 50% of this polymer is present as copolymer. On this basis some understanding of the behaviour can be reached.

3.2.5. Dose-rate effects

All the results mentioned above were obtained at a dose rate of 70 - 80 rad/s. In the following systems the lower dose rate of 7 rad/s was used:

Methylmethacrylate-pine sapwood (Fig. 5, complete conversion at 0. 7 Mrad) Methylmethacrylate/methanol-pine sapwood (0.6 Mrad) Methylmethacrylate/benzene-pine sapwood (0.75 Mrad) Methylmethacrylate/tetrachloromethane-pine sapwood (0.6 Mrad).

TABLE II. COPOLYMER FORMATION IN THE SYSTEM PINE SAPWOOD-METHYLMETHACRYLATE AT DIFFERENT WATER CONTENTS AND VARIOUS DEGREES OF CONVERSION (Dose rate 80 rad/s. The upper set and lower set of data at each water content refer to two methods of determination. In comparing the data the estimated error of + 10 ±5% must be kept in mind)

Water content Percentage copolymer at the degree

С°!°) of conversion 0 .1 - 0 .3 -0.5 0.7 - 1.0

0 -5 -1

-3 +2

6 22, 21, 15 17 07, 13, 05

18, 13, 11 10 13, 13, 17

20 31 30 31

13 44 37

20 49 56

62 67 WESTERN EUROPE 139

TABLE III. COPOLYMER FORMATION IN THE SYSTEM PINE HEARTWOOD-METHYLMETHACRYLATE (cf. Table I).

Water content Percentage copolymer at the degree 07°) of conversion 0.1 - 0.3 ~0.5 0 .7 - 1 .0

0 13 34Í a) 1. 1, 2

09 43 1, 2 , 0

4-10 -28, 22, 47 13, 3 4 -3 4 , 18, 40 06, 1 5

20 7 2 (a)

106

{ a ) The samples were dried by a high-frequency method.

TABLE IV. COPOLYMER FORMATION IN THE SYSTEM BIRCH-METHYLMETHACRYLATE (cf. Table II)

Water content Percentage copolymer at the

(%) d e g r e e of conversion 0 .1 - 0 .3 ~0.5 0.7 - 1.0

0 45 9

51 11

7 44 10

44 14

20 49

63

3. 2. 6. F o rm a tio n o f co p o lym er

The formation of graft-copolymers in the wood matrix was studied by determining the weight of the wood specimens after extraction of the homopolymer. This was done at various degrees of conversion and at different moisture contents. The results are given for methylmethacrylate in Table II for pine sapwood, in Table III for pine heartwood and in Table IV for birch. There are large errors involved in the method of determina­ tion, but the general trend is an increased percentage of copolymer formed 140 KINELL and AAGAARD

at higher moisture contents and a decreased percentage at higher con­ versions. This corroborates the view of the cell wall as one of the poly­ merization loci and with an increased accessibility to initiating centra at a higher degree of swelling. As yet it has not been possible to determine the wood constituents involved in this reaction [4].

3. 2. 7. E m u lsion p o ly m e riza tio n

Some work has been performed on impregnating the wood with an emulsion of monomer in water and then polymerizing by irradiating the system [14]. With this method the wood swells and a higher degree of copolymer is expected to form. The influence of various emulsifying agents (cationic, anionic and neutral) were studied. The technique has been tested for methylmethacrylate and styrene and seems rather promising for the latter monomer.

3. 2. 8. Degree of polymerization

The molecular weight of polymethylmethacrylate homopolymer formed in pine sapwood was found to increase from 25 000 to a maximum of about 1 000 000 at complete conversion. No large difference was found on com­ parison with vacuum polymerization. At higher doses a slight decrease occurred which was probably due to radiation-induced degradation (Fig. 5). The addition of tetrachlormethane gave a molecular weight of less than 20 000 o v e r the w hole dose range.

FIG.5. Conversion of methylroethacrylate in pine sapwood as a function of dose (Mrad). Dose rate: ~7 rad/s.

3.2.9. Distribution of polymer

The distribution of polymer in the interior of the wood specimens was found by means of microscopy to be heterogeneous with the main part of the polymer in the cell lumen. The macroscopic distribution is exemplified in Fig. 6 for poly(methylmethacrylate) in pine sapwood, birch and beech. Except for end effects the density is constant within ± (0. 5 - 1)%. WESTERN EUROPE 141

3. 2. 10. M ech an ical p ro p erties

The mechanical properties were determined for wood-poly (methyl­ methacrylate) systems with three different polymer loadings, and for pine (sapwood) and birch.

10 Position

FIG. 6. Variation of density (p) of wood-polymer samples along 20-cm bars. Pine sapwood (O), birch (V), b e e c h ( □ ) .

The polymer loadings decided on were 0. 15, 0. 40 and 1. 0 g per gram of wood. The last-mentioned amount presented no problems: normal im ­ pregnation and full conversion of the monomer yielded a product of this kind. However, the lower concentrations were not easily obtained by control through the applied dose. In the conversion ranges of interest the poly­ merization rate is very high and therefore accurate dose control was not possible with the irradiation facility available. A technique with solutions of the monomer in benzene and tetrachloromethane was used to obtain samples of the required polymer content. The samples were polymerized in the normal way and afterwards non­ reacted material was evacuated. Another technique was to give the specimens a dose much higher than that needed for complete conversion. In this way some hydrogen gas is produced by degradation of the polymer. When the specimens are heated to the softening temperature of the polymer an expansion of the gas occurs. This then causes the polymer to fill the cell lumen more completely and also to exert a certain pressure on the cell walls. The evaluation of the mechanical strength of these specimens is under way.

3.2.10.1. Hardness: Hardness was determined by pressing a 5-mm steel ball to a depth of one-half diameter with a speed of 6 mm/min and recording the force applied [15]. The results are given in Table V and Fig. 7. For both pine and birch the samples with the highest polymer loading split were tested perpendicular to the fibres after having first been tested parallel to the fibres. Standard deviation for the test series of 10 samples is given. The samples were tested without any correction for surface or end effects, and the values are therefore judged to be low in relation to those that would be obtained for a surface-finished product. The effect of polymer content is quite noticeable. 142 KINELL and AAGAARD

TABLE V. MECHANICAL PROPERTIES OF WOOD-POLYMER COMPOSITES

Wood Polymer Hardness Compression strength Impact strength (g/g wood) (kp/cm!) (kp/cm!) (mkp/cm!) II I 2 c m 4 c m

Birch 0 474 ± 20 442 ± 30 620 ± 40 766 i 60 0 .6 9 ± 0 .2 3

0 .1 5 831 ± 188 688 ± 150 780 ± 92 856 ± 60 0. 69 ± 0 .3 0

0 .4 0 1269 ± 130 1171 ± 65 873 ± 80 878 ± 50 0. 53 ± 0 .2 1

1.0 0 1798 ± 95 1240 ± 54 1242 ± 74 1 .0 3 ± 0 .4 3

P in e 0 537 ± 57 408 ± 34 669 ± 47 791 ± 25 0 .4 1 ± 0 .0 0 9

0 .1 5 709 ± 33 580 ± 49 664 ± 28 788 ± 51 0 .4 6 ± 0 .0 0 6

0 .4 0 968 ± 83 764 ± 63 791 ± 14 710 ± 18 0 .4 4 ± 0 .0 0 6

1 .0 0 1540 ± 388 1263 ± 54 1127 ± 152 0 .7 5 ± 0 .0 0 7

FIG. 7. Hardness (H j) of wood-polymer samples as a function of weight gain of the initial sample. Pine sapwood (O), birch (V ). Open symbols refer to measurement parallel to the grain (1), filled symbols to measure­ ment perpendicular to the grain (2).

3. 2. 10. 2. Compression strength parallel to the grains: The com­ pression strength was determined in a testing machine with fixed pressure pads, with a load increase of about 1400 kp/min [15]. The determinations were made on two sample sizes, 2 cmX 2 cmX 2 cm, and 2 cmX2 cmX 4 cm (the dimensions are ashX r x y . The results are presented in Table V and inFig. 8(a). The variation of the individual results in one set of measurements is large; for the intermediate polymer loadings there is no apparent effect, for samples showing a weight gain of 100% there is roughly a doubling of the com­ pression strength. Further experiments are needed to judge whether the lack of effect at low polymer contents is real and if there is any effect of solvents present in the preparation of the samples. WESTERN EUROPE 143

3. 2. 10. 3. Impact strength: The impact strength perpendicular to the grain was measured in a pendulum testing on pieces measuring 2 cm X 2 cm X 20 cm. The test pieces were fastened at points 18 cm apart and the pendulum hit the middle of the exposed sample [15]. The results are given in Table V and Fig. 8(b). There is little effect at intermediate polymer contents, at maximum weight gain there is an increase in the impact strength of about 50%. The standard deviations for all measurements on birch are of the order of 50%; for pine sapwood the corresponding value is 10 - 20%.

7.

FIG. 8 (a). Compressive strength parallel to the fibres (o), as a function of weight gain of the initial sample. Pine sapwood (O), birch (V ). Filled symbols refer to measurements on 2-cm samples, open symbols to 4-cm samples.

FIG .8 (b). Impact strength (a) as a function of weight gain of the initial sample. Pine sapwood (O), birch (V ).

3. 2. 11. M oistu re s ta b ility p ro p e rtie s

To determine volume and weight changes in samples subjected to equilibration in an atmosphere of standard humidity, the same set of samples were used as in the physical tests. The temperature was 20°C and the relative humidities 60% and 65% for the birch and pine samples, respectively. 144 KINELL and AAGAARD

3.2.11.1. Volume changes : The values for the swelling of the two woods are given in Table VI. It is seen that even small polymer contents affect the swelling of the wood and that birch seems to show the larger effect. For birch the volume swelling is decreased to less than half the value for untreated samples, and for pine the half value is reached for samples which have a weight gain of 1 g/g wood.

TABLE VI. STABILITY OF WOOD-POLYMER COMPOSITES

W ood P o ly m e r S w e llin g Weight gain Weight gain after

(g / g w o o d ) &>) (°i°) (g/100 g dry wood) I d 2 d 3d

Birch 0 5.15 ± 0.32 7.72 ± 1.78 0. 59 0 .5 7 0 .4 8

0 .1 5 1. 56 ± 0 .2 4 5.86 ± 0.26 1. 02 0 .9 6 0 .5 7 (6 . 9 ± 0 .5 )

0 .4 0 2.05 ± 0.19 6. 96 ± 0 .2 5 1. 67 1 .5 0 1 .2 5 (9 .6 ± 1 .0 )

1 .0 0 2 .1 4 ± 0 .2 4 3.51 ± 0.14 0 .4 3 0 .3 7 0 .1 9 (7 .0 ± 0 . 6 )

P in e 0 5. 24 ± 0 .1 2 1 0 .5 ± 0 .4 1 .1 0 .6 1 .0

0 .1 5 4 .3 2 ± 0 .3 8 8.65 ± 0.17 0. 96 0 .3 7 0 .5 3 (10.1 i 1.0)

0 .4 0 4. 25 ± 0. 27 1 0 .9 ±0.6 3 .1 2 .1 2 .1 (15.0 ± 2.0)

1.00 2. 72 ± 0 .2 4 4.38 ± 0.36 0. 87 0 .4 3 0 .4 3 (8.7 ± 1.0)

3.2.11.2. Weight changes : The moisture contents of the wood after equilibration are given in Table VI as weight gain in percent of the dry weight (determined by drying at 102°C ). The weight gain values have been roughly corrected to the weight gain of the wood in the sample and these values are given in parentheses. Also given in the table are the remaining weight gains after 1, 2 and 3 days' drying at 80°C. It is seen that the corrected weight gain calculated on the basis of the wood in the sample is nearly constant. The exceptions are the values for polymer contents of 0.4 g/g wood. These were calculated from polymeri­ zation of the monomer in a 50% by volume solution in tetrachloromethane, followed by evaporation at ambient temperature. Under these conditions a large amount of solvent will remain in the samples and is not released until the polymer is heated above its glass transition temperature. The value for poly(methylmethacrylate) is in the range 80 - 100°C depending on the method of preparation. Even for drying at 80°C these samples show higher values than normal. As an approximation, one can suppose that the moisture in the sample is not bound to the polymer phase and will therefore dry off at the same rate in all samples, while the evaporation of the organic solvent is very slow at 80°C. A rough correction for the equilibrium weight gains can then be made by the differences for first day drying. Corrected in this WESTERN EUROPE 145 way, the average values of weight gain of the wood fall within 10% for birch samples and within 20% for the pine samples. (The large variation in un­ treated birch samples is caused by one very low value, and if this is dis­ regarded the weight gain of the remaining nine samples is 8’. 30 ± 0. 36, a value about 20% higher than that for the treated birch samples. )

3. 2. 11. 3. Time effects in the change of water content of samples: In the drying experiments it soon became evident that samples with a high con­ tent of polymer needed a longer time than samples with little or no polymer. Experiments were then designed to study this effect in more detail. Initially, samples were dried completely and the weights were recorded at time inter­ vals. A typical curve for the moisture uptake is given in Fig. 9(a) for a sample with high polymer content. The scattering of the points measured after some time is explained by changes in the humidity in the laboratory.

FIG .9(a). Moisture uptake as a function of time for wood-polymer material. Half-times: 1660 min (•), 280 min (X), 30 min (O). Tim e scale units differ for the three curves.

The curve can be resolved in a sum of exponentials, as shown in the figure. Analysis was done for a number of wood pieces in a set of treat­ ments. Experiments were also done with poly(methylmethacrylate) where a 0. 5% weight gain was obtained in an atmosphere of 70% relative humi­ dity with the main part of the moisture taken up at a half-life of 25 min. The amount of water taken up by the polymer is small compared with that taken up by the wood sam ple. Experiments were also performed with release of moisture from sam ples. 146 KINELL and AAGAARD

3.2.11.4. Moisture uptake in wood and in wood-polymer materials: Most of the experiments were partly performed at a relative humidity of about 35% and p a rtly at one o f about 55%, som e sam ples bein g analysed at a re la tiv e hum idity o f 72%. The size of the wood pieces were generally 2 cm X 2 cm X 2 cm; in some cases pieces with 4-cm and 20-cm length along the fibres were also used. So far this work is regarded as preliminary on account of the humidity conditions in the laboratory room used. To test the method 10 pieces of pine sapwood were placed under vacuum until they reached constant weight and then subjected to a relative humidity of 73%. After that experiment had been completed the samples were again placed under vacuum and subjected to a relative humidity of 38%. The temperature was kept at 23 ± 1°C during the experiments. The results from the resolution of the curves (Fig. 9(b)) are given in Table VII. There are indications of an increase in half-time with increasing density of the wood.

FIG. 9(b). Moisture uptake as a function of time for untreated pine sapwood. Half-tim es: 280 min (•), 20 min (O). Tim e scale units differ for the two curves.

Some results for samples of different polymer contents are summarized in Table VIII for experiments at a relative humidity of 73% at 23°C. Most data refer to pine samples, but some data for birch are also included. Water is taken up at a rate 20 times slower when the polymer loading is of the order of 1 g/g of wood. Moisture uptake was determined even for a preparation of -cellulose having a small content of hemicellulose. Half-times of 355 ±20 min for 90% of the adsorbed moisture and of about 12 min for the last 10% are obtained. WESTERN EUROPE 147

TABLE VII. ANALYSIS OF WATER UPTAKE ACCORDING TO A FIRST ORDER MODEL FOR THE SAME SET OF 10 PINE SAPWOOD SAMPLES (DIMENSIONS: 2 cm X 2 cm X 2 cm) AT TWO VALUES OF RELATIVE HUMIDITY

Relative humidity Half-time of Uptake (%) diffusion C7o) (m in )

73 293 ± 29 90.7 ± 1. 9

18.2 ± 4.6 9

38 292 ± 22 88.4 ±1.4

1 7 .0 i 2 .1 11

TABLE VIII. THE EFFECT OF POLYMER CONTENT ON THÉ RATES OF WATER UPTAKE IN WOOD-POLYMER SAMPLES (Dimensions: 2 cm X 2 cm X 2 cm. Relative humidity 73%. The results are given as half-times in min. Numbers in parenthesis are the uptake in %)

W ood Half-times at the polymer content (g/g of wood) of

0 - 0 . 2 ~ 0 .4 - 0 . 5 - 1

N u m ber o f sam ples 10 2 2 2 4

P in e 293 ± 29 1650 ± 10 1880 ± 20 1710 ± 20 5260 ± 520

(9 0 .7 ± 1 .9 ) (6 3 ± 3 ) (6 2 ± 2) (8 7 ± 1) (88 ± 1)

1 8 .2 ± 4 .6 265 ± 15 120 105 ± 15 108 ± 12

(9 ) (31 ± 3) (3 2 ± 2) (1 1 ± 1) (9 ± 1)

N u m b er o f sam ples 10

Birch 383 ± 45 9600

(9 2 ± 15) (8 1 )

1 6 .9 ± 2 .3 281

(8 ) (1 5 )

15

(4 )

3.2.11.5. Release of water from wood: Analysis of the water release was completed for some sets of untreated wood samples. The experiment was performed by equilibrating the wood samples in a moisture chamber kept at a relative humidity of 56 ± 1% and weighing the samples in the 148 KINELL and AAGAARD

TABLE IX. MOISTURE RELEASE FROM WOOD SAMPLES (Dimensions : 2 cm X 2 cm X 2 cm. Relative humidity difference 56% to 32%. M eans o f 4 sam p les)

W ood H a lf- t im e R elea se

(m in ) Cfr)

Pin e 860 ± 65 66 ± 7

1 1 5 1 12 34

Spruce 860 ± 12 68 ± 6

125 ± 32

B irch 1200 ± 130 65 ± 11

300 ± 50 35

B eech 900 ± 85 72 ± 6

115 ± 28

laboratory room at a relative humidity of 32%. The results are summarized in Table IX. The half-times are much larger than would be expected for moisture uptake with regard to hysteresis phenomena in the wood-water system. The rates of release of absorbed moisture seem to be very similar in different woods with the exception of birch. The data in Table VIII in­ dicate that birch may also react more slowly in absorption of moisture than the other woods analysed.

3. 2. 12. M achining p ro p e rtie s

Wood-polymer materials were regularly machined for three different purposes: test samples were regularly milled to produce the material used for extraction of homopolymer, samples were sawed for tests of homo­ geneity, and samples were machined in a variety of ways for production of exhibition objects. All the above-mentioned machining was done with tools for work with plastics or metals. Preliminary testing was also done with wood-working to o ls.

3.2.12.1. Cutting machines : Milling or turning on a lathe can easily be done with modern tools. Large amounts of materials have been milled. Samples containing spruce caused a higher rate of wear in the tools than the more homogeneous samples of other wood species. Tube-shaped objects have been turned on the lathe to a wall thickness of the order of 2 mm. Rotary wood-working planing machines gave acceptable su rfaces.

3. 2. 12. 2. S aw s: The m a teria ls w ere sawed on band saws and on r o ­ tary saws. Sawing perpendicular to the fibre axis did not present any pro­ blems, However, sawing parallel to the fibre axis required cooling. In this case the sawdust easily cemented together with the polymer as the WESTERN EUROPE 149 temperature increased above the softening point and lubrication therefore was necessary in some samples in addition to cooling. With normal wood and metal saws the surface needed finishing after sawing. When a rotary saw of the type used for perspex was used, a certain amount of polishing was obtained from the inner part of the rotating blade, and this made the surface very acceptable.

3. 2. 12. 3. M iscella n eou s techniques em p lo y ed : A ccep tab le su rface finishing was obtained with emery paper or steel wool. Samples with a high polymer content could be polished by the same means used for per­ spex. Gluing can be done with some two-component glues. This problem has not yet been thoroughly studied.

3. 3. Technology of wood-polymer materials

At present no work has been done in Sweden with regard to producing wood-polymer combinations on a larger scale. It is felt that a necessary condition for this is the sm all-scale production of a sufficient amount of standard samples for more thorough testing of the material with respect to mechanical properties. One of the problems that should be investigated is the influence of knots and various other inhomogeneities of the wood on the effect of polymer loading. However, such a programme has been de­ layed due to the lack of a suitable radiation source. In the near future sources w ill be available both at the AB Atomenergi in Studsvik and at the radiosterilization plant AB Radona at Skârhamn north of Gothenburg. It is believed that the technology of impregnation used in the preser­ vation of wood with various protective agents can also be applied to monomer impregnation. A pressure procedure is generally used. There has been some collaboration with industrial firm s and the possibility of combining impregnation with polyethyleneglycol with radiation- produced polymers in wood has been discussed. Experiments were per­ formed to prepare beech heartwood-polymer combinations as spacers in fuel cells. Samples of beech and pine heartwood-poly(methylmethacrylate) were produced for parquet floor. Rollers for the spinning industry made from birch poly(methylmethacrylate) were tested but found to be too hard. The same polymer in birch and beech was used to obtain a material for knife handles. Another prospect for application of these combinations is as material for rulers instead of wood from the white beam-tree, which at present is not easily available in Sweden. Finally, the use of thin sheets of wood-polymer materials glued to a supporting fibre-board was discussed and some samples were prepared.

3.4. Market and economy

Market research is planned. An estimation of the production costs of wood-polymer materials in Sweden was made [16] based on technical feasibility studies in the United States of America. An evaluation of capital investment and production costs was made for the plant-scale production of 32 t/d from softwood, ordinary Swedish depreciation, interest and profit rules being adopted. The cost dependence on monomer type and percentage, plant capacity and radiation dose were analysed in particular. In Table X the selling-price is given in US cents/kg. The importance of the influence of monomer content on the price is quite evident. This emphasizes the 150 KINELL and AAGAARD

TABLE X. THE ESTIMATED SELLING-PRICE IN US CENTS/kg FOR WOOD-POLY (METHYLMETHACRYLATE) COMBINATIONS IN SWEDEN (1966 PRICES)

Amount of monomer Capacity 32 t/d Capacity 16 t/d in the products Dose (Mrad) Dose (Mrad) о 0 .5 сл 1 .5 3 t-» сл

5 29 31 33 32 35

25 40 42 45 45 46

35 53 54 57 58 60

commercially important role of surface impregnation, the production of veneer and the use of a cheap monomer.

4. CONCLUSIONS

Few projects have met with such great interest as that for improving the properties of wood by incorporating polymers into the wood matrix. The reason for this is not that methods previously tried were relatively unsuccessful and could not fulfil the demands imposed by multipurpose uses. In most cases research on wood-polymer combinations was started as part of a programme to find peaceful uses for nuclear energy, and the initiative as a rule did not come from people concerned with wood and wood products. It is important to classify the wood-polymer materials correctly among all other methods of wood treatment. Only in this way can the new method be properly evaluated with regard to other techniques. It is also important that wood specialists take an active part in this evaluation. There is a growing shortage of several varieties of wood species in many countries and often a good substitute for a material is not easy to find. A need therefore exists for a high-quality, improved low-grade wood which can be used instead of a naturally high-grade wood. Today wood-polymer combinations have been studied in most Western European countries and almost the same experience has been gained in all laboratories. It is possible to produce wood-polymer combinations which, for many purposes, have very good or even excellent properties. However, there are many unsolved problems, the most important of which are to find cheap monomers, to incorporate the polymers in the wood in such a way that a minimum amount gives a maximum reinforcement of the structure, to make practical surveys of the effect of polymer in woods of various grades and not only on carefully selected materials, and to study the techno­ logy of radiation sources suitable for irradiation of sheets and boards in large quantities (or the equivalent problem if other ways of initiation are chosen). An important view is also that a wood-polymer combination is generally not to be regarded as a raw material. On the contrary, the impregnation with polymer has to be looked upon as a link in a production chain. The treatment must be carried out mainly on prefabricated objects. WESTERN EUROPE 151

REFERENCES

[1] GÜTLBAUER, D ., PROKSCH, E., BILDSTEIN, H., Ôsterr. Chem. Ztg. 67 (1966)349. [2] EURATOM, Working Document on Irradiation, Euratom Symposium Organized for the EEC Countries, October 1966, Brussels, Belgium. [3] SINGER, K. A .J., Proc. Second Tihany Symp. Rad. Chem. (1967)715; private communication. [4] GIBSON, E.J., LAIDLAW, R. A ., SMITH, G. A ., J. appl. Chem. 16 (1966)58. [5] RONDENAY, F ., private communication. [6] BÜRMESTER, A ., Moderne Holzverarbeitung 44 (1964); Materialprtlfung 6 (1964) 95. [7] CENTRAL INSTITUTE FOR INDUSTRIAL RESEARCH, private communication. [8] MOSSBERG, E ., Svenska Handelsbankens Index No. 6 (1967) (supplement). [9] MOREN, R.E., CENTERWALL, K .B .S., (M o och bomsjô AB, Ôrnskôldsvik, Sweden) Swedish patent No. 157 302 and several patents in other countries with priority in Sweden from 10 October, 1952, [103 MOREN, R.E., CENTERWALL, K .B .S., Mo och Domsj6 AB, Technical Information, No.64. [11] MOREN, R. E ., Holz Roh- und Werkstoff 23 (1965) 142. [12] KINELL, P.O ., AAGAARD, P., A study of wood-polymer combinations, Forskningsr&dens laboratorium, Report LFK-9 (1967); see also AAGAARD, P., Svensk Kem. Tidskr. 79 (1967)501 (in Swedish). [13] KENT, J. A ., WINSTON, A ., BOYLE, N.. USAEC Rep. ORO-600 (1963). [14] GOTODA, M ., unpublished work. [15] THUNELL, B. eta l. f Swedish Forest Products Laboratory Reg, No. 650503/249/1, 651111/338 and 651201/339. [16] CARLESON, G ., Svensk kem. Tidskr. 79 (1967) 549 (in Swedish). FINLAND

CONTRIBUTED BY J.K. MIETTINEN DEPARTMENT OF RADIOCHEMISTRY, UNIVERSITY OF HELSINKI, HELSINKI, FINLAND

1. BACKGROUND

When the first paper on WPC was published by the Russian authors Karpov et al. in 1960 [1], new facilities were being planned for the Department of Radiochemistry at the University of Helsinki. As wood is the main export material of Finland, a 10 000-Ci cobalt-60 source, suitable for research on WPC and other related problems, was included in the plans. The new laboratory with the irradiation facility was inaugurated in April 1964 and research on WPC immediately commenced. It was first carried out by graduate students only and was mainly concentrated on the use of methyl methacrylate (MMA) and Finnish birch, fir and pine [2], until an important observation was made in the summer of 1966, namely, that mixtures of polyesters and styrene were suitable for preparation of WPC[3], In the autumn of 1966 the pace of this research was increased and an im ­ pregnation facility of stainless steel was constructed capable of with­ standing pressures up to 20 atm. This facility makes it possible to im­ pregnate about 20 kg of WPC in a batch, and the results obtained with it are described in this paper. Concurrently with our Department, research on WPC was also started at the research laboratory of the Neste Oy Oil Refinery near Porvoo, Finland. This company has only used chemical curing in an attempt to develop a technique requiring less capital cost than that based on radiation curing. Up to 90% styrene is used in the monomer mixture in the method briefly described in a recent publication [4, 5]. Several Finnish wood companies have recently started research on im­ pregnation of veneer and plywood by monomers which can be chemically cured. Mixtures of polyesters and styrene have been used by at least one company, and semi-commercial production of plywood for flooring and containers for ocean transport is expected to start within a few months. No information on results of this research has been published so far.

2. NATURE OF THE MATERIALS TREATED

The main material studied by the author's Department was wood, but preliminary experiments on impregnation of plywood and fibre-boards have also been carried out. Four species of Finnish wood were extensively studied: (1) birch (Betula sp. ), (2) alder (Alnus glutinosa), (3) aspen (Populus trémula), and (4) Pine (Pinus silvestris). Some experiments were also carried out on spruce (Pincea abies or P. excelsa). Neste Oy used the same wood species [5].

152 FINLAND 153

With an overpressure of 6-9 atm. , birch and pine give a WPC con­ taining about 45% polymer, aspen about 55% and alder 55 to 60%. Birch and alder can be easily and evenly impregnated, while the other three wood species cannot. They usually contain some heartwood which cannot be impregnated, and even in the sapwood there remain non-impregnated a r e a s . Alder is originally much softer than birch, but it gives a WPC of about equal strength because it takes up approximately 30% more polymer. The physical properties of the four first-mentioned wood species, non­ impregnated and impregnated, are described below. As mentioned above, the possible polymers that were mainly studied were methyl methacrylate and copolymerates of polyesters and styrene. To determine the suitability of different polyesters and some additives (polyethyleneglycols), birch was impregnated with 10 different mixtures and MMA and tested for some physical properties. These results are also described below. It will be seen that the nature of the polymer has little effect on the properties of the WPC compared with the effect of the wood species. Only the cheapest, easily polymerizable monomer mixture can therefore be considered for economic reasons.

3. IMPREGNATION AND POLYMERIZATION TECHNIQUES USED

3.1. Impregnation

Clean air- or oven-dried timber (8-10% moisture) or half-fabricated articles such as shafts or handles of tools are impregnated in the usual way using vacuum or overpressure of 6-8 atm. (Fig. 1). Our usual im­ pregnation cycle is:

(1) Evacuation (to a pressure of 20 mm Hg) 30 min; (2) 1 atm. N2, 5 min; (3) Evacuation (20 mm Hg) 30 min; (4) Filling the container with the liquid monomer; (5) Brief vacuum for degassing; (6) 1-6 atm. N2 over the monomer, 2-4 h.

With vacuum +1 atm. the empty space in wood is half filled, birch taking up about 50% monomer, and pine about 70%. We mostly used over­ pressure, as our copolymerization mixtures are rather viscous. With 6-9 atm. overpressure for 3 h birch takes up about 100% of its dry weight of m onom er and pine even 150%. The s p e c ific density of the product then becomes about 1. 1, some 95-98% of the empty space in the wood having been filled. Impregnation is often carried out in nitrogen because oxygen inhibits polymerization. If chemical catalysts are used they should be added at this stage, which slightly limits the preservation of the excess monomer. As there always has to be some space between the specimens in the impregnators, more than half of the monomer usually must be reused. Even with added catalysts, e.g. 0. 5-1% benzoylperoxide, the monomer can usually be preserved for some weeks at a low temperature, below 0°C. When radiation polymerization is used nothing needs to be added into the monomer mixture, which can thus be recovered in a pure 154 MIETTINEN

FIG. 1(a). Facility used for impregnation of wood and fibre boards by monomers. 1. Pressure tank, 20 atm .: diam.20 cm, length 110 cm, volume 40 1. 2. Reserve tank. 3. Vacuum. 4. Pressure meter. 5. Surface level reading glass. 6. Pressure (air or N2). 7. Safety valve.

(b )

FIG. 1(b). Photograph of the facility described in Fig. 1 (a ). The glass test tube visible in the foreground is used for impregnation with pressures up to 1 atm.

state. Impregnation usually takes 2-8 h. Special experiments showed that where Finnish wood types were concerned monomer only penetrated through the tubes, i.e. along the fibre direction. The radial penetration was nil. However, material up to 2 m in length can be filled by 9 atm. overpressure in 3 h, and probably- longer pieces of material as well if a higher pressure and longer impregnation time are used. Microscopic examination revealed that in pine only summerwood is impregnated (Fig. 2). Since a volume reduction of about 8 to 20% takes place during polymerization, a 'surface effect1 of 0. 5 to 2 mm and an 'end effect' of 2 to 10 mm are usually noticed. FINLAND 155

FIG.2. Microscopic preparation of pine impregnated with dyed M MA. Only summerwood is impregnated (d a rk ).

3. 2. P o ly m e riz a tio n by gam m a radiation

Polym erization by gamma radiation is carried out by keeping the timber, usually in a metal or plastic container, under nitrogen atmosphere in a radiation field. The half-value thickness of cobalt-60 gamma is about 11 cm of WPC and the dose rates are preferably between 10 and 100 krad/h. In these dose-rate limits the total dose required for complete polymerization is, with several monomers, a function of the dose rate to the 0.3 power. When dose rate is increased from 10 to 100 krad/h, the total dose required for MMA is doubled from 0. 5 Mrad to 1 Mrad. A typical 60Co source for a pilot plant is that of the author's laboratory, a plate-form source of 10 000 Ci of 60Co giving about 50 krad/h at a distance of 0. 5 m and 10 krad/h at a distance of about 1 m (Figs 3 and 4). The higher the radiation intensity the faster is the curing.. Since the polymerization reaction is exothermic and the temperature may easily increase to over 130°С within the wood, thus damaging the material, curing cannot be carried out too rapidly - 20 to 100 h are usually used for radiation poly­ merization. With a dose of about 1-1.2 Mrad approximately 98% of MMA is polymerized. With mixtures of polyester and styrene in an approximate ratio of 1:1 about 0. 9 to 1. 1 Mrad is usually needed. Mixtures containing more polyester are more rapidly polymerized. Less than 0. 5% of styrene usually remains non-polymerized. 156 MIETTINEN

0 i 2 3 fn ______1 i______i______I—

FIG.3. Gamma irradiation facility with a 10 000-Ci №Со source (plate form, 20 cm X 30 cm ). The source is m echanically lifted from outside the cell to the irradiation position between the samples which are kept on the tables.

3.3. Chemical curing

In the research process of Neste Oy the reaction is started by warming the impregnated timber to about 80°C. The timber is then maintained at about 80-100°С until polymerization is complete. This is called curing. By the use of suitable retardants the rate of polymerization is kept low enough so that the temperature does not increase harmfully. In our ex­ periments we discovered that if 0. 5 to 1% benzoylperoxide is used as the sole catalyst with a polyester-styrene mixture, an exothermal peak is still formed after 24 h curing at 20 to 40°C if the temperature is then raised to 80°C. About 50 to 60°C seems to be the curing temperature where no peak exotherm is formed, but the curing takes place gradually during a period of 24 h (Fig. 5). In moist (8 to 12%) wood some 3 to 4% styrene and in dry wood about 1 to 2% styrene may remain non-polymerized. With this process we obtained products which are essentially sim ilar to those obtained with the radiation-curing method. FINLAND 157

FIG.4. Inside view of the 10 000-Ci “ Co facility shown in Fig.3. The cylindrical counterbalance of the source plate is visible in the foreground. The steel and plastic containers contain impregnated wood samples, and the polythene bottles monomer mixtures.

4. RESULTS IN TERMS OF PHYSICAL PROPERTIES AND DIMENSIONAL STABILITY OF THE WPC PRODUCTS

4. 1. Impregnation of birch with 10 mixtures of polyester-styrene arid with M M A

To select a suitable polyester-styrene mixture for larger tests of physical strength and dimensional stability, birch was impregnated with 158 MIETTINEN

FIG.5. Curing of birch-WPC by 0.5% cyclohexanon peroxide. The mixture contains: soredur H75: soredur M10: styrene (45:20:35), - oven temperature : 60°C; - oven temperature: 80°C. Sample 1; 70 cm X 70 cm ! sample 2: 35 cm X 70 cm cross-section bar. The soredurs are commercial polyesters already containing about 30% styrene. Preliminary curing: 24 h at 20°C.

10 mixtures of polyester-styrene and with MMA and tested for dimensional stability and three physical properties. The results were recently published in Finnish [6] and are briefly described below. Results on dimensional stability, obtained by samples submerged in water for three weeks at room temperature, are presented in Table I. In this test the best improvement was obtained with MMA (No 6): tangential swelling was only 23% and radial swelling 27% of the untreated control. Mixture No 2, which contains 10% polyglycole, is almost as good: tangential swelling 36% and radial swelling 29% of control. Water uptake was reduced to about 1/4 in most WPC samples. Bending strength (5 test pieces of each), elasticity modulus (5 pieces) and compression strength (10 pieces) of the same series are presented in Table II. Improvement of bending strength was smallest (28%) in No 6, MMA, while polyester mixtures showed an improvement varying between 34 and 60%. Compression strength improved in most cases by 50 to 80%. The wood selected for these test pieces was sawn precisely along the fibre direction so that it would be devoid of faults and oven-dry when im­ pregnated. It can be seen that differences between different polymers are slight. The statistical variance of the results is not given in Table II but it was approximately (one standard deviation):

Bending strength and elasticity modulus

polyester-styrene-WPC ± 15% MMA - WPC ± 5%

Compression strength

polyester-styrene-WPC ± 9% M M A - W P C ± 4% FINLAND 159

TABLE I. DIMENSIONAL STABILITY OF BIRCH-PLASTIC COMBINATES

Dimensional changes % Water uptake Plastic composition Plastic content Tangential Radial Increase in (per cent o f wood weight) (%) length M iddle End Middle End (%)

1. Soredur 42.8 3.8 6.3 2.9 4. 8 0.1 15.9 H75 + 31% styrene 0 6.8 7.4 5.7 6.1 0.3 60.4 (SOAB)(a>

2. Soredur H75 + 47.3 3.0 5.1 1.6 3.1 0.1 14.6 31*70 styrene + 10% 0 8.4 8.9 5.5 5.8 0.2 75.8 H T400 (M odolog p olyglyk ole)(b)

3. Soredur H75 + 47.0 5.3 6.9 4.5 4.6 0.15 26.3 31% styrene + 10% 0 8.6 9.2 5.6 5.4 0.35 69.6 PLY 1500 (M odolog polyglykole)

4, A lp olit 983 HL + 47.4 4.3 5.8 4.2 6.1 0.1 20.4 30% styrene 0 8.1 8.2 7.3 7.4 0.35 73.8 (Polyplex A-S)

5. Lam ellon 78 + 41.9 5.8 7.3 4.7 5.3 0.2 20.0 32% styrene + 15% 0 7.9 8.2 5.6 5. 7 0.45 46.0 La mellón 6 (Scado-Archer-Daniels)^

6. M M A 47.0 2,2 3.9 1.6 2.3 0.1 13.3 (Rohm-Haas)(e ) 0 9.6 9.8 5.9 5.9 0.3 57.3

7. Lam ellon 71 + 47.0 4.8 6.1 4.1 5 .4 0.2 23.4 30*70 styrene 0 8.2 8.6 5.6 5.9 0.3 67.5

8. Lam ellon 41 + 40.0 3.8 6.6 3.0 5.2 0.1 15.8 30% styrene 0 11.1 10.8 4.9 5.3 0-4 61.9

9. Lam ellon 23 + 41.6 4.9 7.0 4.7 6.5 0.1 21.1 30% styrene 0 8.4 8.9 7.2 7.3 0.3 59.4

10. Lamellon 51.6 5.5 6 .8 ' 3.1 4.1 0.1 24.1 F1-21-1P + 0 9.7 9.8 5.1 5.4 о:з 83.6 30% styrene

11. Lam ellon 78 + 48. 9 4.8 6.5 3.2 5.0 0.1 19.9 30% styrene

^ Svenska Oljeslageri AB, Molndal, Sweden. (b ) M o och Domsjó AB. Ornskoldsvik, Sweden. Polyplex A -S , Stfborg, Denmark. Scado-Archer-Daniels, Zwolle, Netherlands. Rbhm-Haas GmbH, Darmstadt, Federal Republic o f Germany.

Differences between the strength values are of the same degree, and this indicates, first, that the type of the polymer has not much effect on the strength of the WPC, and, second, that a much greater number of parallel test pieces is required for better statistical accuracy.

4. 2. Large test series with four wood species and two polymers

To obtain comparative data on WPC made of MMA and polyester-styrene, extensive series of tests were carried out in collaboration with the Wood- Technical Laboratory of the Finnish State Institute for Technical Research (Director: Prof. F.E. Siimes). A detailed description of the test pro­ cedures and results will be published elsewhere [7], but the results of six physical tests are briefly summarized below. Birch, alder and sapwood of aspen and pine were investigated. Birch and alder were im­ pregnated both with MMA and with polyester-styrene (55% styrene) and compared with non-impregnated controls. 160

TABLE II. TESTS ON PHYSICAL STRENGTH OF BIRCH-PLASTIC COMBINATES MIETTINEN FINLAND 161

The test pieces were selected from a large supply of first-grade timber and sawn along the fibre direction to a size 5 mm greater than the final measures. They were equilibrated to a moisture content of 8 to 10% before impregnation. For each test 50 faultless parallel pieces were selected from over 200 pieces: 30 pieces medium and 10 lighter and 10 higher than medium density wood. Impregnation was carried out by the standard procedure described above: irradiation with60Co gamma rays with a dose rate of 12 krad/h and a total dose of 1. 2 Mrad (for pine 1. 5 Mrad).

4.2. 1. Test methods

Different standard methods were used and were slightly modified when n ecessa ry.

( 1 ) Compression strength parallel to the fibre direction : DIN-52185. Test piece 2. 5 cm X 2. 5 cm X 10 cm. (2) Static bending strength and elasticity modulus: BS 373-1938. Test p iece 2. 5 cm X 2. 5 cm X 65 cm . Loadin g speed 2. 5 m m /m in. (3) Tensile strength parallel to the fibre direction: DIN-52188. Loading speed 600 kp/cm2 min. (4) Shear strength: ASTM D 143-50. Test piece 2 in.X 2 in.X 2. 5 in. Loadin g speed 0. 024 in./min. (5) Hardness: Modified from Janka. Since the original ball (diam. 11.2 mm) caused splitting of WPC, a smaller ball (diam. 5. 6 mm) was used. Test piece 5 cm X 5 cm X 15 cm . (6) Abrasion resistance: Taber abraser according to ASTM recommen­ dation. Test piece 10 cm X 10 cm X 0. 6 cm. Abrasion wheel CS-17. Load 1 000 kg. Abrasion volume was measured'by weighing the piece before and after 1 000 rounds.

5. R E S U LTS

In Table IHthe results of six physical tests are summarized. Detailed results of these and three other tests (impact strength, bending strength under dynamic stress and accelerated dimensional stability test) will be published elsewhere [7]. Birch gave the best results in all these tests when untreated. The other three species showed little difference when untreated. In addition, after impregnation and polymerization, birch-WPC gave the best absolute values in most tests. Alder combined with polyesters also yields excellent final products; for example compression strength (1 200 kg/cm2) and shear strength (radial 170 kg/cm2, tangential 200 kg/cm2) are about the same as in birch-WPC. Hardness is even higher in alder-WPC due to a higher plastic content (55% versus 42%). For the same reason, abrasion is less in alder-WPC. In this respect, however, MMA is considerably better than polyester. Since the original strength values of alder are generally about 40% lower and the plastic content of the alder-WPC is about 30% higher, the relative improvement of the alder values is much greater that that of b irch. 162

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The strength values of the WPC made from alder and pine are generally lower than those of birch and alder, probably mainly due to more uneven fillin g . The absolute values of WPC's, especially those made of birch and alder, are very high and compete favourably with those of most natural hardwoods.

5. 1. Prelim inary tests with oriental woods

The International Atomic Energy Agency requested us to treat a number oí small samples oí oriental woods, sent by different Member States, with polyester-styrene (1:1). The samples were impregnated with the standard procedure described above. Because of the small size of the samples only compression strength and hardness could be determined. The tests had to be performed on pieces slightly smaller than normal: compression strength was determined on pieces measuring 2 cm X 2 cm X 9 cm and the hardness on pieces measuring 2 cmX4 cmX4 cm. The results of the compression strength test in Tables IV to VI are given in kilograms per cross-section of 4 cm2, and when compared with the values in Tables II and III the figures have therefore to be divided by 4 Hardness is presented according to Janka (in kg, with the small ball (diam. 0. 56 cm) against the fibre direction). The results for WPC are presented in Tables IV-VI and those for hardboard and bagasse-board in Table VII. The most important figures are. the plastic contents obtained, as they give an idea about whether the wood species in question can be impregnated to a useful extent or not. It can be seen that many of the wood species were not capable of being sufficiently impregnated by the polyester mixture, e. g. No. 4 in Table IV, Nos 3 and 4 in Table V, and Nos 1, 2, 5, 7, 10 and 11 in Table VI, and were therefore not improved. Regarding the physical strength, the results obtainable from two test pieces are very crude in­ deed, but they may be used as a preliminary guide for selection of wood species for further studies. As abroad generalization, it can be stated that in cases where the plastic content exceeds 40%, the improvement of compression strength and hardness is remarkable. The greatest relative increase in the samples in Table IV was obtained with the low-density wood (0. 39), white deodar 2, from India, which gave a WPC containing 62% polymer and showed an improvement of 150% in co m p ressio n strength and 950% in hardness. In Table V the best absolute and relative improvements are noticed in samples 1, 5, 6 and 8, in which the plastic content is between 40 and 52%. In Table VI only No. 12, Santol, has more than 40% polymer and shows a good improvement. Numbers 3 and 9, which contain only 27% polymer, show relatively good improvement, however. Number 9 has a lower density and lower polymer consumption. The best final strengths, compression 1 400 kg/cm2, were obtained with wood species No. 4, bokbok, and No. 8, lamutanbagyo, which have only 24 and 29% polymer in the WPC. The relative improvement, 22 and 19%, is rather modest. With the bagasse-boards only hardness was tested. In spite of the small plastic content, sample 2 from the Philippines (Table VII) showed a tremendous improvement in hardness (2750%). 164 TABLE IV. COMPRESSION STRENGTH AND HARDNESS IN WPC MADE OF WOODS FROM PAKISTAN AND MIETTINEN COMPRESSION STRENGTH AND HARDNESS IN WPC MADE OF WOODS FROM AUSTRALIA, THE REPUBLIC OF CHINA FINLAND 165 166

TABLE VI. COMPRESSION STRENGTH AND HARDNESS IN WPC MADE OF WOODS FROM THE PHILIPPINES MIETTINEN FINLAND 167

TABLE VII. PLASTIC CONTENT AND HARDNESS OF SOME FIBRE­ BOARD SAMPLES TREATED BY POLYESTER STYRENE

Plastic per cent Hardness N a m e of final product U n treated T re a te d Increase in treated (k g ) (k g ) m

Hardboard samples from Pakistan

K a d am - 1 20

G ew a - 2 11

C iv it - 1 19

Bagasse-board from the Philippines

S a m p le - 1 60 30 140 400

S a m p le - 2 18 18 510 2750

Bagasse-board from the Republic of China

S a m p le - 1 37 70 480 580

5.2. Weather resistance

The weather resistance of birch-WPC was studied by Tammela [5] with an accelerated weather resistance test (Weather-Ometer, Atlas Electric Devices Co; ASTM D 529-62, В periodicity), in which the test pieces were periodically kept for 40 days in rain, u. v. -light (60°C) and -18°C. The WPC completely maintained its form and no cracking oc­ curred, but its surface became rougher and its colour faded. Test pieces of untreated birch, teak and oak were deformed and their surfaces and colour changed more. In birch and oak many cracks occurred. When kept for one year buried in earth, untreated birch was completely de­ stroyed by micro-organisms but the WPC was much better preserved. In July 1967 a weather resistance test was started in this laboratory [8]. It w ill .take at least one year before reliable results can be obtained, but the first observations made three months after the beginning of the test show the same change of surface quality and colour of unlaquered WPC as that mentioned above. However, WPC coated with a thin layer of alkyd resin lacquer has remained essentially unchanged so far, shows a smaller moisture uptake than unlacquered WPC, and a much smaller uptake than lacquered but non-impregnated wood.

6. STUDIES IN PROGRESS

The Department has started three experiments regarding the utilization o f W PC . 168 MIETTINEN

One involves an experimental parquet floor in a school at Helsinki, where birch-WPC (polyester-styrene), oak-WPC (MMA) and untreated heavily-lacquered oak will be compared under intensive use. The second experiment concerns a set of window frames to be tested in Finnish saunas (steam bath rooms), and the third experiment is on a series of skis covered on the friction surface with a thin veneer of WPC. The first results of these tests can be expected by the end of 1968. An investigation of the mould and fungus resistance of WPC in controlled laboratory tests and of rot resistance in the field is being carried out by the Timber Preservation Laboratory (Director: Prof. V. Aho) of the Finnish State Institute for Technical Research. The results of the labora­ to ry tests are expected to be a vailab le in 1968. A Scandinavian symposium on WPC and other plastic-treated fibrous materials is planned for May 1968. Our viewpoints, interests and plans for future development in this field are to some extent apparent from two recent review articles [9, 10].

7. S U M M A R Y

A brief review is given on research carried out in the author's labora­ tory on the preparation of wood-plastic combinâtes of four Finnish wood species, birch, pine, alder and aspen. The suitability of different poly­ esters is especially investigated, and the physical properties of WPC obtained by a typical mixture of polyester-styrene in the approximate ratio of 1:1 are compared with those of WPC obtained with methyl metha­ crylate in the same wood. Both radiation curing and chemical curing with 0. 5 to 1% benzoyl peroxide or cycloheanonperoxide and 60°С temper­ ature yield roughly sim ilar products; in the latter case about 3% styrene may remain non-polymerized. Some physical properties of polyester- WPC are better than those of the corresponding MMA-WPC, and some are slightly less good, but the differences are small. Preliminary re­ sults on the capability of polyester-styrene to impregnate 35 Far-Eastern wood species and on the compression strength and hardness tests on the WPC obtained as well as on the non-impregnáted control are also re­ ported. Some results on the weather resistance tests on WPC are also given and plans for future research are briefly described.

REFERENCES

[1 } KARPOV, V. L. et al. , Nucleonics 18 (1960) 88. [2] MIETTINEN, J.K. , Kemian Teollisuus 23 (1966) 1084 (in Finnish). [3] MIETTINEN, I.K. , Finnish Pat. appl. No. 548/67. [4] TAMMELA, V. , Finnish Pat. appl. No. 3416/66. [5] TAMMELA, V. , Kemian Teollisuus 24 (1967) 183 (in Finnish). [6] MIETTINEN, I.K. , AUTIO, T., Kemian Teollisuus 24, 12 (1967) (in Finnish). [7] MIETTINEN, I.K. , AUTIO, T., SIIMES, F. E. , CLLI1A, T., to be published. [8] USENIUS, A., AUTIO, T ., MIETTINEN, J.K., unpublished. [9] MIETTINEN, J.K., "Present status of research on wood-plastic combinations” , Radioisotopes in the Pulp and Paper Industry, Proceedings of a Panel, Helsinki, 9-13 October 1967, IAEA, Vienna (in press).

[10] AUTIO, T. , "Impregnation of cellulosic fibrous materials by vinyl monomers using radiation for grafting and cross-linking", Radioisotopes in the Pulp and Paper Industry, Proceedings o f a Panel, Helsinki, 9-13 October 1967, IAEA, Vienna (in press). EUROPE

CONTRIBUTED BY T. CZVIKOVSZKY AND J. DOBO RESEARCH INSTITUTE FOR PLASTICS, BUDAPEST, HUNGARY

1. IN T R O D U C T IO N

The preparation of wood-plastic combinations can be regarded as a special field of graft-copolymerization. It is therefore quite understandable why this idea was first introduced by graft-copolymerization specialists [1-3]. On the basis of the theory and technique of radiation-induced graft- copolymerization, which has been greatly developed since 1950, wood-plastic combinations appeared simultaneously in the United States of Am erica and in Europe. As is known, intensive American research on wood-plastic combinations is based on four patents by Kenaga [2] from 1958, which were published in 1963. The worldwide interest in the matter was initiated, how­ ever, by Karpov's paper of 1960 [5] based on Soviet patents from 1958 and 1960 [3, 4 ].

2. UNION OF SOVIET SOCIALIST REPUBLICS

Karpov's paper [5] drew attention first of all to the basic problem of the degradation of wood during the course of irradiation. The mechanical pro­ perties of wood begin to decrease at radiation doses of over 1 Mrad, and above 10 Mrad this decrease becomes very serious. Radiation-induced wood-plastic combinations should therefore be prepared by using radiation doses not higher than a few Mrad. In this case radiation degradation is to a large extent offset by the improvement due to polymerization. Karpov impregnated wood with different vinyl monomers which were then polymerized by irradiation. The original structure of the wood was completely maintained in these combinations. Impregnating wood with mono­ mers is much easier than with viscous polymer melts, since elevated temperatures and high pressures are not needed. By varying the monomers, the conditions of impregnation and the irradiation, products of various pro­ perties can be prepared. Combinations with polystyrene, polymethyl acrylate, polymethyl methacrylate and polyacrylonitrile were studied in detail. The most interesting results were obtained with monomers which dissolve their own polymers. Pines exhibited weight increases as high as 100% or even higher after such treatment, with a simultaneous increase of pressure strength (up to 300% of the original) and of bending strength (up to 160% of the original). The bulk weight also increased. The excellent water resistance of wood-plastic combinations also first became known from Karpov's paper which also described the good chemical and microbiological resistance of wood-plastic combinations prepared by irradiation. Karpov also considered some practical fields of application. The dimension-stabilized, highly solid wood-plastic combinations make very useful industrial wood. Wood-polystyrene combinations, for example, were

169 170 CZVIKOVSZKY and DOBÓ used for preparing excellent foundry patterns. These materials proved useful because of their increased resistance against moisture, but some other properties were also better than those of woods protected by other methods. Besides general industrial use, wood-plastic combinations may be useful in various branches of the building industry, transportation, electrical industry, etc. It is noted that by radiation copolymerization other materials such as textiles and paper can also be modified. Birch was combined with polystyrene and polyacrylic acid by Krasovitskaya [7] and a very simple method of impregnation was used. The wood samples were soaked with monomer for a few days. Forty to fifty weight per cent of styrene and 15 - 20% of acrylic acid was taken up by the wood. The impregnated samples were packed in cellophane foil and irradi­ ated with a eoCo source. The mechanical properties of these combinations were not significantly improved. It was found that only a minor portion of the polymers formed were chemically bound to the wood: only 3-7% of the poly­ styrene content could not be extracted with benzene. This small grafting conversion could be only slightly improved by increasing the radiation dose. In 1962-1963 most of the research work in this field was done in the United States of America. Some publications indicated, however, that the work was also being continued in the USSR [8, 9, 14, 15]. Kalnin'sh [14] tried to soak wood with liquid or gaseous ammonia; the soaked wood was then irradiated and compressed at a pressure of 80 kg/cm2. In another paper Kalnin'sh reported on the polymerization of formaldehyde, acetone and other compounds in wood [15]. These attempts, however, deviated from the main line of the research and apparently did not have much success. Meanwhile the Soviet radiation research made considerable steps in the direction of industrial applications. At the Karpov Institute in Moscow, where much experience in radiation chemical plant design has been accumulated [41], a pilot plant for producing wood-plastic combinations by radiation has recently been developed with a capacity of half a ton per day. In this plant beech, pine, spruce and other woods are being combined with polystyrene, polymethyl-methacrylate, poly­ vinyl acetate, polyvinyl chloride and with their copolymers. Distilled monomers are used for impregnation, since with technical grade quality too high an irradiation dose would be needed. Wood is mainly impregnated by evacuation but the use of overpressure is also possible. The wood in the container is first placed under vacuum, then it is soaked with monomer at room temperature and after a certain soaking time excess monomer is removed by nitrogen gas flow. The sample is irradiated by 6QCo gamma rays in the same 15- to 100-litre containers. The K60000 and K120000 type Soviet 60Co sources produce fairly uniform gamma doses in these large containers. Wood generally takes up monomer up to 20-70%, the radiation dose being 1-2 Mrad (maximum: 5 Mrad). At a dose rate of 30 rad/s this corresponds to a total processing time of the order of 10 hours. The maximal thickness of wood used in these experiments is 100 mm, since at greater thicknesses the heat effect would be too great. Because of the strongly exothermic poly­ merization of the vinyl monomers the temperature within the samples has been found to increase by up to 40-50° C. The device is also capable of processing sheets with dimensions of 5 cm X 50 cm X 100 cm. Thus the stage where wood-plastic combinations can be industrially exploited has now been reached in the USSR. A parquet sample made of such material is being exhibited in the Pavilion of Atdmic Energy at the permanent Exhibition of the Achievements of National Economy in Moscow. EUROPE 171

3. FEDERAL REPUBLIC OF GERMANY

In central and western Europe the problem of wood plastic combinations also aroused considerable interest and experiments in this field were performed in the Federal Republic of Germany [10, 12, 15 - 19, 21, 23, 25, 27 - 30, 35, 38, 43, 45] . First the effects of irradiation on wood were studied [10, 12, 16, 17, 23, 38]. The results which had been previously obtained by Karpov [5] and Krasovitskaya [7] were confirmed and some new results were also obtained. As can be seen in Fig. 1, high radiation doses would seriously decrease the mechanical properties of wood, but at sm aller doses ( 105-106 rad) these properties were even somewhat improved by irradiation. The impact strength, bending strength and pressure strength of wood could be increased in this way.

r-S'Z- 8 o к 3 4 0)с \ 1 -20 N s' V ■£ "40 N СП i I -60 1Л \ s -80 \ -100 10' 102 10! ltf 1C? 10s 10’ 10' 10“ rad

FIG. 1. Effect of gamma irradiation on the strength of pine [38]. 1. Tensile strength; 2. Impact strength; 3. Bending strength; 4. Pressure strength.

After thorough preliminary research work, Burmester indicated in his thesis of 1966 a promising new direction in the production of wood-plastic combinations on the basis of crosslinkable oligomers: polyesters, diiso­ cyanate resins and epoxy resins. This method differs somewhat from the original idea of wood-plastic combinations: the wood is impregnated not with monomers, but with 'half-polym ers'. These systems, however, contain monomers as well, and are thin enough to impregnate the wood. We shall deal with these experiments which constitute one of the most interesting new directions of wood-plastic research studied by several independent research groups, in a separate part. A special trend in wood-plastic combination research was initiated by H. Orth, who applied the impregnation technique to improving the properties of chipboard [35, 45]. The bending and tensile strengths as well as the modulus of elasticity were improved, but the surface hardness of such com­ binations decreased. Orth also investigated some chemical methods of initiation for the preparation of plastic-impregnated chipboard. Good results were obtained with redox-initiator systems. With poly-methyl-methacrylate- combined chipboard, an improvement of about 300% in bending strength, elasticity modulus and surface hardness was achieved, while the improvement in tensile strength attained the enormously high value of about 1000%. The absolute values are, however, not so good. From the point of view of technology this method seems to be somewhat unjustified, since polymers can be introduced by simple means into the chipboard during processing. 1 7 2 CZVIKOVSZKY and DOBÓ

4. UNITED KINGDOM

In the United Kingdom Gibson et al. [20] investigated the grafting of methyl methacrylate on birch and on podo in the presence of dioxane and water. They used commercial methyl methacrylate without distilling, purified only by washing with a 5% solution of NaOH and drying. The wood was impregnated with the monomer by evacuation and overpressure, and the soaked wood was packed in polyethylene foil and irradiated. Interesting new results were obtained by irradiation with the 10-kCi 60Co source at Wantage Research Laboratory and with the nuclear pile fuel element source at Harwell. Main attention was directed to the anti-shrink efficiency and to the grafting efficiency, it was shown that the swelling agents were very important. Methyl methacrylate would only swell pine in the presence of water or other solvent (e.g. dioxane) which made the monomer penetrate into the walls of the wood cells. The results are shown in Table I. Swelling in­ creases the efficiency of grafting. Similar results had been obtained before in radiation chemical grafting onto synthetic polymers with strong hydrogen bonds, e.g. onto polyvinyl alcohol [51, 52].

TABLE I. EFFECT OF IMPREGNANT COMPOSITION ON SWELLING OF SCOTS PINE [20]

Imprégnant composition {%) Tangential swelling (%) Methyl methacrylate D io x a n e W ater

3 8 .6 5 6 .3 5 .1 5 .0 5

4 3 .2 52 Л 4 .1 4 .6 6

5 1 .5 4 5 .4 3 .1 4 .1 9

5 3 .2 4 6 .8 - 2 .8 S

- - 100 4 .5 3

- 100 - 4 .8 5

100 - - 0 .8 5

Treatment with swelling agents, however, would result in a decrease of the anti-shrink efficiency of the polymer formed, so that it could even become negative. This is illustrated in Fig. 2. Gibson and coworkers obtained significant amounts of graft copolymers by irradiating wood containing a solution of methyl methacrylate in dioxane. The ratio of the grafting to the homopolymer, however, decreased with increasing radiation dose [Fig. 3]. Other experience with grafting onto synthetic polymers indicates that sim ilar results must be treated with caution, because the efficiency of extraction from the wood matrix can be very low and, correspondingly, the real ratio of grafting to hofnopolymeri- zation can be much lower than observed. After extraction the cellulose and lignin were separated from the product under sufficiently mild conditions. These experiments have shown that if there is real grafting onto wood, it must be onto the lignin and not onto the cellulose which forms the cell-walls of the wood. EUROPE 173

20 ¿0 60 %

FIG. 2. Effect of polymethyl methacrylate loading on the anti-shrink efficiency in birch [20]. • impregnated with pure monomer О impregnated with aqueous dioxane solution of monomer.

FIG.3. Effect of dose on the amount of unextractable polymer produced by irradiation of birch impregnated with dioxane solutions of methyl methacrylate [20]. Total polymer content: 70^o; dose-rate: 0.125 Mrad/h.

F. L. Dalton at Wantage Research Laboratory reported on new wood- plastic combinations at the Conference of the British Nuclear Energy Society in October 1967 (Industrial Application of Ionising Radiation in Chemical and Allied Industries, 1967). These combinations are based on beech, birch, and pine, while methyl methacrylate, styrene, acrylonitrile and mixtures of them were used as monomers.

5. F R A N C E

According to the report of a meeting of the Eurisotope Bureau (EURATOM) on 18-19 October 1966, research work is also going on in France in the field of wood-plastic combinations. At the conference of the British Nuclear Energy Society mentioned above, some indication of the research work in France was also given although the author did not at that time quote any publications from French laboratories. According to reports beech im ­ pregnated with monomers with and without swelling agents was investigated in French laboratories and the importance of the presence of moisture was emphasized. Recent information indicated that measurements on methyl methacrylate with radiation and chemical initiation are also going on. In the Scandinavian countries Denmark, Sweden and Finland, very interesting new results have been obtained in the last few years. In these exp erim en ts many new id eas w e re introduced [22, 32, 33, 39, 41, 42, 49, 50]. The Atomic Energy Commission of Sweden organized a conference on wood-plastic combinations in Studsvik on 11 November 1966 [31]. The co- 174 CZVIKOVSZKY and DOBÓ ordinated research work in such countries with immense experience in wood processing w ill surely lead to further important theoretical and practical achievements.

6. D E N M A R K

K. A.J. Singer from Ris^, Denmark, presented some interesting results at the Second Symposium on Radiation Chemistry, Tihany, Hungary [22 ]. He compared the effects of irradiation with different sources (10- kCi 60Co, 10-MeV microwave linear accelerator) and reported results obtained with different kinds of wood and with different monomers. The results obtained by combining wood with styrene-aerylonitrile copolymer are most interesting. Copolymerization is very important in every field of the plastics industry. Similarly to the alloys in metallurgy, the copolymers make it possible to prepare materials with optimal combinations of properties. It is evident that the favourable properties of copolymers are also useful in preparing wood-plastic combinations. Combination of wood with a copo­ lymer of styrene and acrylonitrile is most interesting, since styrene- acrylonitrile copolymers themselves are very important structural materials based on relatively inexpensive raw materials. Styrene can be very easily copolymerized with acrylonitrile. It makes the strong hydrogen-bonded structure of polyacrylonitrile somewhat loose and elastic and makes it correspondingly easy to process. On the other hand, the bending strength, impact strength and heat resistance of polystyrene is considerably increased by copolymerization with acrylonitrile. The styrene-acrylonitrile copolymer is at certain compositions soluble in the mixture of the monomers and can be correspondingly polymèrized to a transparent block. The best results in copolymerization of styrene with acrylonitrile in wood have been obtained at a molar ratio of 60:40 of the monomer components. This corresponds to the azeotropic monomer mixture, i.e. the components are copolymerized at the same constant ratio. The system acrylonitrile-styrene can easily be polymerized in wood by irradiation, and there are certain very important improvements with respect to the pure polymers. By polymerization of pure acrylonitrile in wood the polyacrylonitrile formed would precipitate, since it is not dissolved in the monomer. On the other hand, polymerization of pure styrene in wood would require too high an irradiation dose because of the protecting effect of the benzene rings of styrene. Singer has shown that these difficulties can be completely overcome by mixing acrylonitrile with styrene. For radiation copolymerization of this mixture, much lower doses are needed than for pure styren e (F ig . 4). The copolymerization rate of styrene with acrylonitrile depends, of course, on the wood used (Fig. 5) and also on the radiation source. Ac­ cording to Singer, with a 10-MeV linear electron accelerator and a dose rate of about 2 X 1010 rad/h only 30-40% of the total monomer content could be converted into copolymer at a total dose of 10 Mrad. The cobalt source has proved to be much more efficient. The temperature during irradiation has only a slight effect on copoly­ merization (Fig. 6). The overall activation energy of the process is about 2 kcal/mole. This is in agreement with the results obtained by the investi­ gation of graft-copolymerization kinetics [51, 52]. It has been shown that EUROPE 175

FIG.4. Polymerization of vinyl acetate (VA), methyl methacrylate (MMA), styrene-acrylonitrile mixture 60:40 (ST-AN) and styrene (ST) in pine [22]. Irradiation: 60Co, 2.105 rad/h.

FIG. 5. Polymerization of styrene-acrylonitrile FIG. 6. Effect of temperature on the polymerization 60:40 mixture in different wood species [22]. of methyl methacrylate in spruce [22].

TABLE II. MOLECULAR WEIGHT OF RADIATION-INDUCED POLY (METHYL METHACRYLATE) IN DIFFERENT WOODS [22] Electron dose: 10 Mrad.

Irradiation temperature C on version Type of wood Molecular weight (° C ) (%)

Spruce -7 8 9 640 000

Spruce 0 45 750 000

Spruce 25 58 790 000

P in e 25 35 280 000

B eech 25 21 170 000

in highly viscous media, e.g. in a polymeric matrix, as a result of the increase of the activation energy of the chain termination, the overall poly­ merization rate only slightly depends on the temperature. The important effects of swelling and the accelerating effect of carbon tetrachloride observed earlier by several authors are also supported by the measurements of Singer. The molecular weights of the polymers extracted from the wood are shown in Table II. As can be seen, the molecular weights increase somewhat with increasing temperature. This increase, in accor­ dance with theory, is less pronounced than for radiation homopolymerization 176 CZVIKOVSZKY and DOBÓ of pure methyl methacrylate. The absolute molecular weights obtained in wood, however, are much higher than those obtained by homopolymerization at sim ilar conditions. In the first stage of radiation homopolymerization, the average molecular weight is about 104 with a dose rate of 2 X 1010 rad/h at room temperature [51]. These observations are also in agreement with those obtained in other grafting measurements [52]. Interesting data were obtained by Singer on true grafting in wood- polymer combinations. In the presence of water a great part of methyl methacrylate is grafted to wood, while in the absence of water it is not. The efficiency of grafting is strongly dependent on the type of wood. In spruce in the presence of water 82% of the polymer uptake was found to be graft copolymer, while in pine and in beech it was only 40%.

7. SW EDEN

In Sweden wood-plastic combination research is sponsored by the Atomic Energy Commission. Research work has been done by Kinell and Aagaard in Studsvik since 1964. In a recent review of this work [39], data on Swedish pine, spruce, birch and beech combined with polymethyl metha­ crylate are discussed, and data on other polymers such as polybuthyl metha­ crylate, polystyrene and polyacrylonitrile are also reported. Kinell used monomers purified by alkaline washing and subsequent drying. The samples were packed in aluminium foil and irradiated with a 60Co gamma source. The dose required for complete polymerization was investigated as were the effects of different solvents, the ratio of grafting to homopolymerization, the molecular weight of the polymer formed and the mechanical properties of the products. Kinell studied in detail the most critical step of preparing wood-plastic combinations: the impregnation. He used the dying technique to study the penetration of the monomer in wood. In a large number of samples he studied the impregnation efficiency, i.e. the extent to which the free pores of wood are filled up. The volume of the pores is well determined by the gross specific weight of the wood (free volume model):

w here

Vf is the free (pore) volume (cm3); V is the total volume of the sample (cm3); p is the bulk density (g/cm3); and pw is the density of a hypothetical, absolutely dense wood substance, its value for every kind of wood being 1. 54 g/cm3.

By modifying the original formulation of Kent [46] Kinell defined impreg­ nation efficiency, i.e. the utilization of the pores, as follows:

Impregnation efficiency = ----— PM g EUROPE 177 where M is the weight of the liquid taken up by the wood (g); and pM is the density of this liquid (g/cm3). The impregnation efficiency defined in this way was found to be propor­ tional to the drop of the pressure used before impregnation. This is illus­ trated in Fig. 7, where it is shown that total utilization of pores can be reached in some woods. According to these measurements pine sapwood and birch can easily be impregnated. Beech can also be easily impregnated but only up to 75-80% pore utilization. All heartwoods are difficult to im preg­ nate, especially that of beech. Other factors which influence impregnation, e.g. the springwood-summerwood effect, have also been studied. To improve the impregnation efficiency an attempt was made to perform a preliminary extraction of the wood and to use an oscillating pressure reduction, but results were unsatisfactory. Impregnation was found to be efficient at low temperatures. According to Kinell impregnation efficiency is not appre­ ciably influenced by water content. In the case of extreme swelling the free volume model cannot be used.

',o

>s S 0,75 '5 о с 0,50 о ' ï S 0,25

0,9 0,75 0,5 0,25 0

Pressure re d u c tio n ra tio

FIG.7. Impregnation efficiency as a function of impregnation pressure for different woods [39]. О pine sapwood; □ beech; • pine heartwood; x spruce. Soaking time: 30 min.

The polymerization of methyl methacrylate in pine sapwood is sim ilar to that in weathered blocks. Polymerization starts at a constant rate and after a time a strong gel effect is observed. This is illustrated in Fig. 8 by comparison of the conversions with molecular weights. Polymerization rate exhibits an interesting dependence on radiation dose rate. According to earlier measurements by Kenaga [46] the initial poly­ merization rate of styrene in pine seems to be proportional to the 0.46th power of the dose rate. On the basis of Kinell's measurement it is possible to investigate the total polymerization process as a function of the dose rate. In Fig. 9 conversion curves for methyl methacrylate in pine sapwood are shown for different dose rates. If, for a rough comparison, we take the average polymerization rates between 0 and 100% conversion, these are found to be proportional to the 0. 76th power of the dose rate. Correspondingly, the efficiency of radiation usage is not so strongly decreased by.using higher dose rates as it would seem from the data derived from the initial poly­ merization rates. It should be pointed out, however, that this effect is not a purely kinetic one, and a more detailed investigation of the high conversion process would be highly desirable. The ratio of graft-copolymer to homopolymer in pine sapwood was found to depend strongly on the water content of the wood. With a water content of 20% the ratio of grafting is increased to 30-40%. 178 CZVIKOVSZKY and DOBÓ

M W '

0,5 1,0 1,5 2,0 Mrod

FIG. 8. The conversion of methyl methacrylate and the molecular weight of the polymer in pine sapwood as a function of the radiation dose [39]. Dose rate: 80 rad/s.

05 10 15 M rad

FIG .9. The conversion of methyl methacrylate in pine sapwood [39]. Dose rate: О 7 rad/s; • 80 rad/s.

For combinations of pine heartwood, spruce, birch, and beech with methyl methacrylate the conversion and grafting data were scattered much more than those in pine sapwood. Some interesting experiments were also performed by using mixtures of styrene-acrylonitrile and butyl methacrylate- methyl methacrylate. Effects of tetrachloromethane, benzene and of some polar solvents were also studied. It has been found that swelling of the wood is essential for the formation of wood-polymer combinations, but the swelling itself is detrimental to the properties and quality of the product. This contra­ diction has not been resolved. On the other hand, it would seem worthwhile to prepare wood-plastic combinations by using mixtures of two or three different m on om ers.

8. F IN L A N D

In Finland very interesting studies on wood-plastic combinations have been in progress at the Department of Radiation Chemistry, University of Helsinki, and at the Research Laboratories of Neste Oy Company since 1966 [32, 33, 41, 42, 49, 50]. In the Neste Oy Laboratories chemically initiated wood-plastic combinations are being studied, the radiation chemical studies being carried out at the University by Miettinen. His investigations have indicated that Finnish arch and alder are excellent raw materials for this process as they can easily be impregnated and do not contain substances which would inhibit polymerization. Fir, pine and aspen are often unevenly impregnated. Heartwood does not take up monomer, even under pressure. In sapwood localized unimpregnated areas also remain after processing. Miettinen also studied wood-plastic combinations with different mono­ mers and with such monomer pairs as vinyl-acetate-acrylonitrile, and vinyl-acetate-methyl methacrylate. The most interesting combinations are probably those prepared with polyester resins. These are discussed later in d etail. EUROPE 179

9. A U S T R IA

In Austria Gütlbauer's group is doing research work in this field. An interesting review paper of the work appeared recently [34] .

10. C Z E C H O S L O V A K IA

At the Department of Radiation Chemistry of the University of Bratislava (S. Varga) and at the Department of Radiation Chemistry of the Isotope Institute in Pardubice [36, 47], research is under way in this field. Mr.Pesek in Pardubice is working on radiation-, chemical- and peroxide-initiated grafting on cellulosics. His experiments with gaseous monomers for grafting on viscose fibres, papers and other cellulose-containing materials are of considerable interest [47]. This method may also be very interesting for wood-plastic combinations from the economic point of view, since the use of gaseous monomers may increase monomer utilization.

11. H U N G A R Y

In Hungary wood-plastic combinations are being studied at the Department of Radiation Chemistry of the Research Institute for Plastics, Budapest, in co-operation with the Institute of Quality Control of Wood, Budapest [26, 37, 44, 46, 48]. Combinations of wood with monomer mixtures and polyester oligomers are being studied by the radiation- and chemical-initiation methods. Combination of wood with copolymers by introducing mixtures of two or more monomers is a very promising way of producing structural materials of favourable properties. Some of our data on the combination of pine with two-monomeric systems are shown in Table III. As indicated in this table, good specific quality factors of bending strength and impact strength are achieved for pine - vinylchloride - vinylacetate prepared at about 1.5 atm. overpressure with liquid monomer mixtures irradiated at room temperature. These factors can probably be further improved, since the copolymer of vinylchloride and vinylacetate is known to be an excellent, tough and flexible resin for paints, adhesives, etc.

12. SOME CURRENT PROBLEMS WITH WOOD-PLASTIC COMBINATIONS

Here we would like to deal with two problems of wood-polymer research studied mostly by European researchers: first, the combination of wood with crosslinkable oligomers, and secondly, the comparison and combination of chemical and radiation initiation.

12. 1. Wood-plastic combinations on the basis of crosslinkable oligomers

The idea of crosslinking polymers in wood with divinyl compounds was introduced by Kent and Raff [46] . The combination of wood with crosslinked polymers derived from oligomers, however, started quite recently. It can be considered proof of the general interest in this problem that the investi­ gations were begun simultaneously but independently by three different 180 CZVIKOVSZKY and DOBÓ EUROPE 181 research groups in Germany [29, 38], Finland [33, 41, 49, 50] and Hungary [37, 46, 48]. The most important resins used for this purpose are polyesters, polyisocyanate and epoxy resins. These materials represent intermediates between monomers and high polymers. They can easily be crosslinked by vinyl monomers to form infusable, insoluble polymer networks. Such materials are often combined with reinforcing materials such as glass fibres, and the resulting reinforced plastics are widely used as structural materials. The least expensive among them is polyester, which is also used in the modern wood industry. Data on pine and beech combined with polyester resin are given in Table IV after Burmester [38]. Similar improvement was obtained by using diisocyanate resin. In this case, however, as can also be seen from the results presented by Burmester, radiation does not offer any advantage. Such resins can be crosslinked by adding multiple alcohols, in this case by the cellulose itself crosslinking through stepwise poly-addition. One of the authors of the present paper combined beech with polyester resin and compared the properties of the product with those of the material used in the textile industry for shuttles [46, 48]. The results are given in Table V. As can be seen, the product is very much like beech processed at very high pressures and at high temperatures (Lignostone and Lignovit) although its bending strength is less. In a quite r e c e n t publication Miettinen [50] reports on the fairly high bending strengths of such wood-polyester combinations. These results are given in Table VI. The abrasion resistance of these products is even more improved (200-500%) together with the hard­ ness (400-600%). The results allow us to hope that by making use of the new possibilities offered by the oligomeric system, e.g. by using polyester resins especially prepared for this purpose, further improvements of properties can be ach ieved.

12.2. Preparation of wood-plastic combinations by chemical initiators

The preparation of wood-plastic combinations by the monomer im preg­ nation technique originated from radiation chemistry. The initiation of polymerization by irradiation has the advantage that the process of im preg­ nation is well separated from the polymerization and that the exothermic polymerization reaction can easily be controlled. The amount of heat released by the polymerization of vinyl monomers is about 100-300 kcal/kg. The release of such amounts of heat makes it extremely difficult to control polymerization initiated by thermally activated initiators. This may result in an uncontrolled chain reaction and in very high temperatures. Thus a serious change in the physical properties of the system may set in before the polymerization is over, some of the resin might be expelled from the wood and the distribution of the polymer w ill be correspondingly uneven. The quality of the polymer formed in such a way is also much lower than that obtained by controlled chain reaction, e.g. by radiation initiation. (A discussion of these factors can be found in the literature on grafting [51, 52].) These may be the reasons why so few references can be found in the recent literature on the use of chemical initiators in the production of wood-plastic combinations [41, 46]. The authors of the present paper attempted to compare chemical initiation with radiation. One system studied was styrene-acrylonitrile, the other being polyester. 182

TABLE IV. THE INCREASE OF MECHANICAL PROPERTIES OF POLYESTER-COMBINED WOOD [38] ZIOSK ad DOBÓ and CZVIKOVSZKY EUROPE 183 184 CZVIKOVSZKY and DOBÓ EUROPE 185 186 CZVIKOVSZKY and DOBÓ

Beech and hornbeam were combined with a styrene-acrylonitrile mixture of equal parts by weight. The unpolymerized monomer was removed from the samples under vacuum. The results are given in Table VII. Thus chemical initiation is advantageous with regard to polymer uptake but dis­ advantageous where uniformity of the sample is concerned. The best uni­ formity was achieved when chemical initiation was combined with radiation. For combinations of wood with polyester resins the possible use of chemical initiation instead of radiation was considered by all three in­ vestigators of wood-polyester combinations. It can be seen from the data of Burmester presented in Table IV that the properties of chemically-ini­ tiated polyester-wood combinations are no worse than those made by radi­ ation initiation. A very important fact was, however, pointed out by Miettinen [41, 42], namely, that with chemical initiation in the pure poly­ ester resin the temperature inside the sample is raised by 200°C from room temperature, while with radiation the rate of heat release is very easy to control by means of the dose rate. Miettinen used an extremely small amount of a double (redox) chemical initiator for these comparative measurements; the results are shown in Fig. 10. A sim ilar rise in temperature was observed by the authors of this paper during peroxide-initiated thermal polymerization of pure polyester resin. The temperature increase is also very high with chemically-initiated polymerization in wood. With radiation initiation the temperature is only very slightly increased, even with high dose rates. These results are shown in F ig . 11.

0 5 10 15 20 Hours

FIG. 10. Temperature increase during the polymerization of polyester [41]. X: Chem ical initiation with 0.6% cyclohexanon hydroperoxide and 0.006% Co-naphtenate. 1-6 (radiation initiation) -

l : i n N 2 ; 2 : in air at 58.2 krad/h ; 3 :in N 2; 4: in air at 23.3 kradAi; 5: in N?; 6 : in air at 5 . 6 k rad /h .

j 1 1 1

to Thermochemicol (8(£60^40^ 100 _Лл1 . / и \ / > and Radiation-chemical hordening(S, S¡) s' 80 N \ г / \ О 9) . g- 60 /

1------u £ к ——-Till 2 4 6 8 Hours

FIG. 11. Temperature increase during the polymerization of polyester-beech system [48]. Chem ical polymerization with 1.5% benzoyl peroxide started at 80*0, 60eC, 50°C and 40°C. S: radiation polymerization a t 1 0 5 rad/h. : radiation polymerization with 1.5% benzoyl peroxide at room temperature, 1 0 5 rad /ti. EUROPE 187

Because of the high radiation resistance of styrene, complete setting of the resin by irradiation would require doses as high as 1. 5 Mrad. It therefore seems worthwhile to use a combined catalytic system uniting the advantages of both initiating methods (curve S¡ in Fig. 11). By adding 1. 5% benzoyl peroxide to the resin its storability is not affected too much and setting by radiation is considerably accelerated. In this case too, the temperature increase remains below 10°C.

13. S U M M A R Y

It can be seen from this brief review that research on wood-plastic combinations has made great progress in several European countries, especially in the last few years. Wide-ranging investigations have been conducted on the quality of the products and on the most favourable process conditions taking wood qualities and requirements in the different countries into account. These results have brought the status of wood-plastic combi­ nations research in several countries close to semi-industrial or industrial realization. Besides the main lines of wood-plastic research, some new ways and methods have been developed by European researchers. The combination of wood with crosslinkable oligomers, primarily with polyesters, may lead to a new kind of reinforced structural material. Considerable im ­ provement and 'tailor-m ade' qualities can be expected from copolymer- combined wood through the use of monomer mixtures. Polymerization with gaseous monomers could assure a better utilization of monomer, while combination of radiation and chemical initiation may lead to savings in cost and time, together with improved product qualities. This work is still not very far advanced. Nevertheless the great impetus of the research provides hope that through these and other ideas and results new economic and technological perspectives w ill be opened for the production of wood-plastic combinations in Europe.

REFERENCES

[1] BALLANTINE, D .S., MANOWITZ, B. Fission Products Utilization. VIII. Studies on the use of radiation as a catalyst for chem ical reactions, USAEC Rep. BNL-389, Brookhaven National Laboratory, (May 1956) 19. [2] KENAGA, D .L., Stabilization of wood and wood products, US Patent 3.077,417 - 3.077,420, Feb.5, 1958; Publ. : Feb.12, 1963. [3] FREIDIN. A .S.. MALINSKY, Yu.М .. KARPOV, V .L., ROMANOV. N .T., Avt.sv. SSSR. 122219; 10.04.1958. [4] FREIDIN, A .S., MALINSKY, Yu.М .. KARPOV. V .L., ROMANOV, N .T .. Avt.sv.SSSR. 126 562 1 . 0 3 . 1 9 6 0 . [5] KARPOV, V .L ., MALINSKY. Yu.М .. SERENKOV, V .I., KLIMANOVA, R.S., FREIDIN. A .S.,

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[ 6] FREIDIN. A. S., M odifikatsiya svoystv drevesiny s pomoshchyu ioniziruyushchikh izluchenii (Modification of wood properties by ionizing radiation) Derevoobr.Prom ., M oxow 9 (1960) 15. [7] KRASOVITSKAYA, T .J., Opyt modifikatsii drevesiny putyom polim erizatsii propitiivayushchikh drevesinu monomerov pod deyestviyem gamma luchey; ACADEMY OF SCIENCES OF THE USSR, M odification of wood by polym erization of impregnating monomers by gamma radiation. Trudy II. Vsesoyuznogo soveshcheniya po radiatsionnoy khimii, 1960. Sll.p .Izd . Akad.Nauk. SSSR (Moscow) 1962. 188 CZVIKOVSZKY and DOBÓ

[ 8] FREIDIN, A .S ., MALINSKY, Yu.M ., KARPOV, V .L ., "Effect of ionizing radiations on wood and its components" Conf. on Peaceful Use of Atomic Energy, Tashkent, 1961. Izd. Akad Nauk Uzbekh SSSR, Tashkent, (1961). [9] FREIDIN, A .S ., Deystvie ioniziruyushchey radiacii na drevesinu i ее komponenty (Effect of ionizing radiations on wood and its components), Goslesbumizkat, Moscow (1961). [10] BECKER, G ., BURMESTER, A ., Veranderung von Holzeigenschaften durch Gamma-Strahlung, M aterial- priifung 4 11 (1962) 416-26. [11] Uluchsheniye svoystv drevesinu pod vliyaniem obrabotki monomerami i radiatsiey (Improving properties of wood by monomers and radiation), Gidroliz.lesokhim.Prom. Moscow (1963) 2. [12] SEIFERT, K ., The chemistry of gamma irradiated wood, Holz Roh-u. Werkstoff 22 (1964) 267. [13] KALNIN’SH, A .J., Konkurent m etalla - plastifitsirovannaya drevesina (Rivalry of metals - wood plastic combination) Priroda, No. 9 (1964) 76-80. [14] KALNIN’SH, A .J., Plastifikatsiya drevesiny (Wood plastic combination) Izv. Akad.Nauk Latvian SSR. 4 201 (1964) 48-55. ' [15] SANDERMANN, W ., Neue Holzwerkstoffe mit Hilfe von Gammastrahlen, Holz-Zentralblatt 90 52 ( 1 9 6 4 ) . ~ [16] BURMESTER, A ., Holz, Kunststoff und Gammastrahlung, Holz-Zentralblatt 64/65 (1964). [17] BURMESTER, A ., Veranderung der Druck- und Zugfestigkeit sowie der Sorption von Holz durch

Gammastrahlung, Materialpriifung 6 (1964) 95-99. [18] ORTH, H ., Versuche zur Verminderung derQuellung des Holzes, Moderne Holzverarbeitung 69 (1965) 3 6 4 . — [19] BURMESTER, A ., Verbesserung des Querdruckwiderstandes von Holz, Holz-Zentralblatt 121 (1965). [20] GIBSON, E.J., LAIDLAW, R.A., SMITH, G .A ., Dimensional stabilization of wood 1. Impregnation with m ethylmethacrylate and subsequent polymerization by means of gamma radiation, J.appl.Chem . 16 (1966) 58. [21] Holz, Kunststoff und Gammastrahlen, Die Holzbearbeitung 4 (1966) 13-14. [22] SINGER, K .A .J., "Wood plastic combinations prepared by irradiation with gamma-rays and high energy electrons", Proc. Second Symp. on Radiation Chemistry, Tihany, Hungary, May 1966, Publishing House of the Hung. Acad. Sci. Budapest (1967) 715. [23] BURMESTER, A ., Einfluss von Gammastrahlung auf chemische, morfologische, physikalische und

mechanische Eigenschaften von Kiefem - und Buchenholz, Materialpriifung 8 6 (1966) 205-11. [24] KOLLMANN, A ., Neue Holzwerkstoffe durch Bestrahlung, Holz-Zentralblatt 92 49 (1966) 905-7. [25] BURMESTER, A ., Stand der Entwicklung von Holz-Kunststoff-Verbindungen aus strahlenpolymerisierten

Kunststoff-Monomeren, Die Holzbearbeitung 13 6 (19 6 6 ) 5 . [26] CZVIKOVSZKY, T ., Improving wood by radiation chem ical grafting: Literature compilation, National Atom ic Energy Commission of Hungary, Isotope Institute, Budapest (1966). [27] BURMESTER, A ., Besseres Schraubenhaltenvermôgen von Holz durch Verwendung von Kunststoffmonomeren, Holz-Zentralblatt 92 100 (1966).

[28] Grossere Festigkeit durch Gamma Strahlen, Holzindustrie 8 (1966) 229. [29] BURMESTER, A ., Holzvergiitung durch Verwendung von niedermolekularen Stoffen und Gamma Strahlung, M itteilungen der Deutschen Gesellschaft fiir Holzforschung 53 (1966) 96-99. [30] Holz, Kunststoff und Strahlen, Holz-Zentralblatt 92 130 (1966) 2306. [31] SVENSK KEMISK TIDSKRIFT, TPK symposiet ll.n o v.1966. Studsvik, Symp. on wood plastic combination, Studsvik, Sweden, Svensk kem .Tidskr., painossa, ilm .luult.helm ik. (1967). [32] MIETTINEN, J., AUTIO, T ., Plastimpregnering och gammabestralning som Traforadlingsmetod (Impregnation with plastics and gamma irradiation as a method for improving wood), Teknist Forum

8 6 19 (1966) 587. [33] MIETTINEN, J.K ., M uovilla Kyllástetty puu ( Wood-plastic combination), Kemian Teollisuus 23 12 (1966) 1084. [34] GÜTLBAUER, F., PROKSCH, E., BILDSTEIN, H ., Strahlungsausgehârtete Holz-Kunststoff-Kombinationen, Ôsterr. Chem . Zeitung. 67 (1966) 349-61. [35] ORTH, H., AMMON, R., BURKARD, W., CONZELMANN, H., SCHULZE, J., Neue Versuche mit Holz- Kunststoff-Kombinationen, Holz-Zentralblatt 92 148 (1966) 2592. [36] VARGA, S., KOSIK, М ., Radiacne chemické efekty v sústavach: drevo-vinylovy monomer (Radiation chem ical effects in wood-vinylmonomer systems), Jademá Energie, Prague 13 2 (1967) 62. [37] CZVIKOVSZKY, T ., LUKÁCS, V ., Method of manufacture with crosslinked polymer chemically modified (improved) wood, Hungarian patent application, 27 Febr.1967. [38] BURMESTER, A ., Zur Vergtitung von Holz durch strahlenpolymerisierte Kunststoff-Monomere, Holz Roh- u. Werkstoff 25 (1967) 11. EUROPE 189

[39] KINELL, P.O ., AAGAARD, P., A study of wood-polymer combinations, Forskningsradens Laboratorium, Studsvik, Nykoping, Sweden, Rep. No.LFK-9, 13 (1967). [40] BREGER, A .H ., Osnovy radiatsionno-khimicheskogo apparato-stroeniya, Atomizdat, Moscow (1967). [41] MIETTINEN, J.K ., Sâteilypolymeroinnilla valmistettu "muovipuu" (Wood plastic combinations prepared by radiation chem ical polymerization), Paperi ja Puu 49 2 (1967) 11. [42] MIETTINEN, J.K ., Research in Finland on wood-plastic combinations, Lecture given at the Plastic Manufacturer’s Association M eeting, April 5, 1967, Helsinki. [43] ORTH, H ., Elektronenbeschleuniger fur die Holzindustrie, Moderne Holzverbeitung 2 4 (1967) 211. [44] CZVIKOVSZKY, T ., KOLOSV.ÁRY, G ., Sugárkémiai úton készült fa-müanyag kombinációk (Wood

plastic combinations by the radiation chem ical method), Faipar, Budapest, 1Л 6 (1967) 164-170.

[45] ORTH, H ., Holz-Kunststoff Kombinationen, Gummi-Asbest-Kunststoffe 6 (1 9 6 7 ) 6 6 6 . [46] CZVIKOVSZKY, T ., Wood plastic combination by monomer impregnation and radiation polymerization,

Report of the Plastics Research Institute, Budapest 8 ( 1 9 6 7 ). [47] PESÉK, М ., JARKOVSKY, J., Radiacni roubováni cellulózy metylmetakrylátem v parni fázi preiradiacni technikou (Irradiation grafting of cellulose by m ethyl m ethacrylate in vapour phase by preirradiation technique), Chem icky Prumysl 17 (1967) 482. [48] CZVIKOVSZKY, T ., KOLOSVÁRY, G ., Holzvergütung durch strahlenpolymerisierte Hochpolymere (Improving wood by radiation-induced high polymers), Plaste und Kautschuk 14 9 (1967) 623. [49] MIETTINEN, J.K ., "Present status of research on wood plastic combinations: a review", Radioisotopes in the Pulp and Paper Industry, Proceedings of a Panel, Helsinki, 1967, IAEA, Vienna (1968) 9. [50] MIETTINEN, J.K ., AUTIO, T ., "Tests on physical strength of wood plastic combinations". Paper presented at the Panel on the Application of Radioisotopes in the Pulp and Paper Industry, Helsinki, 1 9 6 7 . [51] CHAPIRO, A ., Radiation Chemistry of Polymeric Systems, Interscience Pub., New York (1962). [52] DOBÓ, J., Structural and kinetic factors in graft copolym erization, Report of the Plastics Research Institute, Budapest (1964). UNITED STATES OF AMERICA

CONTRIBUTED BY G.J. ROTARIU AND W.E. MOTT DIVISION OF ISOTOPES DEVELOPMENT, UNITED STATES ATOMIC ENERGY COMMISSION, WASHINGTON, D.C. 2054, UNITED STATES OF AMERICA

1. BACKGROUND

A research and development program on the radiation curing of wood impregnated with a monomer was initiated in the United States in 1961 by the U.S. Atomic Energy Commission at West Virginia University; this program has continued until today (1-7).

The USAEC has also sponsored three studies covering different geo­ graphical areas of the country, in an attempt to determine the potential of wood-polymer materials (8-10). Another effort led to the design of a 200 pound per hour pilot plant for the manufacture of wood-methyl methacrylate materials and projected costs for a 300 pound per hour production plant (11). And the most recent AEC study involved the evaluation of over 8000 pounds of wood-polymer materials by 68 manufacturers of wood products; the wood-polymer materials utilizing 41 species of wood were produced for the AEC by Lockheed-Georgia Company, Dawsonville, Georgia (12). In 1965, studies on the thermal-catalytic production of wood polymers were begun at the College of Forestry, Syracuse University, Syracuse, New York (13-16).

2. RESEARCH AND DEVELOPMENT

During the last two years, research and development has been di­ rected at evaluating mixed-monomer systems, optimizing impregnation and polymerization methods and systems, and providing an intercomparison of physical and mechanical properties of different types of wood-polymer materials.

2.1 .____Monomer and Mixed-Monomer Evaluation

2.1.1. General

The major effort on monomer and co-monomer evaluation has been per­ formed at West Virginia University. Since 1961, West Virginia University has examined more than 150 monomers as potential candidates for woods im­ pregnation; about 50 have been experimentally evaluated in detail. The most promising of these technically are listed in Table I. Woods investi­ gated during this monomer evaluation program include: white pine (Pinus storbus), loblolly pine (Pinus taeda). ponderosa pine, yellow poplar, red oak, redwood, sugar maple, black cherry, teak, mahogany, walnut, birch,

190 MAJOR MONOMERS EVALUATED NTDSAE O AMERICA OF STATES UNITED

(a) 1967 191 192 ROTARIU and M OTT and ash. Experience has shown that of these, loblolly pine, black cherry and teak are the most difficult to treat.

Important factors to be considered in the selection of an imprég­ nant in the radiation-production of wood polymers include:

1 . C o s t ,

2. East of handling and of impregnation,

3. Radiation dosage required for complete polymerization,

4. Heat of polymerization, and

5. Physical and chemical properties of the final product (in­ cludes compatibility with the wood).

Polymer compatibility with the various wood resins must not be overlooked; the degree of interaction of a given monomer with the resins of a given wood species is rarely the same as that with the resins of another type of wood.

The research program at West Virginia University has identified three monomer systems that appear to offer some degree of universality, and in the light of the five factors just given seem to have the most promise. These are methyl methacrylate, styrene-acrylonitrile, and vinyl chloride. From the handling and final-product property standpoints, methyl methacrylate appears to be superior. However, styrene-acrylonitrile and vinyl chloride have a basic economic advantage, styrene-acrylonitrile being available at about 12 cents per pound, vinyl chloride at 8-9 cents per pound, compared to methyl methacrylate at 21 cents per pound.

The principal difficulty with styrene-acrylonitrile arises from the fact that at the optimal weight mixture of 60-40, the heat of polymeri­ zation is roughly double that of methyl methacrylate. Such energy release, if contained within the irradiation package itself without dissipation, would raise the temperature of the product being manufactured to an un­ acceptable level. A possible solution is to decrease the rate of reaction in the time period when most of the energy is released (17).

Vinyl chloride exhibits an equilibrium vapor pressure of about three atmospheres; it is a gas at one atmosphere and room temperature. Preliminary experiments have indicated the need for pressurization to 125 psi to avoid vapor-pocket formation during the polymerization process. This requirement will undoubtedly add to the complexity, and hence cost, of a production facility utilizing vinyl chloride impregnation.

2.1.2. Development of More Resilient Polymer Systems

Impregnation with methyl methacrylate or styrene-acrylonitrile results in a wood-polymer product with a hard finish. It was felt that a product made with a rubber-like, flexible polymer might have greater impact strength and increased resilience. Accordingly, a large series of monomer combinations were investigated by West Virginia University in the search for a flexible polymer. Various combinations of the following monomers were evaluated: styrene, methyl methacrylate, vinylidene chlo­ ride, methyl, ethyl, and butyl acrylates; and acrylonitrile. The most promising of these are listed in Table II. PROMISING COPOLYMER IMPREGNANTS о Я • «н л 1 О м С Й W и 61 о и С *-3 е с 4J *И(Ü D ф •i4 1*4 tO X ОЙ s-' и 44 l-> о £ •И *H Ф rH О CO 00 *н •н и 5 <$ w с со U СО О f-l о и о и tu •и со Q E ф 5ч h а 5 О -U О л о СО Ф ^ С Б Ф О со ОЙ Ф /■—S N»*' CO PU CC i-4 rÛ Я и CO «•—s ф О ■Ы >• о со d) О vO С о •С 4->ТЭ г—) СО и ^ гЧ Я > «-н •н •о со •н ÛÛ -Ü я а»•я 4J 32 о о R>S S'S UT 1ЛUT о s О и 0) г- гЧ 4 О со и ¿1 Я ТЭ ^ с - СОí-i Т5сс - 4= - 3 1-1 1Г)• ■*-* X JZ /*\ ф О X Я О И £ J-» СГ> О i-Ч О &■£ 5^ ■и *и с и со и ф со ^ ф и 01 >> а> а >«, со тэ 3 1 • 1-4 >> NTDSAE O AMERICA OF STATES UNITED N.' /*\ тэ О •н •и 1-1 л я ф ф о и с о со гЧ о X X гЧ т—1 гН см f-t ой I—и•н TJ и X "0 < ¿J я 4-» 42 и m m о О В*« 8*5 со О ф V-* со э 0) Ф О С Я Ф ^ гЧ Ф сО тэ 1 i-H•

*и 'X ч/ о •н •|Ч тз > я ф О и с 3 - о о X л см гН *г1 Н - t—1l-ч гЧ гЧ ТЗ ой •н « с « л с < ü я о О 5-S 5*2 U <у •U ш ю •и о и СО - со *-( ф ф *н о -м h >•> я ф со ТЭ >S 1 со • м /*ч о 1 4= я -Н о о см со »— i-Н г*Ч со ТЗ (“Н Л i—1 г-Н ой •и JÜ }-1 р- < я м м о см оо о О 5*2 5^ 4-1 Ф 4J О 0 • <0 СО V4 ф и ф 4-» И ф и 3 J *н (J 1 1 »н Я \ о O' 4= ТЭ < и о о т—t 00 СМ i—1 см ТЭ \ Û0 т? Л н <Л > ^ Я 4J Я о «-н 5^ со 5^ 1 •м *н (Ц V о 3 со ^ СО ТЭ ^ гН Ф *rW p Т1***Ф о Щ Л j m • £ л (0 %«/ у"ч о и X. i-Н я •и ф ф Я ^ Н С аи-s с о и О I-H чО X о со о сЧ ТЭ ТЭ тЗ 1—1•г^ •в И > •И 00 Я •и g~2 Ш СО ф ^ ф р о Ф со с • : «ч х. \ r-N гЧ о -С с х Н Я ь г t-Ч г*« тэ JS и m гЧ о В^“ В-“ я 4J J ЕЧ4J 4-» СО 0 00 ф О и сО Ф э Рч Ф >> со о /~ч сО ON i—( чО 1л

.methylol propane trimethacrylate 193 194 ROTARIU and MOTT

Additionally, certain cross-linking agents were added to some of the monomer mixtures in the hope of producing flexible structures by con­ trolling the degree of cross-linking at the ends of polymer chains while maintaining adequate chain length. Another possible benefit of using a cross-linking agent is a reduction in the gel-point time, and hence the overall dose for complete conversion. Some of the cross-linking agents evaluated were: trimethylol propane trimethacrylate (98ç/lb); trimethylol propane triacrylate ($2.00/lb); and, divinyl benzene (90ç/lb).

For these tests, the monomers were purified by distillation; the cross-linking agents were used as received. The mixtures were introduced into 5 ml vials and sealed under nitrogen; the vials were then introduced into water-tight copper tubes and irradiated in a water-shielded cobalt-60 facility. In general, four or five samples of each mixture were run for various periods of time to ascertain the dose needed for 100% conversion. Samples were considered completely polymerized when all of the polymer was hard and lacked a strong monomer odor. These experiments with cross- linking agents were preliminary, and as shown in Table II not particularly successful for the systems studied.

2.1.3. Evaluation of Plasticizers and Other Additives

Plasticizers have been added to monomers with the aim of obtaining a reduction of the heat generated during polymerization, and hopefully to reduce the overall cost of the imprégnant -- all with no increase in radia­ tion requirement. A series of commercially available plasticizers have been evaluated by West Virginia University (6). (See Table III). The evaluations were performed with methyl methacrylate-plasticizer solu­ tions containing up to 50% plasticizer by volume. The solutions were in­ troduced into test tubes, purged with nitrogen gas, sealed and irradiated. Monomer controls were irradiated along with the monomer-plasticizer sys­ tems. If either the monomer or monomer-plasticizer or both were not com­ pletely polymerized at the planned dose, the experiment was repeated at a longer irradiation time. Successive experiments were run to ascertain the dosage required for complete polymerization and the nature and appearance of the polymers. Dose rates were determined using Fricke dosimetry to an accuracy of plus or minus 3%.

The main objectives of the plasticizer program were achieved. For example, during polymerization, a 50% - 50% mixture of Santicizer 630-methyl methacrylate, generates 117 BTU/lb. versus 234 BTU/lb. for methyl methacrylate alone; further, its cost is 17.5ф lb. versus 21

Of the additives tested, Santicizer 141, a phosphate, was found to have fire retardant properties. However, Phosgard C-22-R, an organo- UNITED STATES OF AMERICA 195

TABLE III LIST OF COMMERCIALLY-AVAILABLE PLASTICIZERS USED

Approx. Price Plasticizer in 1965 ($/lb.) Manufacturer

Fhthalates (a) Dimethyl 0.21 Monsanto Diethyl .21 tt Dibutyl .21 if Saniticizer 165 .15 и Saniticizer 213 .22 it Saniticizer 214 .24 it Saniticizer 630 .14 и Saniticizer 631 .14 it Saniticizer 636 .15 «

Sebacates

Dibutyl 0.66 Harchem, Eastman Dioctyl .57 Harchem Ditenzyl .91 Harchem

Adipates

Dioctyl 0.23 Monsanto, Eastman Di-iso decyl .23 Monsanto Di-n-octyl n-decyl .23 Monsanto

Polychlorinated Phenyls

Aroclor 1221 0.14 Monsanto Aroclor 1232 .14 Monsanto Aroclor 5460 .14 Monsanto

Polymeric

Harflex 300 0.58 Harchem и Harflex 325 .43 Harflex 330 .42 и it Harflex 375 .74 NP - 10 .35 Eastman Others Triacetin 0.29 Eastman Tributyrin .65 Eastman Saniticizer 141 .34 Monsanto Butyl Oleate .24 Harchem Butyl Stearate .24 Harchem Dioctyl Azelate .35 Eastman (a) Monsanto Company, St. Louis, Missouri 63166. (b) The Harshaw Chemical Company, 1945 East 97th St., Cleveland, Ohio 44106. (c)Eastman Kodak Company, Distillation Products Industries, Rochester, N.Y. 14603 196 ROTARIU and M OTT phosporus fire retardant material manufactured by Monsanto Chemical Company, is superior.

2.1.4. Total Radiation Needed for Complete Polymerization

Another recent accomplishment has been the experimental verifi­ cation that the total radiation needed for complete polymerization is a function of the dose rate to the 0.3 power (6). This dose rate dependence was studied over the range 0.1 to 1.0 megarads per hour for the following systems.

1. Styrene-acrylonitrile (60:40 by weight) in birch, sugar maple, yellow poplar and white pine.

2. Methyl methacrylate in birch, sugar maple and yellow poplar. r 3. Methyl methacrylate-Phosgard (88:12 by weight) in red oak, yellow poplar and loblolly pine.

4. Ethyl acrylate-acrylonitrile (80:20 by weight) in red oak, yellow poplar and loblolly pine.

The data are given in Fig. 1 (6). Other observations from this study are:

1. The radiation required for total polymerization of methyl methacrylate in wood is reduced by 7-107. by the addition of 12% (by weight) of Phosgard C-22-R.

2. The radiation required for complete polymerization of methyl methacrylate, methyl methacrylate-Phosgard (88:12), and ethyl acrylate-acrylonitrile (80:20) in the low dose rate area is greater in white pine than in hardwoods and loblolly pine due to the inhibition of the reaction by the resinous constit­ uents in white pine.

3. The radiation required for complete polymerization of methyl methacrylate and styrene-acrylonitrile (60:40) in red oak and loblolly pine is the same as required for these monomer systems in birch, sugar maple and yellow poplar.

2.2 ._____ Impregnation and Polymerization Methods and Systems

The impregnation and polymerization methods and systems currently in use in the United States are discussed in another paper prepared for this Panel. (18)

2.3 ._____ Physical and Mechanical Properties

In early 1965, a program was initiated, under U.S. AEC sponsor­ ship, to assess the changes in physical and mechanical properties of wood-polymer materials as a function of monomer and monomer loading level. This continuing program involves a cooperative effort between Research Triangle Institute, Raleigh, North Carolina; North Carolina State University, Raleigh, North Carolina; and West Virginia University, Morgantown, West Virginia. To date, West Virginia University has pro­ duced more than 4000 wood-polymer test samples from four species of wood. UNITED STATES OF AMERICA 197

FIG .l. Effect of dose rate on the total dose requirements for complete polymerization of various systems.

Impregnation has been with four types of monomers (methyl methacrylate; methyl methacrylate (88%)-Phosgard (12%); styrene (60%)-acrylonitrile (40%), and ethyl acrylate (80%)-acrylonitrile (20%,) and at four loading levels (0%, 33%,, 66%, and 100%, of the theoretical maximum monomer loading). North Carolina State University tested these 4000 samples for toughness, static bending, hardness, rate of dimensional change in water vapor, abrasion, vibration, compression perpendicular to grain, and tension per­ pendicular to grain. The data are now being analyzed by the Research Triangle Institute. The final report on this project should be available by the autumn of 1968.

The statistical design for the entire project procedure was de­ fined by Research Triangle Institute, with aid from North Carolina State University.

The manner in which samples were selected for testing is de­ picted in Fig. 2. For each test, e.g., toughness, 16 basic specimens were required for each wood species. However, in order to obtain ade­ quate statistical reliability two or more replications (repeats) for each test were needed. The number of groups (i.e., the number of replications) needed from each log for each type of test reflected past experience concerning the amount of variability for that particular test. For example, toughness is a property which exhibits a relatively high degree of variability and this test had to be repeated or replicated four times within each log (or sixteen times for each species of wood). The largest number of test samples used was for the toughness test, 853; the smallest number, for the vibration test, 193. Some preliminary hard­ ness and abrasion data are shown in Figs. 3 and 4; the data is subject to revision.

A mathematical model of wood-monomer materials that enables one to predict the mechanical, thermal and electrical properties of wood 198 ROTARIU and MOTT

FIG.2. Schem atic drawing illustrating how logs were cut for specimens used in the testing program. polymers has recently been developed at the School of Forestry, Syracuse University. Experimental verification has been performed with a basswood- methyl methacrylate composite in bending, compression, thermal conduc­ tivity and electrical conductivity tests (19-20).

3. PATENTS

Four patents on wood polymers have been issued in the United States to date (21). These relate to the initial treatment of wood with swelling agents. Additionally, there are six patent applications on file with the U.S. Patent Commission — one by Winston and Kent, West Virginia University (22), three by A. H. Feibush, Air Reduction Company (23), and two by W. A. Loeb, Gamma Process Company (24).

4. COMMERCIALIZATION ACTIVITIES

4.1._____Companies and Products

At present,there are at least four companies in the U.S.A. that have facilities for the manufacture of wood-polymer materials: American Novawood Company, Lynchburg, Virginia; Atlantic Richfield Company, Philadelphia, Pennsylvania; Lockheed-Georgia Company, Marietta, Georgia; and American Machine and Foundry Company, Lowville, New York. The total combined production capacity for these companies is estimated to be about 800,000 board feet (or 4.0 million lbs.) per year. Although the annual production rate is not known, it is certainly far short of this. UNITED STATES OF AMERICA 199

SIDE HARDNESS

M M A

Red Oak Loblolly ■“ Yellow Poplar

i Polymer L о a ding

FIG.3. Variation of side hardness (load, in lbs) with polymer loading, for methyl methacrylate in four woods.

4.1.1. The American Novawood Company

Radiation-produced polymer materials have been commercially available for about two years. The American Novawood Company of Lynchburg, Virginia, has played an important role in bringing this new material into commercial use. This company was formed in September 1964, and shortly thereafter, developed a small scale production capacity using a nuclear reactor as a source of gamma radiation. During 1965, production continued on a small scale; with the products primarily used for test and evaluation and for phototype construction.

In the fall of 1965, construction began on a cobalt-60 wood- polymer production facility, which went into operation in March 1966. By the early fall of 1966, materials were being distributed for consumer use. 200 ROTARIU and MOTT

FIG. 4. Variation of abrasion (thickness loss in inches) with polymer loading, for white pine impregnated with four monomer solutions.

During the last years, the potential of literally hundreds of applications have been investigated and evaluated. A fair number of these have fallen by the wayside, at least temporarily, because of the inadequacy of available processing techniques and monomers. Many others, however, after long periods of prototype testing, are beginning to find satisfactory acceptance by the manufacturers, and sales promotion efforts are continuing to introduce new products to the market place.

American Novawood is presently manufacturing a line of parquet flooring called "Gammapar" in four wood species; red oak, white oak; maple, and walnut. All but walnut are produced in eight standard colors including wood tones and natural. American Novawood1s product line also includes stair treads, risers, thresholds, and doorsills in red oak and in all UNITED STATES OF AMERICA 201 colors. Veneer panels have been produced on an experimental basis for some time in sizes up to 24 inch x 66 inch; thicknesses have been as low as 1/40 inch. The surface evaporation problem has been reduced to a point where the 1/40 inch thick material can be sanded and pojished without sand-through. However, the yield is still quite low due to the brittle­ ness of product, color nonuniformities, and other defects (25).

4.1.2. Lockheed-Georgia Company Extensive technical and marketing development activities on wood- polymer materials have been underway at the Lockheed-Georgia Nuclear Laboratory for over three years. Present production capacity for these materials (LOCKWOOD) is reasonably estimated to be 250,000 board feet per year using the new cobalt-60 irradiator (200,000 curies). The effort at Lockheed-Georgia, while involving considerable research and development activity, has been directed primarily toward extending the research in­ formation derived by West Virginia University and others to a large scale production operation and to the tailoring of wood-polymer composites to meet specified customer requirements. At varying levels of detail well over 100 wood types have been processed by Lockheed-Georgia using about a dozen vinyl monomers. Major effort has beendevoted to production of material using methyl methacrylate, which is considered at this point to be, overall, the most attractive monomer in spite of its fairly high cost.

In 1966, the Lockheed-Georgia Company carried out an AEC-sponsored experimental program to prepare wood-polymer products from woods supplied by 68 manufacturers of wood products and to compile a summary of the manu­ facturers evaluation of the wood-polymer products (12). Some 8000 lbs. of wood-polymer products were prepared from 41 different woods.

Extensive effort has been devoted to working with manufacturers representing a large number of end product applications. Lockheed-Georgia activities involve both the production of wood-polymer lumber and the custom processing of specific items supplied by potential users. This approach has been used not only to interest manufacturers in the use of wood polymers but also to determine the applicability of the wood-polymer process to many products".

Results of these industrial activities have been interesting in that they indicate fully that a wood polymer may not be nearly so applicable for a potential end product as a preliminary evaluation, based primarily on the physical properties, might suggest; the converse has also proved to be true in a number of cases. It appears that introduction of wood polymers into commercial products in sizeable quantities will be a long term effort. It is believed that the optimism which abounded several years ago — the feeling that requirements for wood polymers would outstrip availability of the materials -- has not been borne out. The material has, by and large, not proved to be a panacea to the wood-products industry. There is strong resistance to the cost of materials currently available from Lockheed and other companies. While physical properties of the treated woods tend to be improved, not all properties meet apparent customer requirements. For example, the indications are that the staining characteristics, chemical resistance, and ability to process semi-finished products without un­ desirable side effects such as warping or other dimensional change must be generally improved. Further, there is reason to believe that successful commercialization of any specific wood-polymer product will follow only after there has been an adequate developmental effort on that specific product. In summary, the Lockheed-Georgia Company feels that the future for wood polymers still looks attractive, but that full realization of the potential of this family of new materials will require both time and money (26). 202 ROTARIU and MOTT

4.1.3. Atlantic Richfield Company

Atlantic Richfield, the most recent entrant in the commercial wood-polymer field, will have its production facilities at the Nuclear Materials and Equipment Corporation (NUMEC), a wholly-owned subsidiary. The nuclear facilities of the State of Pennsylvania at Quehanna, Pennsylvania have been leased by NUMEC; production will be with a variety of cobalt-60 irradiators.

This facility will be used for the radiation-production of Permagrain, a pre-finished parquet-panel flooring. Permagrain contains a fire retardant and is reported to exhibit qualities superior to natural red oak, 100% vinyl, and epoxy terrazo. Nominal dimensions of one panel are 12 x 12 x 5/16 inches. Atlantic Richfield plans to produce a few hundred thousand square feet of Permagrain in 1968 and a million or more in 1969.

4.1.4. American Machine and Foundry Company

In January 1965, the American Machine and Foundry Company, Bowling Division, Lowville, New York, built a small pilot plant to make prototype billiard cues of wood polymers. This first semi-production unit, employing the heat-catalyst method, was constructed of steel pipe two inches in diameter and four feet long. A hot water tank was used for the surge tank, and the plastic connecting hose was purchased from a dairy supply house. Curing was carried out by placing the monomer-impregnated wood cue blanks in a pipe capsule which in turn was placed in their dry kiln overnight. Total cost of the unit was reported to be $195 (19).

FIG.5. Photo of the American Machine and Foundry Co. production facility for making billiard cues. The worker is shown pouting the m onom er-catalyst solution into the reservoir funnel for subsequent introduction into the impregnation chamber im m ediately below. The curing oven is on the left. UNITED STATES OF AMERICA 203 2 0 4 ROTARIU and M OTT

The first full-time production unit was built in March 1966, and consisting of an impregnation chamber ten inches in diameter and three feet long. About seventy cue blanks could be prepared at a time. Pipe capsules containing the monomer-wood cues were still placed in a dry kiln for curing

During the early months of 1967, a larger production unit was constructed at a cost of about $1000. The impregnation chamber was en­ larged by cutting the three-foot chamber in half and welding a three-foot section of ten-inch diameter pipe between the two ends. (See Fig. 5). This new unit can impregnate 150 billiard cue blanks at a time. A special curing oven was constructed from a ten-inch diameter, six-feet long pipe having appropriate flanges and caps welded on each end. Half-inch copper pipe was wound around the outside of oven and covered with asbestos insula­ tion. The temperature is maintained at the desired level of 65° C by means of a steam regulator valve. (It has been observed that in the wood the exothermic peak does not rise higher than 85° C (182°F). See Fig. 6.) The curing oven is placed alongside of the impregnation chamber for mini­ mum handling of the monomer-wet stock. Catalyzed monomer is stored in a refrigerator at zero degrees centigrade. The time for a complete run, including the impregnation and curing,is about six hours. This production unit has operated satisfactorily and has consistently produced high quality cues. AMF estimates production costs at about twenty cents per cue; present production is about 150 cues a day (19).

Since the total twenty-four hour output of the American Machine and Foundry Company thermal-catalyst production system is not needed for billiard cues, other products are being made for evaluation by the Company1 research and marketing groups. In addition, there is some production of wood polymers for evaluation by other wood-product companies.

4.2.______Production Considerations

4.2.1. Upgrading Low-Quality Wood

With the emergence of a better understanding of wood-polymer processing has come the realization that the upgrading of low-cost soft­ woods does not necessarily have the great potential for immediate applica­ tion once attributed to it. The fact is that to convert a softwood into a product having physical properties equal or superior to a hardwood can cost more than the cost differential between hardwoods and softwoods. The utilization of low priced monomers such as styrene and vinyl chloride could change this picture particularly for a softwood that gives a high yield of suitable wood-polymer products.

It has also become apparent that impregnation and polymerization is not the hoped-for solution to the problem of the defects found in many species of wood. The wood-polymer process per se does not guarantee the use of low-cost defective material in premium-wood applications! That is, whether the wood is hard or soft, high-grade lumber is needed to pro­ duce a high-quality product, wood polymer or otherwise.

4.2.2. Product Handling

The American Novawood Company has reported (25) that in the handling of shaped items full attention must be given to the dimensional specifications on the finished product. This is because distortions, quite similar but generally in the reverse direction to those found in the kiln drying of wood, occur during the polymerization process. These UNITED STATES OF AMERICA 205 distortions are usually most pronounced in samples containing both heart- wood and sapwood since monomer more readily penetrates sapwood than heart- wood. Very thin, flat items may exhibit cup or warp, or a straight piece may have a bow or bend after conversion. Further, in the case of a cylindrical item, the cross section might change from circular to oval due to the fact that the tangential swelling is about twice the radial swelling. Experience has shown that when the economics permit, distortion is best handled by machining. A machine cut on a wood-polymer piece fol­ lowed by sanding and polishing will always produce a better appearance than sanding and polishing alone.

Increases in overall product yield will occur principally when the wood has undergone close selection and cutting before impregnation and polymeric conversion. As the items being treated approach closer and closer to the desired final shape, less and less monomer is required. The lowest cost product is achieved when the pre-shaped items are shell loaded.

The shell loading technique is presently being used by American Novawood for the processing of thresholds, stair treads, and risers. These products are machined to the desired final cross-sections before impregnation, polymerization, sanding, and polishing.

4.2.3. Color Uniformity

Maintaining uniformity of color has been a very important problem in the production of wood-polymer items. It is especially diffi­ cult when the size of the item is large. Imperfections in the wood, which are normally handled by standard staining and finishing operations, are not so easily taken care of after impregnation and curing. Many types of heartwood are not always uniformly impregnated and thus lead to discolora­ tion in the final sanded, polished product. Where this has been a great problem, the only solution has been to select white sapwood material. Of course, any selection procedure increases the cost and has been a particu­ lar stumbling block in the adoption of wood polymers in the furniture industry.

5. RADIATION VERSUS THERMAL-CATALYTIC PRODUCTION

The following is a comparison of the radiation and thermal- catalytic methods of producing wood polymers. It is based on information recently provided by the American Novawood Company (25), the School of Forestry, Syracuse University (19), and the School of Forestry, North Carolina State University (27).

5.1.______Physical Properties

With non wood-swelling systems there appears to be no major differences in the properties of the wood polymers formed by radiation- induced and thermally-catalyzed polymerization so long as acid catalysts are not used in the latter. However, if a swelling agent is employed to get monomer into the fine structure of the wood fiber wall, then chemical bonding of the monomer with the cellulose and lignin of the wood and a general upgrading of properties might be accomplished by the radiation, but not by the thermal-catalytic, approach. (Note: Present wood-polymer processing involves penetration and filling of the fiber cavities but little or no deposition of monomer within the fiber walls.) 206 ROTAFIU and MOTT

5.2.______Economics

A thorough study has not been made of the relative costs of producing wood polymers by the radiation and thermal-catalytic methods. It is likely, however, that capital costs would be higher for a radiation plant than for a thermal plant, operating costs lower. The radiation method would then have the advantage for high volume applications, the thermal-catalytic method for low.

As the American Machine and Foundry billiard cue operation demonstrates, the attractive feature of the heat-catalyst method is that a small unit can be installed in a woodworking plant in a minimum of time at little expense. According to the American Novawood Company, however, relatively few products can be thermal-catalytically produced at lower costs than by radiation, especially at this stage of market development. (For example, cost for the radiation-production of billiard cues is estimated at 20 cents per cue in batches of 3600 versus AMF's reported cost of 25 cents.) Its principal interest in the thermal- catalyst approach has been for products having very low effective target densities, the American Novawood cobalt-60 irradiator having been designed for efficient operation with target materials having approximately unit density. In such cases, gamma rays are absorbed very inefficiently and the cost per pound of product for conversion is very high. In the thermal- curing of such a product, there is no factor equivalent to this gamma utilization efficiency and thus, at times,a sizeable cost savings can be made through the use of the thermal-catalyst method.

REFERENCES

(1) KENT, J., WINSTON, A. and BOYLE, W., "Prepration of wood-plastic combinations using gamma radiation to induce polymerization; effects of gamma radiation on wood," US AEC Report ORO-600 (March 1, 1963), available from the Clearinghouse for Federal Scientific and Technical Information, National Bureau of Standards, U. S. Department of Commerce* Springfield, Virginia, 22151.

(2) KENT, J., WINSTON, A. and BOYLE, W., "Preparation of wood-plastic combinations using gamma radiation," US AEC Report ORO-613 (September 1, 1963), ibid.

(3) KENT, J., et. al., "Preparation of wood-plastic combinations using gamma radiation to induce polumerization," US AEC Report ORO-628 (May 14, 1965), ibid.

(4) KENT, J., et. al., "Preparation of wood-plastic combinations using gamma radiation to induce polymerization: impregnation of wood with acrylic monomers," US AEC REPORT 0R0-2945-4 (April 1, 1966). ibid.

(5) KENT, J., et. a l ., "Studies of radiation polymerization of vinyl monomer in relation to wood-plastic combinations," US AEC Report ORO-2945-6 (September 21, 1966), ibid.

(6) KENT, J., WINSTON, A., BOYLE, W., and TAYLOR, G., "Preparation of wood-plastic combinations using gamma radiation to induce polymeri­ zation," US AEC Report ORO-2945-7 (March 17, 1967), ibid. UNITED STATES OF AMERICA 2 0 7

(7) LOOS, W.E. and KENT, J., "Topical report on fastening of wood-plastic combinations," US AEC Report ORO-2945-9 (September 1, 1967), ibid.

(8) SOUTHERN INTERSTATE NUCLEAR BOARD, "Commercialization of the process of manufacturing radiation produced plastic impregnated wood in the southern region," US AEC Report TID-22774 (1966). (See Reference 1 for source of availability).

(9) EVANS, J.C., et. al.,"Commercialization studies on wood-plastic combinations process," US AEC Report NYO-3569-1 (1965), ibid.

(10) ROHRMAN, C.A., "Irradiated wood-plastic materials commercialization in the pacific northwest and great lakes regions," US AEC Report BNWL-261 (1966), ibid.

(11) FRANKFORT, H. and BLACK, K.M., "Engineering and evaluation study for the manufacture of wood-plastic composites," US AEC Report KLX-1876 (1966). ibid.

(12) ROBERTS, P.J., BRIDGES, W.L. and BURFORD, A.O., "Industrial evaluation of radiation processed wood-plastic composites," US AEC Report 0R0-3415-1 (1966), ibid.

(13) MEYER, J.A., "Treatment of wood-polymer systems using catalyst-heat tech­ niques," Forest Products Journal 1¿ (1965) 362.

(14) MEYER, J.A., "Make wood-plastic combination materials in your plant," Woodworking Digest 68^ (1966) 35.

(15) SIAU, J.F. and MEYER, J.A., "Comparison of the properties of heat and radiation cured wood-polymer combinations," Forest Products Journal 16^ (1966) 47.

(16) HEBBLE, K., et. al., "How one company built a simple, inexpensive heat-curing wood-plastic production unit," Forest Products Journal 2 (1967) 19.

(17) BOYLE, W.R., College of Engineering, West Virginia University, Morgantown, West Virginia; personal communication.

(18) MOTT, W.E, and ROTARIU, G.J., "Impregnation and Polymerization Methods and Systems Used in the Production of Wood-Polymer Materials", IAEA Study Group on Impregnated Fibrous Materials, Bangkok, Thailand, November 20-24, 1967.

(19) MEYER, J.A., Department of Chemistry, State University College of Forestry at Syracuse University, Syracuse, New York; personal com­ munication.

(20) SIAU, J.F., Ph.D. Thesis, The physical properties of wood-polymer composites, June 1968. State University College of Forestry at Syracuse University, Syracuse, New York.

(21) Patent Nos. 3,077,417; 3,077,418; 3,077,419; 3,077,420. Issued to the Dow Chemical Company, Midland, Michigan, February 12, 1963.

(22) Patent Application No. 404,195, A. Winston and J. Kent, West Virginia University; filed October 1964. 208 ROTARIU and MOTT

(23) Patent Application Nos. and filing dates: 391,810 (filed August 24, 1964); 576,187 ( filed August 29, 1966), and 613,057 (filed January 31, 1957), A. M. Feibush, Air Reduction Company, Murrayhill, New Jersey.

(24) Patent Application Nos. 620,708 (filed March, 1967) and 630,202 (filed March, 1967), W. A. Loeb, Gamma Process Company, Inc., New York, New York.

(25) BARRETT, Lawrence G., President, The American Novawood Corporation, Lynchburg, Virginia; personal communication.

(26) BURFORD, A. 0., Lockheed-Georgia Nuclear Laboratories, Lockheed- Georgia Company, Dawsonville, Georgia; personal communication.

(27) GILMORE, R. C., Superintendent, Wood Products Laboratory, School of Forestry, North Carolina State University, Durham, North Carolina; personal communication. EUROPE: A SUMMARY

CONTRIBUTED BY A. BURMESTER BUNDESANSTALT FÜR MATERIALPRÜFUNG, BERLIN-DAHL EM, FEDERAL REPUBLIC OF GERMANY

1. INTRODUCTION

The first reports of investigations into methods of improving the qualities of wood by impregnation with monomers which were then poly­ merized in the wood by means of high-energy radiation were published by V. L . K a rp o v and co w o rk ers in 1960 [1] and L . T . H arm ison and J. A. Kent in 1962 [2]. Subsequently, corresponding experiments were performed in numerous laboratories in different countries. This report is a survey of research results which have been obtained so far in Europe. Similar research work has been carried out in Austria.[3], Belgium [4], Czechoslovakia [5], Denmark [6], Finland [7, 8], France [9, 10], the Federal Republic of Germany [11-22], the United Kingdom [23, 24], Hungary [25, 26], the Netherlands [27], Poland [28-30], Sweden [31, 32], and Yugoslavia [33].

2. T E S T R E S U LTS

Some papers deal with the effects of gamma-radiation on the properties of wood and wood-base materials. Most of them concern investigations of wood-monomer compositions in which polymerization is achieved by chemical and physical processes.

2.1. Effects of radiation on wood and wood-base materials

On the basis of results obtained by G. Becker and A. Burmester [11], K. Seifert [21] investigated the modification of the chemical composition of pine, spruce and beech wood exposed to radiation doses of 10 to 10s rad and found that a modification may already be observed at 10 rad. The gas composition of air in irradiated wood (which even affects the sensitivity of sheet zinc towards corrosion) throws some light on the degree of degrada­ tion [11]. Tests with Hylotrupes bajulus larvae, termites and wood- rotting fungi on irradiated wood revealed a change in resistance to deterioration [11]. Chemical modifications entail physical and mechanical changes of the wood properties. J. Polcin and M. Karhanek [30] state that with an electron microscope no significant changes were recognized on the surface of the cell walls of spruce, beech and poplar up to a dose of 5 1 07 rad. When J. Jokel [33] determined the linear absorption coefficient, he found that the intensity of gamma-radiation was reduced in its passage through wood. The rate of reduction was almost the same in dry and moist m a teria l.

209 210 BURMESTER

Apart from a change in the water absorption capacity of irradiated wood [11], A. Burmester [14] observed an influence on the sorption of water vapour through pine and beech wood with a dose as low as 10 rad. A comprehensive investigation of the effects of gamma-radiation on the strength properties of pine, spruce and beech wood with radiation doses of 10 to 2.9 X108 rad was carried out by A. Burmester [14] (Fig. 1).

FIG .l. Influence of y-radiation on the strength of pine wood.

Wood fibre and wood particle boards were exposed to radiation and were investigated for changes in hydroscopicity, water absorption, thick­ ness, swelling and strength properties by M. Lawniczak and others [28, 29].

2. 2. Polymerization of monomers in wood by means of high-energy radiation

Most of the studies concerned methylmethacrylate and styrene, but some other monomers were also investigated. As the test results are so voluminous, only some fundamental characteristics of the papers referred to will be singled out for the sake of the survey.

2.2. 1. Methylacrylate

H. Orth et al. performed experiments to improve wood particle boards with methylacrylate. They obtained only slight strength improve­ ments due to insufficient retention.

2.2.2. Methylmethacrylate

Investigations carried out by M. De Proost and others [4] on spruce and poplar wood with a retention of 100% methylmethacrylate revealed an in c re a s e in the bending strength o f 110 and 60%, re s p e c tiv e ly , and a reduction in swelling of 60 and 85%, respectively. E.J. Gibson [23] found that methylmethacrylate barely penetrates the cell wall and that chemical compounds are formed with lignin rather than with cellulose. K .A. J. Singer [6] carried out investigations with methylmethacrylate which were prim arily intended to explain the different effects of gamma EUROPE: A SUMMARY 211

Gamma dose,Mrad

FÏG.2. Gamma-radiation-initiated polymerization of styrene-acrylonitrile mixture (60:40) in different wood species.

and electron radiations. A higher dose of electron rays as compared with gamma rays is required to obtain the same degree of polymerization. H. Orth obtained improved strength properties by impregnating particle boards with methylmethacrylate [20].

2.2.3. Acrylonitrile

K. A. J. Singer [6] performed tests with acrylonitrile mixed with styrene. Varying with the wood species, different doses were required for complete polymerization (Fig. 2). H. Wilski [22] stated that no significant strength increases were achieved by impregnating spruce wood despite a recorded weight increase of 80%. An 8% weight increase of wood particle boards reduced tensile strength, hardness and impact bending [20].

2.2.4. Diisocyanate

Tests performed by A. Burmester [12, 13] with diisocyanate revealed that this monomer reacts with the hydroxyl groups of the wood and the water even without radiation. Additional radiation results in only a slight improvement of the wood properties. Compression strength, bending strength and impact bending of pine and beech wood are considerably im­ proved, and sorption and swelling are reduced.

2.2.5. Formaldehyde

Pre-irradiation of wood with a dose of 107 rad and subsequent gasing with formaldehyde causes reduced sorption and swelling and simultaneously improves the strength properties by a chemical linkage of formaldehyde with reactive groups of the wood. [16]. 212 BURMESTER

2.2.6. Styrene

Impregnation of lime wood with styrene, both alone and combined with bulking agents, resulted in depositions in the cell walls and copoly­ merization with cellulose and polyoses. Fifty per cent polystyrene im­ proved the anti-shrink efficiency by 50%. These results, compiled by R. A. Laidlaw and others [24], emphasize above all the different effects as compared with impregnation with methylmethacrylate. K. A. J. Singer [6] also studied impregnation with styrene to carry out the comparison of electron and gamma radiation already mentioned. By extraction with benzene [10] J.K. Puig and J. Laizier investigated the residual amount of polymers in beech wood after impregnation with styrene and styrene-water mixtures and subsequent exposure to gamma radiation. They found that styrene alone is not chemically bound; in connection with water, however, it is bound to a considerable degree. A. Burmester [13] and J.K. Miettinen [8] experimented with mixtures of polyester and styrene. Copolymerization was induced at 107 rad. Water absorption was reduced by 50% by 0. 2 g polymeride per cm3 wood. A retention of 30% styrene in wood particle boards noticeably retarded the swelling rate [20].

2.2.7. Vinylacetate

Vinylacetate was used by K. A. J. Singer. A dose of 1. 5 Mrad induced 100% and 30% polymerization in pine and beech wood, respectively (30). The strength properties of spruce wood impregnated with vinylacetate were not affected [6].

2.2.8. Vinylpropionate

Impregnation of particle boards with vinylpropionate [20] produced a retention of as little as 1. 6%, thus increasing the bending strength by 12% but decreasing toughness by as much as 90% and hardness by 38%.

2.3. Polymerization of monomers in wood by catalysts or heat

Catalysts or heat can be used instead of gamma, rays to achieve poly­ merization. The advantages and disadvantages will not be dealt with here. It is debatable, however, whether or not the products produced by these different methods exhibit different properties. K. Griffioen [27] impregnated spruce, beech and hemlock with methyl­ methacrylate which polymerized under the influence of catalysts and heat. Data on moisture absorption, swelling, strength properties and decay resistance are presented, without comparing them, however, with non­ irradiated polymerized material. In Finland birch wood is impregnated with styrene and hardened with a catalyst [7]. Economic considerations dictated the use of a catalyst instead of a radiation source. Several papers deal with the use of polyethylene glycol to improve wood [26, 32]. This substance imparts considerable dimensional stability to wood. Investigations on the strength properties have so far not been carried out. TABLE I. CHANGE IN THE PROPERTIES OF WOOD AFTER POLYMERIZATION OF AN IMPREGNATED MONOMER ® s 6 s s £ a. S. *> -a £ о ■s g to i s ^ i § 4 CO a. О 8. S u „ 8 ¡ Q 00 2. ^ & 00 oc -S E £ . Ë 8 s; s Я с H i I E B.è о g E E a u о — S 'З. ■S i >ч <4 S

w 5 XI 1

+ о с a. § oor o 1 й 4 1 .5 Picea +11Í -60 « В 00 £ i Ю O 110 I + 6C o я s o i Pinus + V ? o o ■41 o + + «5 [ з; 45 1 Betula 1 + 1É 2 EUROPE: A SUMMARY A EUROPE: o m i ■4* o + fr в + 5 с -20

, 70 I L _ + “ i t g

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2 06 o o + o + s 8 Pinus +20 -42 P3 s « o m «o l-f rp o + + » Fagus -54 te « o C© o + V + S i Pinus -40 •в i CD *0 U. o» л + 4- <1 ' rt3. -41 -34 o o w 4* u 50 Tilia -50 со US o c- Ю o -s. + £ £ > 4 40 Pinus + 2Î -25 n o № СО N o + + Й 2 a и 28 I Fagus -50 S o O + 116 4.3 Picea j ■Ss 3 « > 41 i § o & 1.5 Pinus 1 o o с a. 213 214 BU RM ES TER

4) U C s 3 rH

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S ^ 00 s *i ê « ■e s

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H o 8 S-4 o Д Ю g _ ê + + + E o U

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S i o C c O c o 'û. u o e 2 i r ^ a. B o S ® c Ï . 1 II % o. э .g- Э 1 1 > £ bb (Л S w Я U H EUROPE: A SUMMARY 2 1 5

A. Burmester investigated the potential use of pulp sulphite liquor to improve wood [18] and found that the strength improvements equalled those imparted by monomers. Shrinkage is reduced by approximately 50% due to depositions in the cell walls. Particularly promising results are obtained by mixing sulphite liquor with creosote.

2.4. Survey of results

Finally, Table I presents a survey of the property improvements achieved with different monomers. The data are perforce incomplete, since the individual investigations had different aims.

3. USE OF POLYMER WOOD

In Europe industrial production of polymer wood is only slowly making headway. A French company produces gun stocks and tool handles of polymer wood. A Finnish company has developed a process in the labora­ tory for using catalyst hardeners. In the Federal Republic of Germany some companies are interested in stabilized wood and surface-hardened board material. Economic considerations limit, however, a broader application of this process. A. Burmester therefore suggests that wood be improved only where it is likely to be exposed to greater stresses, e.g. railway sleepers [19]. The screw-holding power of solid wood [15] and above all of wood particle boards [17] may be markedly improved by impregnating the bore-hole.

4. S U M M A R Y

In a concise survey of the research work conducted on polymer wood in Europe, the effects of gamma rays on the properties of wood and wood- base materials are discussed. Subsequently, the most important results of investigations into the improvement of wood with the monomers methyl- acrylate, methylmethacrylate, acrylonitrile, diisocyanate, formaldehyde, styrene, vinylacetate, vinylpropionate, polyethylene glycol and pulp sulphite liquor are reported. The extent of industrial manufacture and applications is mentioned.

REFERENCES

[1] KARPOV, V. L. , MALINSKY, J. M. , SERENKOV, V .I. , KLIMANOVA, R.S. , FREIDIN, A. S. , Radiation makes better wood and copolymers, Nucleonics 18 3 (1960) 88-90. [2] HARMISON, L. T ., KENT, J. A. , Radiation and monomers improve properties of wood, Nucleonics 20 3 (1962) 94. [3] CÜTLBAUER, F ., PROKSCH, E ., BILDSTEIN, H ., Strahlungsausgeh'ártete Holz-Kunststoff-Kombina- tionen, Osterr. Chem. Ztg. 67 (1966) 349-61. [4] DE PROOST, M ., HOEYBERGHS, H ., SCHIETECATTE, W ., Belgische Forschungsarbeiten iiber die Anwendung der Bestrahlungstechnologie zur Herstellung von Holz/Kunststoff-Verbindungen, Eurisotop Arbeitsunterlage N o.45, Brussels (1966). [5] VARGA, S ., KOSIK, M ., Radiacne chemické etekty v sústavach: Drevo-vinylovy monomér, Jaderná Energie 13 2 (1967) 62. 216 BURMESTER

[ 6 ] SINGER, К. A.J*. Wood-Plastic Combinations Prepared by Irradiation with Gamma-Rays and High Energy Electrons. II. Symp. on Radiation Chemistry, Tihany (1966). [7] MIETTINEN, J. K ., "Research in Finland on wood-plastic combinations’^ Paper presented at Plastic Manuf. Assoc. Meeting, Helsinki (1967).

[ 8 ] MIETTINEN, J.K ., Herstellung von Holzkunststoff-Kombinationen durch ionisierende Bestrahlung, Paperi ja Puu 49 2 (1967) 51-64. [9] FEUILLET, J ., Technologische Eigenschaften von Holz/Kunststoff-Verbindungen, Eurisotop Arbeits- unterlage No. 45, Brussels (1966). [10] PUIG, J.R ., LAIZIER, J., Bedeutung der Pfropfung bzw. der Hohlraumausfiillung bei Holz/Kunststoff- Verbindungen, Eurisotop Arbeitsunterlage No. 45, Brussels (1966). [11] BECKER, G ., BURMESTER, A ., Veranderung von Holzeigenschaften durch y-Strahlung, M aterial- priifung 4 11 (1962) 416-26. [12] BURMESTER, A ., Versuche zur Vergiitung von Holz durch strahlenpolymerisierte Kunststoff-Monomere Thesis, Univ. Hamburg(1966). [13] BURMESTER, A ., Versuche zur Vergiitung von Holz durch strahlenpolymerisierte Kunststoff-Monomere. Holz Roh-u. Werkstoff 25 1 (1967) 11-25. [14] BURMESTER, A ,, Einfluss von Gamma-Strahlung auf chemische, morphologische, physikalische

und mechanische Eigenschaften von Kiefem - und Buchenholz, Materialp'rüfung 8 6 (1966) 205-11. [15] BURMESTER, A ., Besseres Schraubenhaltevermogen von Holz durch Verwendung von Kunststoff- monomeren, Holz-Zbl. £2 100 (1966) 1791-92. [16] BURMESTER, A ., Versuche zur Behandlung von Holz mit monomerem Formaldehydgas unter Ver­ wendung von Gamma-Strahlen, Holzforsch. 21 1 (1967) 13-20. [17] BURMESTER, A ., Verbessertes Schraubenhaltevermogen von Holzspanplatten, Die Holzbearbeitung

1 4 2 (1967) 19-20. [18] BURMESTER, A. , Vergiitung von Holz durch Zellstoffsulfitlauge, Holz-Zbl. 93 (in press). [19] BURMESTER, A ., Verbesserung des Querdruckwiderstandes von Holz, Holz-Zbl. 91 121 (1965) 1 7 9 1 - 9 2 . [20] ORTH, H ., AMMON, R ., BURKARD, W. , COUZEIMANN, H. , SCHULZE, ]. , Neue Versuche mit Holz-Kunststoff-Kombinationen, Holz-Zbl. 92 148 (1966) 2592-96. [21] SEIFERT, K ., Zur Chemie gammabestrahlten Holzes, Holz Roh-u. Werkstoff 22 7 (1964) 267-75. [22] WILSKI, H ., Bestrahlte Holz-Kunststoff-Kombinationen, Eurisotop Arbeitsunterlage No.45, Brussels (1966). [23] GIBSON, E .J., LAID LAW, R. A. , SMITH, G. A. , Dimensional Stabilization of Wood. I. Im­ pregnation by means of gamma radiation, J. appl. Chem. 16 2 (1966) 58-64. [24] LAIDLAW, R. A ., PINION, L. C. , SMITH, G .A ., Dimensional Stabilization of Wood. II. Grafting of vinyl monomers to wood components, Holzforschung 21 4 (1967) 97-102. [25] CZVIKOVSKY, T ., Doktori disszertáció. Bp. Miiszaki Egyetem Mtianyag Tanszék (1966). [26] VIDENINA, N .G ., I.OMELCSENKO, S ., Radiacionnaja szopolim erizacija poliglikol-maleinatnuh szo sztirolom, Plaszticseszkie Maszszii 12 (1966) 5-7. [27] GRIFFIOEN, K ., Eigenschaften von Holz-Kunststoff-Verbindungen, Eurisotop Arbeitsunterlage N o.45, Brussels (1966). [28] LAWNICZAK, М ., RACZKOWSKI, J., Über den Einfluss der Gammastrahlung auf die Eigenschaften von harten Holzfaserplatten, Holztechnologie £> 3 (1964) 204-09. [29] LAWNICZAK, М ., RACZKOWSKI, J., WOJCIECHOWICZ, B ., Einfluss der Gammastrahlung auf einige Eigenschaften von Spanplatten, Holz Roh- u. Werkstoff 22 10 (1964) 372-76. [30] POLCIN, J. , KARHANEK, М ., Einfluss der ionisierenden Strahlung auf Holz, Holzforschung 18 4 (1964) 102-08. [31] KINELL, P. O. , AAGAARD, P ., A Study of Wood-Polymer Combinations, Forskningsradens Lab. Studsvik, Nykoping, Rep. No. LFK-9 (1967). [32] MOREN, R ., Die poly'áthylenglykol-Impragnierung von Holz und ihre Auswirkungen bei Holz- trocknung und Holzbearbeitung, Holz Roh- u. Werkstoff 23 4 (1965) 142-52. [33] JOKEL, J ., Einfluss der Holzfeuchtigkeit auf die Absorption von Gamma-Strahlung, Drevársky Vÿskum 10 2 (1965) 61-73. STATUS AND TECHNOLOGY OF POLYMER-CONTAINING FIBROUS MATERIALS IN THE EASTERN HEMISPHERE

Abstract

STATUS AND TECHNOLOGY OF POLYMER-CONTAINING FIBROUS MATERIALS IN THE EASTERN HEMISPHERE. A series of reports by specialists from Australia, India, Japan, Korea, Pakistan, the Philippines, the Republic of China, Thailand and Viet Nam describes past work and future plans, and outlines potential areas of exploitation.

AUSTRALIA

CONTRIBUTED BY J.G. CLOUSTON AUSTRALIAN ATOMIC ENERGY COMMISSION, LUCAS HEIGHTS, N,S.W ., AUSTRALIA

1. INTRODUCTION

Enough commercial irradiators with particle accelerators or cobalt-60 sources have been built in recent years to give confidence that the tech­ nology for treating material with gamma or electron radiation is practical and well established. Experience has shown that irradiation of packaged materials, with gamma radiation, involves a complex arrangement of conveyors to ensure efficient utilization of the radiation, particularly when the treatment requires a dose in the megarad range. It is therefore impractical to consider that sm all-scale irradiators might favourably compete on economic grounds with conventional methods to achieve sim ilar results. It is the capital cost, apart from intangible considerations, which places any proposed radiation process at a disadvantage with respect to alternative methods even though operating costs and material costs may be low. Furthermore, high capital cost demands a high utilization rate and an assured long-term market for the product to minimize the radiation cost per unit. It is intended in this contribution to the study group to survey briefly the possibilities for an irradiated wood-polymer process in terms of the existing technology in Australia,

2 1 7 218 CLOUSTON

2. THE PROSPECTS FOR IRRADIATED WOOD POLYMER COMBINATIONS

The polymerization of monomers impregnating solid permeable sub­ strates such as fibrous materials by using the penetrability and chemical effects of ionizing radiation is in principle attractive. Published work, which has so far concentrated on the properties of wood-polymer combi­ nations, has demonstrated at laboratory and pilot plant level the practica­ bility of producing a material claimed to be superior in many respects to the untreated material. There are, however, two questions which manu­ facturers immediately ask when the subject is discussed: what will it cost to produce? and where can it be usefully used? The first question is more readily answered than the second because the costs of monomer and timber and the costs of impregnation and irradiation are available. The second query has no simple answer. A ll organizations and wood technologists contacted were intrigued by the wood-polymer specimens we received from the United States. The scepticism that was expressed is associated more with the prospects for a local market for manufactured articles in competition with natural timber veneers, plywood and particle board. There are few industries in Australia capable of the research and developmental effort needed to evolve a commercially acceptable wood-polymer article and which also have a suitable marketing organization. In one respect, however, the prospects in Australia for development of wood-polymer products are unique. A commercial irradiation plant capable of treating up to 18 000 000 lb of material per year to a dose of 2 Mrad has been operating continuously since June 1960. The irradiator owned by Westminster Carpets Ltd. and designed by the United Kingdom Atomic Energy Authority has been described in detail by Murray [1] . The facility cost US$1 000 000, about half of which was debited to the initial source loading of 500 000 Ci of cobalt-60. This type of plant has in principle the capacity to treat wood-polymer combinations. Whether or not it is practical to use the facility, the existence of the irradiator provides a realistic situation for estimating the minimum costs for irradiation.

2.1. The basic radiation cost

The characteristics of the Westminster irradiator are, briefly, as fo llo w s :

(a) The present source strength is about 500 000 Ci of cobalt-60 in the form of a plaque 13.5 ft long and 7. 5 ft high. (b) The production rate for material of density 30 lb/ft3 is about 650 lb/h, representing a radiation efficiency of about 24%. (c) The conveyors are integrated to standard pallets to support loads up to 700 lb. (d) The system is automated to ensure a dose of 2 Mrad at the centre of a package 23 in. high by 31.5 in. wide by 50 in. long. (e) A dose of 2 Mrad is obtained in a 40-h cycle. The mean dose rate is 50 000 rad/h, but during two periods of two hours during the cycle the dose rate would be about 250 000 rad/h at the surface of a package adjacent to the source. AUSTRALIA 219

(f) The standard charge published by the company for service irradiation is US$20. 24 per pallet load for an order exceeding 20 pallet loads.

If a 700-lb load per pallet is assumed, the cost for irradiation would be 2.88Ç per megarad-lb. This cost compares favourably with the 4.8Ç per megarad-lb estimated by Iannazzi and others [2] . However, it repre­ sents the minimum cost for unpackaged wood. The treatment of unpackaged wood is not practical because, apart from considerations of heat gene­ ration and the effect of oxygen on the rate of polymerization as discussed by Frankfort and Black [3], there is a potential explosion and fire hazard from low flash-point vapours in the oxidizing atmosphere of the irradiation chamber. Some form of hermetic sealing or vapour trapping would be n ecessa ry . Frankfort and Black proposed the use of metal containers with an integrated system for cooling and maintaining an inert atmosphere. Sub­ stantial metal containers would not be a disadvantage provided the dose specification for complete polymerization was less than 2 Mrad. Although the quantity of material treated per pallet would be reduced, there is a sufficient margin between the practical basic cost of 2.88Ç per megarad-lb and the cost of 4.8Ç per megarad-lb estimated in the Iannazzi report to believe that 5Ç per megarad-lb would be an upper lim it. The cost of the timber substrate, the monomer and the impregnation steps would be the most sensitive factors in assessing the economics of the process, to­ gether with such intangibles as the scale of the process and the location of the impregnation plant.

2.2. The cost of timber

Australian timber is sold in competition with imported timber. Retail prices were chosen as the basis of comparison. A representative selection of the retail prices for Australian and imported timber dried, seasoned and dressed is given in Table I. On the basis of cost and availability, Radiata pine would be a possible choice as the substrate for softwood- polymer combinations. It is a penetrable timber of medium density and easily handled and worked. Its penetrability is claimed to be advantageous for ease of preservative treatment when it is subject to insect attack or is used in conditions causing decay. The properties of low shrinkage and good gluing quality have been used to advantage for fabricating massive timber members. The density of Radiata pine is 30 lb/ft3 (Table II) or 2. 5 lb/superficial ft, and the cost for the timber would be 7. 26ç/lb.

2.3. The cost ef monomer

Studies of wood-polymer combinations have mostly stressed the possi­ bility of combining different softwoods with the relatively inexpensive large-volume commercial monomers. Methylmethacrylate, vinyl acetate, vinyl chloride and styrene are four which have been systematically studied [4] . In Australia the cost of these monomers when purchased in quantities greater than one ton is 22ç/lb for methylmethacrylate, 20ç/lb for vinyl acetate and vinyl chloride, and 13ç/lb for styrene. Consequently, the basic cost for monomer-impregnated timber will depend on the percentage by weight in the substrate. The enhanced physical properties depend on 220 CLOUSTON

TABLE I. RETAIL COSTS OF SOME AUSTRALIAN AND IMPORTED TIMBER

Dried, seasoned and dressed

T y p e Cost in US cents per superficial foot

A u s tr a lia n

Radiata pine 1 8 .9 2

S assafras 2 3 .8 4

C o a c h w o o d 3 3 .5 7

Yellow carabeen 2 8 .4 8

Brush b o x 2 7 .6 3

Grey ironbark 2 9 .5 7

Im p o rted

Douglas fir 3 3 .0 0

H e m lo c k 2 7 .8 0

Pacific maple (Meranti) 2 9 .9 2

R a m in 2 9 .8 3

Western red cedar 3 0 .2 7

R e d w o o d 3 7 .4 0

Ponderosa pine 3 4 .8 4

the percentage by weight of polymer in the wood. Such physical properties as toughness, abrasion resistance, hardness, compression, etc. all increase with increase in polymer content, and loadings greater than 100% by weight have been studied [5] . If development were undertaken it is unlikely that more expensive monomer systems, which would have to be imported, would be explored.

2.4. Impregnation

It has not been possible to obtain a cost estimate for batch impregnation plants. The procedure is well known to the timber industry and is well TABLE II. PHYSICAL PROPERTIES OF SOME AUSTRALIAN TIMBERS 6 6 2 p 3 op ,2 ft)rj Ё os ш Д э S g*i¡ = «s E о *ij с Й с . h .2 £ a > ей ы s 1 ,3 s AUSTRALIA h — -TíI— É00 « ci rt *¿¡ 5 g g

3 SP a g S E «3¿3 c 3 H oí 2 oo,2a 2 £ 2 « > H 00 ^ о Ol Ю Ю ■з I s - О *-4 .2 В o Çг*•o - г г - о о 2 м>.2 § о 4 I c-

e 221 222 CLOUSTON established for timber preservation to decrease decay, prevent insect attack and reduce inflammability. The practice of timber preservation by impregnation has been adopted in all Australian States. Vacuum pressure treatment is used for the preservation of transmission poles, marine timbers, fence posts and building timbers from attack by termites, rot and fire hazards. Although this step is considered to present no unusual difficulties, research and development would be necessary to devise suit­ able impregnation methods, and, if the Westminster irradiator were used, to design suitable containers to meet the requirements of anaerobic ir ­ radiation and cooling. The capital outlay would depend on the design capacity of the plant, its location relative to the irradiator and the need for ancillary storage, preparation and handling areas. The previous com­ parison of commercial radiation costs suggests that impregnation costs for plant of the same capacity in Australia would not be very different. The cost of this step can therefore be considered to be not less than 3ç/lb for 5 000 000 lb/yr, 1. 74

2.5. The basic cost of the process

Assuming sufficient developmental work to define a specification for a wood-polymer composite and presuming a market for 5 000 000 lb/yr, we can calculate that the basic cost would range from about 25ç/lb for Radiata pine impregnated with 100% styrene to about 35ç/lb for the same timber impregnated with 100% methylmethacrylate. These estimates can be considered to be maximum costs for doses up to 1 Mrad based on the retail price of Radiata pine. Although they involve an extrapolation for impregnation costs from United States to Australian conditions, they pro­ vide a basis for judging the feasibility of the process in Australia. The significance of these costs would depend on the value and utility of the product. In the case of Radiata pine, enhanced durability in exposed situations, greater dimensional stability and insect resistance would add to the value of the timber. Whether these improvements are sufficiently desirable to justify the extra costs of impregnation and irradiation belongs to the second question asked by manufacturers, for which, as previously mentioned, there is no simple answer. However, since the Westminster irradiator possesses the essential design features for a wood-polymer irradiator and has operated reliably for several years, the practicability of what might seem to be the most speculative and novel part of the concept has been demonstrated.

3. THE STATUS OF IRRADIATED WOOD-POLYMER RESEARCH IN AUSTRALIA

No major development of irradiated wood-polymer combinations has been undertaken in Australia by industrial or government research organi­ zations. It should not be inferred that there is no interest in the potential of this method for altering the physical properties of fibrous materials. However, the need and prospects for commercialization of a process established at pilot plant level in the United States of Am erica and under close investigation in Europe have not yet seemed sufficiently attractive AUSTRALIA 223 to Australia to warrant intensive research effort. Enough basic infor­ mation is available for industry to develop the technology and evaluate the product. The major polymer manufacturers and building industries are aware of developments through the literature, their overseas principals, or by overseas visits. Imperial Chemical Industries of Australia and New Zealand, Ltd. has an experimental cobalt-60 irradiator and is investigating radiation-initiated polymerization and graft-polymerization. Australian Consolidated Industries is another major company interested in the po­ tential of radiation processing and has a cobalt-60 irradiator. Westminster Carpets Ltd. is interested in extending the use of its irradiator and in­ creasing the range of materials treated. The main centre for forest products research in Australia is the Division of Forest Products of the Commonweath Scientific and Industrial Research Organization, Melbourne, Victoria. The division conducts research into the fundamental chemical, physical and mechanical properties of Australian timbers and undertakes investigations to assist in the effective use of Australian forest products. Each Australian State has wood tech­ nology laboratories incorporated with the State forestry authorities. The Irradiation Research Section of the Australian Atomic Energy Commission is primarily responsible for research investigations associ­ ated with the technological use of radiation. Projects concerned with radiation sterilization, food preservation and radiation chemistry are being undertaken. Technological assessments are usually undertaken in co-operation with specialists attached to the Research Establishment. Research contracts and liaison are also maintained with universities to expand the effort and basic knowledge of the chemical and biological effects of radiation.

4. SOME ASPECTS OF THE FOREST PRODUCTS INDUSTRY IN AUSTRALIA

4.1. Timber supply

The contribution to the gross national product during 1964-65 by the forest products industries was about $500 000 000. The value of exports was $16 000 000. Th e total A u stralian requ irem en ts fo r tim b e r and paper could not be met by local production, and, to satisfy demand, forest pro­ ducts worth $203 000 000 w ere im ported. The contributions o f variou s industries are summarized in Tables III, IV, V and VI. Australian forests provided 95% of the hardwoods but only 35% of the softwoods. State forestry authorities have a programme for planting fast-growing trees for greater self-sufficiency. The area able to produce com m ercial timber is a small fraction of the total area of Australia. Hardwoods predominate and the eucalypts are indigenous to about 94% of the area, but only about 40 of the 600 species of eucalypts are used commercially. Hardwoods other than Eucalyptus cover about 6% of the forested land in Australia. The two basic forest types containing trees other than eucalypts are the tropical and sub-tropical rain forests of coastal New South Wales and Queensland and the temperate rain forests of southern Victoria and Tasmania. The species growing 4 2 2 TABLE III. VALUE OF PRODUCTION*3’ FROM CHIEF WOOD-USING INDUSTRIES - AUSTRALIA [6] ($A000's) CLOUSTON o « .o *o “ f 1 — — So — E = В о о Эс -a о s-§ 8g £ e О в D. — I 2 a. rt

i 3 ■f 2. -3 s3 TABLE IV. VALUES OF IMPORTS OF FOREST PRODUCTS(a) - AUSTRALIA UTAI 225 AUSTRALIA E ¿ S g Eа a >> .О» ° О 9 g. .9 í 2 CLOUSTON 226 TABLE V. VALUE OF EXPORTS OF FOREST PRODUCTS*3' - AUSTRALIA I a I ! ï ê Л 'S. о uaЛ -e0 e E S « 00 О I AUSTRALIA 227

TABLE VI. ESTIMATED WHOLESALE VALUE OF FOREST PRODUCTS CONSUMED IN AUSTRALIA [6]

($ A 0 0 0 's)

1 9 3 8 - 3 9 1 9 4 6 -4 7 1 9 6 0 -6 1 1 9 6 1 - 6 2 1 9 6 2 -6 3 1 9 6 3 - 6 4 1 9 6 4 - 6 5 *

P ro d u ctio n 4 2 664 90 362 4 4 1 5 3 6 4 2 4 2 1 0 4 4 4 684 48 3 678 50 3 320 Im p o rts 1 9 4 4 4 40 788 1 8 6 5 6 4 1 3 2 644 1 5 8 8 9 6 17 8 202 203 346 E xports 2 960 4 7 3 2 1 1 9 1 2 1 2 1 9 6 1 2 9 8 1 1 5 842 16 1 4 7

N e t v a l u e 5 9 1 4 8 1 2 6 4 1 8 6 1 6 1 8 8 5 4 4 658 590 599 646 038 690 5 1 9

Provisional. in these forests are known collectively as rain forest or brushwood s p e c ie s . The native forests of Australia are deficient in softwoods. A large fraction of the forest reservations is rugged, inaccessible mountain country and because they mostly contain a mixture of species are classed as inferior forests. An important species of natural softwood is white cypress pine which is predominant in New South Wales and Southern Queensland. It is particularly valuable because of its durability and resistance to termites. The production from State Forests is regulated to maintain reserves and continuity of supply. Planned afforestation programmes are being undertaken in Australia on the advice of the Australian Forestry Council which has recommended that the rate of softw ood planting be in crea sed fro m 40 000 to 75 000 a c re s p er y ea r fo r the next 35 years. The characteristics of the six species of timber supplied by the Australian Atomic Energy Commission to the Agency prior to this meeting for impregnation and treatment by irradiation and thermal methods are listed in Table II. The Division of Wood Technology of the Forestry Commission of New South Wales selected them as representative of Australian timbers readily available in commercial quantities. Extensive plantation of Radiata pine (Pinus radiata D. Don) has been encouraged as part of the programme for developing the timber resources of the country. This timber is being used for general construction, floor­ ing, cladding, decorative lining, joinery, furniture and plywood. It is not suitable for exposed situations unless it has been impregnated with a non-leachable preservative. Sassafras (Doryphora sassafras Endl. and Daphanda micrantha (Tul.) Benth) is used for internal joinery, furniture, plywood and wood-working. It is also available in commercial quantities but is not recommended for exposed positions. It is about 30% heavier than Radiata pine. It grows in the coastal brush forest of New South Wales and Southern Queensland. The same considerations apply to Coachwood (Ceratopetalum apetalum D. Don) which grows in a sim ilar location and 228 CLOUSTON also on the adjacent ranges. It is not recommended for exposed positions but the sapwood is resistant to attack by Lyctus borers. Yellow Carabeen (Sloanea woollsii F. Muel) and Brush Box (Tristania conferta R. Br) grow on the edge of the rain forest of New South Wales and along the Queens­ land Coast. Brush Box is used where a high resistance to wear is required, for example in flooring and panelling but, although it is very resistant to termite attack, it is only moderately resistant to decay. It is almost twice as heavy as Radiata. Yellow Carabeen, although about as dense as Sassafras, is susceptible to attack by borers and must be impregnated with a preservative. The cost listed in Table I includes a charge of 2.2Ç for impregnation. Grey Ironbark (Eucalyptus paniculata Sm.) is an example of a local hardwood. It grows in most coastal districts of New South Wales. It is hard and tough, and not easy to cut and work. It is nevertheless very attractive in appearance when polished. At 70 lb/ft3it is 2. 3 times as dense as Radiata and is used for all types of construction, especially applications requiring great strength or durability such as rail­ way sleepers, piles, poles and flooring.

4.2. The manufacture of polymer-containing fibrous materials

The manufacture of resin-impregnated board and paper-based deco­ rative laminates in Australia with melamine, urea and phenolic resins is substantial. Figure 1 shows the growth of wood-based panel production in the p eriod 1950 to 1965. The Australian market for hard fibreboard is increasing at a rate barely in excess of population growth. There were originally three Australian manufacturers of hard fibreboard. In January 1967, the three companies amalgamated to found a single manufacturing and marketing organization, Hardboards (Australia) Ltd. The total production of hard- board in the p reviou s y e a r was about 340 000 000 ft2, and 70 000 000 ft 2 was exported. There is no specific export market for the product, which is sold wherever buyers can be found and in places as far apart as the West Indies and the West Coast of Africa. The amalgamation was initiated to rationalize the raw-material supplies and available shipping space to export. The market for soft fibreboard has been constant for several years and the growth of particle board began when the industry was established ten years ago. It is of some interest to note that until 1960 the manufac­ ture of soft fibreboard in Australia was based on bagasse and developed as a by-product of the sugar industry. In 1960 the company converted the process to use pulpwood as the parent material. It was more economical to use the bagasse as a fuel for sugar refining than to transport it several hundred miles to the fibreboard m ills. The pineboard is claimed to be a superior product with better dimensional stability. Radiata pine and Ponderosa pine are the basic sources of the pulp. The local raw material is obtained as thinnings and deformed trees from State forests. Two companies manufacture decorative laminates for the local market. The process is the conventional high-pressure method in which kraft paper bonded with phenolic resins and surfaced with melamine-impregnated deco­ rative sheets is compressed at pressures in excess of 1000 lb/in2 and at a temperature of 140°C. In 1966, about 24 000 000 ft2 of laminate was produced. The material retails at an average price of about $1.40/lb. AUSTRALIA 229

Y Е Л Й

FIG .l. Production of wood based panel products in Australia [63 •

Th e export o f these m a te ria ls is n eg lig ib le . In 1966 about 4 000 000 ft2 was imported. Excluding the manufacture of paper, the production of fibreboard and decorative laminates are the principal processes in which cellulose ma­ terials are impregnated with polymeric substances to produce composites for building and constructional use. There are several industries manu­ facturing decorative building products by pressing resin-bonded paper and plastic sheets onto particle board, hardboard and plywood. This is a de­ veloping trend in the use of resin-impregnated materials.

5. CONCLUSIONS

In Australia the prospects for development of wood-polymer composites depend essentially on the utility of the product. The market is small in comparison with those in Europe and North America, and, unless a unique advantage or use could be demonstrated, the product would be competing with native and imported timbers, particle board and decorative laminates in a limited area. The use of electron radiation to cure monomer-based surface coatings is a field with more immediate potential, because it offers the possibility of continuous processing rather than the batch methods practised with thermal treatments. The use of gamma radiation for initi­ ating polymerization in solid permeable substrates, such as wood, is an 2 3 0 CLOUSTON application at present limited more by the cost and quantity of the monomers needed to obtain a satisfactory product than by the cost of irradiation.

REFERENCES

[1] MURRAY, G .S., Nucleonics 20 (1962) 50. [2] IANNAZZI, F.D. el a l., Technical and Economic Considerations for an Irradiated Wood-Plastic M aterial, USAECRep. TID-21434 (1964). [3] FRANKFORT, I.H ., BLACK, K .M ., Engineering and Evaluation Study for the Manufacture of Wood- Plastic Composites, USAEC Rep. KLX-1876 (1966). [4] KENT, J.A. et a l., "Manufacture of wood-plastic combinations by use of gamma radiation", Industrial Uses of Large Radiation Sources I (Proc. Conf. Salzburg, 1963) IAEA, Vienna (1963) 377. [5] GREENE, R. E., BAKER, P .S., Recent developments in the production of wood-plastic combinations, Isotope and Radiat, Technol. 3 (1965-66) 115.

[ 6 ] FORESTRY AND TIMBER BUREAU, Annual Report for 1965, Department of National Development, Commonwealth of Australia (1966). INDIA

CONTRIBUTED BY V.K. IYA ISOTOPE DIVISION, BHABHA ATOMIC RESEARCH CENTRE, TROMBAY, BOMBAY, INDIA

1. IN T R O D U C T IO N

Forest resources such as wood and bamboo and other fibrous materials such as bagasse, jute and coir constitute important basic raw materials for the economic development of India. In spite of the variety and number of trees growing in India, the country is facing a shortage of high-grade timbers such as teak, sal (Shorea robusta) and deodar (Cedrus deodara), which are used in construction work requiring mechanical strength and durability. This shortage is reflected in the present trend in India to carry out all construction work in concrete and steel, even where timber is more suitable. This situation arose partly from the indiscriminate use of the better species for all types of work. The growing demand for timber (section 3 below) can be met only if the weaker and less durable varieties, which now serve mostly as fuel wood, can be more efficiently utilized. Table I lists the Indian woods which show promise for development into wood-polymer combinations. Species such as the Indian oaks, birch, maple, walnut, yew, ash, pencil cedar wood and Indian rose wood are required for special items such as decorative furniture, cabinets, sports goods, guns and rifles, and have been scarce or difficult to obtain from the remote Himalayan regions where they grow. Most of these have to be imported at increased prices to meet the demands for these purposes. Cheaper woods such as toon (Cedrela toona), mango, sissoo (Dalbergia sissoo) and silver oak, which are grown in the plains as shade trees and in plantations, can, after suitable treat­ ment, be used as effective substitutes. The built-in finish, the possibility of introducing colouring matter, and the extra hardness and abrasion resistance attributed to wood-polymer combinations should be special attractions. The extra cost for treatment may be more than offset by this aspect and there should be no difficulty in finding a market for WPC in India. However, the situation may not be the same with WPC for general utility, and a significant reduction in the cost of treatment should be aimed at if it is to be made popular. WPC from cheaper monomers such as styrene and ethylene should be the most promising in this field.

2. RESOURCES FOR THE PRODUCTION OF WOOD-POLYMER COMBINATIONS AND OTHER FIBRE-POLYMER COMBINATIONS IN IN D IA

2.1. Timber

India is one of the richest countries in the world in the variety of her indigenous timbers, having more than 2500 different species compared

231 232 IYA INDIA 233

TABLE II. DISTRIBUTION OF FOREST TYPES

In 100 0 h a A s °¡o o f t o t a l

Temperature forests:

C o n ife r o u s 2 6 0 0 3 . 3 5 500 7 .0 Broad-leaved 2 9 0 0 3 . 7

Tropical forests:

D e c id u o u s . 62 696 8 0 .0

E v e r g r e e n 9 4 0 0 72 896 1 2 . 0 9 3 .0

O th ers 800 1 . 0

T o t a l 78 396 1 0 0 . 0

with about 40 in Great Britain and about 200 in Am erica [1] . The total area of land in the country claimed as forest is 78.4 million hectares. The distribution of forest types is given in Table II [2] . The coniferous forests are confined to the Himalayan region and con­ sist mainly of deodar (Cedrus deodara), chir (Pinus roxburghii and P. longifolia), blue pine, spruce and fir, with a total growing stock of about 308 million cubic metres. The broad-leaf forests occupy 75.8 million hectares (96. 7% of the total forest area) and have a total growing stock of about 1820 million cubic metres. They include a variety of species, of which only a few have the required properties combined with easy access. Teak, sal (Shorea robusta), laurel and gurjun (Dipterocarpus indicus) and a few others belong to this class.

2.2. Bamboo

Two species of bamboo are found extensively in Indian forests - D endrocalam us strictu s and Bam busa arundinacea. A total o f 3 600 000 hectares of forest area are bamboo growing. Bamboo-is also extensively cultivated by villagers in their homesteads to meet local needs and in fact is found in almost all states except Jammu and Kashmir. It constitutes one of the most important natural resources of India - the annual pro­ duction being of the order of 1.56 million tonnes as against 17. 8 million tonnes of woods. These figures are, however, only indicative - the re­ corded removals form only a small part of the total consumption [2] .

2 .3 . Jute

Jute production is confined to the north-eastern parts of India - mainly Bengal, Assam and Bihar. However, after Pakistan, India is the largest producer of this fibre, which is the most important foreign-exchange earning material grown in the country. The total area under cultivation 4 3 2 TABLE III. PRODUCTION OF RAW AND PROCESSED JUTE IN INDIA 3 3 S 3 .3 a л s л ■a S .a ■S § д a -ga 8. > я “g 2 ° e я m а) о < <0£2 . f a. I

■B о ac s

IYA

1966-67 - 11000

(estimated) INDIA 235 is about 800 000 h ecta res, with an a vera g e y ield o f about 1170 kg/h ectare. Seventy-nine m ill companies with total of 75265 looms produce processed jute goods. The figures for the production of raw and processed jute and their export are given in Table III [3] .

2.4. Bagasse

Bagasse is used in the pulp and paper industry. The consumption of bagasse for the year 1960 was nearly 100 000 tonnes (air dry), and it is expected that this w ill go up to 800 000 tonnes in 1975 [2].

2.5. Fibrous materials used in the manufacture of cordage and ropes

The principal cordage fibres used in India are sisal, manila, henequen, true hemp and sunn-hemp. The Indian sunn-hemp is next in importance to jute and the annual production exceeds 100 000 tonnes. The fibre is used mainly for making ropes, strings, twines, etc. required for agricultural purposes. The greater bulk of manila, sisal and henequen is, however, imported into India. Relatively small amounts of sisal are produced in Orissa, Bombay and other places (1000 tonnes). Indigenous fibres such as Bombay aloe fibre (total production: 2000 tonnes) and coir are also used. Small quantities of true hemp are available in the country [4] .

2 .6 . C o ir

India is the largest coir producing country in the world, with her coco­ nut plantations covering an area of 7.46X 105 hectares, most of which is concentrated in tHe coastal strip of Kerala. In the year 1961-62 India pro­ duced 1. 62X 10® tonnes of coir fibre, 4 . 43X 105 tonnes of coir yarn and 2.57X 104 tonnes of matting from a coconut yield of about 4720 m illion nuts [3] . The industry is now partly on a cottage basis and partly distributed throughout about 150 factories. Rubberized coir, which is an effective and cheaper substitute for foam rubber for a variety of purposes, is already in production. Similar coir-polymer combinations can be en visaged.

2.7. Monomers

Ethylene, propylene, vinyl chloride, styrene and limited quantities of vinyl acetate are produced on an industrial scale in India. Small quanti­ ties of methylmethacrylate (about 150 tonnes/yr) are also available from acrylic scrap. It is planned to increase the production of polyethylene fro m about 26 000 tonnes in 1967 to about 100 000 tonnes in 1970-71. P r o ­ duction of indigenous vinyl chloride is expected to increase from about 27 000 tonnes in 1967 to about 100 000 tonnes in 1970-71, while the pro­ duction of styrene is expected to increase from about 10 000 tonnes to 35 000 tonnes during this period. The construction of new petrochemical factories at Visakhapatnam and Mettur and the expansion of those in the Bombay area will increase the availability of Indian monomers [3] . 2 3 6 IYA

2.8. Status of wood preservation in India

Conventional wood treatment with coal-tar creosote, arsenic and other inorganic salts is well known in India. A number of wood preservation plants of the small-scale open-tank type as well as the large-scale pressure- injection types are in existence in the country, mainly for the treatment of railway sleepers. In 1961 there were over 70 wood preservation plants with a total annual capacity of about 300 000 m3 [5] . Specifications for the installation of impregnation plants as well as a classification according to the degree of treatability of sapwoods and heartwoods of commercial Indian timbers have been issued by the Indian Standards Institution [6, 7] .

3. CONSUMPTION OF WOOD AND BAMBOO IN INDIA

3.1. Utilization of wood

In India only about one third of the total wood produced is used as in­ dustrial wood, the remaining two thirds serving as fuel wood, while in North Am erica industrial wood forms 83% of the total wood consumed. With progressive industrialization it is estimated that the consumption of in­ dustrial wood, which now amounts to about 10 million cubic m etres, will be more than 16 million cubic metres by 1975 [2] . The greater part of industrial wood consumption in India is for the following end uses:

(a) Building material: this includes timber and plywood used for housing, non-residential constructions and rural uses. (b) Mining: this includes timber used for pit props, sleepers and construction. (c) Transport and communications: the major utilization is for rail­ way sleepers, ship and boat building, power, telephone and telegraph poles, railway coaches, wagons, trucks, boxes and carts. (d) Wood-working industry: the major consumption is for furniture, textile-m ill accessories, pencils, battery separators, tool handles and other miscellaneous items such as toys, sports goods, shoe-lasts and h e e ls . (e) Packaging excluding tea-chest plywood. (f) Pulp and paper. (g ) Rayon. (h) Matches.

Table IV gives a summary of the present and potential requirement of industrial wood by major groups from 1960 to 1975 [2] . Table V lists the different species of timber commonly used for these pu rposes.

3.2. Utilization of bamboo

Industrial use of bamboo for paper manufacture accounts for nearly 17.6%, non-industrial uses accounting for the remaining 82.4%. Among the major non-industrial uses are housebuilding, bridges, reinforcement INDIA

TABLE IV. SUMMARY OF PRESENT AND POTENTIAL REQUIREMENTS OF INDUSTRIAL WOOD BY MAJOR GROUPS FROM 1960-1975

In thousands of cubic metres

C a te g o r ie s 19 60 1 9 6 5 19 7 0 1 9 7 5

1. Building M aterial

(a) Timber:

H o u sin g 1 8 0 0 2 1 5 0 2 5 0 0 3 200

Non-residential constructions 300 350 400 500

R u ra l uses 600 700 800 1 1 0 0

Total Building 2 700 3 200 3 700 4 800

(b) Plywood and boards:

Com m ercial plywood 83 1 7 0 330 500

Fibre board 28 7 1 1 4 2 2 1 2

Particle board - 28 5 7 1 4 2

Total plywood and boards I l l 269 5 2 9 8 5 4

2 . M in in g 660 790 1 0 6 0 1 3 2 0

3 . Transport and communications 1 7 0 0 2 0 0 0 2 1 0 0 1 8 0 0

4 . W ood-working industry 690 840 1 0 2 0 1 2 4 0

5 . Packaging excluding tea-chest plywood 620 1 0 1 0 1 3 4 0 1 9 0 0

Tea-chest plywood 1 0 4 1 1 1 1 2 2 1 3 3

72 4 1 1 2 1 1 4 6 2 2 0 3 3

6. Pulp, paper and rayon 5 7 1 7 0 3 5 4 1 5 6 0

7 . M a tc h e s 1 7 1 2 69 3 1 1 36 8

Total : Major requirements 6 8 13 8 659 1 0 5 3 6 1 3 9 7 5

Minor requirements 1 0 2 0 1 2 9 9 1 5 8 0 2 0 9 6

(Cottage Industries, handicraft, etc. s 1 5 % o f t o t a l)

Grand total 7 833 9 9 5 8 1 2 1 1 6 1 6 0 7 1 238 IYA

TABLE V. INDIAN WOOD SPECIES FOR INDUSTRAL USES

Categories Properties required Species of wood in common use

1. Building materials Strength, durability, Teak, deodar(Cedrus deodara), sal, steadiness, hardness babul (Acacia arabica), sissoo (Dalbergia sissoo), chir (Pinus longifolia)

2, Transport and Strength, durability, Teak, sal (Shorea robusta), sissoo, communications length, straightness deodar

3. Wood-working industry: Appearance, lightness, Teak, ebony, sissoo, Indian rose- strength, freedom from wood, walnut Joinery and cabinet cracking, splitting and making, furniture w a rp in g

4. Packaging Lightness, ease of Fir, spruce, chir, mango w o r k in g

5. Match industry Straightness of grain, Semai (Bombax malabaricum), pa pi ta good fissility, freedom (Sterculia campanulata) fr o m knots

6 . Sporting requisites Long-fibred straight Indian oaks, maple, walnut, yew, grain and free from ash d e fe c t s

7. Toys Fine texture, Haldu (Adina cordifolia), teak, appearance, colour deodar, sandalwood

8 . Plywood - Hollock (Terminalia myriocarpa), hollong (Dipterocarpus macrocarpus), gurjun (Dipterocarpus spp), vellapine (Vateria indica), mango (Mangifera indica), w a ln u t INDIA 239

TABLE VI. PRODUCTION AND CONSUMPTION OF BAMBOO BY END USES, INDIA (1953-55)

Q u a n t it y Quantity air dry Percentage C a t e g o r y in (thousand tonnes) o f t o t a l m illio n s

Construction 1 3 7 . 6 55 0 3 5 . 2

R u ral uses 1 1 6 . 2 4 6 5 2 9 .8

P a c k a g in g 3 0 .2 1 2 1 7 . 7

Pulp manufacture 6 8 .9 2 76 1 7 . 6

Other end uses 3 7 . 8 1 5 1 9 . 7

T o t a l 3 9 0 .7 1 5 6 3 1 0 0 . 0

of river embankments, scaffolding, agricultural uses such as bamboo baskets, carrying poles, tool-handles, bamboo furniture, packaging con­ tainers, etc. The consumption of bamboo for the varioiis end uses is given in Table VI [2] .

4. WORK ON POLYMER-CONTAINING FIBROUS MATERIALS IN INDIA

Work on wood-polymer combinations is under way at the Isotope Division, Trombay, to study the feasibility of producing these combinations from indigenously available wood species and monomers and other additives, and to gain first-hand experience of the various techniques before taking up the design of a pilot-plant-scale irradiator. In selecting the wood species, lighter, cheaper and less durable varieties are given more attention, so that the almost unlimited stock of these woods could be made to supple­ ment the fast dwindling stock of the naturally durable and expensive timbers such as teak. Extensive work has been reported by earlier workers on the vinyl and acrylate systems [8-10] and it has been concluded in general that wood- polymer combinations with improved properties could be obtained from suit­ able wood species by using radiation polymerization. Work on these systems was therefore limited to checking their compatibility with Indian wood varieties and investigating the possibility of obtaining further improvements by addition of different plasticizers. Styrene systems have so far received comparatively less attention in spite of the low cost of the monomer. This has been due to the rather high radiation doses required to polymerize styrene [8] . We have per­ formed detailed studies on systems containing styrene, various plasticizers and catalysts. Comparative studies of the thermocatalytic [11] and radi­ ation techniques have also been carried out to ascertain the optimum con­ ditions for the production of wood-polymer combinations with styrene. A 2 4 0 IYA technique based on preheating the impregnated sample in the absence of a catalyst prior to irradiation has been found to reduce the radiation dose required for complete polymerization. Partially polymerized styrene in carbon tetrachloride solution was tried as imprégnant with completion of the polymerization by radiation, since this process appeared to be possible at a substantially reduced radiation dose. Heat evolution in the sample during polymerization was also expected to be less. The techniques based on thermal-cum-radiation treatment and the use of partially polymerized styrene avoid the use of free radical catalysts which are expensive and are likely to introduce serious problems in large-scale handling [12] .

4.1. Experimental

(a) Chemicals: Styrene monomer (technical grade supplied by M/s. Polychem Lim ited, India) was purified by repeatedly washing with dilute alkali to remove any added inhibitor, drying and distilling under reduced pressure. A comparison with the reagent as received from the manufacturer, however, did not show any appreciable difference in the total dose required for poly­ merization or the time taken for thermo-catalytic polymerization. Partially polymerized styrene and styrene-plasticizer mixtures were prepared by heating these for 14-18 hours in an air oven at 90-100°C until a viscous s e m i-s o lid resu lted . Im pregn ation was c a rrie d out with 120 and 200% wt./vol. solutions of these monomers in carbon tetrachloride. Methyl­ methacrylate, vinyl acetate, dehydrated castor oil and benzoyl peroxide were obtained from the Regional Research Laboratory, Hyderabad, and used without further purification. The other plasticizers used, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, and diisooctyl phthalate, all of technical grade, were supplied by M/s. Indo Nippon Chemical Company, Bombay. (b) Wood specimens: In the experiments for establishing the compatibility of Indian wood species for wood-polymer combinations with methylmethacry­ late, vinyl acetate, etc., samples with the dimensions 6 in. X 4 in. X| in., 7 in. X 5 in. X ^in. and 4 in. X 3 in. X f in. were treated depending on the requirements for different test specimens. For the comparative studies of different polymerization techniques with styrene systems f in. X l£ in. cylindrical specimens suitable for comparative measurements of com­ pressive yield strength parallel to the grain were used. (c) Preliminary studies: As a first stage, polymerization studies were carried out with the various monomer systems outside wood. Samples sealed in pyrex glass containers were given thermal and/or radiation treatment to determine the conditions for giving a hard, solid product. (d) Impregnation of wood samples: The wood specimens were first seasoned in a vacuum oven for 24 hours at 50°C. Since the specimens were small in size, impregnation was carried out by a full vacuum atmospheric pressure cycle. The samples were evacuated for 2 hours at less than 1 mmHg, the monomer added and the system released to atmosphere as soon as the samples had absorbed enough monomer to sink below the surface. The soaking was continued for another hour. A system is now under design for impregnation under pressure for the more viscous mixtures and for more refractory wood types. The samples for radiation polymerization were sealed in a polythene wrapper and those for thermo-catalytic studies were sealed in pyrex glass tubes. INDIA 241

(e) Polymerization: Irradiation at different dose rates was carried out in the early stages of our programme in the two Canadian Gammacells, models 200 and 220 (dose rates 0.9 Mrad/h and 0.34 Mrad/h, respectively). Since the dose rates in the Canadian cells were considered rather high, subsequent work was carried out mostly in Gamma Chambers 900 and 300 (dose rates 0.13 and 0.30 Mrad/h, respectively), designed and fabri­ cated at the Isotope Division of the Bhabha Atomic Research Centre, India. In thermo-catalytic studies 0.2% wt./vol. of benzoyl peroxide was used as the free radical catalyst [9] . In a few experiments a mixture of 0.2% wt./vol. benzoyl peroxide and 0.1% wt./vol. dimethyl aniline were used, but this did not show any significant reduction in the time taken to complete the polymerization, as compared with the pure catalyst. The heating was carried out in an air oven at temperatures ranging from 70 to 110°C. (f) Post polymerization treatment: The samples after polymerization were stripped of the unreacted monomer by pumping in a vacuum oven at 50°C until constant weight. The percentage conversion and the polymer loading were calculated in conformity with the general practice as follows:

Weight of dry sample after polymerization Weight of dry and re m o v a l o f bare sample unreacted monomer % conversion = X 100 Weight of sample Weight of dry just after bare sample polymerization

Weight of dry Weight of dry sample after bare sample polymerization % p o ly m er loading =------X 100 Weight of dry bare sample

(g) Testing methods: ASTM methods for the testing of rigid plastics as adopted by Feibush [10] were used in comparing the physical properties of treated and untreated samples. Compressive yield strength, Brinnel hardness, resilience, abrasion resistance and dimensional stability were thus compared.

4.2. Results and discussion

Table VII gives the results of studies relating to the dependence of the degree of polymerization on the total dose received for the different Indian wood-monomer combinations tried. The effect of dose rate on this factor studied for vellapine-methylmethacrylate combination is incorpo­ rated in this table. The observations follow the same trend indicated by previous workers in their studies on similar wood varieties. It was observed that the total dose required for complete polymerization increased with increasing radiation dose rate. Table VIII presents data regarding the physical properties of treated and untreated specimens. It was found 242 IYA

TABLE VII. EFFECT OF DOSE ONPERCENTAGE CONVERSION OF MONOMERS IN WOOD SAMPLES

„ . . . r Dose rate Total dose P e r c e n ta g e Description of system (Mrad/h) (M ra d ) co n v e r s io n

1. Vellapine - MMA(a) 0.9 0 .4 5 3 7 . 2

0 .9 6 2 .6

1 . 3 5 6 0 .4

1 . 8 9 2 . 1

2 .2 5 9 2 .8

2 . 7 9 8 .0

2. Vellapine - MMA^ 0.34 0 .3 4 3 8 .8

0 . 6 8 7 3 . 1

1 . 0 2 5 6 .2

1 . 1 9 6 8 .4

1 . 3 6 8 0 .4

3. Vellapine - MMA 0.13 0 . 3 1 3 1 . 5

0 .5 8 5 2 .3

0 .9 3 7 9 .6

1 . 2 9 3 . 4

1 . 4 9 5 . 7

4. Vellapine - VA(a) 0.4 0 . 2 2 8 .5

' 0 . 4 3 2 .5

0 .9 3 8 .0

2 . 4 9 3 .0

3 . 2 9 8 .5

5. Teak - MMA(a) 0.9 1 . 8 4 6 .0

2 . 7 7 3 .0

4 . 5 9 2 .0

(a) Data communicated by the Chemistry Division, Bhabha Atom ic Research Centre. that the treatment improved the properties considerably, an exception being vellapine-polyvinyl acetate combination, which did not show any marked improvement in strength. The best results were obtained with methylmethacrylate in comparatively light woods such as chir, vellapine and silver oak; compressive yield strength improved by 50-100%, static bending strength by 10-50%, hardness by 300-600%, and water absorption decreased by a factor of 5. INDIA 243

TABLE VIII. PHYSICAL PROPERTIES OF TREATED AND UNTREATED WOOD SPECIMENS

Physical properties

P o ly m e r S t a t ic lo a d in g B rin n el Compressive b e n d in g System studied h ard n ess yield strength ( 1 ° ) stre n g th , B.H.N. ( k g / c m г ) fracture load (k g ) T a n g e n t ia l R a d ia l

1 . V e lla p in e N il 3 . 3 2 . 5 5 7 3 90

2 . Vellapine - PVA 75 6 . 2 - 530 1 0 2

3. Vellapine - PMMA 7 5 1 1 . 9 1 5 . 2 7 5 1 1 1 6

4 . Ebony N il 3 .6 6 3 . 1 3 4 7 3 -

5 . Ebony - PVA 42 5 .5 2 5 . 2 5 78 -

6 . Ebony - PMMA 40 6 .3 3 8 . 6 8 23 -

7 . T e a k N il 2 .4 7 - 550 12 0

8 . T e a k - P V A 1 5 2 .5 9 - 685 17 6

9 . Teak - PMMA 9 3 .4 6 - 780 140

1 0 . S ilv e r O a k N il 2 .3 4 - 488 4 7

1 1 . Silver Oak - PMMA 1 0 2 .1 8 - 5 5 1 50

1 2 . Silver Oak - PMMA 2 5 3 .2 5 - 580 54

1 3 . Silver Oak - PMMA 30 3 . 7 5 - - 62

1 4 . Silver Oak - PMMA 50 4 .6 5 - 6 1 5 74

1 5 . C h ir N il 3 . 1 2 . 3 4 5 2 76

1 6 . C h ir - P V A 4 2 3 . 9 2 . 1 4 8 4 9 1

1 7 . C h ir - P V A 1 1 0 4 . 7 2 . 8 530 10 4

1 8 . Chir - PMMA 3 7 . 5 6 . 5 ' 7 . 9 74 0 1 1 4

1 9 . Chir - PMMA 9 3 1 6 . 2 1 5 . 6 9 10 12 6

PVA - Polyvinyl acetate ; PMMA - Poly methylmethacrylate (Data 1 to 14 communicated by the Chemistry Division, Bhabha Atom ic Research Centre)

Table IX gives data on the methylmethacrylate plasticizer systems. Phthalate plasticizers were found to yield homogeneous solid products up to the concentration tested (25% wt./vol.), while dehydrated castor oil- methylmethacrylate gave milky white solids up to 30% wt. /vol. of de­ hydrated castor oil. Preliminary results in wood substrates show that whereas pure methylmethacrylate alone showed an improvement of about 70% in compressive yield strength, an equal loading of dehydrated castor oil-methylmethacrylate (20-30% wt./vol.) gave an improvement of over 244 IYA

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г. Impregnation with partially 28 polymerized (heating for 51.5 20 h) species from 120°¡o 63 wt./vol. solution in carbon tetrachloride 246 IYA

TABLE XI. COMPARISON OF THERMOCATALYTIC AND RADIATION POLYMERIZATION OF STYRENE SYSTEMS (RESULTS OBTAINED OUTSIDE WOOD)

System Treatment Observations

1. Pure styrene in glass vials Irradiation at 0.3 Mrad/h Hard, transparent solid up to 20 Mrad

2. Pure styrene in glass vials Irradiation at 0.13 Mrad/h No apparent change up to 10 Mrad

3. Pure styrene in glass vials Irradiation at 0.13 Mrad/h Hard, transparent solid up to 13 Mrad

4. Styrene-DCO (10% wt./vol. ) Irradiation at 0.13 Mrad/h Hard solid mass, m ilky up to 10 Mrad white in colour

5. Styrene-DCO (20% wt./vol.) Irradiation at 0.13 Mrad/h Hard solid mass, m ilky up to 10 Mrad white in colour

6. Styrene-DCO (30ft wt./vol.) Irradiation at 0.13 Mrad/h Hard solid mass, m ilky up to 10 Mrad white in colour

7. Styrene-DCO (35% wt./vol.) Irradiation at 0.13 Mrad/h Excess DCO was found to up to 10 Mrad remain on the top as a separate layer

8. Styrene-DMP (5 to 25% wt./vol.) Irradiation at 0.13 Mrad/h Hard, transparent solid. for 8.5 to 7.2 Mrad Tota l dose required for complete polymerization decreases slightly at the higher concentrations

9. Styrene-DEP, DBP, DOP, Irradiation at 0.13 Mrad/h Hard, transparent solid. DIoP (containing 5 to 25% for 9.2 to 8.1 Mrad Tota l dose required for of plasticizer) complete polymerization decreases slightly at the higher concentrations

10. Styrene-BPO (0.2%) Heated at 90-100*C for Hard, transparent solid about 12 hours

11. Styrene-BPO (0.2%) + DCO(20%) Heated at 90-100 ®C for M ilky white, hard solid about 30 hours

12. Styrene-BPO (0.2% ) + Phthalate Heated at 90-100*C for Soft, semi-solid plasticizeis (20%) about 10 hours

13. Styrene-BPO (0 .2% ) + Phthalate Heated at 90-100®C for Hard, transparent solid plasticizers (20%) about 15 hours

14. Styrene + Phthalate plasticizers Heated for 24 hours at 90-100eC Hard, transparent solid (5 to 20%) and then irradiated at 0.13Mrad/h up to 2.6 Mrad

15. Styrene-DCO (5 to 20%) Heated for 24 hours at 90-100 eC M ilky white, hard solid andthenirradiatedat0.13 Mrad/h up to 2.6 Mrad

DCO - Dehydrated castor oil: DMP - Dimethyl phthalate; DEP - Diethyl phthalate; DBP - Dibutyl phthalate; DOP - Dioctyl phthalate: DIoP - Diisooctyl phthalate; BPO - Benzoyl peroxide. INDIA 247

100%. Slight improvement has also been recorded for the methylmethacrylate phthalate systems over methylmethacrylate. The results are, however, inconclusive and further work is in progress. Dehydrated castor-oil-methylmethacrylate systems on heat treatment at 100°C for 24-144 hours outside wood substrates showed the formation of two distinct solid layers, the upper layer soft and brittle and the lower layer hard and opaque. Amongst the phthalate methylmethacrylate systems dioctyl phthalate-methylmethacrylate also formed two layers under the same conditions. Systems containing dimethyl phthalate, diethyl phthalate, dibutyl phthalate and methylmethacrylate, however, remained homogeneous transparent solids. Tables X and XI present data on the styrene systems. It was found that addition of plasticizers decreased the radiation dose required for complete polymerization. In wood substrates (Pinus longifolia) styrene plasticizer systems did not show any significant improvement .over wood untreated by radiation polymerization, In the thermocatalytic method pure styrene gave improvements to the extent of 50-100% over untreated wood. The addition of plasticizers in this case was ap­ parently not advantageous.

TABLE XII. EFFECT OF PREHEATING ON THE DOSE REQUIRED FOR 95% POLYMERIZATION OF STYRENE SYSTEMS

Temperature - 90-100°C Dose rate - 0. 13 Mrad/h Initiator added - None

T h e r m a l R a d ia tio n T o ta l tr e a tm e n t tre a tm e n t S y s te m M o n o m e r Plasticizer d o se t im e t im e (M ra d ) (h) (h)

1 S ty r e n e N il - 1 1 5 1 5

S ty r e n e N il 1 2 . 5 7 0 .3 9 .2

S ty r e n e N il 1 7 . 5 46 6 ..0

S ty r e n e N il 24 26 3 . 4

2 S ty r e n e D L oP - 20°Jo w t . / v o l . - 49 6 . 4

S ty r e n e N il 18 2 4 3 . 1

S ty r e n e N il 24 1 6 . 2 2 . 1

3 S ty r e n e D C O - 20°jo w t . / v o l . - 65 8 .5

S ty r e n e N il 18 26 3 . 4

S ty r e n e N il 25 2 0 .3 2 . 6

DLoP = Diisooctyl phthalate DCO = Dehydrated castor oil 248 IYA

In studies carried out with the thermal-cum-radiation process good improvement in properties was obtained with styrene. The dose required for complete polymerization varied with the time of preliminary heating. For a preliminary heating period of 12-24 hours at 90-100°C, the dose required to complete the polymerization decreased from 9.2 Mrad to 3. 4 Mrad as compared with 15 Mrad required for pure styrene, and from 6.4 Mrad for styrene-diisooctyl phthalate to 2.1 Mrad after heating for 24 hours. Table XII and Fig. 1 give data on these systems. This process also gave the best overall results with wood substrates, and an improve­ ment of 50-60% in compression yield strength was obtained for polymer loadings varying from 40-50%.

FIG .l. Effect of preheating on the dose required for polymerization of styrene systems.

5. CONCLUSION

The Indian Atomic Energy Commission has a sizable programme for production and utilization of cobalt-60. While several hundred thousand curies of this isotope are being produced in the CIRUS, megacurie quantities will be available every year for the power reactors now under construction. Adequate resources of various fibrous materials are to be found in India. To meet the need for conserving the limited resources of superior woods, a programme is under way to develop polymer-containing varieties of the cheaper types of wood. The results of the work carried out in this field so far have been encouraging, and, in particular, techniques involving thermal treatment, in the absence of catalysts, subsequently followed by radiation, seem to be promising for styrene systems. Research and development will continue with emphasis being laid on production of fibre-polym er combinations with jute, bamboo, bagasse, etc., which are available in large quantities. At present, ethylene, propylene, vinyl chloride, styrene and limited quantities of vinyl acetate are produced on an industrial scale in India. Small quantities of methylmethacrylate are also available from acrylic scrap. The construction of new petrochemical factories at Visakhapatnam and Mettur and the expansion of existing ones will increase the availability of monomers. INDIA 249

ACKNOWLEDGEMENTS

The work reported here was carried out by a team of scientists in the Isotope Division. The author is grateful to them for their enthusiastic co-operation. The author also wishes to thank Dr. J.S. Aggarwal, Deputy Director, Regional Research Laboratory, Hyderabad, for valuable dis­ cussions and for the generous supply of chemicals.

REFERENCES

[1] TROTTER, H ., Manual of Indian Forest Utilisation, Oxford University Press (1940) 115. [2] VENKATARAMANY, P., Timber Trends and Prospects in India, 1960-1975, The Ministry of Food and Agriculture, Department of Agriculture, Government of India (1962). [3] TIMES OF INDIA, Times of India Handbook for 1967, Times of India and Allied Publications, Bombay (1967). [4] COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH, The W ealthOf India - Industrial Products. Part II, Council of Scientific and Industrial Research, India (1951) 196-206. [5] FOREST RESEARCH INSTITUTE, 100 Years Of Indian Forestry (1861-1961) II, Forest Research Institute, Dehra Dun, India.

[ 6 ] INDIAN STANDARDS INSTITUTION, Guide for Installation of Pressure Impregnation Plants for Timber, IS: 2683-1966, Indian Standards Institution, New Delhi, [7] INDIAN STANDARDS INSTITUTION, Classification of Com m ercial Timbers and Their Zonal Distribution, IS: 399-1963, Indian Standards Institution, New Delhi.

[ 8 ] KENT, J.A. e ta l., Preparation of Wood-Plastic Combinations Using Gamma Radiation to Induced Poly­ merization. USAEC Rep. ORO-2945-7 (1967). [9] KENT, J.A. et a l., Modification of Wood with Polymers Formed by High Energy Radiation, USAEC Rep. TID-18907 (1963). [10] FEIBUSH, A .M ., Research on Application of Radiation-Induced Reactions in Gases, USAEC Rep. NYO-3334-1 (1965). [11] MEYER, J.A ., Treatment of wood-polymer systems using catalyst-heat techniques, Forest Prod. J. 15(1965) 362-65. [12] ROHM AND HAAS COMPANY, Personal communications from M/s Rohm and Haas Company, United States of Am erica. JAPAN

WOOD-PLASTIC COMPOSITES

CONTRIBUTED BY T. HIRAYAMA CENTRAL RESEARCH LABORATORY, SHOWA DENKO K .K ., OTA-KU, TOKYO, JAPAN

1. IN T R O D U C T IO N

Radiation chemistry research has made rapid progress in Japan over the last ten years, and many encouraging results have been obtained with radi­ ation polymerization and graft-polymerization as well as in other fields. Several papers on wood-plastic composites (WPC) have been published in Japanese journals, but very little work on actual applications has been reported. This general review of basic studies and studies of the application of WPC in Japan is divided into three parts: radiation methods, chemical methods (catalyst-heat treatment) and the scope of future research and development.

2. BASIC STUDIES WITH WPC IN JAPAN

2.1. Radiation method

2.1.1. Micro-structures and soluble components

Murayama [1] studied changes in the micro-structures and soluble components of -«food materials due to degradation under irradiation. The samples, the source and the measurements are described below.

Samples: (A) Cedar, Japanese cypress, beech, lauan 4 cm X 4 cm X 0. 3 cm (fibre direction). (B) Beech sapwood meal, 50-60 mesh, extracted with alcohol:benzene (1:1).

Radiation source: Van de Graaff type accelerator (1.8 MeV, 50 ц A, 2 X 105 rad/s).

Measurement: For samples (A) (a) water absorption rate, (b) swelling due to absorption of water, (c) moisture absorption rate. For samples (B) (a) moisture absorption rate, (b) soluble component in hot water, (c) soluble component in 1% NaOH, (d) soluble component in 0.36%, 14.4% HC1.

250 JAPAN 251

X-ray diffraction, infra-red absorption spectra, and deuterium dis­ placement were also determined for the extraction residue of sample (B).

R esu lts

(1) No drastic change was observed in water absorption rate, moisture absorption rate, or swelling due to water and moisture absorption after irradiation with an electron beam of 106- 5 X 108 rad. (2) A rapid increase in the amount of extractable matter was observed at about 5 X 107 rad in the relationship between dose rate and the amount of matter extractable from wood meal irradiated with the electron beam. (3) The amount of matter extracted increased with time until at 72 hours the relationship was nearly linear. (4) This increase in extractable matter was due to the dissolution of the non-crystalline part and to disintegration of the cellulose caused by degrada­ tion of the m icro-crystalline structures. (5) No change in lattice constants was observed with X-ray diffraction studies. (6) No change was observed in the X-ray diffraction and i. r. spectra of the irradiated wood meal (below 5 X 108 rad), but a change was found in D2O uptake and this relationship was linear. (7) The reason for the above may be that substitution reaction arid absorption were affected by minute changes in the poorly ordered amorphous region which could not be observed with X-ray diffraction or i. r. spectra. (8) A series of uptake data under specified conditions can be a relative measure of crystallinity. (9) Moisture absorption rate tended to be small for samples which give large crystal/non-crystal ratios obtained from X-ray diffraction patterns. Equilibrium moisture content also decreased with increasing ratio. (10) The major cause of changes in the properties of irradiated wood meal was the disintegration of the cellulose, which is the main skeletal component of wood materials.

2. 1.2. Formation of free radicals

Murayama et al. [2] further studied the formation of free radicals. ESR observations were made on wood and wood meal irradiated with 60Co gamma-rays (dose rate: 2.2 X 104 rad/h, total dose: 0.5 - 1.0 Mrad). Radical concentration decreased rapidly in the first 4-5 hours in wood and cellulose irradiated in air (e. g. the number of spins became less than half of the original concentration of approximately 1-2 X 1018 spin/g). When 1500- 3000 cellulose units were assumed to be present in one chain, the number of spins corresponded to 1-2 free radicals in one cellulose molecule. This indicated that unpaired electrons were located at the ends of the m olecu le. Takashima et al. [3] also studied this problem on irradiated Japanese cypress, Formosan cypress, cedar and lauan. They mentioned that dis­ integration took place because of degradation of the cellulose chain under 1 X 10s rad irradiation. 252 HIRAYAMA

FIG .l. Experimental procedure.

2. 1.3. Radiation graft-copolymerization

Murayama et al. [4] also studied radiation graft-copolymerization of wood. They gave the name ' Plamo-wood' to the material obtained by irradiating wood impregnated with monomer. They classified the materials into four groups (Figs 1 and 2):

(1) Wood with graft-copolymer only; (2) Wood with both graft-copolymer and homopolymer; (3) Wood with polymer on both the surface of the m icellar cavity and the surface of the intercellular cavity (prepared in the presence of catalyst at an elevated temperature by the use of a polar solvent; and (4) Wood with polymer on the surface of the intercellular cavity only (prepared in the presence of catalyst at an elevated temperature by the use of a non-polar solvent). JAPAN 253

Their discussion includes the relationship between conditions of treat­ ment and yield, grafted polymer on the surface of the m icellar cavity with respect to moisture absorption and swelling of treated wood, homopolymer effects, relationship between the active site of reaction and the active centre of moisture absorption in wood, and mechanical and chemical properties.

Samples: various tree species. Monomer used: various monomers, mixtures also employed. Radiation source: 60Co (450 Ci, 2. 3 X 104 rad/h); Van de Graaff type accelerator (1. 8 MeV, 50 цА, 2. 5 X 105 rad /s).

R esu lts

Measuring the expansion rate of wood can provide an indication of the degree of chemical change on the surface of the m icellar cavity in wood. (1) The specific gravity of W PC's with the same polymer content was © > (з)> (2) > Çî) (Fig.3) and the expansion ratio was © > © > © > © (Fig.4). Therefore, it was possible to determine on which su-rface of the m icellar cavity or intercellular cavity polymerization took place. In wood of type© polymerization also took place on the surface of the m icellar cavity, but nearly all of this polymer could be extracted with solvents and the product was therefore different from ©. (2) The relationship between graft rate and expansion rate of the surface of the m icellar cavity was linear. (3) Even with the same graft rate, moisture absorption ratio and swelling ratio (ratio of treated to untreated wood with respect to moisture absorption value and swelling value) were different (moisture absorption ratio > swelling ratio) (Fig. 5). This is due, on the one hand, to the fact that the branched polymer combined with several active sites of the surface of the m icellar cavity reduces the degree of swelling, and, on the other hand, to the continued absorption of water molecules by the unchanged hydroxyl group. (4) Anti-swelling efficiency (A .E .): 1. Graft rate and A.E. are related to each other. 2. In terms of A. E. © > © > © > © (Fig. 6). With type©, relationship between A.E. and polymer content is linear in the region where the latter is 5 -40%. (max. A. E. : ~ 90%). With type©, the slope changes around 20% polymer content. This is due to the existence of homopolymer which does not contribute to the swelling property. 254 HIRAYAMA

F1G.3. Relationship between polymer content and density. (¿) Wood holding graft copolymer only. (2) Wood holding both graft copolymer and homopolymer.

( 3 ^ Wood holding polymer on both surface of m icellar cavity and surface of intercellular cavity (prepared in presence of catalyst under elevated temperature with use of polar solvent). (J) Wood holding polymer on surface of intercellular cavity only (prepared in presence of catalyst under elevated temperature with use of non-polar solvent).

FIG.4. Relationship between polymer content and expansion in tangential direction.

FIG.5. Relationship between graft ratio and moisture absorption and swelling ratios.

FIG. 6 . Relationship between polymer content and A.E. (symbols as in Fig.3).

Samples of type (3) show less than half the A .E. displayed by those of type (T) . Practically no anti-swelling efficiency was observed with type ©below a polymer content of 40%. (5) Anti-shrink efficiency (A. S. E. ): In terms of A. S. E. © > © > ® >©. From the above results Murayama et al. concluded that the active groups on the surface of the m icellar cavity which contribute to wood JAPAN 255 swelling are also active centres of reaction in the graft-polymerization of wood-vinyl type monomers. The tensile strength depends on the polymer content. At 100%, the tensile strength was approximately three times that of wood irradiated at 70°C with a total dose of 1 X 106 rad.

Dn - D, A. E. = - s------X 100 ü o w h ere : D0 = expansion rate of untreated wood test piece, and Di = expansion rate of treated wood test piece.

Lo - L о n = —^— ¿x loo i L о

Dn - D„ A .S .E . = — - X 100 о w here: D0 = shrinkage rate of untreated wood test piece, and D 2 = shrinkage rate of treated wood test piece.

D„ = Ьзт Ls X 100 5 w here: L 2 = length of wood test piece after it had been kept at 20°C and 65% r.h. for one week, L 3 = length of wood test piece after it had been kept at 25° С and 98% r.h. for one week, and L 5 = length of wood test piece after it had been kept at 105°C for one week.

2.1.4. Radiation-induced styrene polymerization

Nakatsuka et al. and Hirai et al. [5, 6 ] carried out radiation-induced polymerization of styrene in wood and studied the physical properties of the composites. They compared the differences between wood types from deciduous and coniferous trees.

(a) Irradiation of wood

(i) 60Co gamma rays: No change in the compression strength parallel to the longitudinal direction and/or in the modulus of elasticity was found for cedar, Japanese cypress, Formosan cypress and lauan up to 1 X 108 rad. (ii) E lectro n beam : C edar and lauan w e re degraded by irra d ia tio n o f 950 M rad so that they could be easily broken under the finger tips.

(b) W PC

(i) Lauan-styrene system

Compression strength parallel to the longitudinal direction: strength increased with increase of polymer content. Maximum value of the 256 HIRAYAMA

strength at 50% content was 1.6-fold, and at 100% content and 150% content, it was 1,8-fold and 1.9-fold, respectively.

Moisture absorption rate (20°C, 95% r.h., 25 days): untreated wood ...... 23% 8% polym er content . . 17% 50% polymer content . 10% 100% p o ly m e r content 7%

(ii) Difference of tree species for styrene polymerization

Woods from deciduous trees (birch, Japanese judas, beech, magnolia, lauan and zelkova) showed no drastic differences. Heartwood from such conifers as cedar, Formosan cypress, arborvitae or Japanese cypress allowed no polymerization or only a low polymerization rate. Sapwood from cedar, Japanese cypress and Sawara cypress allowed a high rate of polymerization. Methanol extraction as a preparatory treatment improved an otherwise low rate of polymerization in cedar heartwood. The rate decreased when methanol extract from cedar heartwood was added to the styrene.

2.2. Chemical method (catalyst-heat treatment)

Goto et al. [7] attempted to improve bamboo by catalyzed thermal polymerization. Styrene and MMA, containing 0. 2 - 1. 0% of benzoyl peroxide, were impregnated under low pressure into bamboo (Phyllostachys pubescens Nazel) with the following dimensions: 1.2 cm (longitudinal) X 1 cm (tangential) X 0. 3 cm (radial). Polymerization was carried out at 68°C after the test piece had been wrapped in aluminium foil. Some examples of the results with a styrene polymer content in the range 4-20% are as follows: Water absorption decreased with increasing polymer content. Minimum swelling rate was observed at a polymer content of 5%. Bending strength was constant above a polymer content of 10% (1.4 times that of untreated material). Modulus of elasticity and bending strength at elastic limit increased propor­ tionally to polymer content (modulus of elasticity was 1. 3-fold and bending strength at elastic limit was 1. 7-fold at a polymer content of 18%. ) Taneda [8] studied graft-polymerization of styrene to wood fibres at 70°C, using K2S20 8, Ce(N03)4, 2NH4NOs and Щ 0 2 as initiators. These chemicals are believed to be effective in graft-polymerization to cellulose and several kinds of non-ionic, anionic and cationic em ulsifiers. Graft rate increased when 0.45% H 2O2 and 0. 1 - 2% emulsifier were added and heated for 5 hours. Among the emulsifiers tested, the cation type yielded the best graft rate (30-280%). The following observations were made on the physical properties of treated wood fibre: Equilibrium moisture content decreased with increasing graft rate, being about one third at 100% graft rate. Fibreboard was made from treated and untreated fibres to test their physical properties. The bending strength of fibreboard from treated fibres was 2-3 times that of untreated. The water absorption rate was 1 /20, the equilibrium moisture content was 1/2-1/3, and the friction index l/5. Ohashi et al. [9] studied the polymerization of monomer impregnated' into wood in the presence of a catalyst at normal temperature and pressure, JAPAN 257 or at lower pressure. They impregnated aqueous solutions of methyl acry­ late monomers and/or methylmethacrylate monomers where the valency of the methyl is two or higher, along with an aqueous solution of the polym eri­ zation catalyst to form a water-insoluble polymer in the spaces of the wood stru ctu re.

D eg ree o f sh rin kage: 30%. Water absorption: approximately 76% of untreated material. Compression strength: 1. 7-fold that of untreated. Tensile strength: 1. 6-fold that of untreated. Shearing strength and differences of shrinkage and strength due to anisotropy of wood were also improved.

Examples of catalyst: ammonium persulphate, potassium persulphate, sodium persulphate, sodium perborate, hydrogen peroxide, barium peroxide, ammonium perchlorate and barium perchlorate.

3. STUDIES OF THE APPLICATION OF WPC IN JAPAN

3.1. Radiation method

Yamana and Murayama [10] studied the application of WPC to the fabrication of railroad ties. They expected improved strength (especially nail-holding power and prevention of wear by rails), utilization of softwood, improvement in water resistance, decay and rot resistance, and increased w eight.

Sam ples: Japanese cypress, beech, 100 mm X 200 mm X 300 mm. M on om er: MMA + styrene + AIBN (Azobis-isobutyronitrile) 0. 1-1%, 25% of MeOH was also added to the above. Evacuation: 700-730 m m Hg, 60 m in. P r e s s u r e : 5-10 kg/cm 2, 30 min. Irradiation: dose rate 4 X 104 rad/h, total dose 2 X 106 rad. H eating: 5 h at 65°C after irradiation.

Japanese cypress cracked. Nail-holding power was inadequate. Murayama's work [11] consisted in inducing flame retarding properties into wood and wood substances. Table I shows the results for WPC. The following four experiments were performed to obtain flame retarding material (called Flamo-wood) without damaging the improved properties of WPC (Plamo-wood).

(1) Wood material was first treated with commercial flame retardant for wood and was then processed in the normal way for preparation of WPC. (2) Wood material was treated in the normal way with flame retarding vinyl-type monomer. (3) Material was treated in the normal way with vinyl-type monomer containing flame retardant. (4) Reactive flame retardant was mixed beforehand with vinyl-type monomer so that the retardant would enter the main and branch chains of the polymer. 258 HI RAY AM A

TABLE I. FLAME-RETARDING WPC

T r e a tm e n t ( 1 ) ( 2 ) (3) (4)

Total polymer formation 4 5 . 6 2 0 .3 4 6 .7 4 8 .3 efficiency {°jo)

Amount of flame-retardant (%) 1 9 . 5 2 0 .3 1 8 .3 1 4 . 3

Extraction rate after one month 1 0 . 2 1 . 2 6 . 8 4 . 1 in w a te r {%

Extraction rate after 10 h in 2 5 .3 1 3 . 4 2 1 . 7 2 2 .4 hot benzene C#>)

Inflammation time 5 m in 20 s 1 m in 1 2 s 5 m in 40 s 6 m i n l 2 s

M echanical properties in +++ + ++ +++ comparison with untreated wood

(1) Wood m aterial is first treated with com m ercial ñam e retardant for wood and then receives the normal treatment to prepare WPC. (2) Wood material is normally treated with flame-retarding vinyl-type monomer. (3) M aterial is normally treated with vinyl-type monomer containing flam e retardant. (4) Reactive flame retardant is mixed beforehand into vinyl-type monomer so that the retardant enters into the main and branch chains of the polymer.

Horioka, Osaka and Haraguchi [12] studied changes in the A. S. E. ofbeech, birch and Yezo spruce (30 mm X 30 mm X 5 mm) by using radiation grafting treatment. The monomers included MMA and others, which were previously impregnated into the wood. They also studied the mechanical properties of treated birch and Yezo spruce (200 mm X 20 mm X 300 mm). The results are presented below:

(1) W eight in c re a s e : 60 - 80%. (2) Hardness of birch: untreated, both radial and tangential section . . . 1.5 kg/cm2; treated (weight increase 80%), radial . . . 14. 0 kg/cm2, tangential . . . 14. 3 kg/cm 2. Hardness of treated white pine (MMA) increased proportionally to total polymer content. (3) Modulus of rupture in bending: increase by 20- 40%. • (4) Shearing strength: in crea se by 75%. (5) Compression strength: increase by 60%. (6) Swelling and shrinkage: decrease to less than 20% of that of un­ treated material. Water absorption of treated pine and maple was lower than that of un­ treated . (7) Abrasion resistance: remarkable increase. JAPAN 259

(8) No inferiority without painting in comparison with painted un­ treated material, could be used as outdoor material. (9) Possible to use usual adhesives (Table II). (10) Buffing gives extremely glossy surface.

TABLE II. BONDING OF WPC(a)

Bonding strength and wood failure

D o se r a te A d h e s iv e Normal test *3 Hot and cold water (rad/h) ( k g / c m 2) test(b) (kg/cm 2)

wood failure (fy ) wood failure {%)

1 0 5 3 5 .0 7 (92 ) 3 4 .3 0 (57) U re a resin

1 0 6 3 5 .5 6 (87) 2 8 . 1 6 (64)

1 0 s 3 3 .0 2 (87) 3 0 .5 7 (76) Resolsinol resin

1 0 s 3 7 .7 3 ( 6 6 ) 2 8 .4 4 (50)

1 0 s 2 2 .1 3 (62) 2 8 . 1 4 (4 1 ) Folmaldehyde phenol re s in 1 0 6 2 7 . 7 7 (93) 2 7 .0 4 (54)

1 0 s 3 7 .0 5 (99) 2 7 .8 7 (89) Epoxy resin

1 0 6 3 1 . 7 2 ( 8 8 ) 3 1 .2 0 (1 5 )

Horioka, K., Osaka, K ., Haraguchi, T ., unpublished work, (k) Average value was obtained from 20 pieces.

3.2. Chemical method (catal.yst-heat treatment)

Miyagi and his coworkers [13, 14] prepared WPC by means of catalyzed thermal polymerization.

(1) Beech (40 cm X 5 cm X 5 cm), styrene and MMA. Temperature for polymerization: 45-70°C (70-100°C inside the wood). A longer period was required for treatment with increasing monomer quantity per unit surface area in wood. No difference was observed in bending strength of WPC prepared from beech and Japanese cherry birch by the two methods.

(2) Experiment on 100 cm X 10 cm X 10 cm wood materials with vinyl-type m onom er.

Polymerization conditions should be set according to the dimensions of the materials, the moisture content, monomer content and tree species. The optimum condition for treating the material (100 cm X 10 cm X 10 cm) was found to be the range of monomer content of 0.20 - 0.26 g/cm3 of wood.

(3) Samples of loom shuttles and golf-club heads were prepared. 260 HIRAYAMA

4. SCOPE OF RESEARCH AND DEVELOPMENT OF WPC

The preceding review was a general outline of the works on WPC published in Japan. Within the scope of the radiation method, the main stress is on the formation of radicals in wood under irradiation and changes in mechanical properties due to degradation, as well as on the polymerization of vinyl-type monomers by radiation. Catalyzed thermal polymerization processes by chemical means are being investigated. With regard to the application of WPC, much attention is paid to physical properties related to dimensional stability such as swelling due to water absorption and moisture absorption. This is because of the large seasonal humidity changes in Japan. Other mechanical properties are also discussed with a view to developing the advantages of wood and improving the defects. Some trial production batches have already been produced in Japan by both the radiation and the chemical methods, and their marketability is now being investigated. In 1966, collaborative studies on WPC between France and Japan were started. In the meeting held this year it was agreed that the French would take charge of density and fabrication studies, while Japan would investigate the dimensional stability and flame retardancy of WPC. Some promising applications for WPC are for flooring, veneer, exterior panels, sashes, furniture (both outdoor and indoor), musical instruments, sporting goods and ornaments. Loom shuttles are also being prepared for the textile industry. The main points being considered in the development of WPC are:

(1) How to reduce the cost of irradiation and/or chemical (heat- catalyst) treatment. (2) How to use cheaper monomers. The present cost of monomers in Japan is as follows:

ethylene, propylene 30 yen/kg vinyl chloride 45 styrene, butadiene 60 vinyl acetate 70 acryl nitrile 80 m ethylmethac rylate >100

(3) How to select the combination of wood and monomer'. (4) How to impart special properties in addition to dimensional stability such as flame retardancy, resistance to insects, resistance to fungus and rot, colouring, hardness, toughness and ease of fabrication, etc.

REFERENCES

[1] MURAYAMA, T ., Wood Industry, Japan 18 2 (1963) 2. [2] MURAYAMA, T. et al., 16th Annual Meeting of the Society of Wood Research, Japan, No. 365 (1966). [3] TAKASHIMA, T. etal., ibid. No.572 (1966). JAPAN 261

[4] MURAYAMA, T. et al., 13th Annual Meeting of the Society of Wood Research, N o.216 (1963); 14th Annual M eeting of the Society of Wood Research, No. 301 (1964); 13th Annual M eeting of the

Society of Polymer Science, Japan, 3F26 (1964); Proc. 6 th Conf. on Radioisotopes, A/RC-11 (1964); 15th Annual Meeting of the Society of Wood Research, Japan, N o.206 (1965); ibid. N o.207 (1065); 2nd Annual M eeting on Radioisotopes in the Physical Sciences and Industry, Japan, 20a-III-5 (1965); 14th Annual Meeting of the Society of Polymer Science, Japan, 2D08 (1965); 16th Annual M eeting of the Society of Wood Research, Japan, N o.363 (1966); ibid. No. 364 (1966); Proc. 7th Conf. on Radioisotopes, B/@ -12 (1966); 15th Annual Meeting of the Society of Polymer Science, Japan, ID11 (1966). [5J NAKATSUKA, T ., HIRAI, N. et al., 15th Annual Meeting of the Society of Wood Research, Japan, N o.208 (1965).

[ 6 ] HIRAI, N ., NAKATSUKA, T. et al. 16th Annual Meeting of the Society of Wood Research, Japan, N0.362 (1966). [7] GOTO, T . et al., 17th Annual Meeting of the Society of Wood Research, Japan, No. 120 (1967).

[ 8 ] TANEDA, K. etal., ibid. No.121 (1967). [9] OHASHI, K. et al., Japan Patent 27747 (1965). [10] YAMANA, N .. MURAYAMA, T ., 16th Annual Meeting of the Society of Wood Research, Japan, No. 366 (1966). [11] MURAYAMA, T ., 16th Annual Meeting of the Society of Polymer Science, Japan, 3B26 (1966). [12] HORIOKA, K ., Radioisotopes, JapanlJ3 7 (1967) 27; HORIOKA, K ., OSADA, К., HARAGUCHI, T ., unpublished. [13] MIYAG1, I. eta l., 16th Annual Meeting of the Society of Polymer Science, Japan, 3B27 (1967). [14] MIYAGI, I. e ta l., 11th Japan Congress on Materials Research, 332 (1967). RADIATION GRAFTING OF VINYL COMONOMERS TO WOOD

CONTRIBUTED BY T. MURAYAMA GOVERNMENT FOREST EXPERIMENT STATION, MINISTRY OF AGRICULTURE AND FORESTRY, TOKYO, JAPAN

The author has been studying graft-copolymerization of wood materials and the preparation of WPC by radiation since 1961 and has submitted 15 reports on the subject to the academic societies concerned. He named this type of material 'Plamo-wood' and studied its mechanical properties to determine possible new applications. It became apparent that it is most desirable to reduce the total dosage to a minimum and this problem must be solved first before successful commercialization can be realized. The total dosage was reduced to about 1 /3 to 1/5 (0. 2 to 0. 5 Mrad) of that re­ quired for the manufacture of the WPC commercialized in the United States of America, the essentials of whicji are given below. Two methods of manufacturing WPC have been reported in the United States, one being thé radiation method, established by the AEC in 1960, and the other the chemical method (making use of a polymerization initiator) which was proposed by J. A. M e ÿ e r et al. in 1966. However, the specimens used with the latter method are limited in size. The author examined these two methods and compared them with each other. As pointed out by Harmison, the use of large-sized specimens in the polymerization initiator method will give rise to the following problems, which may lead to deterioration in the properties of the wood material.

(1) A temperature gradient will be steepened because of the low heat conductivity of wood material. (2) High temperature and high pressure during polymerization by this method have a bad effect on the internal structure of wood.

It is desirable, on the other hand, to keep the total dosage to a minimum in the radiation method, although inherent mechanical properties of wood do not deteriorate under 1 Mrad of irradiation. The author performed experiments on the following selected subjects:

(1) Reducing the quantity of initiator used in the polymerization initiator method to 1/10 to 1/20 of that used in ordinary methods to remove as many of the above-mentioned defects involved in the initiator method as possible, that is to say, lowering the heat of polymerization and the pressure during polymerization together with the extent to which impurities are mixed; the re-use of recovered monomers-which remain unreacted was also studied. (2) Controlling polymerization speed by controlling atmosphere and temperature during irradiation. (3) Examination of monomer combination and its ratio and how to prepare a treating liquid to which a bridging agent is added.

262 JAPAN 263

VOLUME OF THE NATURAL CELLULOSE COMPOSITION

FIG .l. Relation between apparent specific gravity in g / c m 3 and volume of the natural cellulose composition.

F I G . 2 . Theoretical rate of impregnation calculated from F ig.l.

(4) Controlling every condition so as to keep the temperature inside the wood below 70°C. (5) Capability of treating material at any water content, that is, treating it in the process before monomer impregnation at a water content of less than 22%. (6) Keeping the total dosage below 0. 2 to 0. 5 Mrad.

Figure I shows the relation between apparent specific gravity in g/cm3 and volume of the natural cellulose composition, while Fig. 2 shows a theoret­ ical rate of impregnation calculated from Fig. 1. REPUBLIC OF KOREA

CONTRIBUTED BY CHWA-KYUNG SUNG OFFICE OF ATOMIC ENERGY, SEOUL, REPUBLIC OF KOREA

1. G E N E R A L

In describing the present status of composite materials made from fibrous materials and synthetic polymers, it should first be mentioned that Korea produces almost no polymer-wood combinations. However, Korea has been very active in the production of various resin-fibrous material combinations that mainly employ thermosetting resins as binding agents to improve the quality of woods'and other fibrous materials. Plywood, chip board, hard board and straw board are some examples. Korean forest resources are not sufficient to meet industrial needs. Only a small amount of domestic pine timber is used for ground pulp pro­ duction. However, plywood production, which started some ten years ago, has increased to where domestic consumption is now fully supplied and annual exports are now worth more than 40 million US dollars. Although whole log timber for the industry is imported, urea and formalin for adhe­ sives are produced domestically. To develop an effective means for using waste lumber, chip board, fibre board and hard board have been produced since 1962 and the production of straw board has been started as a means of utilizing agricultural wastes. The history of the plastics industry is also short, but rapid developments are in progress. Condensation and fabrication of thermosetting resins such as amino plastics have been successfully carried out for nearly ten years and the production capacity is gradually increasing. In the field of thermo­ plastics, fabrication is mainly carried out with imported polymers such as polyvinyl chloride, polyethylene, polystyrene or cellulose acetate. However, plants producing polyvinyl chloride have been completed and the annual production is expected to be 13 000 t from 1968 on. Furthermore, plans for the construction of a comprehensive petrochemical industry, which is one of the major projects of the second five year plan starting in 1967, have been completed. These plans call for an additional polyvinyl chloride production of 23 000 t, a polyethylene production of 20 000 t and a polystyrene pro­ duction of 12 000 t by 1970 or 1971. It should finally be mentioned that emulsion polymerization of vinyl acetate and acrylics and plate moulding by bulk polymerization of methylmethacrylate are successfully carried out with imported monomers. Research on polymerization is being carried out at several universities and at the National Industrial Research Institute. At the Atomic Energy Research Institute, radiation polymerization and grafting are being studied. However, research on wood-plastic composite material cannot be said to be intensive. A large research group from several institutes,, including the Atomic Energy Research Institute and the Korean Institute o? Science and Technology, which is to specialize in industrial research and development and w ill commence operation by the end of 1968 after the completion of its building, plans to enter this field comprehensively.

264 REPUBLIC OF KOREA 265

2. RESOURCES OF MATERIALS TO BE TREATED

The total accumulation of wood resources in Korea being estimated as about sixty million cubic metres, the domestic supply of lumber lags far behind the dem and. Only 110 000 t o f lum ber, about 90 000 t o f which is for ground pulp and about 20 000 t for semi-chemical pulp, are being used for pulp production. This quantity only forms part of the domestic con­ sumption of ground pulp, and 150 000 t of this m aterial have to be imported. All pulp other than ground pulp is, of course, imported. Most of the lumber for pulp production is of coniferous origin, especially red pine, but the quantity of poplar is gradually increasing as a recent trend. The quantity of imported log timber, mainly lauan from South-East Asia, is increasing so rapidly that imports reached 1 082 000 t in 1966. This wood is used mostly for plywood production, but also for flat and square timber. Imported lauan in Korea could consequently be considered as the largest source of raw material for wood-plastic composites in quantity; however, there are other types of wood to be studied which have been used for making furniture, handicraft articles and other products, though large amounts have already been taken over for the production of boards, plywood and plastics. Persimmon; maple and paulownia are some examples. Bamboo is also grown in the southern part of Korea, but the quantity is small. The next possible source of fibrous material other than wood is agri­ cultural wastes. Rice straw, 5-6 million tons of which are produced annually and utilized mainly for roofing material, feed, fuel and composite ihanure, and 2 million tons of barley straw might constitute a large poten­ tial source of raw material, although board production has been started and pulp production is planned from rice straw. More than 300 000 t of rice hulls are produced annually, and this may also be considered as a raw m a te ria l. Two other types of fibrous material should be mentioned: The rush, Cyperus exaltatus Retz, provides material for handicrafts, its skin is utilized for making bags and matting, the soft inner part of its stem for slippers and the leaves for bags and cushions. The second material is skin fibre from the stem of the kutsu bean, Pueraria thunbergiana Benth, which is used successfully, incorporated with paper, for making decorative wall p aper.

3. BOARD, ITS PRODUCTION AND PROPERTIES

Plywood production in Korea is, as mentioned above, very intensive. However, this is outside the scope of this meeting. One hard-board plant using lumber waste as raw material and having a production capacity of 20 t per day has been in operation since 1962. The product has been employed for flooring, the interiors of buildings and radio and television parts. Semi-hard board with a lower specific gravity than hard board is mainly used for acoustic tiles. It is expected that the total demand for hard board in 1971 w ill be around 30 000 t. The plant is about to expand its production capacity to 50 t per day. The physical properties of this product are as follows: 234 kg/cm2 flexural strength, 0. 98 specific gravity and 6.4% moisture content. 266 CHWA-KUNG SUNG

Straw board has a specific gravity of 0. 6 - 0. 7, 150- 200 kg/cm2 flexural strength and 7-19% moisture content. Particle or chip board with around 400 kg/cm2 flexural strength is also produced with waste timber from plywood plants. Urea resin is used exclusively as the binder or adhesive for the pro­ duction of the above-mentioned boards except for a small quantity of phenol resin used for hard board. Recently, a polyvinyl acetate emulsion blend has been tested for special purposes. The domestic supply of urea, 600 000 t of which is to be produced annually for fertilizer, and of formalin, the annual production of which is about 45 000 t, presents no problems. It should finally be noted that decorative sheets from melamine resin and unsaturated polyester resin are being produced, though the quantity is still small. The establishment of Korean Industrial Standards for boards is being discussed and those for plywood have already been formulated. US Specifi­ cations and Japanese Industrial Standards are tentatively being applied to grading and testing boards.

4. FUTURE PROSPECTS

As already mentioned, the production of polymer-containing fibrous materials in Korea is mainly limited to board from more or less waste materials incorporated with thermosetting resins. Woods containing thermoplastic polymers have, to my knowledge, never been introduced; however, the latent market for these new materials in Korea is by no means small in the fields of furniture, building interiors, handicrafts and parts for industrial products such as pianos, textile machinery or radio and television sets. The moulding of poly methylmethacrylate sheet, the condensation and moulding of unsaturated polyester and the emulsion polymerization of vinyl acetate and acrylics for surface coating and adhesives have been facilitated by laboratory studies and pilot tests. Laboratory studies on these new wood-plastic materials aiming at commercialization will be carried out within the next few years. When their specific properties are fully recognized, the active use of these materials may be possible within several years. PAKISTAN

GRAFT-POLYMERIZATION UNDER IRRADIATION AND ITS EFFECT ON WATER REPELLENCY AND RESISTANCE TO CERTAIN MICRO-ORGANISMS

CONTRIBUTED BY M.H. AWAN AND ATHER HUSAIN CHEMISTRY DIVISION, PAKISTAN ATOMIC ENERGY CENTRE, LAHORE, PAKISTAN

1. INTRODUCTION

The fibre from the jute plants Corchorus capsularis and C[. olitorius consists [ 1J of cellulose (69-78%), lignin (10-15%), furfuraldehyde (9-11%), xylen (10-12%) and fat (1%). Jute fibre is commercially used for making sacks for packing purposes and is an important item of Pakistan's foreign trad e. It was intended to graft-copolymerize jute with various monomers with the idea of determining its water absorption and resistance to m icro­ organisms. Such studies would enlarge the scope of the commercial utili­ zation of jute fibre. Graft-copolymerization or graft-polymerization in our studies invariably refers to soaking jute with monomers under the conditions of the experiment.

2. E X P E R IM E N T A L

Styrene, methylmethacrylate and acrylonitrile were obtained from B.D.H., London. The chemicals used were of A.R. quality. In each case, the monomer (100 ml) was freed from the inhibitor and purified by succes­ sive treatments with sodium hydroxide (2%; 20 ml) twice, saturated solution of sodium bicarbonate (20 ml) twice and finally with distilled water (20ml) twice. The monomer was then dried over anhydrous sodium sulphate and distilled under vacuum. Acrylonitrile and methylmethacrylate were at room temperature (20-21°C) and styrene at 50-55°C. Doubly distilled monomers were used throughout. Barnstead water redistilled over potas­ sium permanganate and then over potassium dichromate solutions under a stream of oxygen was used for making the monomer solutions. All the glass apparatus used for irradiation was heated to 500°C for three hours before use. A cobalt-60 source (Gammacell-220 supplied by A.E.C.L., Canada) was used for irradiation. The dose was determined by a Fricke [2] dosimeter, with ferrous sulphate solution containing sodium chloride, as suggested by Dewhurst [3] using G(Fe3+) = 15.6. The dose rate varied between 7. 95 and 7. 71 X 1020 eV/min per litre. No correction was applied for the density of the solution or of the jute fibre.

267 268 TABLE I. GRAFT COPOLYMERIZATION OF STYRENE ON JUTE WN n HUSAIN and AWAN PAKISTAN 269

Jute samples in each case were dipped in water for two hours, then washed with benzene and methanol for eight hours in the cold, dried at 70-75°C and finally stored in a desiccator. Pre-weighed jute samples pro­ cessed in the above manner were placed in an ampoule with B14 cone and socket joints, the latter having a side-tube for sealing. The solvent-water mixture was poured into the ampoule in an amount sufficient to cover the jute sample. The ampoule was then evacuated by the freeze and thaw method and sealed at the side tube. The seal was broken after the irradi­ ation, the jute sample taken out and refluxed in a soxhlett apparatus. To remove the homopolymer, samples irradiated with methylmetha­ crylate or styrene (in solvent-water mixture) were refluxed with benzene for eight hours. Those irradiated with acrylonitrile (in solvent-water mixture) were refluxed for twenty hours with dimethylformamide. Samples grafted with styrene-acrylonitrile were first refluxed with benzene for eight hours and then with dimethyl formamide for twelve hours. After refluxing, the sample in each case was dried, at 60-70°C and finally dried in a desiccator to constant weight. All monomer mixtures described herein were made by volume.

3. RESULTS AND DISCUSSION

Neither styrene nor acrylonitrile were successfully grafted onto jute in the absence of water and solvent (methanol or acetone), whereas grafting occurred easily in the presence of a solvent-water mixture. It appears that diffusion of the monomer to the inner layers of the jute fibre occurred only in the presence of polar solvents such as water or methanol. Usually the dosage curves showed the induction period attributed to the small amounts of oxygen remaining behind in the evacuated solutions. Even though soxhletting of the homopolymer was in all cases carried out to constant weight, the possibility of interstitially blocked polymer cannot be ruled out. No definite conclusions with regard to the true nature of the graft could be drawn. Table I summarizes the results of experiments on the graft copolymeri­ zation of styrene onto jute in various monomer-solvent mixtures. If acetone was replaced by methanol - a more polar solvent - percentage grafting increased tremendously (50. 0% in No. 3 as compared with 7.4% in No. 2). Mixtures of styrene-methanol-water mentioned under Nos 4 and 5 afford reasonably good graft. Graft-copolymerization carried out in a mixture of styrene-ethanol-water and styrene-methylmethacrylate-water grafted well onto jute. Styrene also graft-copolymerizes very well in a dioxane-water mixture (Fig. 1 ).

3.1. Graft-copolymerization of acrylonitrile on jute (Table II)

Acrylonitrile in the absence of solvents does not graft onto the jute under the conditions of the experiment, even at large doses. The presence of methanol is essential for graft-polymerization to occur. It appears that diffusion of the monomer is facilitated by methanol- water mixtures. Pure acrylonitrile, since it polymerizes fast, is difficult to work with. Even with grafting in solvents, short irradiation time inter­ vals were always chosen to minimize the formation of homopolymer on the jute fibre as well as to keep the medium homogeneous. 270 AWAN and HUSAIN

OOSE(HOURS)

F IG .l. Graft copolymerization on jute fibre in styrene:dioxane:water (33:65:15).

Dose rate : 7.95 X 10 20 eV/min per litre.

FIG. 2. Graft copolymerization on jute in styrene-acrylonitrile mixture.

D o se r a t e : 7 . 7 1 X l O 20 eV/rr.in per litre.

It is worthy of note that 'grafting' occurs very well in a mixture of styrene-acrylonitrile. An irradiation time (3.0 hours) was arbitrarily chosen and the percentage of graft was measured for varying styrene: acrylonitrile ratios as shown in Fig. 2. This graph clearly indicates that in the region shown the total graft is proportional to the styrene ¡acry­ lonitrile ratio (by volume). In view of the fact that no grafting occurs with styrene or acrylonitrile alone, further work is needed to elucidate the mechanism and the mode of grafting. Nevertheless, it may be mentioned that if styrene has already been grafted onto jute (in a monomer- solvent- water mixture), acrylonitrile could be added onto the grafted jute, presum­ ably to the styrene graft. The same is true for styrene grafting onto samples that have already been grafted with acrylonitrile (in monomer- solvent-water). PAKISTAN 271

3.2. Tests performed on 'grafted' .jute

Two sets of tests were conducted on jute samples grafted with styrene, with styrene-acrylonitrile or with styrene followed by acrylonitrile. These tests concerned, first, resistance to certain micro-organisms and, secondly, water absorption or moisture retention. The latter tests were conducted on jute fibre as well as on woven jute.

(a) Resistance to certain micro-organisms

The 'grafted' jute samples were tested for resistance to the attack of the micro-organism Aspergillus niger 67, grown in a favourable medium. Both grafted and ungrafted samples did not show any growth for as long as fifty days. The full growth on these samples took a long time. The photo­ graphs reproduced here were recorded after about one year. In the case of samples grafted with styrene (Fig. 3 (a)-(c)), the grafted samples were affected to a much sm aller degree as compared with the control samples. Samples with graft as low as 10.8% (not reproduced here) also showed very restricted growth. It is obvious from these photographs that increasing the percentage graft adds to the resistance to m icro­ organisms. In the case of samples grafted in a mixture of styrene- acrylonitrile (70:30 by volume) (Fig. 4 (a)-(d)), the grafted samples did not suffer any attack whereas the controls were tremendously affected. Saggfe,. ш rmgt m -

FIG.3. Resistance of styrene-grafted jute to micro-organisms after a period of one year's growth, (a) Control jute sample (no graft) ; 272 AWAN and HUSAIN

FIG.3 (cont.). (b) Jute sample containing styrene graft ( 19.2%) ;

FIG. 3 (cont. ) . (c ) Jute sample containing styrene graft ( 34.47o). P;\KXCT 4 N 273

FIG.4. Resistance of styrene-acrylonitrile-grafted jute to micro-organisms after a period of one year's growth, (a) Control jute samples (no graft) ;

.У# '.'. £ Vr Г

FIG .4 (c o n t .). (b ) Jute samples containing acrylonitrile-styrene graft ( 10.27o) ; 274 AW AN and HUSAIN

FIG .4 (c o n t .). (d ) Jute samples containing acrylonitrile graft ( 16.3%). PAKISTAN 275

FIG. 5 Resistance of jute samples first grafted with styrene and then with acrylonitrile.

(a) Jute samples containing styrene graft ( 24. 0%) and acrylonitrile graft (1. Q°]o) ;

FIG. 5 (cont. ). (b) Jute samples containing styrene graft ( 3 . 4 °¡ó ) and acrylonitrile gralt ( 24.4% ). Controls for comparison for these samples were the same as shown in Fig.3( a ). 276 AWAN and HUSAIN

Interesting results are shown (Fig. 5(a) and (b)) in grafted samples - first grafted with styrene and then with acrylonitrile and vice versa. Those that had higher grafted acrylonitrile showed more resistance to the attack of these micro-organisms than the samples with a higher styrene graft.

(b) Tests for water absorption and moisture retention

Tests on woven jute: Woven jute pieces 3 in. X 4 in. in size with a percent­ age of graft were weighed and dipped in water (67-70°C) for two minutes and then hung in an atmosphere of water vapour (50-53°C) for half an hour. These pieces of jute were pressed between folds of filter paper and weighed.

F IG . 6 . Water-retention tests for styrene-acrylonitrile-grafted samples, о : % water uptake by weight after dripping off water; Д: after keeping in the oven for ten minutes; □ : after keeping in the vacuum desiccator for one hour; V : after keeping in the vacuum desiccator for three hours.

FIG. 7. Water-retention tests for styrene-grafted samples. PAKISTAN 277

TABLE III. WATER RETENTION TESTS ON STYRENE-GRAFTED SAMPLES

G ra ft Per cent water-retention after exposure to steam for 2.5 hours, N o . <%) oven drying (80eC :15 min) and vacuum desiccator (30 min)

1 . 9 8 .7 2 .9

2 . 9 7 . 4 3 . 3

3 . 1 0 4 .0 3 .0

4 . 1 0 4 . 1 2 . 2

5 . B la n k 4 6 .0

6 . B la n k 4 2 .0

7 . B la n k 5 5 .0

Then they were placed in an oven at 90°C for ten minutes and weighed again. After the second weighing they were placed in the desiccator and weighed after intervals of one hour and three hours. All samples tested in this fashion grafted earlier with styrene-acrylonitrile (70:30 by volume). The results are shown graphically in Fig. 6. It is obvious that the increasing amount of graft imparts greater water retention to the samples.

Tests on jute fibre: Weighed samples of jute, blank as well as grafted, were exposed to an atmosphere of steam over a boiling water bath for a period of two and a half hours. The samples were then pressed between filter-papers and placed in a vacuum desiccator forhalf an hour and weighed. The percentage water retention is shown in Table III. Figure 7 shows the tests carried out on another set of styrene-grafted samples. In all these tests, the samples were first soaked in water at 75°C for five minutes, then exposed to steam for two and a half hours and kept in an oven at 95°C for half an hour and weighed. When these samples were further kept in a vacuum desiccator for eight hours, the grafted samples were completely dried whereas the controls still carried 20% moisture.

REFERENCES

[1] NORMAN, A .G ., Biochem.J. 30 (1936) 831.

[ 2 ] FRICKE, H., HART. E.J., J.chem.Phys. 3 (1935) 60. [3] DEWHURST, H .A ., J.chem.Phys. 19 (1951) 1329. EFFECT OF PERCENTAGE GRAFT ON THE BREAKING STRENGTH OF JUTE YARN

CONTRIBUTED BY M.H. AWAN, DIN MOHAMMED AND QAZ.I ABDUL QADIR CHEMISTRY DIVISION, PAKISTAN ATOMIC ENERGY CENTRE, LAHORE, PAKISTAN

1. IN T R O D U C T IO N

It was noticed during the tests conducted on the grafted jute (preceding paper) that water absorption in these samples decreases and resistance to certain micro-organisms increases. An investigation was carried out to determine whether the strength of jute on graft-copolymerization (under gamma radiation) would undergo any change. Variation in strength on 'grafting' in view of these improved properties would have a direct bearing on the commercial utility of jute fibre.

2. E X P E R IM E N T A L

All the chemicals were of A. R. Grade. Styrene, methylmethacrylate and acrylonitrile were obtained from B.D.H., London. The monomer in each case was washed twice with sodium hydroxide (2. 0%, 20 ml), twice with saturated solution of sodium bicarbonate (20 ml) and then twice with distilled water (20 ml). The monomer was then dried over anhydrous sodium sulphate and distilled under vacuum. Triply distilled water was used to prepare the monomer solution. All the glass apparatus used for irradiation was heated to 500°C for three hours before use. A Fricke dosimeter [1] was used for the estimation of the dose-rate using G (Fe3+) = 15.6. The dose rate ranged from 4.03 - 4.27 X 1020eV/min per litre. No correction was applied for the density of the jute or of the solution in these dose-rate measurements.

2.1. Graft-copolymerization with styrene

The jute yarn was first washed with distilled water (20-21°C) and then soxhletted with benzene for one hour and dried. It was then cut into pieces of equal length (about ten inches), and these were tied together at the two ends by loops of thin cotton thread. Pre-weighed samples of yarn - about forty in number - were placed in a mixture of styrene-methanol-water in a ratio of 33:66:1. 5. For each gram of jute yarn, 20. 0 ml of monomer- methanol-water was used. The sample was placed in the above mixture in an ampoule with B20 cone and socket joints, the upper joint carrying a narrow side tube for sealing. The ampoule was then evacuated by the freeze and thaw method and sealed at the side tube. It was then irradiated with a cobalt-60 source (Gammacell-AECL-220). The samples were then removed and soxhletted for eight hours with benzene to remove the homopolymer. They were dried at 55-G0°C for two hours, then dried in a desiccator for two hours and reweighed.

278 PAKISTAN ¿¡'

2.2. Graft-copolymerization with methylmethacrylate and acrylonitrile

The procedure was essentially the same as in the case of styrene- grafting. The jute yarn was first washed with distilled water (20-21°C) and then treated with benzene in cold for half an hour and dried. In the case of graft-copolymerization with methylmethacrylate, the monomer: methanol: water ratio was 5:3:1 (by volume) and with acrylonitrile 8:1:1 (by volume). In the case of 'grafting' with methylmethacrylate, the jute samples after irradiation were soxhletted with benzene in the same manner as that de­ scribed for styrene-grafting above, whereas with acrylonitrile grafted samples after the irradiation were soxhletted with dimethylformamide for eight hours. The samples in the two cases were then dried in a manner sim ilar to that for styrene-grafted samples.

2.3. Measurement of breaking load of jute yarn (grafted and ungrafted)

The tests for breaking strength of grafted and ungrafted samples were carried out on a Goodbrand Single Thread Yarn Strength Tester (0. 25 t capacity). The length of the yarn, i.e. the distance between the gripping screws, was fixed at 6| in. for each test. This was the maximum length that could be fixed on this machine. The mean of the tests for 35-40 threads was taken to express the breaking load per 6| in. Humidity and temperature were recorded in each case.

Three blank (control) experiments were carried out. (a) Pre-irradiation treatment of jute yarn with benzene in cold, drying, weighing and then dipping in a mixture of styrene-methanol-water(33:66:1.5 byvolume), evacuating, keeping at room temperature (21.0°C)for 2.5 hours and finally washing with benzene in cold, drying.and weighing. (b) Pre-irradiation treatment with benzene in cold, drying, weighing and then dipping in a mixture of styrene-methanol-water (33:66:1. 5 by volume), evacuating, keeping at room temperature (21.0°C), soxhletting with benzene for eight hours, drying and weighing. (c) Treatment with benzene, drying, dipping in a mixture of styrene- methanol-water (33:66:1. 5 by volume), evacuating, irradiating and washing with benzene in cold (not soxhletting) and drying and reweighing (33. 3% graft).

The breaking load in each case was determined as described above. Experiments under (a) and (b) proved that dipping alone in monomer mixture does not result in any decrease in breaking strength. Soxhletting at the end of irradiation does not result in any decrease in strength.

3. RESULTS AND DISCUSSION

Jute fibre is extremely non-uniform. As found in nature, it varies widely along its length. It also differs from one individual fibre to another. The jute yarn on which these tests were done also showed large variations in strength. The tensile strength as such could not be measured, since measurement of the flexible yarn was not possible. The method of testing was confined to the measurement of breaking load for a fixed length of the yarn in each case. 280 AWAN et aL

TABLE I. EFFECT OF RADIATION ON THE BREAKING STRENGTH OF JUTE YARN (UNGRAFTED) Dose-rate: 4. 18 X 1020 eV/min per litre Relative humidity: 70.5-71% T e m p e ra tu re : 20. 2 - 20. 5° С

Tim e of irradiation Breaking load N o . (h) (lb s / 1 £ i n . )

1 . 0 . 0 13.22 ± 2.19

2 . 1 . 0 12.25 ± 1.78

3 . 2 . 0 11.64 * 1.59

4 . 4 .0 10.83 ± 1.94

5 . 6 . 0 11.71 ± 2.21

6 . 8 . 0 10.36 ± 1.41

7 . 1 0 . 0 ■ 9.65 ± 1.33

From these experiments it becomes obvious that irradiation alone (Fig. 1, Table I) decreases the breaking load. Figures 2, 3 and 4 indicate the relationship between percentage graft and total breaking load per 6f in. length of jute yarn. The relationship expressing total breaking load in lbs/6^ in. and time of irradiation is shown in Figs 5, 6 and 7 and Tables II, III and IV. It is remarkable that the graft-copolymerization brings down the breaking load (Figs 2, 3 and 4) much more rapidly than the irradiation alone. It may be recalled [2] that jute fibre mainly consists of cellulose (69-78%) and lignin (10-15%). Since the nature of grafting is not yet well understood, it is difficult to find the cause of this degradation.

F IG .l. Graph between time of irradiation and breaking load: irradiated but non-grafted. Dose rate: 4.18 X 10го eVAnin per litre. PAKISTAN 281

"¿GRAFT------„

FIG.2. Graph between breaking load and percentage graft of styrene in styrene:m ethanol:water (33:66:1.5). Dose rate:4.03 X 10го eV/min per litre.

FIG.3. Graph between breaking load and percentage graft of methylmethacrylate in monomer :methanol: water (3:5:1). Dose rate: 4.27 X 10го eV/hiin per litre.

It is quite likely that, on 'grafting', the recombination processes in cellulose on irradiation are hampered by free radicals ensuing from the monomers and this results in sharper degradation. 'Blank (control) experi­ ments have established that dipping in the monomer mixture alone does not result in a decrease of the breaking load, nor does the soxhletting process at the end of irradiation result in any decrease of strength. 282 AWAN et aL

FIG.4. Graph between breaking load and percentage gïaft of acrylonitrile in monomer:methanol:water

(1:8:1). Dose rate: 4.27 X 10 20 eV/friin per litre.

FIG.5. Graph between the time of irradiation and breaking load: Curve A - ungrafted (irradiated only).

Dose rate: 4.18 x 10 20 eVAnin per litre. Curve В - grafted samples in styrene:methanol:water (33:66:1.5).

Dose rate 4.03 x 10 20 eV/fain per litre.

■ B la n k n o g ra ft A 1 9 . 6 $ g r a ft X 2 .2 6 % g r a ft V 2 6 .5 % g r a ft • 5 .8 9 % g r a ft + 4 5 .5 % g r a ft Ф 1 1 . 9 % g ra ft © 1 3 2 .0 % g r a ft

If it is assumed that the total strength (E) in jute itself is due to (a) strength of cellulose linkages, i.e. hexose-hexose linkages (Ej), (b) cellulose-lignin linkages (E2) and (c) lignin-lignin linkages (E3), the total strength can be expressed by

E = E j + E 2 + Eg PAKISTAN 283

It is assumed that all linkages under (a), (b) and (c) contribute equally to the strength. This assumption could be fairly valid for cellulose linkages (a) but would not hold good for lignin-lignin linkages. It would be still less certain for cellulose-lignin linkages.

F IG . 6 . Graph between breaking load and time of irradiation in monomer :methanol: water (5:3:1).

D o se r a t e : 4 . 2 7 X 1 0 20 eV/fain per litre.

FIG.7. Graph between breaking load and time of irradiation inmonomer:methanol:water (1:8:1).

Dose rate: 4.27X 10 20 eV/min per litre. 284 AWAN et aL

The brittleness of jute fibre suggests, from the length of the fibre, a good orientation of the constituent molecules. This orientation cannot be neglected in the yarn either, so that only a component of the strength of these linkages mentioned under (a), (b) and (c) along the length could be contributing to the strength of jute. If we neglect the variation of strength in the linkages and the orientation effect, the rate of change of strength with dose (time t) under the conditions could be given as

dE £ ^ 2 d E 3 dt ” dt + dt + dt

In case of decrease in strength on graft-copolymerization under irradiation, it is suggested that lignin-cellulose linkages might well be the most affected (“jj2) . Further work in this direction would show the contribu­ tion of these factors to the diminution of strength of jute on graft- copolymerization under irradiation. In these measurements it is very unfortunate that the standard deviation as indicated in the tables, in spite of measuring the 35-40 samples mentioned in each case (Tables I-IV), was rather high. Nevertheless, the trends of the breaking strength on grafting are very prominent and definite. In one set of experiments, blank unirradiated samples - after the measurements of breaking load - were weighed after they had given way to the breaking load. The measurement of breaking load per unit weight of fibre in each case did not improve the standard deviation. Microscopic counting of single threads in the yarn (each non-uniform in itself) was extremely tedious and was not tried. The variation in temperature and humidity, in view of the large standard deviation, presumably does not affect the results. The authors are grateful to the Director, Central Testing Laboratories, Lahore, for making the testing facility available and to the Director, Jute Research Institute, Dacca, for supplying the jute yarn.

TABLE II. EFFECT OF STYRENE GRAFTING ON THE BREAKING STRENGTH OF JUTE YARN Dose-rate: 4. 0 X 1020 eV/min per litre Temperature: 15.5°C

Time of irradiation Graft Breaking load Relative humidity

(h) (%) (lbs/ 6 i i n . ) (%)

1 . 0 . 0 0 . 0 12.08 ± 2.53 53

2 . 0 . 5 2 . 2 6 1 0 . 7 7 ± 2 . 2 0 53

3 . 1 . 0 5 .8 5 11.37 ± 1.95 53

4 . 1 . 5 1 0 .9 0 10.98 ± 2.42 53

5 . 2 . 0 1 9 .6 0 11.07 ± 2.65 53

6 . 2 .5 2 6 .5 0 10.48 ± 2.39 53

7 . 3 .0 4 5 .5 0 9.20 ± 2.21 65

8 . 3 . 5 7 6 .3 3 8 . 1 2 ± 1 . 5 8 65

9 . 6 . 1 0 1 3 2 .0 5 . 3 7 ± 2 .5 0 65 PAKISTAN 285

TABLE III. EFFECT OF METHYLMETHACRYLATE GRAFTING ON THE BREAKING STRENGTH OF JUTE YARN Dose-rate: 4 . 27 X 1020 eV/min per litre Temperature: 15.0-16.1°C

Tim e of irradiation G ra ft Breaking load Relative humidity N o . (m in ) С°t°) (lbsAH in.) (%)

1 . 2 5 .5 2 7 .8 1 2 . 5 3 ± 1 . 6 5 7 3

2 . 4 0 .0 6 3 .8 8 .3 7 ± 1 .4 8 5 5 .8

3 . 6 0 .0 1 2 7 . 5 5.55 ± 1.315 5 1

TABLE IV. EFFECT OF ACRYLONITRILE GRAFTING ON THE BREAKING STRENGTH OF JUTE YARN Dose-rate: 4.27 X 1020 eV/min per litre Temperature: 20.2-20.5°C Relative humidity: 70. 5-71. 0%

Tim e of irradiation G ra ft Breaking load N o . (m in) ( 1 ° ) (lb s/ 6 £ in .)

l. 0 . 0 0 . 0 1 3 . 2 1 ± 2 . 1 9

2 . 1 5 .0 7 . 3 1 3 .0 9 ± 2 .0 0

3 . 2 5 .0 7 . 7 1 2 . 8 1 ± 1 . 8 1

4 . 6 0 .0 9 .8 1 2 . 6 9 ± 1 . 7 5

5 . 1 2 0 . 0 1 3 .0 1 2 . 2 7 ± 2 . 1 3

REFERENCES

[1] FRICKE, H., HART, E.J., J.chem.Phys. 3 (1935) 60. [2] NORMAN, A.G ., Biochem.J. 30 (1936) 831. THE PHILIPPINES

CONTRIBUTED BY LETICIA S. BONOAN PHILIPPINE ATOMIC RESEARCH CENTER, PHILIPPINE ATOMIC ENERGY COMMISSION, MANILA, THE PHILIPPINES

1. INTRODUCTION

Fibrous materials (timber and fibres) constitute one of the most steady dollar-earning industries in the Philippines. In 1966 the produce from this industry alone was worth 1061 million pesos, which was almost 6% of the country's national income. The total timber production amounted to 3 325 541 899 board feet, o f which 15. 2% was consum ed lo c a lly and the rest exported to different countries, with Japan as one of the largest im ­ porters. The Philippines produces quite a number of varieties of timber and fibre which have earned a good reputation for quality in the world market. However, there are also other varieties of timber and fibres which need improvement to gain a market. Plastic impregnation of these fibrous materials seems a very promising technique for improving their quality. Plastic impregnation of fibrous materials, being a relatively new field, has only recently been started in the Philippines. So far, only the Philippine Atomic Research Center (PARC) has been working in this field. Exploratory studies were initiated in November 1966, under the supervision of Dr. A. Swallow, the IAEA expert in radiation chemistry. Initial work was confined to wood plastic combination (WPC).

2. M A T E R IA L S A N D M ETHODS

The wood chosen for this study is a highly porous wood, Anthocephalus cadamba, locally known as Kaatongan bangkal or the 'm iracle' tree. This tree is of special interest to the University of the Philippines Research Products Institute because of its very rapid growth. In spite of this ad­ vantageous quality, however, its timber has not been commercially utilized due to its porosity and softness. Since WPC transforms its products into a much harder wood which retains the desirable characteristics, we decided to use the 'm iracle' tree for our initial research on WPC. Moreover, the high porosity of this specimen and its rapid growth make it suitable for this type of investigation. A review of literature shows that methylmethacrylate is one of the most successfully used monomers in WPC. We therefore decided to use this monomer for our initial work. The feasibility of using hydroxypropyl methacrylate was also investigated. The usual four basic steps in the production of WPC were followed, nam ely:

286 THE PHILIPPINES 287

(1) Pretreatment of the wood. (2) Impregnation of the wood with the monomer. (3) Irradiation to effect polymerization. (4) Drying.

We intended to use wood samples measuring 2 in. X 2 in. X 12 in. for studies on both methylmethacrylate and hydroxypropyl methacrylate, but due to the limited supply of the hydroxypropyl methacrylate monomer we had to use sm aller wood samples, 2 in. X 0. 33 in. X 0. 33 in. Only one method of impregnation and polymerization was employed. For polymerization purposes, gamma rays from a 500-Ci 60 Co source were utilized. Impregnation was achieved by the vacuum soaking process. The irradiation vessel for the methylmethacrylate study was a cylindri­ cal aluminium Vessel 16 in. long with a wall thickness of 1/4 in. The vessel was welded closed at one end and provided with a flange and bolted cover at the other. An outlet was provided for introducing and draining the mon­ omer. For the hydroxypropyl methacrylate study, the vessel was a glass tube large enough to hold the sample, with a side arm leading to a vacuum pump and fitted with a one-holed stopper in which a dropping funnel was in serted .

2.1. Pretreatment of the wood

Samples of Kaatongan bangkal were cut into the appropriate sizes mentioned above, polished with sand paper, weighed and placed inside the vessels previously described. The vessel was evacuated with an ordi­ nary laboratory vacuum pump to a pressure of about 1 mmHg and the system was held at reduced pressure for 30 min.

2.2. Impregnation of the wood with the m o n om e r

While the system was under vacuum the cylinder was flooded with sufficient monomer to completely immerse the wood. Methylmethacrylate was used unpurified, but the hydroxypropyl methacrylate was first puri­ fied. Nitrogen gas was then admitted to the vessel. The wood was allowed to soak in the monomer overnight for the methylmethacrylate and for 30 min for the hydroxypropyl methacrylate. The system was next vented to atmos­ pheric pressure and the excess monomer drained off. The wood was wrapped in saran, then weighed and once again placed in the cylindrical vessel and flushed with nitrogen gas.

2.3. Irradiation

The cylinder containing the wood was then positioned in a 500-Ci 60 Co source and exposed until it had received a total dose of 3. 5 Mrad for the methylmethacrylate samples and 0. 5 Mrad for the hydroxypropyl metha­ crylate samples. Figure 1 is a graph of the effect of dose on the weight increase of the wood treated with methylmethacrylate. Figure 2 shows the effect of dose on the per cent polymer loading with hydroxypropyl methacrylate as the monomer. 288 BONO AN

DOSE ( MEGARAOS )

FIG .l. Effect of dose on the increase in weight of wood using methyl methacrylate as monomer.

2.4. D ryin g

After irradiation, the wood in the cylinder was vacuum dried (two days for methylmethacrylate and five hours at 100°C for the hydroxypropyl methacrylate). The samples were then removed from the cylinder and w eighed.

3. RESULTS OF TESTS FOR MECHANICAL AND PHYSICAL PROPERTIES OF TREATED WOOD

Although our initial studies on the methylmethacrylate and hydroxypro­ pyl treatment of wood is admittedly.crude, our initial findings show that the physical appearance and some of the mechanical properties of the pro­ duct are substantially improved. 120- H PHILIPPINES THE О 0> — А ( — c Û A s О « 289 290 BONO AN

The finished wood product retained most of the desirable characteris­ tics of the wood, besides possessing many improved properties. The new product was much harder, making it more resistant to scratches. It had a higher compression strength and abrasion resistance. The colouring of the wood was greatly improved, making the grains more visible. The new product was likewise dimensionally stable. Water and moisture ab­ sorption were greatly reduced. The wood could be machined, even with conventional equipment, to give it a hard,beautiful satin finish. However, one disadvantage of the WPC product was its inferior nail-holding property. Methylmethacrylate-treated samples were submitted to the Tests and Standards Division of the National Institute of Science and Technology (Philippines) for the testing of some mechanical properties, namely, static bending and hardness. Samples treated with the hydroxypropyl methacrylate could not be subjected to these tests as they fell short of the specific dimensions. A ll tests performed were according to ASTM Standard D 198-27. Other tests were performed in our laboratory. These included di­ mensional stability, density and compression. The test results are given below.

Static Bending: The modulus of rupture for the methylmethacrylate- treated wood was increased by 32. 6% for wood dimensions of 12 in.X 15/32 in. X 15/32 in. and a load varying from 49. 5-63. 8 lb.

Hardness: The sample submitted for this test cracked, so that no data can be presented.

Density Measurements: Density measurements were carried out on an air dry basis with the room temperature at 25°C and a relative humidity o f 60%. The volume of the wood samples was measured by means of a vernier caliper. An increase of 93% was noted.

Dimensional Stability: Pieces of treated and untreated wood were soaked in water at 25°C and at atmospheric pressure. Samples were withdrawn every few days, weighed and resoaked. Results showed that the water ab­ sorption of the treated wood was 110% less than the untreated wood after a maximum soaking time of 33 days (Fig. 3).

Compression: With a laboratory carver press, samples of treated and untreated wood were subjected to increasing pressures perpendicular to the grain until the wood samples cracked. An increase of 140% in the compression strength was obtained.

In the light of the favourable results obtained in these initial studies on WPC, a thorough investigation in this field is planned. Cheaper mon­ omers, preferably those available or produced locally, will be used. The treatment of bigger wood specimens will be considered, and the 4 m X 5 m X 5 m dry gamma room in the reactor will be used for the irradiation process. Expansion of this study to other varieties of timber which are abundant in the Philippines is likewise planned. Another project which is currently being studied is the utilization of kenaf fibres as a source of cellulose in graft polymerization. Kenaf plant, THE PHILIPPINES 291

SOAKING TIME ( DAYS )

FIG.3. Effect of soaking time (days) on the per cent of water absorbed.

scientifically known as cannabinus Linn. , produces fibres which are con­ sidered to be the most promising substitute for jute in the manufacture of sacks. It is more profitably raised in the Philippines than jute, and its commercial production has, in fact, been given promotional support by the government since 1951. It is more easily propagated and cultivated and has a higher fibre yield than eithér cotton or abaca. At the present stage of our study on kenaf fibres, only the collection and bleaching of the crude fibre has been accomplished. The use of various monomers such as methylmethacrylate, methylacrylonitrile, acrolein, and acryloni­ trile is being planned. The expansion of these studies to other varieties of fibre is also being considered. The Philippines produces a wide variety of other fibres, among them bamboo, buntal, rattan, bagasse, coco-coir, abaca, ramie, maguey, kapok, cotton and pina, most of which are exported crude and, quite ironi­ cally, re-imported as finished material. Ramie, for instance, is exported to Japan, where it is blended with tetoron to decrease its creasability. It is hoped that the graft polymerization process will improve some of the qualities of these fibres. The application of this process to pina fibre is particularly attractive; pina is a beautiful and durable fabric when finished, but is not at all washable. 292 BONOAN

4. POTENTIAL MARKETS

At present the sector most interested in WPC is the wood-carving industry. This is mainly because the country is running short of the wood species used by this industry and also because the use of soft wood would cut down carving time, which would mean greater production. It must also be noted that the wood species proposed for WPC is a very low grade wood of practically no commercial value which grows very rapidly (about 3 yr for a good-sized tree). On the other hand, the present status of our technology requires that the wood be carved roughly before impregnation and finished only after the treatment. This method would mean a great increase in handling costs, since the wood carving industry is scattered all over the country. Another factor which we have to con­ sider is the availability and cost of the monomer. If all the different factors mentioned above are taken into consideration it is at present very hard to assess the successful use of WPC in the wood-carving industry, but the potential is there. It should also be mentioned once again that in 1966 the produce from the timber industry alone amounted to almost 6% of the national income. 15. 2% of the commercial timber produced was consumed locally, mostly in construction, and 84.8% exported to various countries. If low-grade wood could be improved by treatment with a monomer so that it would be of com­ parable quality to hard wood, then all our hard wood could be exported and the WPC product used locally. With the 1966 figures this would mean an increase of 15. 2% in income for the wood industry. Other potential applications of WPC would be in flooring, railing, and electrical posts. For these purposes the addition of fire retardants is very important.

REFERENCES

[1] The Statistical Reporter XI 2 (April-June, 1967) 8 . [2] BUREAU OF FORESTRY, Annual Report of the Bureau of Forestry (1966). [3] INTERNATIONAL ATOMIC ENERGY AGENCY, Industrial Uses of Large Radiation Sources I (Proc, Symp. Salzburg, 1963) IAEA, Vienna (1963). [4] KENT, J. A. et a l., Preparation of Wood Plastic Combination Using Gamma Radiation to Induce Polymerization (May 1965).

[5] GREENE, R .E., BAKER, P .S., Eds, Proc. Information Meeting on Irradiated Wood Plastic Materials, Chicago, 111. (1965-1966). REPUBLIC OF CHINA (TAIWAN)

CONTRIBUTED BY UNG-PING WANG RADIOISOTOPE LABORATORY, UNION INDUSTRIAL RESEARCH INSTITUTE, MINISTRY OF ECONOMIC AFFAIRS, REPUBLIC OF CHINA (TAIWAN)

1. HISTORICAL BACKGROUND

In Taiwan many kinds of wood and bamboo are abundantly produced in the mountainous areas (about 70% of the total land area) and sugar-cane is one of the main agricultural products in the plains. Before 1945 Taiwan was under the dominion of Japan and found markets for its timber chiefly on the Japanese mainland. By 1949 small amounts of products such as glued veneer and bagasse-board were being marketed, but both the mechanical strength and the water resistance of these products were very poor because of the low quality of the adhesive agents. In 1950, however, the adoption of urea-formaldehyde resin as an adhesive agent, improved these products remarkably and the plywood and bagasse-board industries developed steadily from this point on. Although the handicraft industry employing polymer-containing bamboo has advanced greatly in the last five years, its production is still on a small scale. It is the plywood industry which is the principal consumer of wood, bagasse and bamboo. This industry not only supplies domestic plywood consumption, but also produces 594 million square feet annually for export (1964) which earns the equivalent of 23 million US dollars. Because of the good dimensional stability and suitably large size of its product, the plywood industry has sharply increased its scale of produc­ tion in the last twenty years. However, the utilization of plywood is lim ited because of the availability of many other wood products which require little processing, e. g. for house-building materials (beams or posts), indoor and outdoor furniture, sports equipment (skis, golf clubs, baseball bats, boating equipment, etc. ) and others. To meet the demand for improved properties in the above-mentioned commercial products and to develop the use of the abundant but less valuable types of wood and of bamboo and bagasse, the project of processing wood-, bamboo-, and bagasse-plastic combinations with gamma radiation has been under way since 1965 at the Union Industrial Research Institute (UIRI) sponsored by the Government of the Republic of China. A detailed description of the status of production of polymer-containing fibrous materials in Taiwan is given here and covers four typical industries including plywood, wood- particle-board, wood-fibre-board and bagasse-board, respectively.

(a) The plywood industry

The plywood industry has achieved significant growth over the past two decades in Taiwan. Annual production has increased from 4 X 105 ft2

293 294 UNG-PING WANG

TABLE I. ANNUAL PRODUCTION OF TAIWAN-PRODUCED PLYWOOD AND ITS MARKET

Y e a r Number of manufacturers Annual production Domestic uses E xp o rt ( f t2 ) ( a ) ( f t2 )(a )

1 9 4 7 3 40 0 000 40 0 000 -

1 9 5 4 5 40 000 000 3 3 000 000 7 000

1 9 5 5 5 4 2 000 000 3 3 000 000 9 000

1 9 5 6 5 4 9 0 0 0 000 3 5 000 000 1 4 000 000

1 9 5 7 6 63 000 000 4 0 000 000 2 3 000 000

1 9 5 8 6 9 7 0 0 0 000 4 3 0 0 0 000 5 4 0 0 0 000

1 9 5 9 7 150 000 000 4 5 000 000 105 000 000

19 60 8 215 000 000 50 000 000 1 6 5 0 0 0 000

1 9 6 1 1 0 254 000 000 5 4 000 000 2 0 0 0 0 0 0 0 0

1 9 6 2 13 400 000 000 60 0 0 0 0 0 0 340 000 000

19 6 3 15 510 000 000 60 0 0 0 0 0 0 500 000 000

1 9 6 4 1 5 656 000 000 6 0 0 0 0 0 0 0 594 000 000

(a) plywood thickness is taken as ¿ in.

in 1947 to 6. 56 X 108 ft? in 1964, and about 90% o f the total production has been exported every year, as indicated in Table I. Among the fifteen plywood manufacturers (October 1964) shown in Table II there are five large-scale manufacturers with a maximum monthly production capacity of about ten million square feet. Plywood is manufactured by pressing thin multiple wooden sheets having an attractive grain-pattern surface together with urea-formaldehyde resin as the adhesive. Hydraulic cold-pressing (2-4 h) is followed by hydraulic hot-pressing (90°-110°C, 1-2 min) to thermoset the resin paste. Wood from many kinds of coniferous trees (Taiwan cypress, Taiwan cedar, Taiwan incense cedar, etc. ) and deciduous trees (stout camphor tree, teak tree, Chinese guger tree, Taiwan zelkova, Taiwan engelhardtia and the lauan tree) are used as raw materials for the thin wooden sheets. Of these, only the lauan tree is not grown in Taiwan but is imported from the Philippines or Borneo. The quantity of lauan timber imported almost meets the demand for the manufacture of plywood for export. Some statistical data on lauan timber imports are given in Table III. The plywood-plants in Taiwan are all well equipped and moder­ nized with partial automation. Analysis of the production cost of plywood indicates that the wood raw material accounts for 50% and the urea- formaldehyde resin for 10%. All other manufacturing costs together therefore make up 40%. It is worth mentioning that the production cost depends on the wood price to a considerable extent. TABLE II. MAXIMUM MONTHLY PRODUCTION CAPACITY OF PLYWOOD M ANU FACTU RERS IN REPUBLIC REPUBLIC OF HN (AWAN) (TAIW CHINA 295 296 UNG-PING WANG

TABLE III. IMPORTS OF LAUAN TIMBER

Q u a n tity P erio d U S D o lla r s (b.m .t.)(a)

1 9 5 4 4 020 0 75 16 6 1 0 2 .3 0

1 9 5 5 1 0 1 9 9 0 1 0 5 44 9 2 9 .6 9

19 5 6 1 6 4 4 4 232 8 2 9 2 7 5 .0 0

1 9 5 7 14 8 7 7 1 5 0 76 3 6 2 5 .5 0

19 5 8 2 8 4 3 9 9 2 2 1 5 4 8 0 3 3 . 1 9

19 5 9 72 6 2 7 947 3 556 932.49

19 6 0 4 5 2 6 4 0 2 1 2 2 7 2 6 1 7 . 9 5

1 9 6 1 95 1 0 5 4 4 0 4 759 548.90

19 6 2 1 1 7 1 2 9 8 3 0 7 5 3 1 6 0 8 .0 5

19 6 3 226 555 786 12 341446.76

- .

Board measure feet

(b) The wood-particle-board and wood-fibre-board industry

Wood-particle-board and wood-fibre-board have been manufactured with the same technical process as plywood since 1958, but employ, of course, different raw materials. The former uses wood chips and the latter wood fibres. In Taiwan the object of these two wood industries is to achieve a wider commercial utilization of wood materials originating from the branches or waste products of trees. The industrial processing of wood-particle-board consists in chipping, size-screening, drying, mixing adhesive resin, pressing (cold and hot), humidifying and trimming the final product, while that of wood-fibre-board also includes the process of steaming (to expel the essential oils) and digesting and crushing wood1- chips. The annual production of two manufacturers is indicated in Table IV. The production of these two industries is rather smaller than that of plywood and mainly meets the demands of domestic consumption.

(c) The bagasse-board industry

Thirty-five years have passed since bagasse-board was first produced by the Taiwan Sugar Corporation as a by-product of the sugar industry. Annual production had reached fifty thousand metre-tons by 1964, con­ suming 5% of the total bagasse by-product, 25% of which is consumed by the paper industry and 70% by the Taiwan Sugar Corporation as fuel. Although several kinds of bagasse-board were produced before 1950, their mechanical strength and stability (especially water resistance) were very poor due to the low quality of the adhesive agents. However, the adop­ tion of urea-formaldehyde resin for the manufacture of bagasse-board has created great improvement and development. Accordingly, a new market for use in housing materials or furniture has opened up in Taiwan since the bagasse m aterial is cheaper (in sheets of 4 ft X 12 ft) than the wooden REPUBLIC OF CHINA (TAIWAN) 297

TABLE IV. ANNUAL PRODUCTION OF WOOD-PARTICLE-BOARD AND WOOD-FIBRE-BOARD (1960-1964)

W ood-particle-board W ood -fibre-board Name of manufacturer Domestic uses E xports Domestic uses E xports

1 ( f t z) ( a )

M ei Shin Artificial N o n e N o n e 13 000 000 - 2 300 000 - Wood Corporation 13 500 000 2 400 000

Taiwan Artificial 6 0 0 0 0 0 0 - N o n e N o n e N o n e

Wood Corporation 6 500 000

(a) Plywood thickness is taken as i in . sheets. Because the new bagasse-board is extremely porous, its com­ m ercial utilization is limited due to its high water absorption. To over­ come this dis advantage, methods to improve the new bagasse-board further were studied and an up-to-date manufacturing process was initiated in 1966 - copolymerization of impregnated vinyl monomers in the pores of bagasse-board with gamma radiation at the UIRI. The process is some­ what sim ilar to that of wood-plastic combinations. Typical improvements such as tensile strength increase (50%) and the considerable reduction of water absorption (below one-fifteenth of the original board after im ­ mersion in water for 60 days) have been achieved. An economic and technological evaluation is now under way at the UIRI to estimate the feasibility of producing a bagasse-plastic combination (BPC). The tentative production cost of BPC is shown in Tables V. and VI.

2. NATURE OF THE TREATED MATERIALS

Plywood, wood-particle-board and wood-fibre-board are more stable, harder, stronger and relatively more water-resistant than the original materials used, while bagasse-board manufactured from bagasse and urea-formaldehyde resin remains highly porous. The products, prepared by impregnation of wood, bagasse or bamboo with liquid vinyl monomers which are then polymerized by gamma irradiation, are 1-1.5 times heavier, 1-3. 5 times stronger, and 4-8 times harder than the untreated original materials. In addition,the treated fibrous materials retain their original attractive grain patterns, while their water absorption is reduced considerably.

3. SELECTION OF IMPREGNATION AND POLYMERIZATION METHODS AND SYSTEMS

The impregnation of wood, bagasse and bamboo with vinyl monomers is performed by replacing the air in the vessel with nitrogen,which is evacuated to 10 mm Hg after purging to atmospheric pressure, and then flooding the closed vessel with vinyl monomers. The sample materials 298

TABLE V. COST OF WOOD-PLASTIC, BAGASSE-PLASTIC AND BAMBOO-PLASTIC COMBINATIONS I V) if) 1Л N N N N (N IN IN в о со 2 Е- i со Я N-IG WANG UNG-PING CQ Cuo rt -&s> 1 - Ü o Í 1 oo 00>> '5 M -Q СОs о о a i * с •* 1 1 ■у Xi 1 Н о О *о -о ■О 1 etf О *** о 00С4 *3. '3 .2Р S S га о и 1 Й Си 3 с - о о £ 2 £ О о о. ® S *3. 5 « « 3 '5 с О Ï о £ я 4) Ь т а о 5 J Л •У Е 4) о о о я N о с Е О 1 1 и со О. Û. < £ < > i ? IN и 00 о. > PVA о i со о» о «о о СО о и о В I Z (-1 3 «9 О со Z в> о В тН OI Н 2 Я В в» 2 Z ' н СО со 2 (- Z Н S со (Л о в о 5? Э <л о о Z н 00 REPUBLIC OF CHINA (TAIWAN) 299

TABLE VI. ESTIMATED COST FOR IRRADIATION OF WOOD , BAGASSE AND BAMBOO (100-kCi 60Co irradiation plant)

1 0 6 lbs production/yr 1 0 ® lbs production/yr Cost component 1 0 years amortization 15 years amortization

Plant capital US s 1 0 0 0 0 0 us $ 1 0 0 0 0 0

60C o source cost US $ 1 0 0 0 0 0 us $ 1 0 0 0 0 0

Total capital cost us $ 2 0 0 0 0 0 us s 2 0 0 0 0 0

Depreciation (per year) us $ 2 0 0 0 0 us $ 13 333

Interest (per year) us $ 6 0 0 0 us s 6 0 0 0

Labour (per year) us $ 3 6 0 0 us s 3 600

Overheads (per year) us $ 1 0 0 0 0 us $ 1 0 0 0 0

Source replacement cost (per year) us $ 15 0 0 0 us s 15 000

Plant m aintenance (per year) us $ 2 0 0 0 us $ 2 0 0 0

Total annual operating cost us $ 56 600 us $ 4 9 3 3 3

U n it c o s t

(Treated'with 2.5 Mrad dose) us s 0 .0 5 6 / lb us $ 0 .0 4 9 9 / lb

us $ 0 , 1 2 3 / k g us $ 0 . 1 1 / k g

( N T $ 4 .9 3 / k g ) ( N T S 4 . 4 1 / k g

are soaked for the desired period under nitrogen atmospheric pressure, since the oxygen in air inhibits the polymerization of vinyl monomers. In the case of bamboo, nitrogen purging after the evacuation of air is not necessary because it is of little advantage in the succeeding gamma-ray- induced polymerization of the soaked monomers. When a mixture of vinyl acetate and vinyl chloride (20:80 by weight) is applied as monomer, impregnation is carried out under nitrogen pressure (2-3 kg/cm2). The water content of the materials used is limited to less than 15 wt%, while the bagasse-board is kept below 5 wt%. Higher water-content results in inhomogeneous distribution of plastic materials and uneven mechanical strength of the final products, although a small amount of water can enhance the grafting reaction of the monomer to the cellulose of the fibrous materials. Swelling agents, such as alcohol, acetone, chloroform, chlorobenzene and carbon tetrachloride, are very effective for controlling the heat of polymerization as well as for grafting monomer radicals to the cellulose of fibrous materials. Polymerization is accomplished, after the samples have been en­ capsulated in polyethylene film, by exposing the rotating target samples to gamma radiation with a total dose of 1-2. 5 Mrad at room temperature (15° -25° C). 300 UNG-PING WANG

4. RESULTS IN TERMS OF PHYSICAL AND CHEMICAL PROPERTIES

Typical tests for tensile strength and hardness of WPC and BPC were carried out under the specifications of A. S. T. M. standard D 143-52 for testing small specimens of timber and A. S. T. M. standard D 1037-60T for testing bagasse specimens. Both control and treated specimens were from the same place of origin for correct comparison. The tests were carried out in triplicate with the same conditioned samples and the data given in the tables are their mean values. The test results are shown in Tables VU, VIII and IX. The water-absorption tests were carried out by immersing the WPC or BPC in the water and measuring weight - increases for 60 days. The WPC made from common schefflera (50%PVA content) had a saturation water content of 15 wt%, while the untreated sample had a content of 200%. The BPC evidenced a water saturation of 20 wt%, that of the untreated sample being 240 wt%.

TABLE VII. TENSILE STRENGTH OF COMMON SCHEFFLERA

Sample: Common schefflera (Schefflera octophylla Harms ) Plastic: Polyvinyl acetate

Tensile strength

PVA content D e n s ity Parallel to grain Perpendicular to grain R e m a rk № ( g / c m » ) ( k g / c m * ) ( k g / c m 2)

0 0 .4 3 7 5 6 .8 9 0 .0 U n tre a te d

1 4 . 7 0 .6 1 2 9 2 .5 1 1 5 . 2

1 6 . 5 0 .6 9 8 1 0 0 . 6 1 1 8 . 5

1 8 .9 0 .7 8 4 1 1 0 . 5 2 1 8 .0

2 5 0 .8 2 6 1 4 0 .2 2 5 0 .2

4 3 0 .9 1 8 1 8 3 .5 2 9 5 .5

50 0 .9 6 4 1 9 6 .2 3 3 5 .4

TABLE VIII. HARDNESS OF COMMON SCHEFFLERA

Sample: Common schefflera (Schefflera octophylla Harms) Plastic: Polyvinyl acetate

PVA content H ardness R e m a rk

( ° l° ) ( k g / c m 2)

0 7 .6 u n tre a te d

1 4 . 7 9 .9

1 8 . 9 1 5 . 7

2 5 2 2 . 8

4 3 4 0 .3

50 4 2 . 1 REPUBLIC OF CHINA (TAIW AN ) 301

TABLE IX. TENSILE STRENGTH OF BPC

PVA content Tensile strength I n c r e a s e

2 / 8 In, 6 / 8 in . 2 / 8 in . 6 / 8 in . 2 / 8 in . 6 / 8 in . th ic k n e s s th ic k n e s s th ic k n e s s th ic k n e s s th ic k n e s s th ic k n e s s

<%) ( k g / c m 2) ( k g / c m 2) № (%)

0 0 3 1 4 . 5 6 65 - -

2 1 . 4 2 2 .4 3 6 1 . 7 8 3 8 .1 1 5 26

3 0 .5 32 3 8 7 .5 8 6 4 .5 2 3 .2 30

5 2 . 1 5 0 .5 4 2 8 .3 9 6 5 .6 2 9 .4 4 5 .2

5. APPARENT ADVANTAGES OF THE TREATED MATERIAL

It has been found that WPC and BPC made of abundant and less valuable types of wood and of bagasse possess improved properties that enhance their value for commercial utilization. A list of these properties is given below .

(1) Homogeneous density of wood or bagasse-board. (2) Increased hardness (4-8 times that of untreated material) and tensile strength (1-3. 5 times that of untreated material). (3) Considerably reduced rate of water absorption of wood and bagasse-board. (4) Increased weather resistance. (5) Increased resistance to insects.

The penetrating power of gamma radiation and its ability to initiate the free-radical type polymerization of vinyl monomers provide us with the important advantages that the monomer can be recycled and stored without danger of polymerization and the target specimens of wood, bam­ boo and bagasse-board can thus be more rapidly and uniformly treated with polymers.

6. F U T U R E P L A N S

In the Republic of China there is a large and promising market for construction materials and furniture manufactured from WPC and BPC. Another market also exists for Chinese wood or bamboo carvings (both classic and modern), and this field is expected to provide a most promising application of WPC and BPC. Considerable attention has been given to such applications and experiments on these lines have been performed at the UIRI. For example the common echefflera (called the Chiang-Mu tree by the Chinese), which is only used for the manufacture of match boxes and match sticks, was found to be well suited to the manufacture of stable, weather-proof and attractive carvings. It is obvious that a large radiation source capacity can reduce the cost of impregnation and irradiation considerably. The prices of both 302 UNG-PING WANG

monomer and radiation source have a great effect upon the production cost of the WPC or BPC product. According to the experimental results, methylmethacrylate seems to be the best polymer for WPC or BPC; how­ ever, from the economic point of view it is too expensive. Much effort has therefore been concentrated on the copolymerization of vinyl acetate and vinyl chloride in the fibrous materials produced in Taiwan. In the future work will be developed along two basic lines:

(1) Construction materials

(a) The treatment of bagasse-board with the vinyl chloride-vinyl acetate system to increase the dimensional stability and the strength of the board. (b) The improvement of the qualities of cement-sawdust composite board by post-impregnation with vinyl monomers. This kind of composite board is fire-proof and has good compression strength; once the water absorp­ tion and bending strength are improved by graft polymerization this board will be very promising for the utilization of lumber-mill wastes. (c) Bamboo or the products derived from bamboo will also be evaluated as potential construction materials. The programme can be greatly facilitated if simultaneous consideration is given to the architectural side of the problem with regard to the proper use of bamboo.

(2) The improvement of carving products derived from soft and cheap wood

For future development, a pilot plant with 100 000 Ci of 60Co has been planned to study the economics and engineering side of the polymerization techniques. Evaluation of the treated products as materials for housing can then be carried out in the field and their potential can be assessed. For the monomer system, vinyl chloride, which has high G-value and is among the cheapest of all commercial monomers, will be the basis for development. Its annual production of 100 000 tons in Taiwan will require additional research effort to find new applications for this monomer. The impregnated fibrous materials will certainly be the right answer. However, the copolymer system of vinyl chloride-vinyl acetate has proven to be better than vinyl chloride alone. For particular purposes, unsaturated esters w ill also be chosen, particularly for lamination as in reinforced fibre composite.

BIBLIOGRAPHY

[1] Industry of Free China 23 2 (1965) 10-18. [23 Quarterly Publication 16 3 (Published by Bank of Taiwan) (1965) 178-94. THAILAND

RA DIA TION-POL YME RI ZA TION IN THAILAND

CONTRIBUTED BY M.L. ANONG NILUBOL AND SOM MART GREETHONG OFFICE OF ATOMIC ENERGY FOR PEACE, BANGKOK, THAILAND

1. G E N E R A L

Wood-plastic composites produced by means of radiation-induced polymerization of monomers impregnated into the wood have been the sub­ ject of study in many laboratories throughout the world. In general the processes are sim ilar, and the differences that occur are due to variations in technique applied to the particular species of wood available in each country. In Thailand, treatment to improve the quality of wood is being carried out by scientists at the Forest Products Research Division of the Royal Forest Department, Ministry of Agriculture, with the aim of obtaining products which can stand up to weathering and term ite attack. On the basis of their experience, certain types of wood suitable for impregnation have been selected for our study. The Office of Atomic Energy for Peace began studying the impregna- tion-irradiation of certain types of Thai wood in the hope that it might result in better utilization of poor quality wood. The use of irradiated-impregnated wood in Thailand is not necessary at present, since many different varieties of hard wood are available. The production of plywood does not even meet the demand of the local market, thus the introduction of this new technique is not an attractive proposal for the time being. Our experiments can be considered to be very preliminary. We have discovered that impregnation with the aid of solvents such as formaldehyde and carbon tetrachloride failed owing to excessive swelling and distortion of the wood. Later experiments indicated that impregnation in an atmo­ sphere of nitrogen under reduced pressure was more satisfactory. Our irradiation experiments with a dose series of 2. 5 X 104, 2. 5 X 105 and 2. 5 X 10® rad failed because they were carried out in the presence of oxygen, which probably caused evaporation of the monomer used. So far we have experimented with styrene and methylmethacrylate as monomers. Polym erization occurred only on the surface and the products turned out as plastic-coated wood.

2. R A D IA T IO N SOURCE

An 8000-Ci S0Co radiation source at the OAEP was used for these experiments. At present, the dose rate is approximately 0. 675 Mrad/h with a container of 580 ml capacity.

303 304 ANONG NILUBOL and SOMKIART GREETHONG

The types of wood used in the first trials were as listed below:

Botanic name L o c a l name Moisture content (%)

Pterospermum diversifolium BL. Khanan 13.136 Terminalia beUerica Roxb Samor Pipeck 11.261 Calophyllum floribundum Hk. f Krathanghan 11.415 Litsea spp. Thamang 11.961 Chukrasia velutina W. A. Sadao Chang 11.212 Lagerstoemia calyculata Kurz. Tabag Yai 12.78 Castanopsis spp. Khor 12.30 Myristica spp. Chan dong 12. 129 Shorea sericeiflora Fisch & Hutch Kiamkanong 11.772

A ll of these woods were tested for strength and hardness at the Forest Products Research Division. The results at different stages were not considered satisfactory. Further experiments were carried out with makok, rubber wood, sompong, spruce and bamboo, with some improvement in the impregnation technique. The soaking and dipping of the wood samples in monomer was carried out in an aluminium tank in a nitrogen atmosphere. Impregnation was improved, but again the polymerization was not uniform. We believe that the aluminium was too thick and that it might have absorbed some of the radiation. At this stage we are considering whether the economics of impregna- ted-irradiated wood would be attractive to industry. WOOD RESOURCES OF THAILAND

CONTRIBUTED BY PONG SONO FOREST PRODUCTS RESEARCH DIVISION, ROYAL FOREST DEPARTMENT, BANGKOK, THAILAND

According to 'The Book of Siamese Plant Names' issued by the Royal Forest Department in 1948, exactly one thousand species of trees in Thai­ land had been identified before that date. Many more species, including such remarkable ones as Prunus .javanica (T & B) Mig. and Betula anoides Ham., which are typical of the temperate zone, were later added to the list. Of the total number mentioned, 280 species have been registered under the Thai Forest Act as reserved species which cannot be cut without permission from the authority. Timbers of real commercial value, how­ ever, are comparatively few in number and those with high production figures for the fiscal year 1966 are listed in Table I where the wood density of each species is also given. Only twenty years ago, very few species superior in natural durability, strength, dimensional stability and working quality were offered in local timber markets, including Bangkok. Recently, as the demand for timbers increased enormously and with the development of wood-consuming industry, nearly all tree species have become valuable. Some soft species, such as Salmalia malabarica Schott & Endl., which were previously considered to be unusable, have also become important raw materials for pulp and paper, plywood and particle-board manufacturing. Trees of smaller size are also continuously needed for the fabrication of construction materials. The properties of Thai timbers vary widely. Density values, for example, range from 8. 7 lb per ft3 (0. 139 g/cm3) for Alstonia spathulata Blume. , the lightest species, to 84. 1 lb/ft3 (1. 346 g/cm3) for Diospyros mollis Griff. , the heaviest species found in this country. Other properties, in general, are more or less related to the density. The data on treat­ ability of various timbers with conventional preservatives may have some bearing on the study of wood-plastic combinations. Consequently, a classification of some Thai timbers on this basis is also shown in Table I. The treatability classification is based on the treatment of wood with 50: 50 creosote and diesel fuel oil by means of the full-cell process with the following schedule:

Initial vacuum -0.8 kg/cm 2 30 min. Air compression 10 kg/cm2 2 h. Final vacuum -0.8 kg/cm 2 30 min. Maximum preservative temperature: 100°C.

Those belonging to Class I are timbers which can be fully impregna­ ted without air compression. The others are classed according to the retention of preservatives in wood in the following order: more than 120 kg/m 3, 80 to 120 kg/m 3, 40 to 80 kg/m 3, 10 to 40 kg/m 3, and le s s than 10 kg/m3, respectively.

305 306 TABLE I. LIST OF SOME THAI COMMEKICAL TIMBERS OG SONO PONG THAILAND 3 0 7

«в £ V о 8 " to л зe 1 л I S 3 н

< 6 Л O

c3

■s E я a> E £ •a H U < Q

C î (N 03 N 8 0 3

TABLE I (cont.) OG SONO PONG THAILAND 3 0 9

Professor J. K. Miettinen (Radiochemistry Department, University of Helsinki), on his private visit to Bangkok in September 1967, presented some of his findings on the study of wood-plastic combinations. With regard to the selection of raw materials, he reported that four species of woods received from Pakistan for the experiments are among those possessing very good properties for the production of wood-plastic com­ binations. The species are Salmalia malabarica Schott & Engl., Trewia nudiflora Linn., Tetram eles nudiflora R. Br. and Anthocephalus cadamba Mic. It is interesting to note that these four species are also common in Thailand and, in our own experiments with conventional preservative treatment, they all fall in Class I of the aforementioned classifi­ cation. Based on this finding, other Thai woods which should show excellent properties as raw materials for the production of wood-plastic combina­ tions are Alstonia scholaris R. B r., Spondias piñata Kurz. , Mangifara spp., Hymenodictyon excelsum Wall, and Ailanthus fauviliana Pierre. At present, about 51% of the total area of Thailand, or approximately 265 000 km2, is covered with forests of one kind or another. However, it is foreseen that in the future the forest area will unavoidably diminish. To cope with the situation, the general outline of the forest policy is now going to be modified to achieve maximum production per unit area per unit time from the remaining forests. The general idea of the policy is to make the forest composition more homogeneous and, wherever practicable, the natural forest will be replaced by an artificial plantation. The management of the forest in a particular area will be for a definite purpose. It is possible, therefore, that in the future a certain area may be set aside to produce raw materials for the production of wood-plastic combinations if the economic value of the process is proven. VIET NAM

CONTRIBUTED BY LE-VAN-THOI VIET NAM ATOMIC ENERGY OFFICE, SAIGON, VIET NAM

In South Viet Nam, forest covers about 30% of the land area or approximately 6 000 000 ha. Hardwoods comprise about 80% of the timber stock. The total growing stock is not known exactly. Forest inventory is difficult in Viet Nam since some areas are inaccessible in the virgin forest. Overcutting by the population for domestic uses should also be mentioned together with fire damage, destruction by the war, etc. Practically all species of fibrous wood which are common in South- East Asia grow in Viet Nam. Pine trees especially account for about 2% of the forest and bamboo for 1%, and rubber trees, kenaf and jute are abund­ ant. Valuable fibrous materials other than wood are agricultural wastes such as rice straw and bagasse. Table I presents a list of the most common fibrous plants of Viet Nam; their importance, however, cannot be evaluated. In addition, restricted numbers of these plants are consumed by the population of the region where they grow wild. Exploitation is, in fact, purely artisanal and tends merely to meet local needs. Cotton plants (Gossipium herbaceum) grow mainly in Central Viet Nam; the cotton product is not of good quality since the fibres are not very long. The following fibrous plants are found in South Viet Nam:

(a) In the mountainous region (northern region), kenaf (Hibiscus) and jute (Corchorus), the fibres of which were exported in the past. (b) In the western regions, ouate (Bombax) used for the manufactur­ ing of mattresses, pillows, etc. and coconut trees (Cocos nucifera L. ), the fibres of which are used for the manufacture of carpets, mattresses, cords, etc. (c) In the'Plaine des Jones', cyperacees (Cyperus) used for the manufacturing of mats, mattresses, bags, etc. (d) In nearly all regions, bamboo is exploited for various domestic uses.

It is possible to consider large-scale production of textile and other fibrous plants in Viet Nam, if their exploitation becomes more rational in the future. These natural resources are appreciable assets for the country's prospective economy because they may be used either directly or indirectly after impregnation with monomers and irradiation. For wood-plastic combinations, fibrous plants listed in the table can be used as well as other soft woods not mentioned here. At the pres­ ent time, the production of wood-plastic combinations would be too ex­ pensive, since Viet Nam has no suitable radiation source and no locally available monomer. However, it would be interesting to start research

310 VIET NAM 311

immediately on a laboratory scale to determine suitable conditions for irradiation, depending on the local fibrous species. Experiments should be carried out mainly on poor quality wood and other cheap materials, such as agricultural wastes, which have no technical use at present.

TABLE I. LIST OF FIBROUS PLANTS IN VIET NAM

F a m ily S p e c ie s

Am aryllidaceae Agave fourcroy des Lem. Agave sisalana Perrine

Asclepiadaceae Calotropis gigantea (L) R. Br.

Bombacaceae Ceiba pentandra (L), Gaertr. Bombax malabaricum DC.

Borraginaceae Cordia latifolia Roxb.

Bromeliaceae Ananassa sativa Lindley

Cannabinaceae Cannabis stiva L.

Cucurbitaceae Luffa cylindrica Roem* Sechium edule (Jacq. ) Sw.

C y p e r a c e a e Cvoerus m alacceusis Lamk. Cyperus tagetiform is Roxb. Cyperus procerus Rottb. Scirpus grossus L. Lepiromia mucronata.

L i li a c e a e Phormium ten ax Sansevieria cylindrica Bojer Sansevieria latifolia Bojer Sansevieria fasciata Com.

Leguminosae Bauhinia acuminata Butea frondesa Roxb. Crotolaria retusa L. Entada phaseoloides Merr.

Sesbania grandiflora ( I . ) P ers.

M a lv a c e a e Abutilón indicum (Sweet) Gien Gossypium herbaceum L. Hibiscus m utabilis L. Hibiscus rosa-sinonsis L. Hibiscus sabdariffa L. Hibiscus cannabinus L. Hibiscus tiliaceus L. Sida rhom bifolia (L.) Roxb. Sida acuta L. Thespesia populmea (L. ) DC. Urena lobata L. 312 LE-VAN-THOI

TAB LE I (cont.)

Family Species

Marantaceae Donax arundinastmm Lour

M o r a c e a e Broussonetia papyrifera H. Brillon

M u s a c e a e Musa cf. Sylvestris

P a lm a e Boxassus flabellifer L. Caryota ureus (L) Roxb. Cocos nucifera L. Livistonia cochinchinensis Mart. Nipa fructicans Thunb. Warm.

Pandanaceae Pandanus tectorius Sol.

Pentederiaceae Eichhomia crassipes (Mart. ) S e im s

Sterculiaceae Sterculia cochinchinensis Pierre

T i l i a c e a e Corchorus acutangulus Lark Corchorus oliterius L. Corchorus capsularis L. Grewia paniculata Roxb. Muntingia calabuia L.

U r t ic a c e a e Boehmeria nivea (Hook, and Am. ). TECHNICAL PAPERS

FIBROUS MATERIAL RESOURCES IN ASIA AND THE FAR EAST

D.L. STACEY FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS, REGIONAL OFFICE FOR ASIA AND THE FAR EAST, BANGKOK, THAILAND

Abstract

FIBROUS MATERIAL RESOURCES IN ASIA AND THE FAR EAST. The resources of fibrous materials in different countries in the Far East are described in detail. Extensive data on these resources are given.

1. INTRODUCTION

Difficulty has been experienced in the past, and is still being ex­ perienced to a lesser degree, in obtaining forest inventories for the Far East region. This is not surprising since the areas involved are often very large, substantial tracts are in rugged country, often very sparsely settled, with a concomitant lack of communications. Very often large areas are virtually inaccessible in the wet season. However, with the realization that fibrous materials are a natural resource, widely scattered and renewable if appropriate techniques are followed, many countries are carrying out further inventory work. This is either to get information on virgin country or to update old informa­ tion which can be misleading and seriously in error. The alienating of forest land for agriculture, in many cases by shifting cultivation, coupled with very substantial fuelwood uses which are not recorded in the vast majority of cases, means that reports in these regions tend to become outdated very quickly. One other difficulty is that the wood forest, by definition a "large tract covered with trees and undergrowth sometimes mixed with pasture" does not connote the stocking density of the area with the result that this too can vary over an extremely wide range so that sometimes countries with smaller areas of densely stocked forest have more standing wood than much larger forested areas sparsely stocked. Within these lim ita­ tions, however, it may be said that the -Far East has scattered and limited reserves of coniferous forest. All too often these reserves are relatively inaccessible. This is unfortunate since it is the long-fibred coniferous woods which have built up most of the substantial forest in­ dustry in the temperate climate countries. Generally, the region has also many mixed tropical hardwood species which are very heterogeneous. As a result much of the virgin forest does not as yet command a commercial m arket. Temperate zone hardwoods are being used commercially in some countries, mainly in Japan and Korea and at higher latitudes.

3 1 5 316 STACEY ( c ) Total forest area of countries reporting expressed as a percentage of total sub-regional or regional forest area. (d) (d) Refers to total forest ( e) land excluding Including protection a few areas reserves for in which which ownership cutting is not of yet industrial determined. wood is prohibited. RESOURCES IN ASIA 3 1 7

The lack of indigenous long-fibred species has resulted in bamboo being more widely used as an all purpose material, and various grasses, cereal straws, which in many countries are a major source of fibrous materials, and other materials have also been adapted as a fibre resource. Bagasse, particularly in India, has been used as a raw material and both bamboo and bagasse are to provide the raw material for much major pulp and paper industry currently developing in the region. The fibrous wood materials generally available are well summarized in a paper published in 1963 [ 1]. This stated that all the sub-regions of the Far East possessed forest resources capable of supplying their needs for the forseeable future as far as pulp and paper manufacture was con­ cerned, but it specifically mentioned that precise estimates of growing stock, total forest areas and hence potential sustained yields were not readily available because few countries have had their inventories long enough to determine growth increments. Table I gives information on the forests of the various sub-regions and the whole o f the F a r East. It is apparent that:

(a) The forests are very unevenly distributed relative to population. (b) In most of the sub-regions broad-leaved tropical forests predominate. (c) Substantial forest areas are at present economically inaccessible. However, the following data endeavour to show the total fibre resource.

Table II has been derived from many official publications and shows the most prevalent raw resources from each country of the region with the major exceptions of North Korea, Mongolia, and Mainland China. A brief note on each country follows alphabetically, i. e. Australia, Burma, Cambodia, Ceylon, India, Indonesia, Japan, the Republic of Korea, Laos, Malaysia, Nepal, New Zealand, Pakistan, the Philippines, Taiwan, Thailand and Viet Nam.

2. A U S T R A L IA

Australia has 769 million hectares of land of which 206 million hectares or 27% is forested. This forested area is sub-divided into accessible and inaccessible fo re s ts .

2. 1. A c c e s s ib le

(a) Productive forests in use

(i) C oniferou s 200 000 ha. (ii) Non-coniferous 9. 9 million ha. (iii) Mixed woods 2. 2 million ha. (iv) Open forest 100 000 ha.

(b) Productive forest not in use is 12.9 million ha.

(c) Unproductive accessible forest is 104 million ha. 8 1 3

TABLE II. FIBROUS MATERIAL RESOURCES IN ASIA AND THE -FAR EAST STACEY

Bagasse fibre oven dry is calculated at 12.5% of the sugarcane weigh* Straw is calculated at 1.5 times the weight of grain produced. RESOURCES IN ASIA 319

2. 2. In a ccessib le

Inaccessible forests amount to 77. 5 million hectares. The total growing stock is reported to be 2 176 million cubic metres made up of 76 million cubic metres of conifers and 2 100 million cubic metres of hardwoods. However, since indigenous species, together with planted exotic conifers, do not supply total needs, there is a considerable importation of desired wood species, mainly from the North American West Coast, the Philippines and New Zealand. Bamboo does not exist in commercial quantities. Bagasse exists mainly in the tropical area of Queensland and is a poten­ tial supply of 1. 8 million tons of bone-dry fibrous material. Most of this is used as boiler fuel. A little is manufactured into insulating and hardboards. Rubber is produced only to a small extent in Australian New Guinea (5 700 tons in 1965) and therefore rubberwood supplies have no commercial application to the Australian mainland. Total cereal straw amounts to 14.4 million tons, of which wheat ac­ counts for 10. 75 million tons, barley for 1. 6 million tons, oats for 1. 6 million torts; these cereals are the major contributors. Most is used for cattle fodder. Rice straw amounts to only 250 000 tons and is negligible. Australia has sufficient fibrous materials for her general needs and imports consist of preferred materials not obtainable locally.

3. B U R M A

The forests represent a valuable and extensive area of 45. 2 million hectares. Currently, 25. 6 million hectares are productive forest and 16. 8 million are reserved permanent forest. Four per cent are beach, swamp, or tidal forests. Fifteen per cent are wet evergreen while 40% are mixed deciduous type. Dry forest zone accounts for 10%. Dry Dipterocarp species compose 5%. _ Hill forests are 16% and coniferous forests, at 5%, make up the remainder. Bamboo sustained supply is in millions of tons per annum from 9 million hectares of forests comprising some 200 different species. Bagasse exists as a potential supply of 180 000 bone-dry metric tons of fibre annually. Cereal straws amount to 12.3 million tons, of which rice straw ac­ counts fo r 12. 1 m illio n tons. Rubberwood is estimated to be available at 160 000 cubic metres annually if plantations are replanted on a 33-year rotation. Grasses, mostly Saccharum spotanum, reportedly exist in substan­ tial quantities in the Toungoo district but the yield is not available. Burma has extensive fibrous material resources.

4. CAMBODIA

Cam bodia w as re p o rted in 1963 as having 13. 3 m illio n h ecta res with a standing volume of 556 million cubic metres. Forest types are 11% 3 2 0 STACEY dense equatorial type and 22% dense monsoon forest. Dipterocarps ac­ count for 55% of the more lightly stocked forest while only 0. 5% are coniferous. Bamboos occur over 387 000 hectares at an unspecified density. Bagasse fibre was not available. Cereal straws amount to 3. 8 million tons, all of which is rice straw. Rubberwood (Hevea brasiliensis) should be available at 140 000 cubic metres per annum if plantations have a 33-year rotation. Cambodia has sufficient fibrous material for many years.

5. C E Y L O N

The forests are reported to encompass 2. 8 million hectares with a growing stock of 130 million cubic metres. Bamboo is known to exist, but neither the area nor the stocking density was available. Sugar cane bagasse, as bone-dry fibre, only amounts to 12 000 tons p e r annum. Cereal straw totals 1. 18 million metric tons, of which 1. 13 million tons come from rice. Generally, Ceylon has sufficient fibre resources.

6. IN D IA

India, more than most countries, has the serious handicap of un­ balanced geographical distribution of forests relative to the population distribution and this is coupled with transportation difficulties. W ood is stated to' c o v e r 78. 4 m illio n h ecta res o r 24% o f the country, but only 50.0 million hectares are accessible. Coniferous stock covers 2. 6 million hectares in a narrow band across the whole width of northern India, but it only amounts to 3. 3% of the total. Broad-leaved species, at 2. 9 million hectares, account for 3. 7%, and tro p ic a l fo re s t, at 72. 9 m illio n hectares,am ou nts to 93% o f the forest. The growing stock is 2 128 million cubic metres with an annual growth increment of 41. 8 million cubic metres. Bamboo covers 3. 6 million hectares and some 1. 56 million air-dry metric tons are reportedly collected per annum. Bagasse yields some 14. 5 million bone-dry tons of fibre per annum, but currently much is burned as fuel, for steam raising at sugar processing plants. Cereal straws yield 118 million tons per annum, of which rice straw alone provides 69 000 tons. This is the largest annual fibrous resource but much is used for fodder, fuel and fertilizer. Rubberwood should be available at 450 000 cubic metres if trees are on a 33-year rotation.

6.1. Summary

The overall view of India's forest resources and exploitation shows the very unbalanced geographical distribution of forest. RESOURCES IN ASIA 321

7. INDONESIA

Indonesia has a total land m ass o f 190 400 000 h ecta res o f which 121 700 000 h ecta res, o r 64%, is fo re s te d . T h ere is, h ow ever, a m a l­ distribution in areas of dense population, e. g. Java is short of wood supplies whereas the other islands, which are progressively less densely populated, have increasing wood supplies. The forests range from coniferous trees, e. g. Pinus and Agathis species on parts of Sumatra and Kalimantan, respectively, to very densely stocked rain forests, mainly Dipterocarps. Only 14% of the forests have been surveyed and hence an inventory is not possible, but it is quite clear that the wood fibrous resources of Sumatra Kalimantan, Sulawesi and Maluku and West Irian are virtually lim itless in 1967. Almost all the 121 million hectares are tropical rain forest except for several million hectares of savannas in some regions of low rainfall, some 2. 5 million hectares of tidal forests, and 1. 2 million hectares of forest plantations. Bamboo grows readily over Indonesia and is the material most used by 100 000 000 inhabitants as an a ll-p u rp o se m a te ria l. H ence no in ven tory could be taken. Two concentrated areas occur, one on South Celebes with 12 000 hectares of natural forest and the other on East Java where 2 000 hectares of culti­ vated bamboo are near 7 000 hectares of natural bamboo forest. These are the raw material supplies for one existing and one planned pulp and paper mill. Bagasse production in ten major districts amounts to 1. 2 million bone-dry metric tons of bagasse fibre. Cereal straw is available in the amount of 23. 3 million tons per annum. Some 19. 8 million tons of this are rice straw. Rubberwood appears to be available in the amount of 2 800 000 cubic metres per annum, mainly from Sumatran plantations.

8. J A P A N

Japan has a total forest area of 25 053 000 hectares with a reported growing stock of 1891 million cubic metres. Some 953 million cubic metres are coniferous woods and 938 million cubic metres are hardwood sp ecies. The mean annual increment is nearly 61 million cubic metres, of which 34 million cubic metres are coniferous and 27 million are hardwoods. Some 187 000 hectares of bamboo exist but the stocking density is not available. As a by-product of sugar production some 103 000 metric tons of bone-dry fibre from bagasse is available. Cereal-straws provide 28 400 000 metric tons of straw, of which rice straw at 24 200 000 metric tons is the major proportion. Japan has trouble with her fibrous resources and is currently im ­ porting large quantities from overseas. For example, nearly one quarter of the wood requirements for pulp and paper come from overseas at p resen t. 322 STACEY

9. K O R E A , R E P U B L IC OF

The total forest of 6. 7 million hectares has a reported standing volume of 60. 5 million cubic metres. Some 1. 6 million hectares of plantations are included in this. Bamboo only occurs on about 4 000 hectares and is poorly stocked. Bagasse does not occur. Cereal straws amount annually to 9.-2 million tons with rice straw contributing 7. 1 million tons. Straws are mainly used for fuel, fodder, com post and thatching. Korea is acutely short of fibrous raw materials.

10. LAO S

Laos has 15 million hectares listed as forest. Due to current dif­ ficulties an inventory has not been possible, but it is known that there is a very large forest area with good stocking density. Selected in­ ventory work has just commenced. Little information is available except that cereal straws amount to 1. 14 million tons of which rice straw com­ prises 1. 1 million tons.

11. M A L A Y S IA AND SIN G A PO R E (T A B L E III)

Malaysia, comprising West Malaysia, Sarawak and Sabah, has large forests. These forests range from swamp types, through lowland wet e v e rg re e n , m ain ly D ip terocarp s, up to between the 350 and 700 m etre contour.

TABLE III. FORESTS OF MALAYSIA 1962

Sab an Description West M alaysia S a r a w a k M a la y s ia (1 000 h a)

Total forest area 8 8 1 4 6 047 9 1 7 2 2 4 0 3 3

Per cent of total land 6 7 79 75 73

Productive forest 7 6 1 0 2 816 9 1 7 2 1 9 6 4 3

Per cent of total forest 86 47 1 0 0 82

Hill forests, again mainly Dipterocarps, range from the 350 to 1 500 metre contour. Above this montane, forests of oaks and ericaceous species serve mainly for protection. Inventories have not been completely carried out but it is clear that the 19. 6 million hectares heavily stocked are a major raw resource and are being exploited as such. Bamboo occurs throughout West Malaysia in small areas but is not a major fibrous source commercially. Bagasse is non-existant, as sugar cane is not grown. RESOURCES IN ASIA 323

Cereal straws amount to 1. 65 million tons, all derived from rice from 346 000 hectares, some 17 000 hectares of which are doubly cropped. Some 4. 03 million cubic metres of rubberwood could be available per year from the 1. 7 million hectares currently under rubber cultiva­ tion even if only 50% to 60% of the wood were collected from the major estates. Singapore has no fibrous resources except a small amount of sawmill wastes amounting to only some 145 000 green m etric tons.

12. N E P A L

Nepal has a total forest area of 4 532 000 hectares ranging between coniferous forest on the montane slope and mixed hardwoods at lower levels. Some bamboo is reported in the south-east region. A major survey for forest inventory has just been completed. Some 28 000 B. D. М. T. of bagasse fibre is available from sugar production. Cereal straws amount to 4. 9 million tons, of which rice straw com­ p ris e s 3. 3 m illio n tons.

13. N E W Z E A L A N D

New Zealand has a total land mass of 26 871 000 hectares of which 7 365 000 h ecta res, o r 23%, is fo r e s t land. Growing stock is reported as 321 million cubic metres to which coniferous species are stated to contribute 267 million cubic metres, while other species amount to 54 million cubic metres. Extensive coni­ ferous plantations, mainly of pine species, were planted mainly through the years 1925-38 and the whole of the substantial pulp and paper industry is based on this as a raw resource. Indigenous virgin species are diminishing. Rubberwood bamboo and bagasse are non-existant in this country. The total cereal straws amount only to 637 000 tons and most of this is used as cattle fodder. New Zealand's fibrous resources, are, and must continue to be, wood.

14. P A K IS T A N

E ast and W est Pakistan c o lle c tiv e ly re p o rt 3 614 000 h ectares of forest with a total growing stock of 146 million cubic metres. Bamboo occurs extensively and is used for pulp and paper. Some 3. 8 million bone-dry tons of bagasse fibre equivalent are available per year, but most is burned as fuel. Cereal straws amount in total to 35. 5 million m etric tons of which rice straw provides 26. 7 million tons. 3 2 4 STACEY

15. PHILIPPINES

The Philippines are well endowed with natural resources. Some 14. 6 million hectares, or43. 7% of the land mass, is forested; of this some 11.6 million hectares are on the major islands and the total gives a standing wood volume of .1 358 million cubic metres. The bulk of this is on the island of Mindanao. Dipterocarps make up 52% of the species below the 1 000-metre contour and the most widely-known are the lauans, also marketed as 1 Philippine mahogany' . There is considerable scope for very fast grown short-fibred wood species in more plantations. 6. 5% of the forest is in pine species, mainly at the higher levels on Luzon. Bamboo occurs throughout the islands in small scattered areas with no significant fibre contribution. Bagasse fibre amounting to 1.4 million metric tons, bone dry, is harvested, but most is used as boiler fuel in sugar refineries. Cereal straws amount in total to 8. 2 million tons, of which rice straw is 6. 1 million tons. New species of rice are likely to have more grain and less straw. Since only 6 000 tons of rubber is produced annually rubberwood supplies are negligible. Some 135 000 tons of abaca fibre were produced and this indicates than som e 225 000 tons o f abaca w aste w e re available in 1966.

16. R E P U B L IC O F C H IN A (T A IW A N )

1 970 000 hectares or 55% of the land mass is covered with forests. Of these some 395 000 hectares are coniferous while broad-leaved stands cover 1 461 000 hectares. Total growing stock is reported at 226 million t cubic metres (102 million cubic metres of conifer and some 124 million cubic metres of mixed hardwoods). Much of this forest is, however, inaccessible. There are some 114 000 hectares of bamboo, which is a much used com m odity. The equ ivalent of 1 100 000 tons o f b on e-d ry bagasse fib re is p r o ­ duced, but most is used as fuel in the sugar refinery boilers.

17. T H A IL A N D

Forest covers 28 million hectares or 55% of the country. 26 million hectares are productive and have a recorded standing volume of 803 million cubic metres of wood. These forests have been depleted in the past by overcutting, fire damage, illegal encroachment and shifting cultivation which cumulatively results in a low yield. Virgin pine forests account for approximately 4. 7 million cubic metres. Bamboos occur in the west where over 850 000 hectares of bamboo grow with an estimated yield of 7 million air-dry tons. Of this RESOURCES IN ASIA 325 some 1. 65 million tons from 130 000 hectares is stated as being economi­ cally accessible. B agasse a risin g fro m the 1966 crop is estim ated at 440 000 o ven -d ry tons of bagasse fibre. Rubberwood occurs over 629 000 hectares in the south and 70-80% is classed as overmature stands. On a 33-year rotation this should provide 830 000 cubic metres of rubberwood annually. Grasses occur but have not been processed commercially. Hence reliable statistics are missing. Cereal straws amount to 15. 9 million tons, most of which is raw straw at 14.4 million tons. K en af and jute (310 000 tons) w e re produced fro m 225 000 h ecta res in 1964.

18. V IE T N A M

Viet Nam is reported to have an area of 17 146 000 hectares of which 5 620 000 h ecta res, o r 33%, is cla ssed as fo re s t. This is further divided into upland forests of pine species comprising 125 000 h ecta res and hardwood fo re s t o f 5 015 000 h ecta res. T h ese two total 91.4% of the forest. The remaining 8. 6% is made up of mangrove and other aquatic plants. Generally stocking is low and an inventory is not yet possible. Some 60 000 hectares of bamboos occur but their stocking density is not available. Approximately 137 000 tons of bone-dry bagasse were produced in 1964. Straw amounted to 7 300 000 air-dry tons, of which 7 250 000 tons were derived from rice straw.

REFERENCES

[1] Wood World Trends and Prospects. UNASYLVA V ol.20 (1-2) Numbers 80-81, 1966.

PRODUCTION ECONOMICS OF IMPREGNATED FIBROUS MATERIALS

E. ROTKIRCH EKONO, HELSINKI, FINLAND

Abstract

PRODUCTION ECONOMICS OF IMPREGNATED FIBROUS MATERIALS. The basic economic factors to be considered before producing impregnated fibrous m aterials are detailed. A list of reference tables is provided, together with a comprehensive bibliography.

1. INTRODUCTION

In November 1965, at the World Chemical Engineering Congress in Mexico City, a prognosis up to the year 2000 was given for various construc­ tion materials. The most striking statement was that the consumption of plastics doubles every five years. From the condensed information in Fig. 1 it is clear that the curve for the volume of plastics for construction pur­ poses cuts the curve for the production figures for wood panel products (including plywood, block-, fibre- and particle-board) in 1980 and the curve for world production of sawn wood in 1990-1995 [1] . For the industries concerned with natural fibrous raw material this diagram reveals a strong challenge, which is by no means restricted to wood panel and sawn wood products only. There exists an urgent need for new roads of approach. In some areas of the world the industrial production capacity utilizing the available re­ sources of natural fibres has come close to the possible annual removal. Without new sources of raw material — either imported natural fibre ma­ terial or synthetic fibres — these industries must stop their expansion. Vigorous research in this field is carried out in most of the world's respon­ sible centres. This paper is a revised and enlarged version of the paper presented by the author during the meeting in Bangkok. A study of the information made available in Bangkok and further studies of the literature made it possible to arrive at more definite conclusions than were possible in the autumn o f 1967. Even though the facts presented in this paper are based on information available from various currently operating plants and the estimate of the labour needed was made according to the author1 s best available know­ ledge, it should be pointed out that no data are available from actual large- scale production plants producing impregnated fibrous materials such as WPC or combinâtes of synthetic polymers and wood panel products; The following presentation should therefore be taken as an attempt to bring relevant economic data into a systematic form and indicate the relative influence of the various contributions to the total breakdown of

327 328 ROTKIRCH

I960 1970 1980 1990 2000

CALENDAR YEAR

FIG. 1. Expected world consumption of some construction materials. Figures derived from FAO Yearbook of Forest Products Statistics 1966, com pleted with figures from Tim ber Bulletin for Europe 1967 and Modem Plastics, August 1966 [1]. the costs of these new products. The author would welcome a discussion and would naturally be grateful for criticism , corrections and additional information1.

2. THE MANUFACTURER' S QUESTIONS

When faced with the task of incorporating a new material into the production line and — above all — of trying to market a new product, the manufacturer likes to have convincing answers to several questions of the following type:

- Is there a potential market for the new product? - What are the competing products? - What are the consumer's ultimate requirements and how much is he ready to pay for the improvement induced by this new method? - What are the testing results, and how far is research and development to be carried? - Is the product fully developed and ready for the market? - What are the possibilities of incorporating the processing equipment into existing production lines ? - What is the availability of dependable equipment for this special trea tm en t? - What sort of skilled labour is needed? - What are the health and safety requirements if it is necessary to diverge from ordinary industrial practice ? - What is the production economy, and how does large-scale production reduce the cost per unit? - Is it necessary or recommendable to have manufacturers group together to utilize the inherent gain in large-scale production?

A ll correspondence should be directed either to C .K . Beswick, the Scientific Secretary of the m eeting, at the IAEA, or directly to the author. PRODUCTION ECONOMICS 3 2 9

3. MARKETING STUDIES

The programme of this study group meeting includes papers dealing with many of the above-mentioned aspects, such as the status of research and technology of the polymer-impregnated fibrous materials. Marketing studies for wood-plastic combinâtes (WPC) have been carried out in the United States of America [2, 3] and in Sweden [4] . No attempt will be made here to describe the results, as it is felt that various parts of the world would give different indications for the same product. Individual marketing studies are therefore recommended. The new high-quality product created by combining natural fibrous material with synthetic polymers will in the long run doubtless find its appropriate place among especially desirable building and construction m a te ria ls . The two obvious courses to pursue are:

(a) Development and introduction to the market of WPC products with the great variety of items they encompass. (b) Development and marketing of various types of wood-panel products combined with synthetic polymers. These could be either in the form of surface treated sheets of material or fully impregnated panel products.

Methods are available and sufficient basic knowledge has been gathered to enable the interested industry to star.t production if and when the market is considered ready to receive these products.

4. COST EVALUATION

To facilitate the manufacturer1 s judgement an attempt is made to find at least the relative cost figures for manufacturing polymer-impregnated fibrous material. The study includes WPC products as well as polymer-impregnated wood panel products, and catalytic curing is compared with irradiation curing.

4. 1. Manufacturing of WPC products

The costs are split up into four main groups, namely, costs for wood raw material, costs for impregnation, costs for impregnation chemicals and curing costs.

4. 1. 1. Raw m a te ria l

The raw material chosen is Finnish birch, which in Finland is sold to large consumers for US $145/std sawn wood excluding tax2. The figures for loss during manufacturing the product vary widely. The parquet fac­ tories claim losses between 30 and 75% depending on quality and end use. Furniture factories claim raw material losses of the order of 50%. Since the product to be impregnated and cured should be as close to a finished product as possible, the raw material price has been calculated

2 std = standard = 165 ft 3 or 4.672 m3. 330 ROTKIRCH as 8-9 ф. per kg. If 40% impregnation is assumed, the cost contribution of raw material in the end product will be 5 ^ per kg WPC. A closer study of a better defined production process may well reveal that the material mentioned above as a loss can in actual fact be utilized for some useful purpose such as particle-board production. The raw material price should then be credited accordingly.

4.1.2. Impregnation

Impregnation of poles, sawn wood, etc. is a routine affair with ordinary impregnation chemicals. No practical experience of large-scale impregna­ tion with monomers is recorded, but it is assumed that the old impregnation technique mutatis mutandis would be valid even here. Table I includes the cost figures for production capacities of 10 000 t/yr and 100 000 t/yr. The figures arrived at compare fairly well with the re­ ported price for impregnation of sawn wood, poles and logs in Finland. These price figures are 0.6- 1.2 ^/kg, excluding impregnation chemicals and taxes. For the subsequent evaluation an even 1. 0 j /kg is used.

4.1.3. Curing by gamma irradiation

Large irradiation facilities have been in operation since the early nineteen-sixties. They were mainly built for sterilization purposes, but the basic technique and the operational principle can be adopted for handling monomer-impregnated wood. The evaluation of costs is there­ fore based on reported sterilization plant data. The most controversial figure in this evaluation is the estimated cost of the gamma source. The available figures are collected in a diagrammatical form in Fig. 2 and an evaluation of two different cobalt prices is given in Table IV. The author cannot avoid the intuitive feeling that cobalt prices must drop in the future when the slack periods of large nuclear power stations are utilized. The lim it for price reduction is naturally difficult to estimate, but w ill obviously approach the handling costs of cobalt to which some charges by the power station should be added. The capital costs for the facility, excluding source, are given in Fig. 3, and are shown to follow the formula

C(M $) = 0. 75 X D [(M C i)]0'38 where С indicates facility costs in millions of US dollars, while D expresses the final source strength in millions of curies [5]. Incidentally, the portion of the total plant cost due to source investment increases rather rapidly with increasing plant size. This is indicated in Table II and Fig. 4. The direct personnel requirements are specified in Table III. However, the individual wages are not indicated, as they may vary in different countries. Only the bulk sum is accounted according to the Finnish standard and includes compulsory insurance and annual holidays. These personnel requirements may be considered high and rather top heavy. When experience has been gained it is expected that the labour costs will decrease. If impregnation and curing are integrated, these two plants can utilize the same management and supervision. PRODUCTION ECONOMICS 331

TABLE I. IMPREGNATION COSTS EVALUATED FROM AVAILABLE FINNISH IMPREGNATION PLANT OPERATING EXPERIENCE (Finnish standard wages 1968)

(a) Production (t/yr) 1 0 000 10 0 000

Total plant cost (10 6 $) 0 .1 6 0 .6 5

Operation (h/yr) 8 000 8 000

Operating costs (1000 $/yr)

Interest, at 8% / y r 1 2 . 8 5 2 .0

Am ortization over 10 yrs 1 6 .0 6 5 .0

Direct labour 4 0 . 0 ^ 9 5 ,0 ^

M aintenance and repair 5 .0 2 0 .0

U t ilit ie s 7 . 5 3 0 .0

I n su ra n c e 0 .9 4 .0

Total annual cost

of impregnation (10 0 0 $ /yr) 8 2 .2 2 6 6 .0

Specific impregnation cost (¿/kg) 0 . 8 0 .3

(a) M etric tons. (b) One supervisor operating day-tim e: 1 skilled and 1 unskilled for the impregnation

plant, operating in three shifts; 1 sem i-skilled and 1 unskilled for the storage, re­ ceiving and shipping operating in one shift. (c) Same as (b) with addition of 1 skilled operating in two shifts, 2 unskilled operating

in three shifts for the plant and 1 sem i-skilled and 2 unskilled operating in two shifts.

The total irradiation costs are listed in Table IV where the annual and specific irradiation costs for two hypothetical production values, 10 000 t/yr and 100 000 t/yr, are evaluated. For the following estimate the value of 3. 8 ¡é/kg W P C is adopted.

4.1.4. Impregnation chemicals

For bulk shipments of 10 to 20 metric tons of some impregnation chemicals of interest, the prices are as listed in Table V. It is understood that price reductions can be negotiated when larger bulk deliveries are in volved. 332 ROTKIRCH

о □ д

SOURCE STRENGTH, MCI

FIG.2. Cobalt price including encapsulation but excluding transport as function of source strength [24, 28, 2 9 ] . © Prognosis made 1965 [28]. □ Neutron Products price list [29]. Д Expected price limit given by commercial cobalt dealer [24]. • Shipment to Austria, Seibersdorf 1967.

SOURCE STR E NG TH , MCi

FIG.3. Capital cost of gamma irradiation plant. — Total plant; ------Facility excluding source ; — Source, cobalt-60, calculated from Fig. 2.

4. 1. 5. Curing by catalytic methods

For simplicity the costs are assumed to be restricted to costs of additives only. This is not exactly true, but is considered close enough for rough studies like this. The specific cost would then be 1.4 jé/к g WPC for peroxides, 0.2 ^/kgWPC for naphtenates and a small — but for the moment not publicly known — amount for reaction-controlling chemicals. PRODUCTION ECONOMICS 333

TABLE II. PORTION OF TOTAL PLANT COST DUE TO FACILITY AND SOURCE, .RESPECTIVELY

Source strength (10 6 C i)

0 . 0 1 0 . 1 1 . 0 1 . 0 10 0

Facility excluding source (10s $) 0 .1 3 0 0 .3 2 0 .7 5 1 .8 0 4 . 3

Source (“ Со) (10 6 $) 0 . 0 1 2 0 .0 6 0 .3 0 1 . 5 0 1 1 . 0

Total plant (10 6 $) 0 . 1 4 0 .3 8 1 . 0 5 3 . 3 1 5 . 3

SOURCE STRENGTH, MCi

FIG.4. Proportion of total gamma irradiation plant costs. Hatched area: facility excluding source ; dotted area: source.

4. 1.6. Total cost breakdown for WPC products

The specific cost figures mentioned above are grouped together in Table VI for a production rate of 10 000 t WPC/yr. The table shows a comparison of irradiation curing and catalytic curing as well as cost figures for different impregnation chemicals. The ultimate WPC product is calculated to contain about 40% impregna­ tion chemicals. When comparing the catalytic curing method with the irradiation method it was assumed that the catalytic method can accept only 30% styrene in the styrene/unsaturated polyester mixture, while 50% styrene in the same mixture can be used for the irradiation method. Development work may change the prospects of the catalytic method. The Finnish firm Neste Oy has indicated some new avenues of approach, but no published information, are available at the moment (May 1968). The information in Table VIII reveals that the impregnation chemicals play by far the most important role in the WPC production cost. It can also 334 ROTKIRCH

TABLE III. ESTIMATED PERSONNEL REQUIREMENTS FOR IRRADIATION FACILITY

Production capacity 10 000 t / y r 10 0 000 t / y r

Ca) Number of shifts employed 1 2 3 1 2 3

Responsible manager 1 1

Instrument engineer 1 1

S u p e rv iso r 1 1

O p e r a to r 1 1

Handling and shipping

- skilled labour 1 3

- semi-skilled labour 1 1

- unskilled labour 1 1

- truckdrivers 1 1

(b) Total labour cost 63 000 $/yr 93 000 $/yr

^ One shift = 2640 h/yr; 2 shifts = 5280 h/yi; 3 shifts = 8000 h/yr. (b) Finnish standard wages including compulsory insurance and annual holidays.

be seen that catalytic curing is competing on equal ground with irradiation curing, even at the high load factor used in this evaluation. Evidently the catalytic method will be used for low and/or intermittent production. It should also be recommended as a first step, as it does not require large capital investment and could be abandoned if the market shows unwilling­ ness to absorb the new product. The relative importance of the various cost contributions as a function of load factor is shown in Fig. 5.

4.1.7. Comparison of WPC price with noble wood prices

Even though large-scale production w ill reduce the costs of impregna­ tion and curing as indicated in Tables I and IV, this would influence the WPC price in a minor way. The dominating cost portion is due to the chemicals, and their price trend does not show any remarkable downward slope today. Use of these chemicals in very large quantities — for extensive WPC production, for example — would naturally reduce the prices considerably. A comparison of noble wood prices with that of the WPC product shows that WPC could only be considered as a substitute for the most expensive types of noble wood. The prices in Table VII are valid for free delivery to a large consumer's gate, excluding tax. The WPC price includes general ex­ penses equivalent to 40% of the manufacturing costs given in Table VI. These PRODUCTION ECONOMICS 335

TABLE IV. EVALUATION OF GAMMA IRRADIATION COSTS FOR TWO PRODUCTION RATES Source: Cobalt-60

Production capacity (t/yr) 1 0 000 10 0 000

Operation (h/yr) 8 000 8 000

Source мСо (10 6 C i) 1 10

Facility excluding source (10 6 $) 0 .7 5 1 . 8

Source 30(a>- 40 (•>) Ц C i ( 1 0 s $) 0 . 3 0 - 0 . 4 0

15(a)-25(°))S/Ci(106 $) 1 . 5 - 2 . 5

Total plant cost (10 6 $) 1 . 0 5 - 1 . 1 5 3 . 3 - 4 . 3

In te r e s t, 8%/yr (1000 $/yr) 8 4 - 9 2 2 6 4 - 3 4 4

Amortization, 10 yr (1000 $/yr) 1 0 5 - 1 1 5 3 3 0 - 4 3 0

Source replenishm ent, 12.5(7o/yr (1000 $/yr) 3 8 - 50 1 8 8 - 3 1 3

Direct labour ^ (1000 $/yr) 6 3 93

Maintenance & repair^ (1000 $/yr) 7 . 5 18

Insurance № (1000 $/yr) 4 . 5 1 4 - 1 7

U tilities (1000 $/yr) 8 30

Adm inistrative and unforeseen expenses (1000 $/yr) 75 300

Total irradiation cost (1000 $/yr) 3 8 0 - 4 2 0 1230 - 1550

Specific irradiation cost (¿/kg) 3 . 8 - 4 . 2 1 . 2 - 1 . 6

(b) Price charged for delivery in 1967 (35 ООО Ci to Austria). (c) Price lim it estimated by com m ercial cobalt dealer. (d) Table III. (e) Experience figure (United States of America) 0 .1-1.5% on facility cost excluding source.

(0 Practice in United States of Am erica: 0.4 % on total plant cost.

general expenses are assumed to include storage, transport, marketing and due profit. On the other hand, no attention has been paid to losses caused by quality selection. These losses could amount to 10-15%, but no experience is recorded. The high price of WPC products could be justified if the product possessed exactly the qualities required for a specially defined purpose. However, the large cost portion due to the impregnation chemicals leads to the conclusion that impregnation of surface layers or coating solid wood with polymer-impregnated veneer sheets would be the most economic pro­ posal offered at the moment. 336 ROTKIRCH

TABLE V. MONOMER PRICES IN EUROPE (1968) ACCORDING TO PRICE LIST GIVEN BY EUROPEAN CHEMICAL NEWS (1968). CIF 10 to 20-ton shipments.

Europe 1968 Taiwan 1967

( ¿ / l b ) ( ¿ / k g ) (/i/kg) (a)

M o n o m e rs

Vinylchloride 8 .0 1 7 . 6 1 7 . 6

Vinylacetate 1 2 . 0 2 6 .4 2 5 .3

S ty r e n e 8 .2 1 8 .0 2 7 . 4

Akrylnitrit^) 1 6 .0 3 5 .0

Polyester (c) 1 7 . 3 3 8 .0

M ethyl methacrylate 2 0 .0 4 4 . 1 5 5 .0

A d d it iv e s

P e r o x id e s 8 1 .0 1 7 9

Accelerators (naphtenates) 4 3 .0 95

(a) R e f. [ 8 ]. (k) The values are valid in Belgium and England; France reports 50.0, Italy and the Federal Republic of Germany 42-44 ¿/kg.

(c) M ixture of 30-35% styrene + 70-65% unsaturated polyester.

4.2. Manufacturing of impregnated panel products

Under this heading are grouped all kinds of fibre-, particle- and block- boards as well as veneer and plywood. It is understood that one of the main themes of these Proceedings is the study of the feasibility of manufacturing monomer-impregnated, radiation- or catalytic-cured panel products. Special emphasis is put on evaluation of methods to utilize local raw materials such as bagasse, bamboo, jute, etc. The requirements of quality improvements and the technical possibilities of meeting the demand are dealt with elsewhere in these Proceedings. It is therefore assumed that the technical problems are already solved in the processing methods mentioned below. This may not be entirely true, as little work has been carried out with PPC products3. The curing of impregnated panel products puts quite a different demand on the curing methods than the curing of impregnated solid wood products.

3 The author would like to suggest the following abbreviations for convenient every-day use: WPC = polymer impregnated wood products (already in general use), PPC = polymer impregnated panel products. F PC = polymer impregnated fibrous materials (general conception including WPC, PPC, etc.). TABLE VI. TOTAL COST BREAKDOWN FOR WPC PRODUCTION AT A RATE OF 10 000 t WPC/yr n g ^ •3 u S о « о S 4-> ВЛО nS ' h Û) ° 2 # 00 > .3 Ю f o „■ ♦ 8. i fe- 5 S ! 1 - i ) I Й J) «I0) ~ с

•SA •a •55 a a "Sb RDCINEOOIS 337 ECONOMICS PRODUCTION ** 3 ’Й 3 8 M U

« 5 >H U ■5 •4* 3 u P (X Й 5 5 Й 2 2 ■2 -Q СЮ S 1 яз ТЭ0 °* &* » з u °

( c ) Impregnation costs from Table I. (Ф Curing costs from Table IV . ( e ) Excluding transport, storage and marketing costs. 3 3 8 ROTKIRCH

ÍS03 'lOVdflNVW 0ldl03dS PRODUCTION ECONOMICS 339

TABLE VII. COMPARISON OF PRICES OF WPC PRODUCTS WITH PRICES OF NOBLE WOOD WPC specific gravity = 1. 05 t/m3

P r ic e Type of wood or WPC ( $ / m s )

N o b le w o o d

R ed b e e c h 1 1 0 - 1 5 5

M a h o g a n y 1 3 8 - 1 8 5

Iro k o 1 3 8 - 1 9 5

Japanese oak 1 9 0 -2 8 5

Bangkok teak 2 0 0 -3 8 0

P a lis a n d e r 6 2 0 -8 6 0

Radiation cured WPC

impregnated with:

- Methyl methacrylate 3 10

- 30% styrene + 70% unsaturated polyester 280

- 50% styrene + 50% unsaturated polyester 250

- 60% styrene + 40% acrylonitrile 2 2 0

- 80% vinylchloride + 2 0 % vinylacetate 1 9 5

Catalytically cured WPC

impregnated with:

- 30% styrene + 70% unsaturated polyester 250

100 80 60

20

z ?

t F IG . 6 . Electron-beam penetration in unit 0.6 0.2 OX 0.6 Q8 1 2 U 6 20 40 density m aterial as function of energy. ENERGY Me V 340 ROTKIRCH

THICKNESS OF MATERIAL, mm

FIG. 7. Capital cost of particle beam accelerator as function of beam penetration. Figures are related only to com plete accelerator system with shielding.

First of all the panel products are produced on line at considerable speed. This in turn requires fast impregnation and curing methods. On the other hand, it is rather easy to integrate some specially designed process units to facilitate the desired procedure. When this matter is studied it is clear that only radiation by electron accelerator or catalytic curing can be utilized for on-line operation. If a gamma facility were to be used for curing, the obvious line of approach would be to build a separate impregnation and curing plant operating batch- w is e . In the following cost evaluation only catalytic curing and radiation curing with electron accelerators are discussed. For this evaluation the author has especially drawn information from another paper in these Proceedings [6]. The approach with a line emitter described in this paper is a technically sound method, which obviously has advantages when compared with the swinging beam used elsewhere.

4.2.1. Cost of radiation curing with an electron accelerator

The first step is to define the desired depth of impregnation and, with the diagram in Fig. 6, find the necessary beam energy. On the basis of these criteria the size and cost of the accelerator can then be estimated. By utilizing the cost figures in the literature [6,7] an approximate relation between the thickness of the material to be irradiated and the capital cost of the accelerator equipment can be drawn as in Fig. 7. The first part of the line may be fairly adequate, but the part above 10 mm thickness is not properly verified.

4. 2. 2. Comparison of curing methods: a case study

The manufacturing costs of monomer-impregnated fibre-board are studied for a hypothetical production of 10 000 ft2/h. Both the radiation curing and catalytic curing methods are evaluated. It is assumed that an electron accelerator can be built into the production line in an existing factory, and there the costs for space and utilities are left out of the cost breakdown. The equipment for catalytic curing, on the PRODUCTION ECONOMICS 341 other hand, is considered to be easily and cheaply made in the plant repair and maintenance workshop during slack time. Therefore, in this rough estimate the capital investment for catalytic curing is neglected. More detailed studies, however, must take even this capital cost into consideration. The product studied was arbitrarily chosen without any particular ambi­ tion to launch this product as something especially feasible. Porous fibre-board of 1/2-in. thickness and with a specific gravity of 0.3 t/m3 was studied and two cases were evaluated, namely:

(a) Impregnation to a depth of only 1 mm on each side of the board. (b) Total impregnation of fibre-board.

The evaluation for radiation curing then takes the following form. The capital cost for the electron accelerator is taken from the diagram in Fig. 7 and amounts to 0. 14 million US dollars for the surface impregnation and 0. 62 million dollars for the total impregnation. These capital costs are as close to the true cost as possible without formal quotations for the actual equipment being requested. The operating costs of the electron accelerator are given as approxi­ mately $15.4/h. Annual interest is taken to be 8%, and amortization time 5 y e a rs . Table VIII summarizes the radiation curing costs as a function of load factor for the two grades of impregnation. As impregnation chemicals, a mixture of 50% styrene and 50% un­ saturated polyester is used in the radiation curing method and 30% styrene + 70% unsaturated polyester for the catalytic curing method. It is further assumed that surface impregnation absorbs 0. 6 kg of impregnation chemicals per square metre, and total impregnation requires 3.8 kg of chemicals per square metre, of 1/2-in. board. For catalytic reaction the additives comprise 2% peroxides and 0. 5% naphtenates calcula­ ted on the amount of monomer mixture. The costs of chemicals are calcu­ lated from the price list given in Table V. Finally, the fibre-board cost is 18. 2 ф/т 2 on the world market.

4.2.3. Total production cost

The relevant costs for manufacturing 1/2-in. fibre-board are sum­ marized in Table IX for the radiation curing method as well as for cata­ lytic curing. Annual operation is 8000 h. The effects of load factor on the economics of the two curing methods are shown in Figs 8 and 9. These indicate that radiation curing under the above-mentioned circumstances is more economical for 2- and 3-shift operation than the catalytic curing. This is mainly due to the more expen­ sive monomer mixture necessary with catalytic curing. It should be emphasized that the costs of additives in the catalytic method are of the same order of magnitude as the actual radiation curing cost. This in turn diverts the main interest to the difference in monomer acceptable for these different curing systems. As with WPC products, the cost of the impregnation chemicals is the dominating one. The cata­ lytic curing method has one built-in disadvantage which, under certain conditions, could greatly affect the cost pattern, i. e. the difficulties of storing monomers charged with catalyst for a longer period. For sm all- 342 ROTKIRCH

TABLE VIII. RADIATION CURING COSTS AS A FUNCTION OF LOAD FACTOR FOR TWO GRADES OF FIBRE IMPREGNATION 1. l-m m surface layer impregnation on both sides of board 2. Total impregnation

Operation (h/yr) 2 000 5000 8000

1. Surface impregnation

Capital investment (10® $) 0 . 1 4 0 . 1 4 0 . 1 4

Annual interest, 8°}o (1000 $/yr) 1 1 . 2 1 1 . 2 1 1 . 2

Am ortization, 5 yr (1000 $/yr) 2 8 .0 2 8 .0 2 8 .0

Running costs, 15.4 $/h (1000 $/yr) 3 0 .8 7 7 .0 1 2 3 .0

Total (1000 $/yr) 70 1 1 6 16 2

P ro d u ctio n 9 29 m 2/ h (10® m 2/ y r ) 1 . 8 6 4 . 6 4 7 .4 2

Specific curing cost (¿/m 2) 3 .8 2 . 5 2 . 2

2, Total impregnation

Capital investment (10 6 $) 0 .6 2 0 .6 2 0 .6 2

Annual investment, 8°Jo (1000 $/yr) 4 9 .5 4 9 .5 4 9 .5

Amortization, 5 yr (1000 $/yr) 1 2 4 .0 1 2 4 .0 1 2 4 .0

Running costs, 15.4 $/h (1000 $/yr) 3 0 .8 7 7 .0 1 2 3 .0

Production (10 s m 2 / y r ) 1 . 8 6 4 .6 4 7 .4 2

Specific curing cost (¿/m 2) 1 1 . 0 5 . 4 4 .0

scale production this may not be important, but large-scale production would be affected considerably by this problem. A close study of this case shows that the catalytic curing method, because of its negligible capital investment, is able to carry a higher chemicals cost than the radiation curing method. This difference, however, should include even the chemical losses due to the above- mentioned storage difficulties. In the case evaluated, the addition of the cost of impregnation chemicals tolerated by the catalytic method would then be as follows: PRODUCTION ECONOMICS 343

Operation time (h/yr) 2000 5000 8 0 0 0

1. 1-mm layer impregnated on each side of board(%) 19 12.5 11

2. Totally impregnated board (%) 8.8 4.3 3.3

TABLE IX. COST OF MANUFACTURING POLYMER-IMPREGNATED 1/2-in. POROUS FIBRE-BOARD Comparison of curing methods and mode of impregnation at a production rate of 10 000 m 2/h

Curing method R a d ia tio n C a ta ly s is

1-m m layer 1-m m layer Impregnation T o t a l T o t a l e a c h -side e a c h sid e

ia ) R aw m a t e r i a l ( ¿ / m 2) 1 8 . 2 I S . 2 1 8 . 2 1 8 .2

Curing Ф ) (/6/m2 ) 2 . 2 4 .0

- peroxides (¿/m 2) 2 .2 1 3 . 7

- n a p h te n a te s ( ¿ / m 2) 0 .3 1 . 9 ( c j - reaction moderator (jé/m )

M o n o m e rs ( ¿ / m 2) 1 9 . 2 ^ 1 2 1 . 5 (e ) 2 2 . 8 ^ 1 4 4 .3 ^

Total specific cost 0¿/m2 ) 40 1 4 4 4 4 1 7 8

(a ) World market price. See Table VIII. (c) Use reported, but chem icals involved and their prices not published. ( d ) S e e T a b l e V . (e) 50% styrene + 50% unsaturated polyester, (0 30% styrene + 70% unsaturated polyester.

4.2.4. Impregnation of bagasse

Finally, it may be of interest to study the case of bagasse. Even here a hypothetical case is considered and surface-layer as well as total impregnation is evaluated. The method of evaluation is the same as that adopted above, and the results are summarized in Table X. This table also includes a comparison with the Taiwan results reported at this meeting [8] . 344 ROTKIRCH

LOAD FACTOR

FIG. 8. Comparison of specific processing cost for monomer impregnation and curing of fibrous m aterial. Depth of impregnation 1 mm each side. (Î) Curing by catalysis. Monomer used is 30% styrene + 70% unsaturated polyester, 2% peroxides and 0.5% naphtenate as accelerator. ® Curing by irradiation. Monomer used is 50% styrene + 50% unsaturated polyester, (з) Cost curve for catalytic additives (2% peroxides + 0.5% naphtenates related to amount of untreated monomer). (4) Capital and running costs for particle-beam facility. The difference between the curves indicates the cost of monomer. The same as(l)-(3). The figures are calculated for a production of 10 000 ft2/h of 1/2-in. soft board.

FIG. 9. Comparison of specific processing cost for monomer impregnation and curing of fibrous m aterial. Com plete impregnation. (Г) Curing by catalysis. Monomer used is 30% styrene + 70% unsaturated polyester,

2% peroxides and 0.5% naphtenates as accelerator. ( 2 ) Curing by irradiation. Monomer used is 50% styrene + 50% unsaturated polyester, (з) Cost curve for catalytic additives (2% peroxides + 0.5% naphtenates

related to amount of untreated monomer). ( 4 ) Capital and running costs for particle-beam facility.

( Г ) - ( 3 ) The difference between the curves indicates the cost of monomer. ® “ (4) The same as © - © • The figures are calculated for a production of 10 000-ft2/h of 1/2-in. soft board.

The ultimate price of surface-layer impregnated, 20-mm thick bagasse board delivered untreated at 53 jé/m2at the factory gate would be approximately 75 (é/m2. Totally impregnated the same bagasse board would cost between $4 and $5/m2. This treated bagasse board should PRODUCTION ECONOMICS 345

Q 05 S m H w w a < 0 § C <3 m н B a 1 о c\j Q И H É5 О H 05 сц д 1 05 l ’S И Ё Й S О оЙ

05 О Еч H и ся >) О О О Й►—i Рн D с о I “ н -+-> g <ч и cd < од (U 4> c¿ а Сй) СQJ 0) • О йЕ* Хп о < #ООО # 2 л п « Q Ü. И -<-■ 3 Л Н со и з С ю е 0) <у «о в У У Я1 ->* J3 44. Ь£> •гН «в •-* 01 <и .2 Е Г, !s

.5м аu . О а . ю с - (N з U . л J3 и ^ 'З'

Н со 346 ROTKIRCH be able to compete with plywood 10-15 mm thick, which is said to be soldat $ 1. 5 - $ 2.0/m2 in Taiwan. To give bagasse a sporting chance much has to be done to lower the price of the chemicals or, alternatively, only part impregnation should be accepted. The question of protection against termites and rot is still not incorporated.

ACKNOWLEDGEMENTS

The author wishes to express his thanks to the IAEA for its initiative and to the Finnish Ministry of Industry and Commerce, which made his visit to Bangkok possible by putting the necessary funds at his disposal. He is further grateful for the help and support he received from EKONO and to the individuals who critically studied the manuscript. Especially warm thanks are due to Mr. H. Liihr, Prof. J. K. Miettinen, Mr.A.Mâkinen and Mr. U. Roos.

REFERENCES

[1] HOUWINK, R., The synthetics age, Mod. Plast. (August 1966) 98-100; GERRITSEN, J .C ., Prognosis of world consumption of some construction m aterials. [2] VITRO ENGINEERING COMPANY, Engineering and evaluation study of the manufacture of wood-plastic composites, KLX-1876 (TID-4500)/USAEC (1966). [3] ARTHUR D. LITTLE, Inc., Technical and economic considerations for an irradiated wood-plastic m aterial (1964). [4] CARLESON, G ., Marknad och Ekonomi for Trâpolymerprodukter i Sverige, Svensk kem. Tidskr. 79 10 (1967) 549. —

[5] KUKACKA, L.E., MANOWITZ, B. , Estimating gamma-radiation processing costs. Nucleonics (Jan. 1965) 74-78. [6] DALTON, F .L., M cCANN, J.D ., "Radiation engineering in the polymerization of monomers in fibrous m aterials: accelerators, these Proceedings. [7] DALTON, F .L ., The application of ionising radiations to coating and wood plastics. Atom 133 (1967) 2 8 2 -8 8 . [8] UNG-PING WANG, Status and technology of polymer-containing fibrous materials in the Eastern Hemisphere - Republic of China (Taiwan), these Proceedings.

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Atomwirtschaft 12 (1967) 553. BAINES, B .D ., MOSELEY, J ., "Economics of grain irradiation", Food Irradiation (Proc. Symp. Karlsruhe, 1966) IAEA, Vienna (1966) 813. CHEMICAL ENGINEERING, Radiation promises coaters a good cure soon, Chem . Engng (N ov.20, 1967). GERRITSEN, J.С ., Prognosis of world consumption of some construction m aterials, Chem . Engng (Nov. 20, 1 9 6 7 ) . JEFFERSON, S ., "High energy electron and gamma radiation plant - design, construction and econom ics", Food Irradiation (Proc. Symp. Karlsruhe, 1966) IAEA, Vienna (1966) 21. LUHR, H ., Finnish Pulp and Paper Research Association, Personal com m unication. McMILLIN, C. W ., Dimensional stabilization with polymerizable vapour of ethylene oxide. MEYER-JUNGN1CK, W ., TRAGESER, D. A ., WIESNER, L ., Beschleuniger-Bestrahlungsanlagen, Atom­ wirtschaft 11 (1967) 535-39, PRODUCTION ECONOMICS 3 4 7

MEYER-JUNGNICK, W ., TRAGESER, D .A ., WIESNER, L ., Isotopen-Bestrahlungsanlagen, Atomwirtschaft 12 (1967) 592-95. MIETTINEN, J .K ., Kemian Teollisuus 23 (1966) 1084. MIETTINEN, J .K ., Paperi ja Puu 49 (1967) 51. MIETTINEN, J .K ., Radioisotopes in the Pulp and Paper Industry (Proc. Panel Helsinki, 1967) IAEA, Vienna (19 6 8 ) 9 1 . MIETTINEN, J.K ., AUTIO, T ., Tekniskt Forum 86 (1966) 587. MOREN, R ., Diemensions-stabilisering av tra, Sâgverken 6 (1965). MORGANSTERN, K .H ., The technique of radiation curing of coatings on various substrates, Nuclex (1966).

MURRAY, G, S . , Commercial sterilization,N ucleonics 20 (1962) 50. RAUSOKOFF, J .A ., Zunehmender Bedarf fur Grossquellen zur Strahlenkatalyse — Konkurrenzfâhigkeit und Verfahrensvorteile, Atomwirtschaft 6 (1967) 310-12. RINDORF, H ,, "Economics of food irradiation", Food Irradiation (Proc. Symp. Karlsruhe, 1966) IAEA, Vienna (1966) 865. ROSINGER, S ., Fortschrittliche Co-60-Bestrahlungsanlage fur die Strahlenchemie, Atomwirtschaft 6 (1967) 295-99. TOPPARI, V ,, Finnish Woodworking Industries Association, Personal communication. URBAIN, W .M ., "Technical and econom ic considerations in the preservation of meats and poultry by ionizing radiation", Food Irradiation (Proc. Symp. Karlsruhe, 1966) IAEA, Vienna (1966) 397.

POTENTIAL MARKETS FOR WOOD-PLASTIC COMPOSITES IN JAPAN

T. HIRAYAMA CENTRAL RESEARCH LABORATORY, SHOWA DENKO K .K ., O TA-KU , TOKYO, JAPAN

Abstract

POTENTIAL MARKETS FOR WOOD-PLASTIC COMPOSITES IN JAPAN. The marketing possibilities of natural and treated woods are compared. A description is given of the advantages and disadvantages of these m aterials, together with the effects that improved quality might have on marketing prospects. Ex­ tensive reference tables illustrate the change in supply and demand over a number of years.

1. IN T R O D U C T IO N

Before discussing the development of wood-plastic composites (WPC) in Japan, it is important to be informed of the changes in wood supply and demand as well as of forecasts in this respect. It is also important to be aware of changes in wood resources and application, to clarify the ad­ vantages and disadvantages of wood, and to bear in mind the manner in which the geographical conditions and climate of the country can affect them . This paper deals with improvements in the developing utilization of WPC and cites an example of dimensional stability of wood which is fre­ quently discussed in countries such as Japan, where humidity is high. The paper also refers to problems involved in developing the preparation and application of WPC along with its potential markets. Finally, proposals for technical and economic discussions on the future development of WPC are presented.

2. CHANGES IN WOOD SUPPLY AND DEMAND

Forest covers approximately 70% of the land area in Japan, and the annual domestic output of wood reaches 50 million cubic metres. The wood requirement in Japan is continuing to increase with the development of the national economy and it surpassed the level of 70 m illion cubic' metres in 1965, including imported wood, showing an annual growth of 3-5% for the past five years. The requirement for 1967 was about 80 million cubic metres. Table I shows the changes in wood supply classified under do­ mestic and imported wood. As can be seen from the table, the gap be­ tween demand and supply became larger year by year, and the wood imports, which were less than 10% in 1956, grew to over 30% in 1966 and are now approaching 40%, thus showing a high rate of dependence upon imported wood [1,2]. On the other hand, the domestic output, which increased constantly until about 1961 through the development of remote wood resources and the

349 350 HIRAYAMA

TABLE I. CHANGES IN THE SUPPLY OF DOMESTIC AND IMPORTED WOOD AND ESTIMATED DEMAND

Unit : 1000 m 3

Y e a r s 1 9 5 6 1 9 6 1 1 9 6 5 1 9 6 6 1 9 6 7 19 6 8 ( e s t im a t e ) ( e s t im a t e )

Total supply 4 8 5 1 5 6 1 5 6 5 70530 76 8 7 6 8 1 7 5 0 8 4 2 1 1

A. Domestic 4 5 2 3 8 5 0 8 16 5 0 3 7 5 5 1 8 3 5 5 2 10 0 5 2 35 0

L o g 4 5 2 3 8 49 8 9 3 4 9 5 3 4 5 1 0 2 3 5 1 3 1 2 5 1 5 6 4

Forest waste - 923 8 4 1 8 1 2 988 78 6

M i l l w a s te (24 50 ) (4 3 0 7) (4 7 9 4 ) (50 5 2 ) ( 5 2 4 7 )

B. Imported 3 2 7 7 10 7 4 9 2 0 1 5 5 2 5 0 4 1 29650 3 1 8 6 1

L o g 20228 2 2 9 9 1 2 40 34

L u m b e r in g 16 0 5 2 3 2 7 2 4 1 2

C h ip s 50 3 15 0 0 2500

P u lp 2 6 7 4 2 7 9 7 2880

V e n e e r 5 5 5

O th e is 26 30 30

Total demand 76 8 7 6 8 1 7 5 0 8 4 2 1 1

L u m b e r in g 5 0 3 7 3 5 2 3 7 3 5 3 2 5 5

P u lp 1 6 3 7 5 18 0 6 4 1 9 0 4 1

P ly w o o d 6 2 5 7 7 5 6 4 8320

O th e is 3 8 2 1 3 7 5 0 3 5 9 5

Rate of supply (%) :

A. Domestic 93 83 7 1 6 7 6 4 62 o u tp u t

B . Im p o rts 7 1 7 29 33 36 38

Note: The bracketed figures represent approximate output of chips made from saw-m ill waste.

construction of a network of forest roads, has remained static after reaching a level of about 50 m illion cubic metres due to deterioration of production conditions such as reduction in the forestry labour force, rise in wages and the remoteness of woodland. POTENTIAL MARKETS-JAPAN 3 5 1

Table II shows a breakdown of the trend of the demand for logs (raw wood). As seen from the total requirement in 1966, the consumption of plywood shows the largest growth followed by that of pulp and lumber. It also shows that there is a high dependence on lauan timber for plywood manufacture and on lauan, American and Russian wood for the lumber industry [3] . The qualitative content of the demand by species of trees has also undergone a change. Until about 1955 wood from coniferous trees was principally consumed, but a change has been brought about in the trend of wood demand over the past few years by a marked increase in the con­ sumption of wood from deciduous trees and trees of .small diameter and of wood chips. As an indication of the trend of industrial applications of wood, Table III presents the results of a survey on the structure of wood demand conducted on the three main Japanese markets of Tokyo-Yokohama, Nagoya and Osaka-Kyoto-Kobe which consume about 40% of the wooden products in Japan. The field of demand is divided into eight categories such as building, furniture, fittings, civil engineering works, packaging, shipbuilding and vehicles, and the requirements and estimates for each of them for the y e a rs 1965, 1966 and 1967 a re shown. The total o f each y e a r shows a gradual increase, but the requirement for each of the eight categories shows an almost sim ilar value [4] . In addition to the above applications, wood is showing a remarkable growth quantitatively and qualitatively in fields such as plywood, fibre­ board and veneer sheets as well as in the pulp and paper industry.

3. ADVANTAGES AND DISADVANTAGES OF WOOD

Wood is such a fam iliar substance that we tend to forget its special features just as we do in the case of air or water. To get the best out of wood, especially when combining it with another material to create a new product, we should reconsider its advantages and disadvantages (Table IV), and evaluate each of them [5] .

3.1. Advantages of wood

3.1.1. Wood is both light and strong

Wood is very light and almost no wood in dry condition.is heavier .than water. Wood has excellent tensile strength in the longitudinal direction and very good compression strength. On considering the ratio, strength/ specific gravity, one recognizes that a quarter of cedar (2570 kg/cm2) is compatible with iron (640 kg/cm2) with respect to tensile strength and one sixth of cedar (1000 kg/cm2) is compatible with concrete (167 kg/cm2) with respect to compression strength. Wood is therefore a material very useful for shipbuilding and civil engineering and as a building material. Its elasticity is excellent when compared with that of plastics of equivalent w eight. 2 5 3 TABLE II. STRUCTURE OF DEMAND FOR WOOD IN 1966 HIRAYAMA

Note: The bracketed figures show percentages of the previous year. POTENTIAL MARKETS-JAPAN 353

TABLE III. DEMAND FOR WOOD PRODUCTS BROKEN DOWN INTO FIELDS OF USE

Unit : 1000 m3

Y e a rs Species (1966)

D o m e s t ic Uses 1 9 6 5 1 9 6 6 1 9 6 7 Im p o rt ( e s t im a t e ) C o n ife r o u s D e c id u o u s T o ta l t o ta l

№ (°Io) (°lo) m

B u ild in g 7 9 1 3 8388 90 47 7 8 .6 1 . 3 7 9 .9 2 0 . 1 ( 5 6 .8 ) ( 5 6 .7 ) ( 5 7 . 1 )

F ittin g 43 9 4 7 6 5 1 1 2 9 .7 2 . 3 3 2 .2 6 7 .8 ( 3 .2 ) ( 3 .2 ) ( 3 .2 )

F u rn itu re 7 2 4 7 8 1 823 5 .0 3 4 .4 3 9 .4 6 0 .6 ( 5 .2 ) ( 5 .3 ) ( 5 .2 )

C i v i l engineering 1 2 7 9 1 3 8 1 1 4 9 6 7 4 .8 1 0 .6 8 5 .4 1 4 . 6 ( 9 .2 ) ( 9 .3 ) ( 9 .4 )

P a c k a g in g 2 3 7 6 2495 2 6 2 7 8 6 .4 2 .9 8 9 .3 1 0 .7 ( 1 7 . 1 ) ( 1 6 .9 ) ( 1 6 .6 )

Shipbuilding 1 2 7 1 2 6 13 4 6 6 .4 9 . 2 7 5 .6 2 4 .4 ( 0 .9 ) ( 0 .9 ) ( 0 .8 )

V e h ic le s 4 2 4 4 7 3 5 1 5 - - - 1 0 0 .0 ( 3 .0 ) ( 3 .2 ) ( 3 .3 )

O th ers 6 4 1 6 62 682 4 0 .4 3 3 .3 7 3 . 7 2 6 .3 ( 4 .6 ) ( 4 .5 ) ( 4 .4 )

T o ta l 1 3 9 2 3 1 4 7 5 2 15 8 3 5 ( 1 0 0 .0 ) (1 0 0 .0 ) ( 1 0 0 .0 )

Note: Statistics of the three big markets of Tokyo-Yokohama, Nagoya and Osaka-Kyoto-Kobe consuming about 40% of the wood products in Japan.

3.1.2. Wood is easy to work

Wood can be handled with simple carpentry tools since it is a relatively soft material and moreover not brittle. This is also the case with plywood and fibre-board. A technique has recently been developed to join wood sheets with adhesives or connecting devices instead of nails. 3 5 4 HIRAYAMA

TABLE IV. ADVANTAGES AND DISADVANTAGES OF WOOD

A d v a n ta g e s Disadvantages

(1) Light and strong for its weight (1) Properties vary

(2) Easy to work (2) M aterial not homogeneous

(3) Good insulator of heat, (3) Combustible electricity and sound

(4) Adjusts humidity (4) Liable to suffer distortion from moisture

(5) Good appearance (5) Liable to be damaged by fungi and insects

(6) Easily available

3.1.3. Wood is an insulator of heat, electricity and sound

Wood is a mass of cells and cavities and is an excellent insulating m aterial against heat and electricity. It is thus quite suitable for use in buildings. The heat conductivity of iron is about 100 times that of water while that of polyethylene is about one half and of cedar about one fifth that of water. Wood is a good absorber of sound and suitable for the walls of buildings.

3.1.4. Wood adjusts humidity (does not dew)

Wood has a high hygroscopicity, absorbing moisture in a humid atmosphere and releasing moisture when the atmosphere is dry. In a country like Japan, where the humidity is high, this is an advantageous property for a building material; in a concrete dwelling humidity can be a health problem.

3.1.5. Wood is beautiful

The beautiful natural pattern of a wood surface has often been imitated by printing or painting on artificial materials, which seem, however, to be inferior to natural wood.

3.1.6. Wood is easily available

Wood is a very familiar material, particularly in Japan, where it is both abundant and available at a relatively low cost. POTENTIAL MARKETS-JAPAN 3 5 5

3.2. Disadvantages of wood

3.2.1. Wood has varying properties

The strength of wood is not constant, even within the same species, and varies according to the fibre direction (radial and tangential). There­ fore, when wood sheets are combined, special care should be taken to offset the disadvantages of one type of wood with the advantages of another.

3.2.2. Wood is heterogeneous in quality (inequality of properties)

The properties of wood vary even within the same species and they are subject to growth conditions, the age of the tree and the place of growth. Even in one tree there are marked differences in specific gravity and moisture content according to the part and to whether it is sapwood or heartwood. The sawing procedure is affected by these differences and it is therefore necessary to consider the best uses for the properties of wood. It is also important to make efforts to raise good woods of the same quality by choosing the correct tree type. This also affects design.

3.2.3. Wood is combustible

In Japan there are many wooden houses and much cfemage is caused by fire. Wood catches fire at a temperature of 250 to 290°C and burns spontaneously at 350 to 450°C. It thus requires treatment with flame retardants. Plastics are also not flame resistant and improvements in both materials are desirable.

3.2.4. Wood is liable to be distorted by moisture

Although wood has the advantage of adjusting to humidity changes, it shrinks upon drying and expands upon getting wet. This is a drawback. Furthermore, the anisotropy of wood causes a difference in the degree of shrinkage according to direction, and phenomena such as deformation of shape, cracking, warping and distortion occur. To offset these draw­ backs, it is generally important to dry the wood fully prior to use, this drying sometimes being done artificially.

3. 2. 5. Wood is liable to be attacked by fungi and insects

Wood is essentially a carbohydrate and a good food for fungi and insects. Fungi thrive at a temperature of 10 to 40°C and a humidity higher than 80%. It is said that wood does not rot when its moisture content is less than 20% and higher than 150%. Beech especially is liable to decay and wood is normally treated before being used in building foundations, railway sleepers, telegraph poles, etc. Wet wood is particularly susceptible to attack by termit.es, and the insect Lyctus brunneus ruins dry lauan wood imported from the Phillipines and elsewhere. Protection against and extermination of these pests are very important considerations. To define the properties of wood, a comparison is made with four other major materials with respect to physical and chemical properties, fabri­ cation and appearance (Table V). 356 HIRAYAMA

TABLE V. COMPETITION OF MAJOR MATERIALS

M etal Ceramics Glass Plastics Wood

Physical property

Dimensional stability О О О д X

Toughness (Im pact) 0 X X д о

Hardness 0 О О д X

Abrasion resistance О о о X X

Density (D ) L(M) L L S S T ensile strength (T ) 0 X х д о

T/D M S S м L Static bending strength о х х д д Elasticity Д X X д о

Plasticity X X Д о -

Non-splintering о О О д д

Thermal and electrical conductivity L S S S S

Chem ical property

Glueability Д X д о о Stain resistance О О о д д

Acid-base resistance Д О о о X

Insect, fungus and rot Д о о о X

Flame retardancy О О О X X

Weatherability о о о д *

Fabrication

Casting and tempering о д о о - Ease o f fabrication д X X о о M illin g and turning о х X д о

Finishing о д о о о

Nailability - - - х о

Aesthetic property

Appearance о д о о о

Texture о д о д д

Smoothness о д о о о

Permanence o f finish о о о д д

Colouring X о о о д

Others

Anisotropy S S S S L

Humidity adjustment X X X X о

Good L : Large

Medium M : Medium

Inferior S : Small TABLE VI. LIST OF POTENTIAL APPLICATIONS AND PROPERTIES OF WPC a' 6 i s s i ■a J 1 ¡ ô 4) O ï. в 2 С «вe * * X} 4? O < < < < о O о <3 O O о < о OOOO OOOO oooo POTENTIAL MARKETS-JAPAN POTENTIAL < O < O о о о < < O < 1 < O о о O о < о о о о о < O о о о S ■c s I 357 o .. gg

Same or inferior to untreated wood 358 HIRAYAMA

4. PROMISING APPLICATIONS OF WPC

A list [6] has been published in the United States of Am erica identifying uses of wood-plastic composites. This list was developed from letters of inquiry by the USAEC and the University of West Virginia and from sug­ gestions by industrial associations and staff members of Arthur D.Little, Inc. On the basis of this list, the principal potential uses in Japan are given in Table VI, together with some of the properties. Since evaluations were made collectively on an average basis, minor errors may be found in indi­ vidual cases, but a general trend may be obtained from the table. The ideal aim in improving wood is to eliminate or minimize drawbacks and to try to upgrade strength and elasticity. The table shows that dimensional stability is an important and desirable property in all applications. Other properties are not necessarily required for some uses and only dimensional stability is an indispensable property in all cases. In Japan, where humidity is high and varies markedly, dimensional stability is very important in relation to the absorption of m o istu re. The dimensional stability of WPC is excellent in comparison with that of untreated wood, but still further improvement is now being made by many investigators.

5. COMPARISON OF THE DIMENSIONAL STABILITY OF WPC WITH THAT OF OTHER WOOD MATERIALS

Wood expands and shrinks as its moisture content changes, resulting in drawbacks such as warping, distortion and cracking, and, with an increase of absorbed moisture, strength and electrical properties de­ teriorate. Decay also occurs. Horioka [7] concluded that wood neither shrinks nor expands be­ yond the fibre-saturation point (moisture content 28%) but shrinks and expands below this point as indicated by formulae (1), (2) and (3). Rate of shrinkage and expansion radially (straight grain):

aR= 0. 30(^-1^715 W

Rate of shrinkage and expansion tangentially (cross grain):

a r = 0.53(u2-u1)y15 (2)

Rate of shrinkage and expansion in the fibre direction (longitudinal direction):

a L = 0 .0 2 (u 2-u1)7i5 (3)

w h ere 7 15 = Specific gravity at a moisture content of 15%, Uj = Initial moisture content, and u2 = Wood moisture content during use. POTENTIAL MARKETS-JAPAN 359

Experiments have been carried out to impart dimensional stability by improving the hygroscopicity and other properties. To express the degree of dimensional stability, the term anti-shrink efficiency (hereinafter called ASE) is used.

D.-D ASE = X 100 (4) u 0 where DQ = shrink rate of untreated wood and D = shrink rate of treated wood. Horioka[8] measured the effect of shrinkage and expansion on the strength of wood without defects with 35 principal Japanese species of tree (adding one Formosan species) and collected the results. He tabulated valuable data on the anatomical properties of woods, using test pieces of various species that had undergone compression tests so that they could be used as a base for studies on the improvement of wood properties, particularly for impregnation, adhesion, compression, and homogeni­ zation of wood. In addition, to improve the anisotropy of wood, he investi­ gated the anisotropy of beech, which is very abundant in Japan. Results of shrinkage tests related to dimensional stability are given b elow . It was ascertained that the rate of shrinkage for a change in moisture content of 1% in the straight-grain and cross-grain directions is, as a general trend, proportional to the specific gravity, which is represented by the following empirical formulas: Rate of shrinkage for a change in water content of l% .on the cross­ grain surface

ffT=0.53 Tl5[%] (5)

On the straight grain surface

Or = 0.3°7i5 [%] (6)

Dividing Eq.(5) by Eq.(6) we have

aT/aR = 0.53/0.30 = 1.77 (7)

In general, the shrinkage rate of the cross grain is about 1. 77 times that of the straight grain. Experiments made on American woods gave results sim ilar to those obtained with Japanese woods, which shows that the shrinkage rate of wood, regardless of species and place of growth, tends to be directly proportional to specific gravity. The drawbacks of wood distortion, warping, twisting, etc. are due to shrinkage and expansion caused by the absorption and diffusion of moisture and the rate of shrinkage (value given by formula (4)). It is considered that distortion tends to be larger, the greater the ratio of c-T/aR. Since the value of ar ja R represents anisotropy of the shrinkage rate, it is desir­ able to minimize the value as much as possible by reshaping the wood. This is quite important when the wood is to be used outdoors. 360 HIRAYAMA

TABLE VII. DIMENSIONAL STABILITY OF WPC

(a) Plastic content Anti-shrink efficiency (ASE) / (b) W ood “ T R (%) m

C o n tr o l - 2 .8

2 0 - 4 0 ( t /C* 20 -4 0 2 . 4 40 - 5 0 (R) B e e c h 3 5 - 4 5 ( T ) 5 0 - 7 0 2 . 2 5 0 - 6 0

C o n tr o l - 2 .0

20 -25 (T) 20 -4 0 2 .0 20 - 25 (R) M a p le 2 5 - 3 0 ( T ) 50 -7 0 2 .0 2 5 - 3 0 (R)

C o n tr o l - 2 .0 W h ite o a k 30 -40 (T) 1 5 - 2 5 1 . 8 2 0 - 3 0 (R)

C o n tr o l - 1 . 7

10 '20 (T) 2 5 - 4 5 1 . 7 1 0 - 2 0 (R) Red la u a n 3 5 - 4 5 ( T ) 7 0 - 9 0 1 . 5 2 5 - 3 5 (R)

Monomer: M'vlA; Dose rate: 1x10s rad/h; Total dose: 2 Mrad (“ Со, y-ray)

D . - D ( a ) A S E = - ^ — xlO O

L - L D ------L 3 = Length of wood test piece after one week at L s 2 5 ° C , R .H . 98“fc.

Do = Control L 5 - Length of wood test piece after one week at 10 5 ° C .

(b ) a j ~ Shrinkage ratio tangentially, aR = Shrinkage ratio radially.

( c ) T = Tangential f

R = Radial. POTENTIAL MARKETS-JAPAN 361

As representative species of wood widely used in Japan, four types (beech, maple, white oak and red lauan) were chosen and the values of ASE and aT/aR wefe determined, after WPC had been prepared from each species by the radiation method, with MMA as the monomer. The results [9] are given in Table VII. Beech, which is the most abundant deciduous tree in Japan, shows a more marked improvement in dimensional stability (shrinkage rate and anisotropy) than the others. Woods other than maple are likely to have improved anisotropy when the plastic content is high. The rate of shrink­ age of the wood is probably improved to a certain extent, but the plastic content bears no linear relationship to this. Table VIII shows the dimensional stability of WPC in comparison with other treated woods. The ASE values indicate that some other methods are as good as WPC, but many of these are restricted by the treatment temperature, the form of the material to be treated and the deterioration of physical properties. The worst defect is that the appearance of the wood is spoiled while obtaining dimensional stability. A comparison of the radi­ ation method with the chemical method (catalyst-heat treatment) in the preparation of WPC shows that the form er seems to be superior in di­ mensional stability. However, economic considerations are important in the manufacture of WPC.

6. TECHNICAL AND ECONOMIC PROBLEMS IN THE DEVELOPMENT OF W P C

Since most of the problems of cost reduction and product improvement of WPC are already covered by data from Arthur D.Little, Inc. and Vitro Engineering Co. [10], and evaluations have been made of the problems of processing and production plant, we shall consider here some Japanese points of view and indicate various factors common to several countries. Mott and Rotariu [11] discussed features of WPC in their general review of the USAEC's programme on the industrial application of radiation and radioisotopes. Murayama [12,13] designated WPC as 'Plamo-wood' and enumerated the following as its characteristics:

(1) Greater hardness (up to several hundred times) and consequently impact and scratch resistant. (2) Greater tensile and bending strength in the cross-grain and straight - grain directions. The anisotropy of the wood is improved. (3) Compression strength is much greater. (4) Moisture absorption is very low resulting in almost no dimensional changes. (5) Grain and colour of natural wood are retained. (6) Paint finish is simple and attractive. (7) Colouring is possible as desired. (8) Good resistance to decay. When rotten wood is used as the material, the strength is improved and the rotten part constitutes a nice pattern. (9) Can be treated like wood and finished to a hard, smooth and glossy s u rfa c e . (10) Heat resistance can be imparted by incorporating fire-retardant com­ pounds in the copolymerization. 362

TABLE VIII. COMPARISON OF VARIOUS TREATMENTS FOR DIMENSIONAL STABILITY OF WOOD £ s g Q < .2 H Is Mechanical Aesthetic S 4> о 3 4) Impact Treatment E property property •5 и r-Ч о о о о о О rt с oo 4) 3 л Heat treatment only Free « Inferior Inferior 4= СО и «о о Он о о 3 О сб с ьо 5 Same as о о о О 3 об a 00 i Impregnation with ? Free 30 Inferior urea resin untreated U •s £ c~ О § rt с 0£ о 00 4) с Оч rt 4) s % 4) e >4 о 8. о Acétylation 40 • Inferior Inferior о 43 00 о о и о о 3 О S5 4> л Formaldehyde fumigation Free 40 • Inferior Inferior 3 ni43 -о i S i a 8 l i S § 4) 4) и 00 >ч о « аГ 00 о £§ Е в 1 л О <и Same as WPC, radiation method Free • Good untreated •о .а -5 5 2 >N о л й О и О О О I § s 00 4> «5 о о U

V Same as

WPC, chemical method '

Free 30 Good 3 sí

(catalyst-heat treatment) untreated POTENTIAL MARKETS-JAPAN 363

In the plastics industry WPC is described as "a new type of plastics retaining the desirable features of wood, its humidity adjustment ability, natural grain and colour".

Murayama specified the advantages of WPC as follows:

(1) Low-grade wood can be upgraded. (2) Wood saving possible by improved weatherability. (3) Import of special high-quality wood can be reduced by the use of this m a te ria l.

For the following reasons he believes that WPC has excellent prospects:

(1) Grafting of synthesized polymers to the natural polymer, wood, is now possible through graft copolymerization. WPC products combine the ad­ vantageous properties of synthesized polymers with the low-cost wood used as a base material. (2) With the development of the petrochemical and synthetic fibre industries, the raw material for use in manufacturing WPC can be supplied at a low cost and in sufficient quantities. (3) The manufacturing processes (radiation method and chemical method (catalyst-heat treatment)) for WPC are relatively simple.

In the wood industry, WPC is recognized to be a new material, capable of overcom ing the difficulties with which natural wood has been confronted. It may be the long-awaited material which combines all the desirable features of both wood and plastic. The following technical and economic problems are involved in the pro­ duction of WPC:

(a) Raw wood

(1) Comparison of the respective advantages of treating expensive wood or inexpensive wood. (2) Impregnation state differs according to species. (3) Limit of WPC treatment for wood homogenization. (4) Problems involved in using wood from coniferous trees in addition to that from deciduous trees generally used at present. (5) Utilization of wood chips and sawdust.

(b) Monomer used

(1) Combination effect of monomers. (2) Use of low-cost monomers. (3) Balance between the price of the monomer and the consumption of the product. (4) Effective polymerization method on the surfaces of cells (effective impregnation with monomer). (5) Addition of polymerization promoter. 364 HIRAYAMA

(c) Radiation source

(1) Irradiation apparatus for higher conversion efficiency of the source en ergy. (2) Advantages and disadvantages of utilizing radiation sources other than ®°Co. (3) Possible range of dose rate (maximum lim it and minimum limit) and total radiation dose.

(d) Miscellaneous

(1) Advantages and disadvantages of the radiation method and the chemical method in manufacturing WPC. Combination of both methods may bring further improvement. Characteristics of WPC obtained by these methods and comparative economics of the three methods. (2) Problems in working WPC. (3) Additives, particularly preservatives, flame retardant, colouring agents, etc.

ACKNOWLEDGEMENTS

The author is grateful to Dr. K. Danno, Japan Atomic Energy Research Institute, who gave him valuable advice during the preparation of this paper. The author also wishes to thank Dr. K. Horioka, Tokyo University of Agriculture and Technology, and Mr. T. Murayama, Government Forest Experiment Station, Ministry of Agriculture and Forestry, for their interest and suggestions.

REFERENCES

[1] HOSAKA, T ., Wood industry and changes in m aterial supply, Wood Industry (Japan) 22 4 (1967) 4. [2] FOREST AGENCY, Japan, Extent of Wood Demand and Supply in 1967 and 1968, Oct. 1967. [3] FOREST AGENCY, Japan, General Aspects of the Wood Industry, Sept. 1967. [4] FOREST AGENCY, Japan, Statistics of Demands for Wood in 1966, Mar, 1967. [5] TAKCJBO, T ., OGURA, T ., Future Utilization of Wood, March 1961. [6] LANNAZZI, F.D ., PERRY, F.G ., Jr., LEVINS. P.L., LINDSTROM, R .S., Technical and Economic Considerations for an Irradiated W ood-Plastic M aterial, T1D-21434, (USAEC Contract No. AT(30-l)-3332), Arthur D. Little, Inc. Sept. 1964. [7] HORIOKA, K., Kôgyô Zairyo 12 (1966) 1. [8] HORIOKA, K ., Research on the Improvement of Wood, 1st Rep. Study on Properties of Wood with Reference to Its Improvement, Bulletin of the Government Forest Experimental Station, Japan, No. 68 F e b . 1 9 6 4 . [9] SHOWADENKO, K .K ., Technical Report of Showa Denko К. K ., unpublished. [10] FRANKFORT, J.H ., BLACK, K .M ., Engineering and Evaluation Study for the Manufacture of Wood-Plastic Composites, KLX-1876, T1D-4500 (USAEC Contract No. AT (30-l)-3493), Vitro Engineering C o ., June 1 9 6 6 . [11] MOTT, W .E., ROTARIU, G .J., Isotopes Radiat. Technol. 4 4 (1967) 317. [12] MURAYAMA, T ., Radiation-induced graft copolymerization of wood substances, Kagaku Kogyo 16 5 (1965) 445. [13] MURAYAMA, T ., On Plamo-Wood, Sekiyu to Sekiyukagaku 11 4 (1967) 39. STATEMENTS PREPARED BY THE STUDY GROUP

WOOD-PLASTIC COMPOSITES IN THE WOOD-CARVING INDUSTRY IN THE FAR EAST

(JAPAN, THE REPUBLIC OF KOREA, THE PHILIPPINES, THE REPUBLIC OF CHINA (TAIWAN), THAILAND AND VIET NAM)

Only the Republic of China (Taiwan) and the Philippines have shown interest in the use of WPC for wood-carving purposes. Japan and Korea, however, are interested in the possibilities of WPC for the manufacture of such specialized items as shuttles (used in weaving), musical instruments, furniture and sporting goods (such as tennis rackets, baseball bats, skis, etc. ). Viet Nam, Korea and Thailand have at present little or no experience with WPC, but they intend to start work in this area. Generally speaking, these countries possess abundant hard and soft woods and are interested in using soft woods for WPC. The main problem concerns the high cost and the availability of monomers.

JAPAN

The wood-carving industry in Japan is quite insignificant, but, as in Korea, there is considerable interest in the possibility of using WPC for the fabrication of shuttles and other more specialized items such as furniture, television cabinets, sporting goods, etc. Japan has been doing much work along these lines and, together with Taiwan, is probably the most advanced country technologically in the region where WPC is concerned. The availability of monomers is likewise no problem in Japan, but their cost is still too high.

KOREA, REPUBLIC OF

Very little wood carving is done in the Republic of Korea with the exception of a few small items made from willow and poplar. There is, however, an interest in using WPC for shuttles for the weaving industry. Shuttles are made from persimmon wood, which is an especially hard wood, as shuttles must be hard as well as shock-resistant. A weaver uses an average of four shuttles a year and the total requirement of the textile industry is 130 000 p ieces a y e a r. The availability of persimmon wood in the Republic of Korea is only 500 m 3/yr and this is not enough to meet the demand. The wood costs about US $3-4/m 3. The availability of some monomers would not be a problem. At present there is a plant producing polyvinyl chloride, the annual production of which will soon be 13 000 tons. A petrochemical industry is at present being constructed and by 1970 o r 1971 it should produce 23 000 tons of polyvinyl chloride and 12 000 tons of polystyrene per annum.

367 3 6 8 WPC IN THE WOOD-CARVING INDUSTRY

As for wood resources, the Republic of Korea imports logs from neighbouring Asian countries, and considers imported lauan to be the largest potential raw material for WPC. No work on WPC has been done in this country, but by 1968, with the completion of the buildings of the Korean Atomic Energy Institute and the Korean Institute of Science and Technology, comprehensive work will start in this field.

PHILIPPINES

The sector most interested in the use of WPC in the Philippines is the wood-carving industry. This is mainly because the country is running short of the wood species used by this industry and, secondly, the use of soft wood would reduce carving time considerably and consequently mean an increase in production. The wood species proposed for use in WPC is a soft and highly porous wood from a fast-growing tree with practically no commercial value. If this could be utilized for wood-carving purposes with WPC treatment it is possible that the low cost of the wood could offset the high cost of the monomer. The present status of WPC technology in the Philippines, however, requires that the wood be carved roughly before impregnation and finished only after the treatment. This method presents a serious problem, as it would mean a tremendous increase in handling costs considering that the wood-carving industry is not centralized but dispersed all over the country. It should nevertheless not be overlooked that so far only two monomers, namely, methylmethacrylate and hydroxypropyl methacrylate, have been tested. Other monomers will be tried which may not have any shrinking effect. The possibility of using chemical catalysts to induce polym eri­ zation is also well worth looking into. At the present time, the availability and cost of monomers are res­ tricting factors.

REPUBLIC OF CHINA (TAIWAN)

At present Taiwan earns 3 million dollars annually from the wood- carving industry and in two years' time this sum is expected to reach 5 million dollars. Teak and camphor wood are currently used for carving purposes. However, teak and camphor wood are quite hard and carving takes some time. For instance, a highly skilled worker is paid US $ 3/day and can finish one sculpture in three or four hours. Likewise, teak and camphor are dimerisionally unstable and when brought to other countries they usually crack. To overcome these problems Taiwan has ventured into carving a soft low-class wood which is very abundant on the island. This is known as schefflera (in Chinese, Ching Mu tree). This species of wood is used at present only for the manufacture of match boxes and match sticks. Carved products from this soft wood are impregnated with an 80% vinyl chloride and 20% vinyl acetate mixture with a loading of about 50% monomer. The end product is stable, weather-proof and aesthetically appealing. WPC IN THE WOOD-CARVING INDUSTRY 369

The monomer is produced in Taiwan, Outlined below is the cost of produc- tion for an 8-in. wood carving.

(1) W ood $0,034 1.8%

(2) Labour cost $1.5 80.0%

(3) Monomer $0.24 1 17.5% (4) Impregnation $ 0 .9 9 9 J

(5) Painting $0. 05 0.7%

T o ta l $2.8 100.0% FIBRE- AND PARTICLE-BOARD IN ASIA AND THE FAR EAST

Compressed boards for use in construction can be divided into two classes: soft boards and hard fibre-boards. They are based on wood shavings or sawdust and on fibres such as jute, bagasse, etc. There is no doubt that a need exists to up-grade these materials to extend their use in the construction and furniture industries and in doing so the following considerations are important:

(1) Mechanical strength. (2) Inflammability. (3) Wet strength. (4) Protection from insects and fungi. (5) Dimensional stability. (6) Appearance.

Of these, numbers (2), (4) and (6) could be dealt with by conventional techniques, but an impregnation technique might improve all of these properties in one single process. Urea formaldehyde and phenolic resins have been used in some types of board, but water repellancy is inadequate unless excessive amounts of resin are used. It appears that a considerable amount of processing is economically possible to achieve these properties. For example, in the Republic of China (Taiwan) ordinary bagasse board sells at US $30/ton and the up­ graded product must compete with plywood at US $195/ton. If the impregnation of these boards by monomers with subsequent polymerization is to be considered, the following ar.eas must be studied in d etail:

(1) The influence of water content on the impregnation of fibres by monomers and on the properties of the treated board. (2) Methods of impregnation and the possible incorporation of fillers and aeration. (3) Uniformity and extent of impregnation. (4) Degradation of polymers by sunlight, moisture and heat. (5) Problems associated with curing and the selection of the most appropriate method. (6) The possibility of producing board with previously grafted cellulose fib r e s . (7) Cost evaluations, including the choice of available and cheap monomers; the necessity of achieving high production rates to compete with other board-manufacturing processes; the study of nationally available and potential resources. (8) In considering the use of radiation in this area, developments within the petrochemical industry should be closely watched.

370 CONCLUSIONS

Although a number of interesting possible applications of impregnated fibrous materials were discussed in considerable detail during the meeting, it was repeatedly emphasized that the top priority should be given to promoting cheap board-like material for housing construction. Raw material such as mixed tropical hardwooods, jute, bamboo and bagasse are potentially available in large quantities and could be used for this purpose. In view of the fact that the cost of construction materials used at present (plywood, tempered hardboard, etc. ) is several times that of board made from materials such as bagasse, it appears desirable to investigate the possibility of these low-grade materials being improved. As a result of the papers and subsequent discussion at the meeting it is recommended that the possibility of improving the properties of cheap boards by impregnation with suitable monomer systems polymerized in situ be studied. At present the systems which seem most suitable are the 80/20 vinyl- chloride/vinyl-acetate mixture studied in the Republic of China (Taiwan) and the 50/50 unsaturated polyester/styrene system studied in Finland. This work should be carried out on representative boards from the area concerned, and after completed preliminary studies more detailed evaluation and realistic aging studies should be undertaken on larger specim en s. At the conclusion of these studies it should be possible to formulate a realistic plan for a broadly based co-operative research and development p ro gra m .

371

LIST OF PARTICIPANTS

Chairm an

W. E. MOTT Division of Isotopes Development, USAEC, Washington, D. C. 20545, United States of Am erica

Members of the Study Group

Leticia BONOAN Chemistry Department, Philippine Atomic Energy Commission, Manila, the Philippines

A. BURMESTER Bundesanstalt fiir Materialprüfung(BAM), Berlin-Dahlem, Federal Republic of Germany

C. CHU Technological Research Institute, с/o UNDP, Bangkok, Thailand (UNIDO, Vienna, Austria)

J. G. CLOUSTON Australian Atomic Energy Commission, Lucas Heights, N.S.W ., A u stra lia

F.L. DALTON Wantage Research Laboratory, AERE, Grove, Wantage, Berks, United Kingdom

B. Ph. ESSCLINK ASRCT, Bangkhen, Bangkok, Thailand (UNIDO, Vienna, Austria)

A. J. FELICE Commercial Products Division, Atomic Energy of Canada Limited, Ottawa, O n t., Canada

M. G O TO D A Takasaki Radiation Chemistry Research Establishment, Tamura-Cho, Minato-Ku, Tokyo, Japan

T. HIRAYAMA Central Research Laboratory, Showa Denko K . K . , Ota-ku, Tokyo, Japan

373 374 LIST OF PARTICIPANTS

V. K. IYA Isotope Division, Bhabha Atomic Research Centre Trombay, Bombay, India

S. P . K A S E M S A N T A (R a p p o rteu r) Reactor Operations Division, Office of Atomic Energy for Peace, Bangkhen, Bangkok, Thailand

P. -Ô. KINELL Swedish Research Council Laboratory, Studsvik, Nykoping, Sweden

J.K. MIETTINEN Department of Radiochemistry, University of Helsinki, H elsin ki, Finland

A . N IL U B O L Chemistry Division, Office of Atomic Energy for Peace, Bangkhen, Bangkok, Thailand

V. R. RAGHAVAN Electric Power Section, Division of Industry and Natural Resources, ECAFE, Sala Santitham, Bangkok, Thailand

E. ROTKIRCH EKONO, Helsinki, Finland

P . SONO Forest Products Research Division, Royal Forest Department, Bangkok, Thailand

S. SRISUKH UNDP Regional Office for Asia and the Far East, Bangkok, Thailand

D. L. STACEY FAO Regional Office for Asia and the Far East, Bangkok, Thailand

V.T. STANNETT Chemical Engineering Department, North Carolina State University, Raleigh, N. C. United States of America LIST OF PARTICIPANTS 375

Chwa Kyung SUNG Office of Atomic Energy, Sudaimoon - Ku, Seoul, Republic of Korea

Le-Van-THOI Viet-Nam Atomic Energy Office, Saigon, Viet Nam

Ung-Ping WANG Radioisotope Laboratory, Union Industrial Research Institute, Ministry of Economic Affairs, Hsinchu, Republic of China (Taiwan)

Hong-Chien YUAN Union Industrial Research Institute, Ministry of Economic Affairs, Hsinchu, Republic of China (Taiwan)

O b s e rv e rs

S. ARD M O N G O N Science Department, Ministry of Industry, Bangkok, Thailand

G. B E C K E R Bundesanstalt für Materialprüfung (BAM), Berlin-Dahlem, Federal Republic of Germany

W. BOCK-WERTHMANN Office of Atomic Energy for Peace, Bangkhen, Bangkok, Thailand

S. F O O N G K IA T Department of Industrial Promotion, Ministry of Industry, Bangkok, Thailand

V. KANDASWAMY Housing, Building and Planning Section, ECAFE, Sala Santitham, Bangkok, Thailand

S. LUENJAVI Policy and Plans Division, ECAFE, Sala Santigham, Bangkok, Thailand

P. PATHÑOPAS Mining Technology Division, Department of Mineral Resources, Bangkok, Thailand

J.J. PINAJIAN Oak Ridge National Laboratory, Oak Ridge, Tenn., United States of Am erica

D. PURANASAMRIDDHI Board of Investment, Bangkok, Thailand 376 LIST OF PARTICIPANTS

B. N . SO N G K H LA Department of Medical Sciences, Ministry of Public Health, Yodse, Bangkok, Thailand

E. -O. SRIFAUNGFUNG Department of Industrial Chemical Engineering, Chulalongkorn University, Bangkok, Thailand

C. VASHRANGSI Department of Science, Ministry of Industry, Bangkok, Thailand

S. W A R A C H IN The Siam Cement Co. Ltd., Bangsue, Bangkok, Thailand

B. WATTANASERI Department of Science, Ministry of Industry, Bangkok, Thailand

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