THE EFFECT OF WHOLE TREE CHIPS
IN PULP AND PAPERMAKING
by
Bruce W. Halliburton
Thesis submitted to the Graduate Faculty of the
Virginia Polytechnic Institute and State University
in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
in
Forestry and Forest Products
APPROVED: W. 1· -Clas~r, Chairkan
T. A. Walbridge, Jr.
October 1975 Blacksburg, Virginia 24061 ACKNOWLEDGMENTS
A number of organizations and individuals became involved
during the course of this research project and the author wishes to
express his appreciation to them at this time. Two forest products
companies provided financial aid and design and evaluation exper-
tise. and from
Weyerhaeuser Company gave valuable suggestions during the course
of the project and made the necessary arrangements for pulp bright- ness tests. of Continental Can Corporation was very active from the project's inception and followed its progress
through to completion.
and donated much of their time to help solve many details of the actual laboratory work. typed the drafts, and her editing was most helpful. Dr. John Byrne, Dr. Tom Walbridge and Dr.
Geza Ifju served as committee members and helped develop, guide and interpret the experiments. The largest thanks go to Dr. Wolfgang
Glasser, Chairman of the committee. Without his genuine interest and enthusiasm for graduate studies, this project would never have been initiated. His ability to generate enthusiasm made this research an interesting and enjoyable learning experience. Finally, this thesis is dedicated to my wife for her continual support and dedication through my entire graduate career.
ii TABLE OF CONTENTS
Page
ACIQilOWLEDG:t-IBNTS •••••••••••••••••••••••••••••••••••••••••••••• ii
TABLE OF CONTENTS •••.••••••••.•••...•••.•••.•••••••••••••.••• iii
LIST OF FIGURES • .••••••••••••••••••.••••••••••••••••••••••••• v
LIST OF TABLES . ••••.••..•••••••••••••••••••••.•••••.•.••••••• vi
LIST OF APPENDIX TABLES • •.••••••••.••••••.•••••...••••••.•.•• vii
INTRODUCTION • •.•••••••••••••••••••••••••••••••••••••••••••••• 1
Increased Tree Utilization •••••••••••••••••••••••••••••• 1
Methods of Increasing Utilization...... 3 Objectives ••••• ...... 6 LITERA.TURE REVIEW. • • . • • • • • • • • • • . • • • • • • • • . • • • • • • • • • • • • • • • • • • • • 8
Bark...... 8 Topwood...... 12
Branchwood...... 13
Foliage ...... 15
Whole Tree Pulping. 16
MATERIALS AND METHODS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • . • 19
Raw Material Characterization...... 20
Kraft Pulping and Yield Determination...... 21
Black Liquor Analysis. 24
Pulp Testing...... 25
RESULTS • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 2 7
Chip Characterization...... 27
Pulp Yield...... 30
iii Page Black Liquor Characteristics • ...... 37 Handsheet Properties • ...... 37
DISCUSS ION. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 46
Chip Raw Material...... 46 Yield...... 47 Kappa Number and Pulp Color ••• ...... 51 Black Liquor...... 52
Hands beet Properties. • • • • • • . • • • • • • • • • • . • . • • • • • . • . . • • • • • . 53
CON CL US IONS. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 55 LITERATURE CITED...... 57
APPENDIX. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 61
iv LIST OF FIGURES
No.
1. Tree Components According to Keays...... 9
2. Experimental Design...... 23
3. The Relationship Between Yield and the Relative
Amount of Whole Tree Chips. • • • • • • • • • • • • • • • • • • • • • • • • • • • • 32
4. The Relationship Between Kappa Number and the
Relative Amount of Whole Tree Chips ••••••••.••••••••••• 35
5. The Relationship Between G. E. Brightness and the
Relative Amount of Whole Tree Chips •.•••••.•••••••••••• 36
6. The Relationship Between Beating Time to 300 ml
Canadian Standard Freeness and the Relative Amount
of Whole Tree Chips...... 40
7. The Relationship Between Breaking Length and Canadian
Standard Freeness for All Relative Percents of Whole
Tree Chips...... 42
8. The Relationship Between Tear Factor and Canadian
Standard Freeness for All Relative Percents of
Whole Tree Chips. . . . . • . . • ...... • ...... • . . 44
v LIST OF TABLES
I. Chip Input ...... 22 II. Raw Material Characterization...... 28 III. Raw Material Packing Density, Oversize Chips and Ash Content ••••••••••••• ...... 29 IV. Pulping Results ...... 31 v. Kappa Number and G. E. Brightness of Pulp ••••••••••••• 34
VI. Black Liquor Measurements ••••••••••••••••••••••••••••• 38
VII. Paper Ash and Pulp Beating Time...... 39 VIIL Breaking Length of Paper •••••••• ...... 41 IX. Tear Factor of Paper ...... 43
vi LIST OF APPENDIX TABLES
No.
I. Wood and Chemicals for Pulping •••••••••••••••••••••• 61
II. Yield and Coefficient of Variation for Yield
Determination of Each cook...... 62
vii INTRODUCTION
For a variety of reasons, the need for increased utilization of
the world's pulpwood resource became an important topic of discussion in the early 1970's. A logical point to begin better use of wood for products is at the time of harvest: in a conventional southeastern harvesting system, 15-50% of each tree is left in the forest as waste (Belluschi 1974). If all above-ground portions of a tree are harvested and chipped for pulpwood, approximately 85% of each tree would be utilized (Keays 1974a). However, many pulp and paper researchers predict this "whole tree" material would not be suitable for all pulping processes, particularly mechanical and sulfite systems, due to large amounts of bark, juvenile wood and reaction wood contaminants (Keays and Hatton 1974). Other questions put forth are the suitability of this material for bleached products, and the suitability of different species. In order to set the perspective of whole tree harvesting, the following discussion will present the need for increased wood utilization, and how it may be accomplished in the pulp and paper industry. Areas where more information is needed will be explored.
Increased Tree Utilization
The interest of the wood-using industry in better raw material utilization is the result of a number of developments in the early
1970's, some of which are identified in the following: a) New environmental laws prohibiting the burning of slash or logging residues in many states (Keays and Hatton 1974). This has forced
1 2
harvesters to make some use of waste tops and branches. b) As food
prices continue to rise, many landowners in the southeast find it
convenient to harvest existing forests and return the land to
agricultural crops (Zobel and Kellison 1972). The result is a
decrease in commercial forest land. c) Many mills in the southeast
have experienced local wood shortages because of poor weather con-
ditions and increased woodlands labor costs (Zobel and Kellison 1972).
Local shortages of wood have forced mill operators to use alternate
wood sources to roundwood, such as whole tree chips. A further
reaching aspect is: d) a predicted world shortage of wood for
pulping in the near future (Keays 1975). Most authorities agree
that wood consumption for paper products will increase in the future,
and it is the most important reason for increasing utilization now.
Because of the hypothetical nature of future market predications, many different estimates of the supply and demand for pulp and paper production are found in the literature. According to a U. S. Forest
Service estimate, in the U. S. the per capita consumption of wood for all uses in 2000 may be down slightly from present levels
(78 ft. 3 per capita). But the actual consumption of wood may be up
80% due to a population increase (Young and Chase 1965). According to Keays (1975) the world shortfall of wood for all uses in 2000 3 will be in the neighborhood of 200 million m or 88 million tons of oven-dry wood. Keays estimates this shortfall to be 5% of the total demand. As a comparison, the estimated total wood cut in Canada in 3 1974 was 120 million m • Keays has stressed the theoretical nature 3 of the above figures; however, he feels the shortfall estimate is a conservative one.
Methods of Increasing Utilization
Two forest management methods appear to have the most promise for increasing pulpwood utilization: growing trees on shorter rotations (Zobel and Kellison 1972) and whole tree harvesting (Keays
1974b). Short rotation forestry is developing in two major areas: hardwoods grown on a very short rotation (2 years), usually called silage, and pulpwood size trees (8 to 10 inches DBH in 15 years) of both hard- and softwood species. Short rotation forestry depends on the use of genetically improved trees (Zobel 1970) and therefore this concept will not be a commercial reality until the 1980 1 s.
Drawbacks to both concepts are the large amounts of bark, twice that of older trees, foliage and juvenile wood harvested in young trees
(Gilmer 1974). The major benefits are high yield per acre and short investment periods.
The use of branches and tops in combination with conventional bolewood for whole tree utilization in pulpwood operations received sporadic notice in the literature prior to 1959, but it was in that year that organized studies of whole tree harvesting were begun.
Largely the work of Young and co-workers, many reports have since been published on the forest biomass, chip production and pulp quality of several common weed or "puckerbrush" species in the northeastern U. S.
(Young and Chase 1965; Chase, Hyland and Young 1971). The major objective of this work was to point out the benefits of harvesting 4
all above-ground portions of these trees for pulpwood.
Similar whole tree studies on western pulpwood species were
performed by Keays and coworkers (1971, 1972, 1974, 1975). In their
numerous publications, both Keays and Young agree on the main benefits
of whole tree harvesting: increased wood yield per acre, lower
woodlands labor cost, and lower site preparation cost.
The technology for whole tree harvesting became connnercially
available in 1971, and today a number of mobile woodlands chippers
are being marketed. The objective of most whole tree chipping
systems is to harvest all above-ground portions of the tree. Some
efforts have been made to recover the root system of southern pines
(Young 1973); however, this practice has major limitations. According
to Lowe (1973), good quality chip material is being produced by
the above-ground harvesting systems, and the benefits as outlined by
Keays (1974c) and Young (1974) are being realized. The major drawback to whole tree chips lies in the amounts of bark, branchwood and sand included in the raw material (Anon. 1975). Sand may well be the most important contaminant, because it causes extreme wear on mill equipment. For these reasons, whole tree chips presently account for only a small percent of the total chip production in the U. S.
Many reports have been published concerning the suitability of different pulping systems on various tree components and species.
Pertinent articles are discussed in the literature review of this report. It is important to note here that a wide range of effects are reported for the different components of numerous common 5 pulpwood species. This information described the results of pulping bark, tops and branches separately (McKee 1960; Barefoot, Hitchings and Ellwood 1964; Gladstone, Barefoot and Zobel 1970; Zobel 1970;
Bublitz 1971; Glimer 1974; Wahlgren 1974) or the effect of bark and wood mixtures (Martin and Brown 1952; Samuels and Glennie 1958;
Horn and Auchter 1972; Auchter and Horn 1973; Keays and Hatton
1974; Howard and Boon 1975). Keays and Hatton (197la, 197lb, 1972) utilized a precision digester assembly to pulp different tree components simultaneously and to determine pulp yield and quality for each component. In this design, each tree component was pulped in a separate digester, but all digesters were interconnected and had a common liquor. These studies showed that the yield of each component was unaffected by the other components, and therefore these studies may be considered essentially individual component cooks. Eskilsson and Hartler (1973) cooked individual components together in a single digester but held them separate by wire baskets. This procedure allowed individual yield and quality determinations to be made.
All of the above-mentioned studies were essentially aimed at describing how the various tree components of different species responded to pulping. Most reports stressed the need for studying each species individually. Keays and Hatton (197la, 197lb, 1972) made the most comprehensive attempts to describe how mixtures of all components would behave in pulping. A major premise of these predictions was that the effects of any component were simply additive and pulp yield or strength could be pro-rated. However, Keays (1974c) 6 did mention that a synergistic effect, which improved paper strength,
appeared to be operating in wood and bark pulp mixes of some western
species. In other words, the strength of the mixture was greater
than the sum of the individual component strengths. A similar synergistic effect of strength in pulp mixes was reported by
Glasser, Slupsky and Clark (1973) for blends of softwood and peanut hull pulp. Martin and Brown (1952) conducted cooks of southern pine wood and bark mixtures, and they reported a decrease in pulp quality
(color, yield and strength), although the decrease was less than that predicted by 100% bark cooks. In summary, the results of pulping industrial mixes of whole tree chips had not been fully demonstrated.
A topic not fully covered in the literature is the change in pulp quality and yield caused by pulping various percentages of whole tree chips with conventional debarked bolewood chips (Wilkenson
1974). The amount of whole tree chips a mill uses for digester furnish will probably vary indirectly with the local pulpwood supply.
Under these circumstances, the pulping and recovery systems would probably require adjustment to the changing input.
Objectives
Due to a general lack of information concerning southern pine whole tree pulping, it was decided to conduct a series of laboratory pulping experiments which employed loblolly pine whole tree chips as the raw material.
The study was designed to investigate three areas of whole 7 tree chip pulping:
1) The chemical and biological differences between conventional chips and whole tree chips. Conventional chips are usually composed of 100% bolewood, while whole tree chips contain variable amounts of bolewood, topwood, branchwood, bark and foliage. The major differences between these two chip types will be elucidated, and the nature of the variation in whole tree chips will be described.
This information is most easily produced by single specimen studies.
2) The result of pulping mixed whole tree chip components in a sealed laboratory digester. The majority of reports available indicated the various tree components were pulped separately. After a short literature review it became apparent that only small, unconnected pieces of information were available on whole tree pulping of southern pine.
3) The nature of changes that could be expected to develop in a pulping system when the amount of whole tree chips is varied.
This area was developed as a logical extension of pulpwood market fluctuation.
It was decided to study kraft pulping of southern pine
(loblolly pine) because it is the major pulping system and species in the southeastern U. S. Although roots account for approximately
15-20% of the total tree weight and some interest has been expressed in harvesting roots, major drawbacks still exist in the root utilization area of complete tree utilization. LITERATURE REVIEW
Pulping characteristics of individual tree components have
occupied many researchers in recent years. The objectives of their
studies have been to explain the observed differences between con-
ventional pulping of wood and various tree components. The present
discussion will review the literature on kraft pulping of
softwood bark, branchwood, topwood and needles. An evaluation will
be made of each component individually, in terms of pulp yield,
chemical consumption, pulp strength and color. An attempt will be
made to evaluate the usefulness of predicting whole tree pulping
results from individual component cooks. Summaries of reports on
pulping various percentages of whole tree chips are given. An
illustration of whole tree components in softwoods is given in Figure
1, according to Keays (197la).
Bark
The bark of most softwoods in North America amounts to approx-
imately 15-20% of the total above-ground tree weight at merchantable
size; i.e., 8-inch DBH and above (Martin and Brown 1952; Keays 1974a).
Small trees contain significantly higher percentages of bark. Sieve
cells, the longest cells in slash pine (Pinus elliotti, Engelm) bark, account for approximately 40% of the total bark volume (Chang 1954), while tracheids make up approximately 95% of the xylem. The majority of sieve cells are short and tilln-walled in comparison to tracheids.
The remaining 60% of bark volume is composed of rectangular or
8 9
and Folia e
;-----t1ole
Figure 1. Tree Components According to Ke~vs (1971a) 10
isodiametric ray, parenchyma and periderm cells. The chemical
composition of bark presents the greatest problems in pulping
operations.
Martin and Brown (1952) compared bark to wood in southern pine
and found that bark had approximately one-half the carbohydrate
(30% vs. 66%) and twice the lignin (50% vs. 27%) of wood. Some
reports indicate bark lignin and carbohydrate are strongly linked
by chemical bonds (Martin 1969). The structure of bark lignin is
much more varied than that in wood, and many phenolic acids are
present. The amount of extractives is six to seven times greater
in bark than in wood, and a large variety of extractives are present.
Suberin, a mixture of hydroxy-acid complexes not found in wood, is a
chemically stable compound and it acts as a moisture barrier. Bark
ash content of southern pines averages 1.5 to 2.0%, while wood ash
averages 0.42% (Koch 1972). Bark is three times more soluble in 1% hot alkali than wood. In summary, bark is chemically more varied than wood and for this reason pulp systems designed for wood act poorly
on bark. The major drawbacks are low pulp yield (1/3 of comparable wood yield), dark color, and high chemical consumption (25% more
than wood) (Martin and Brown 1952; Sproull, Parker, and Belvin 1957).
Although the pulping characteristics of bark have been determined by 100% bark cooks, it seems more logical to evaluate bark in the percent mixture in which it may normally be found in pulpwood raw materials. The maximum amount of bark in southern pine whole tree chips appears to be 15-20%. Processing and screening can reduce 11
this figure to 5% (Ericksson 1972). Martin and Brown (1952) determined that 10% southern pine bark in a kraft cook would reduce digester yield by 2.5%, increase chemical consumption by 5%, and darken the pulp. Pulp strength was not affected by the bark content.
Keays and Hatton (1974), summarizing the results of six Canadian pulpwood species, concluded that 12% bark would cause a 6% decrease in digester yield, a 4% increase in chemical consumption, darken the pulp and have a negligible effect on pulp strength. Horn and Auchter
(1972) reported very similar results for 12 western pulpwood species except that alkali consumption was somewhat less. Samuels and
Glennie (1958), working with Douglas-fir, reported that 10% bark caused a 4% reduction in digester yield, but no consistent change in chemical consumption. Strength and color of pulp were not affected by bark.
Other factors of pulp quality affected by bark mixtures are residual lignin content, dirt, screened yield and bleachability.
Summarizing the above-mentioned reports on an equal yield basis, bark mixtures have slightly higher lignin content, increased dirt counts and usually lower screened yield. Bark mixes always require harsher bleaching conditions and therefore a reduction in bleached yield of pulp.
There is considerable interest in developing a screen system to remove bark from wood chips. Such a system would allow harvesting systems to chip all portions of a tree and then segregate the woody fraction for pulping. Ericksson (1972), Harkin and Crawford (1972), 12 and Blackford (1961) have been active in this field and their reports describe methods such as drum compression, air or water flotation and gyratory screening. These methods rely on the fracture nature of bark and its low density.
Topwood
The amount of topwood delivered to mills in the future is expected to increase because of whole tree harvesting and a general trend to harvest plantations at younger ages (Zobel 1970). Topwood is usually defined as that part of the stem less than 4 inches in diameter. Topwood contains a higher portion of juvenile wood (up to
90%) and bark (35%) than boles (Keays 197la). Reaction wood is also a major component.
In comparison to mature wood, juvenile wood is lower in density and cellulose content, and has a higher water content. Zobel (1970) reports moisture content equaled 160% and density was 24 lbs/cubic foot for southern pine juvenile wood, while mature wood figures were 103% and 30 lbs/cubic foot respectively. The percent latewood is usually very small in juvenile wood (Panshin and de Zeeuw 1970). Juvenile woody cells are shorter than mature wood cells. Usually this type of wood has developed during fast tree growth, although this is not a rule. Juvenile wood may form during the first 5-20 years of growth, depending on species and growth conditions.
Compression wood may also be a major component of topwood in southern pines, although no figures are found in the literature. In compression wood of southern pines, lignin percent is increased by as 13
much as 9%, cellulose may decrease by 10% and galactan may increase
8%. Specific gravity is up to 33% higher than that of normal wood.
Extractive content is also higher. Branchwood moisture content is
lower than bolewood.
The major characteristics of the southern pine top pulps,
apart from their bark content, are lower yield per cook and the
production of short, thin-walled cells (Zobel 1972). Screened yield
is reduced somewhat (Keays 1974a). Low yield is attributed to the
low density of the wood (Keays 1974a). Cooking rate and chemical
consumption are not greatly affected. The large portion of early- wood in juvenile wood is responsible for the production of shorter and thinner-walled cells. This pulp is well-suited for products
that require high apparent sheet density and good fold and burst strength (Bublitz 1971). Keays and Hatton (1971, 1972) found similar trends for a number of western softwoods. One notable exception was reported by Packman and Laidlaw (1967) for Sitka spruce.
The topwood of this species was measured to be 28% higher in density than the bolewood, and gave a correspondingly higher yield.
As a final note on topwood pulps, color is not affected, but beating time to a freeness level is usually shorter than for the bolewood pulps of many softwoods (Keays 1974a).
Branchwood
Branchwood properties are controlled by their high content of reaction wood, or compression wood in conifers (Panshin and de Zeeuw
1970). In comparing branchwood pulp to conventional stem pulp, yield 14
is lowered by 10% (Keays 1972) and residual lignin content of the
pulp is usually far above comparable pulps from all other tree
portions (Keays 197lc). Chemical consumption is also high for
spruce branches (Eskilsson and Hartler 1973). The marked differ-
ences between normal and compression wood have prompted Keays and
Hatton (197la, 197lb, 1972) to suggest that industry segregate this
material before pulping. In addition to wood differences, bark
content of branchwood is approximately twice that of stem wood for many species (Keays 197lc).
Keays (1974a) has sunnnarized the major pulping difficulties associated with branchwood as low total yield (20-30% lower than
comparable bolewood yields) and dark pulp color. High lignin and alkali extractable hemicellulose content is probably responsible for low yield, although this is highly variable with species. Koch
(1972) mentioned there was no difference in the total pentosan content of normal and compression wood in loblolly pines. The pentosan content in both types of wood is between 20 and 27%.
Pulp color is probably due to lignin content. High wood density and low moisture content may increase the percent screenings, and therefore lower fibrous yield. The presence of bark would further aggrevate the differences between branch and stem wood in pulping by absorbing chemicals, lowering yield and darkening the pulp. Strength is usually much lower in branchwood pulps. Strength loss may be caused by the smaller fraction of cellulose present in branchwood and shorter cell length (Eskilsson 1972). One beneficial aspect of spruce 15
branchwood pulping is an increased yield of tall oil (Eskilsson
and Hartler 1973).
Foliage
The effect of pine foliage in kraft pulping has not been fully
explained, perhaps because the volume of foliage received by mills
is highly dependent on the harvesting system (Keays 197lb). Most
investigations are concerned with foliage biomass, and foliage
utilization other than pulping (Keays 197lb). Koch (1972) presented
data that indicate the foliage on 21 year old loblolly pine trees
averages 4.8% of the above-ground oven dry weight.
In two extensive literature reviews (Keays 197lb; Eskilsson
and Hartler 1973), no pulping results were presented for pine needles.
In a later report, Keays (1975) states that foliage is more damaging
as a contaminant than bark: pulp yield is only 10%, the pulp is very weak and needles increase dirt count. Discussing their own results,
Eskilsson and Hartler (1973) reported that Scotch pine needles
consume large quantities of alkali, and gave a pulp y:ield of20%. Koch
(1972) reported that southern pine needles yield approximated 13%
fibrous material which resembles hemp after treatment with strong
alkali. In kraft pulping, needles will probably increase the amount of monoterpenes in digester relief gas and tall oil in black liquor.
To summarize the results of pulping individual tree components, bark and branchwood have the greatest disadvantages as measured by yield, chemical consumption, paper strength and color. Bark has a chemical makeup much more varied than wood: it absorbs chemicals 16 but gives very low yields, dissolves in alkaline liquors and darkens pulp. Branchwood is much more soluble in cooking liquor than bolewood, giving a lower yield of pulp. Because of its density, branchwood cooks more slowly and reduces screened yield.
Topwood pulp is nearly equal to bolewood pulp in all important parameters. Needles give the lowest yield of any components and consume chemicals; however, the pulp is probably as strong as wood pulp and byproduct yields may be increased.
Whole Tree Pulping
The potential use of whole tree chips for pulping has been most completely described by Keays in a number of articles (1974 a,
1974b, 1974c, 1975). The main force behind the use of this material is the need for more complete utilization of each tree
(Belluschi 1974). Keays (1974c) predicts that the fiber yield per unit area of forest can be increased 12-15% over present levels by harvesting all above-ground portions of coniferous trees. The chips produced by this type of operation are acceptable in size; however, the bark content may average 10-20%.
A major conclusion Keays (1974b, 1974c) draws in two summaries of his work in whole chipping is that the detrimental effect of bark on strength in mixtures of bark and wood pulp is not as great as was expected from the reports on 100% bark pulping.
Similar results were reported by Glasser, Slupski and Clark
(1974) for peanut hull and softwood pulp blends. Martin and Brown (1952) reported that yield and strength were higher than predicted, while permanganate number, chemical consumption and 17
color were lower than predicted. The major explanation given for the
poor predictions was that pure bark cooks were not sufficiently
pulped by the standard wood pulping conditions employed in their
study. Much of the bark was undercooked and did not fiberize. In
another study, on Douglas-fir (Pseudotsuga menziesii, Will.),
Bublitz (1971) reported that the pulp yield of small thinnings was
equal to bolewood yield. In a pro-rated prediction of yield, young
thinnings should have equaled 90% of debarked bolewood yield because of the juvenile wood and bark present (Keays, 197la). Eskilsson and Hartler (1973), reporting on studies of Pinus sylvestris components, stated that mixed component cooks caused no considerable change in kappa number or screenings when compared to values obtained in bolewood cooks. Total yield was slightly lower and chemical consumption was higher in mixed cooks than in 100% bolewood cooks. Although Keays predicts the pulping results of various whole tree chip types in numerous publications, he strongly recommends individual species studies.
Two reports are available on the effects of variable amounts of whole tree chips on mill operations: hardwoods are described extensively by Powell, Shoemaker, Lazar and Baker (1975), and soft- woods are less adequately covered (Anon. 1975).
Although softwood species and pulp systems are not identified, most mills report 20% whole tree chips caused no problems in yield, pulp strength or chemical recovery. This information is difficult to interpret, because the operating capacity of each mill is 18 an important factor in determining the effect of whole tree chips.
Keays and Hatton (1974) estimate that by using 100% whole tree chips, the reduction in per day production of pulp could be as high as 10%. This figure represents 6% loss in digester capacity (from reduced yield and screenings) and an additional 4% increase in chemical recovery. If a mill is operating at full capacity, i.e., limited by digester capacity and/or the chemical recovery system,
100% whole tree chips will have drastic effects on production. On the other hand, if a mill is not at capacity, whole tree chips can increase production by supplying more raw material per acre than conventional harvesting systems. MATERIALS AND METHODS
Woody Raw Material Procurement
All chip material was produced from mature loblolly pine trees,
Pinus taeda L. Four trees, 6-8 inches in diameter at breast height,
were felled from a local stand. Tree age ranged from 21 to 25
years. The objective of this portion of the study was to produce
two types of chips: conventional chips (CC material) and whole tree
chips (WTC material).
After felling, all branches and tops were removed from the
trees, and baled together. The stems were then cut into five foot
lengths and split longitudinally to facilitate chipping. "Conventional"
chips were cut from two debarked stems. Bark, branches, tops and
leaves were excluded from the "conventional" chips. Subsequently,
the conventional chips were thoroughly mixed and placed in labeled
55 gallon drums.
The remaining two stems, with bark intact, were chipped together with the bale of branches and tops. After mixing, this whole tree
chip material was placed in labeled 55 gallon drums. All drums were
stored in a cold room at l0°c. This procedure yielded two basic
raw materials: conventional chips from the woody portion of two
stems, and whole tree chips from the total volume of two trees plus
additional branches and tops from two trees. It is important to note that no soil was included in either type of chip. Chipping was performed by mobile Asplund Chipper (brush chipper).
19 20
Raw Material Characterization
Prior to kraft pulping, both types of chips were sampled to
estimate moisture content, packing density, percent oversize chips,
wood, leaf and bark percent, and ash content. Ten samples were taken
for each test.
Moisture content was determined by drying chips in an oven at
105°C for eight hours. Moisture calculations were based on oven-dry
weight. Packing density, in grams of wet material per liter, was
estimated by determining the weight of a volume of chips in a large
plastic graduated cylinder. The chips were placed in the cylinder
and lightly tapped to produce a near-level surface.
The percent of oversize chips was not actually measured for
the CC material. Instead, all oversize chips were removed by
separating the chips through a vertical bank of vibrating screens.
The CC material used in this study passed a screen with 3/4 inch
openings and was retained on a screen with 1/2 inch openings. WTC material was sampled for percent oversize chips, but pulping was
carried out with unscreened whole tree chips. The wet weight of WTC material that remained on a screen with 3/4 inch openings was divided
by the wet weight of the total sample for a measure of percent
oversize chips.
Because of sorting prior to chipping, CC material was composed
exclusively of wood. WTC material was sampled in order to estimate
the amounts of wood, leaf and bark present. Ten 50-60 g samples were weighed and then separated into wood, leaf and bark. These three 21 portions were placed in separate jars for weighing and oven drying.
Estimates of the three components were thus made for wet and dry whole tree chips.
Ash contents were determined for both chip types according to
Tappi Standard Tl503-58. Each raw material was finely ground, charred in a crucible and ashed at 600°c.
Kraft pulping and yield determination
Kraft or sulfate chemicals were employed to delignify chip material to a yield of approximately 55%. The terms used here to describe the cooking liquors are defined in Tappi Standard Tl203-08-61
(1961).
The basis for each cook was 750 grams of oven-dry material.
Total alkali equaled 18.6%, active alkali amounted to 15%, sulfidity was set at 25%, sodium carbonate was added (3.6% of total alkali) and the liquor to wood ratio was 3.4 to 1. Twenty pulp cooks were made using the above liquor recipe (Appendix Table I) and five different mixtures of CC and WTC raw materials (Table I). The five mixtures, in percent CC to WTC were; 100:0, 75:25, 50:50, 25:75 and 0:100. This procedure resulted in four replicate cooks for each of the five misture groups. The experimental design is illustrated in Fig. 2.
All cooks were performed in a 5 liter stainless steel laboratory digester at 170°c for 100 minutes. The charged autoclave was rotated in an oil bath with an initial temperature of 190°C. After the first
20 minutes, the system temperature equilibrated at 170°c and this temperature was maintained for an additional 80 minutes. Table I. Chip Input.#
Cook Conventional Whole tree Wood Leaf Bark number chip chip percent percent percent percent percent Total Top Branch Bole wood* wood* wood*
1 - 4 100 0 100 0 0 100 0 0
5 - 8 75 25 93 12 17 56 4 3 N N 9 - 12 50 50 86 13 19 51 7 7
13 - 16 25 75 79 14 20 47 11 10
17 - 20 0 100 72 15 22 43 15 13
# All percents are oven dry basis. * Estimated from Keays, 197la, 197lc. 23
Experimental Parameter Sample Size
Chip moisture content 10 per raw material Percent of total material 10 per raw material Packing density 10 per raw material Percent oversize 10 per raw material Chip ash content 10 per raw material Total yield 10 per cook Screened yield 1 per cook Black liquor density 2 per cook Black liquor solids 2 per cook Black liquor ash 2 per cook Paper ash 2 per cook Beating time to 300 ml. CSF 2 per cook Tear factor 4 per beating level Breaking length 10 per beating level
Conventional Chip: Whole Tree Chip (%)
100:0 75:25 50:50 25:75 0:100 ITTl ITTl ITTl ITTl I I I l 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16. 17 18 19 20
Cook Number
Figure 2. Experimental Design 24
At the end of the cooking cycle the autoclave was cooled for
20 minutes in a water bath. The cooled autoclave was opened and
200-300 ml of black liquor were collected and stored in a tightly
stoppered Erylemeyer flask. All of the pulp was removed from the
autoclave and disintegrated as described in Tappi Standard T20503-71.
The disintegrated pulp was washed in a Buchner funnel until the
wash water ran clear. Before storing, the washed pulp was allowed to
dry over night to facilitate moisture content determination. The
remaining moisture in the pulp was allowed to stabilize in a sealed
plastic bag in a cold room at 100 C for three days. Ten 5-10 g
samples were taken from each bag of pulp for moisture content
determination. The total yield of each cook in percent was determined
from the total weight of wet pulp, its moisture content, and total
oven dry chip weight.
Black Liquor Analysis
The black liquor from each cook was analyzed for density, total
solids and ash. Each of the above tests was performed in duplicate
for each liquor sample (i.e., for each cook).
The tests for density, solids and ash were performed on the
same sample of liquor in each cook. Density, in grams per ml, was measured by pipetting 50 ml of black liquor into a weighed round bottom flask. The flask was then connected to a VIRTIS model 10-010
freeze drier and dried to constant weight at-70 0 C. A 3-5 g sample of dry black liquor solids was then ashed in a tared crucible at 600°c. 25
Pulp Testing
A standard pulp beater series was performed following Tappi
Standard T20005-70 (1970). Undercooked chips or knots were not
included in the beating experiments. The only departure from standard
procedure was the amount of pulp used, 200 g instead of 360 g. This
substitution was made because of the small amount of screened pulp
yield per cook, and the large sample for moisture content determin-
ation. The beater series of each cook began with a batch of unbeaten
or lightly beaten pulp, and continued through five additional beating
periods. Canadian Standard Freeness (CSF) was measured in milliliters
according to Tappi Standard T27705-58 (1958). By monitoring CSF, a
series of six pulp furnishes from each cook was collected for
papermaking. A record of beating time required to reach a freeness
level in each series was made.
Screened yield was determined after the beater series in a cook
was completed. The leftover pulp and undercooked chips were
separated by screening against a water jet. Undercooked chips were
retained on the screen (openings 3/4") and fiberized pulp was passed.
Knot or undercooked chip percent was calculated by dividing the oven
dry weight of undercooked chips by 750 g. Screened yield in percent was calculated by subtracting knot percent from total yield percent.
Each pulp in a beater series was used to make seven 1.2 g
handsheets according to Tappi Standard T20503-71 (1971). After the handsheets were conditioned, the moisture content was determined and
sheet basis weights were calculated for use in strength testing. Five 26 sheets from each pulp in a beater series were employed for tensile strength and tear tests according to Tappi Standard T22005-71
(1971). Two tension tests of each sheet were made on an Instron
Table Model testing machine. Tension strength values are reported in terms of breaking length units. Five sheets were tested at once on 2 anElmendorf Tear Tester. Tear strength is reported in dm units of
Tear Factor. After strength tests had been completed, four handsheets from each type of chip mixture group were used to determine
G. E. Brightness on a Martin Sweets Brightness Tester. Relative brightness is reported in G. E. Brightness percent reflectance units.
Four 5-6 g samples of well-beaten paper scraps were collected from the strength tests of each cook. Two samples were employed in duplicate ash determination tests for percent ash in paper. The two remaining samples were used in kappa number tests.
The samples for kappa number tests were oven dried, weighed and redisintegrated. The kappa number of each pulp was determined in duplicate according to Tappi Standard T236m-60 (1960).
The raw data from all experiments was key-punched on cards and analyzed by computer. The Statistical Analysis System (SAS) was employed to produce means, analysis of variance and covariance " I tables, tests of significance, and regression equations. Duncan's multiple range test was used to compare means between raw material groups. RESULTS
Chip Characterization
Conventional chip (CC) material was composed only of wood while whole tree chip (WTC) material was a mixture of wood
(boles, tops and branches), leaf and bark. The average proportion of the three components in WTC material are given in green percents
(Table II): wood= 68%, leaves= 18.5% and bark= 13.5%. Dry weight analysis (Table II) gave approximately the same results: wood = 72%, leaves = 18% and bark = 13%. The coefficient of variation, a measure of sample variation, was approximately equal in the dry and wet condition; however, large differences between the three components were apparent. The woody fraction had a low coefficient of variation (C.V.) of approximately 7%. The foliage component C.V. was 22% and the bark component C.V. was 40%, indicating rather large variation in the sampling of both components.
The overall moisture content for WTC material was 101% and the moisture content of CC material was 124%. The WTC material had the largest moisture content variation, 15%. The woody fraction of WTC material had a low moisture content of 87%. Leaf and bark moisture was determined to be 148% and 107%, respectively. Of all the components in WTC material, bark had the highest moisture content variability, followed by wood and foliage.
There were large differences in packing density, percent oversize chips and percent ash between the two raw materials
(Table III). The average weight per volume was greater for CC
27 •
Table II. Raw Material Characterization.*
1 2 Material Chip S.D. c. v. Percent S.D. c.v. Percent S .D. c.v. moisture Eercent of total Eercent of total Eercent content material material (o.d. (wet) (dry) basis)
Conventional chips 124 7 6 100 0 0 100 0 0 N 00 Whole tree chips 101 15 15
Wood in WTC 87 8 9 68 5 7 72 5 7
Leaf in WTC 148 6 4 18 4 21 15 3 22
Bark in WTC 107 11 10 14 5 37 13 5 40
* Based on ten samples for each variable. 1 Standard deviation of the mean. 2 Coefficient of variation. Table III. Raw Material Packing Density, Oversize Chips and Ash Content.*
1 2 Material Chip S.D. c.v. Oversize S.D. c.v. Chip S.D. c.v. packing Eercent chips Eercent ash Eercent density Eercent content (wet) Eercent g/liter
Conventional chips 299 28 9 0 0.53 0.1 11 N \0 Whole tree chips 191 20 11 35 3 10 2.45 1 40
* Based on ten samples for each variable. 1 Standard deviation of the mean. 2 Coefficient of variation. 30
material (299 g/l) than for WTC material (191 g/l). The variability
of both raw materials was approximately equal in packing density
tests. WTC material had an average of 35% oversize chips while CC
material was prepared to exclude oversize chips (CC material
originally had approximately 17% oversize chips). The percent
ash in WTC material was nearly five times that of CC material,
2.45% versus 0.53%. The C.V. of ash content was nearly 4 times
larger in WTC material (40%) than in CC material (11.3%).
I The per4ent of branch, top and bolewood was not measured in I this study; 'however, some estimates may be calculated from data
I (ll i .j
l ,,,'" t:·l •: (J ') The restilts of pul~ yl~ld'kre'dis~lay~d iJ Table J.V. , AJllalysis C.·) '} '} • ' ~.... '•J l•1 I . - -- of variance.procedures showed no significant ch!ange.i:d'aviercige · I ·,. \ ! u ; :· ;· I l\j \'J HJ total yield , (percent) bdtween the five mixture lgrotips ,i(Fig •.~). . l . :. Jj : : • ~ ~ : • • I .. , .; . .~ ; .:~ ; The yiel~ fo~ a, group was calculated from the average cyield ~f ' ! ;II ·1 i ·1-1 •11
'•) ']: (·I t' the fou'r cooks ~n each group. This measurement. ra~?e~; f~m /,
I I : I l\J {1j (U 54% (0%: WTC), 'to 61% (75~ WTC). The variability, in·:yi~ld :i:erided to I • ,t: ,.!-: ,l ~ I •() I .J I ( ' t\.I l) () l I be high: in the mii.itu~e ~roups high" in WTC mater~al.L~ ~ w'1'c rthaterial = , . I 1 · 1., i I ·,. Whole Tree Total S.D.* Screened S.D.* Screenings S.D.* Chips knots yield a yield b or Eercent Eercent Eercent Eercentb 0 56 2 53 1 3 2 25 54 1 50 1 4 1 w 50 55 3 45 2 11 2 ...... 75 61 5 48 2 13 2 100 57 3 41 2 16 2 * Standard deviation of the mean. a Each value is the average of 40 samples. b Each value is the average of 4 samples. c Each value is the average of 8 samples. 32 70 60 50 I I ...... N 40 'O Legend ..-I (1) + -M Total pulp yield mean - 1 >4 ! standard deviation 30 Screened yield ~ mean -+ 1 standard deviation + Knot yield mean - 1 2. standard deviation 20 10 ± I 0 0 25 50 75 100 Relative Amount of Whole Tree Chips (%) Figure 3. The Relationship·Between Yield and the Relative Amount of Whole Tree Chips 33 4.4% C.V., 25% WTC material= 2% C.V., 50% WTC material= 5.6% C.V., 75% WTC material= 8.9% C.V., and 100% WTC material= 5.1% c.v. Screened yield percent showed a steady drop across mixture groups, except for 75% WTC material (Fig. 3). Analysis of variance showed no significant difference between groups, and again the largest percent variation of the mean was observed in the cooks highest in WTC material. The percent of knots or screenings showed a steady increase from 3% (0% WTC material) to 15% (100% WTC material) (Fig. 3). Comparison of group means at the .05% level revealed two distinct divisions: 0% and 25% WTC material (3-4% knots), and 50%, 75% and 100% WTC material (10-15% knots). The C.V. in knot percent followed a trend similar to that of the previous two yield measures. Kappa number (Table V) showed an increase in average value from 0% to 100% WTC material (Fig. 4). The mixture groups fell into three significant sets of kappa numbers: 0% and 25% WTC material (73), 50% WTC material (89), and 75% and 100% WTC material (111 to 114). The C.V. in kappa number tests was always below 10%, except in the first mixture group. Pulp brightness (Table V) test results exhibited three significant groups (Fig. 5): 0% and 25% WTC materials produced the brightest pulps (an average of 12 G.E. units), 50% WTC material was second (8.4 G.E. units), and 75% and 100% WTC material gave the darkest pulps (6.1 G.E. units). Table V. Kappa Number and G. E. Brightness of Pulp. a a Whole Tree Chips Kappa number S. D.* G. E. Brightness S.D.* Eercent 0 74 10 14 1. 7 25 73 7 12 1. 6 w 50 89 2 8 .9 .t- 75 111 10 6 .3 100 114 5 6 .7 * Standard deviation of the mean. a Each value is the average of 8 samples. 35 120 Legend mean +- 1 110 I standard deviation ,,.. Q) ~ 100 z::l re 0. c.. ::.:: 80 70 0 25 50 75 100 Relative Amount of Whole Tree Chips (%) Figure 4. The Relationship Between Kappa Number and the Relative Amount of Whole Tree Chips 36 16 Legend 15 mean ± 1 standard deviation 14 I st 13 12 11 . 10 µ:i 0 . 9 8 7 6 I I 0 25 50 75 100 Relative Amount of Whole Tree Chips Figure 5. The Relationship Between G.E. Brightness and the Relative Amount of Whole Tree Chj.ps 37 Black Liquor Characteristics There was no significant difference between group averages for black liquor density, solids or ash (Table VI). Density remained nearly constant at 1080 g/l. Solids also showed small group variation from 192 g/l (or 19.2%). Black liquor ash for individual cooks ranged between 60% and 65% although group averages did not significantly vary from 62.8%. Handsheet Properties The time required to reach 300 ml Canadian Standard Freeness (CSF) showed a significant decreasing trend across raw material groups (Table VII). 0% and 25% WTC material required an average of 40 minutes, 50% and 75% WTC material required 30 minutes and 100% WTC material required 26 minutes (Fig. 6). Tests of ash in paper showed 100% WTC material to be signifi- cantly higher than all other groups (Table VII). 100% WTC material had 2.48% ash while the remaining groups varied only slightly from 1.5% ash. Paper test results for tensile strength and tearing resistance are shown in Figures 7 and 8 respectively. No significant between- group differences were shown by analysis of covariance for either tear or tensile tests. The R squared of linear regression, standard deviation of the mean and coefficient of variation for tension and tear tests are given in Tables VIII and IX, respectively. In general, the R squared terms are acceptable for the tear tests and they indicate that a large amount of the data variation is Table VI. Black Liquor Measurements. Whole Tree Black liquor S.D.* Black liquor S.D.* Black liquor S.D.* Chips density solids ash 2ercent g/liter a g/liter a 2ercent a 0 1079 1 186 10 62.3 1 25 1084 1 198 4 62.57 2 w 50 1086 2 195 3 63.29 2 CX> 75 1085 1 193 11 62.48 1 100 1075 1 187 7 63.45 1 * Standard deviation of the mean. a Each value is the average of 8 samples. Table VII. Paper Ash and Pulp Beating Time. Whole Tree Paper S.D.* Beating time S.D.* Chips ash to 300 ml Eercent Eercent CSF min a 0 1°5 0.33 39.25 1 25 2.0 0.31 40.25 1 w 50 1·3 0.34 30.25 2 \0 75 2.1 0.29 30.1 1 100 2.48 0.44 26 1 - * Standard deviation of the mean. a Each value is the average of 8 samples. 40 Legend mean +- 1 I standard deviation 40 ""'Cl) I Cl) Cl) 35 II.Is:: II.I ,... ...-!. s 0 0 C""l ..c:: u 20 ('j II.I 0::: 0 .w 0 25 50 75 100 Relative Amount of Whole Tree Chips Figure 6. The Relationship Between Beating Time to 300 ml. Canadian Standard Freeness and the Relative Amount of Whole Tree Chips Table VIII. Breaking Length of Paper. Whole Tree Breaking length R squared of Standard deviation Coefficient a Chips m, at 300 ml CSF linear regression of the mean of variation Eercent Eercent 0 7438 0.17 7359 175 25 8229 0.3 7611 135 ~ 50 7824 0.3 7300 110 ...... 75 7111 0.14 6802 108 100 6438 0.09 6402 134 a Each value is the average of 40 samples. Legend 9000 0% WTC Haterial 25% WTC Material 50% WTC Material - 8000 ---- 75% WTC Material ,...... ,,,,..,...... - -- 100% WTCMaterial -·- ....--.--~--·-· -· -· 7000 ~ ~~· ... '-"13 ~·/ .a 6000 .µ ___.,,,.... l>O /'/ ... s:: Q) ...~ r-1 A"/ l>O 5000 ~ s:: ~~ ../ Tl ~ C1I Q) .,.hh / .. / .. ·_,,,../ .i:-- ,.... 4000 N ~ ~/ . I .·.·· 3000 // I ../ 2000 // 1000 I 800 700 600 500 400 300 200 Canadian Standard Freeness (ml,) Figure 7. The Relationship Between Breaking Length and Canadian Standard Freeness for All Relative Percents of Whole Tree Chips Table IX. Tear Factor of Paper. Whole Tree Tear factor R squared Standard Coefficient Chips at 300 ml of linear deviation of variation 12ercent cs Fa regression of the mean 12ercent 0 78 0.85 1.1 2.0 25 63 0.90 1.1 2.3 ~ 50 66 0.81 1.2 3.2 w 75 60 0.87 1.1 2.0 100 58 0.76 1.1 3.1 a Each value is the average of 20 samples. * Standard deviation of the mean. 140 Legend 130 0% WTC Material 25% WTC Material 50% WTC Material 120 75% WTC Material 100% WTCMaterial N -s 110 '-''"Cl ~ 0 I \ ~ (.) 100 tll ...... 14--1 .. . . ~ ...... ' ', tll Ql 90 ·--~ "·~ ~ f:-1 " .. ~ ~ ~~. ~- 80 "'-·· '~ '· " . 70 ...... ~ __ "'··:. . -...... -- '- "'-,.,_...... 60 ':"-- .. --...... _ ~ ·--·~-··-··-··-~.~ - . ....__... - ·... - ... - . -· - ... 0 800 700 600 500 400 300 200 Canadian Standard Freeness (ml.) Figure 8. The Relationship Between Tear Factor and Canadian Standard Freeness for all Relative Percents of Uhole Tree Chips 45 explained by regression. The same indication is also given by the low standard error and C.V. Relative to all other tests performed in this investigation, tensile strength testing had the largest data variation and the poorest reproducibility. The R squared term is extremely low, 0.09 in 100% WTC material, and standard error and C.V. are very high, up to 175% C.V. in 0% WTC material. Beating tended to make group strength values diverge in tensile tests, and results at 300 ml CSF are given in Table VIII. The 25% WTC material was the highest in average tensile strength, followed by 50%, 0%, 75% and 100% WTC material. In tear tests, 0% WTC material developed the highest strength at 680 ml CSF and remained in this position throughout the rest of the beating series. The remaining average group strengths tended to converge as beating progressed. Although the effect of needles was not measured directly in this study, this component seems to have had a small effect on pulp yield and quality. DISCUSSION Chip Raw Material The raw material used for this study appears to have the normal characteristics found in industry use, except for the high percentage of needles and oversize chips in the whole tree chip (WTC) material (Table I). Keays and Hatton (1974) used 88% wood and 12% bark as an estimated common input mix to calculate the effect of bark in pulping. In general, needles have not been studied in pulping experiments because usually they make up a small portion of the input mix, approximately 5% or less (Keays 197lc and Keays 1975). Eskilsson and Hartler (1973) performed mixed cooks with needles, but they did not state the quantity of needles. The quantity of needles used in the present study (15%) is probably high and somewhat unrealistic. The quantity of oversize chips in WTC material is also high and this figure would be reduced by screening in an industrial plant. The cause of oversize chips is partially due to the equipment used and the type of material chipped. The Asplund machine was not designed to produce quality pulpwood chips, and larger than normal amounts of oversize and undersize chips were produced. However, the small diameter of tops and branches probably contributed to the amount of oversize chips (Keays 1974c). Both conventional and whole tree chips were produced on the same machine, but the oversize percent was approximately double for whole tree chips. The low packing density of the WTC material, 1/3 less than CC 46 47 material, was caused by the large amount of oversize chips, and this could also be improved by screening. Industrial use of this chip material would require screening in order to improve digester packing: without screening a significant decrease in yield per chip volume would be expected. No screening was performed on WTC material in this study so that the extremes of chip input could be examined. The higher ash content in WTC material was caused partially by the higher ash content of bark and needles. However, the extra components in whole tree chips only add 1-1.5% ash to the raw material: additional ash must have been included during chip production. This ash is most likely from soil. It probably was not an excessive amount since it represented only 2.5-3% of the oven dry material. Yield The lack of any significant difference between group total yields is difficult to explain in the face of numerous reports that mixed component pulp yield is 5-6% lower than conventional wood yield (Martin and Brown 1952; Sproull, Parker and Blevin 1957; Samuels and Glennie 1958; Horn and Auchter 1972; Lowe 1973; Keays and Hatton 1974; Howard and Boon 1975). Because ten moisture content determinations were made for each cook and the standard deviation of these determinations was low (Appendixil), the yield estimates given here are very close to the true values. One study (Bublitz 1971) showed no change in yield for whole tree chips of 48 young Douglas-fir; however, permanganant number was higher than for conventional pulp. One objective of this report was to pulp to a constant yield and as a result, kappa number of pulp rose as WTC material was increased. One fact comes to light when the yield of individual cooks is examined; the smallest difference in yield between cooks is observed in 0% and 25% WTC material (2% and 3% respectively) and the largest difference is seen in 50%, 75%, and 100% WTC material (6%, 12% and 5% respectively). This variation was probably caused by the larger amounts of oversize chips, bark, and branchwood in the higher raw material groups. These components do not delignify at the same rate as bolewood (Keays 1974a). The bark component was dissolved or survived pulping as small, hard, dark, flaky particles about 2 mm in diameter. Oversize chips were incompletely delignified because of their size. Cooking liquor did not fully penetrate these chips: although the periphery was fibrous, the interior was relatively solid. Branchwood chips had a similar appearance except that they usually had an easily discernible concentric cross section and were darker brown in color, indicating a high lignin content. Some branch chips were oversize although more than half appeared to be of acceptable size. The high density of branchwood probably accounted in part for their poor pulping results by slowing the penetration of cooking liquor. The large size of some branch chips also hindered penetration. Other important parameters that could have affected yield were 49 the relatively low moisture content of whole tree chips, and the inherent high variability of the WTC material. Although loblolly pine topwood is low in density and high in moisture content as reported by Zobel and Kellison (1972), it is estimated that in this study only 15% of the WTC material was topwood. Branchwood accounted for approximately 24% of WTC material, and dead or dying branches would have greatly lowered the overall chip moisture content. Such dry wood would soak up a disproportionate volume of liquor, cause uneven delignification and exhaust chemicals. The high variation in sample raw chip composition is an important area of discussion. The standard deviation about the mean was approximately 22% for foliage, and 40% for bark in WTC material. The large sample size (10 samples for each chip material) tends to support the conclusion that unscreened chips are naturally variable in their wood, bark and leaf composition. It is strongly suspected that themeanfigures of wood, leaf and bark for WTC material listed in Table I were not reproduced in all cooks, especially those cooks in the 75% W'lCmaterial group. The large variation in yield of this group may have been caused by unusually high volumes of either needles or bark. Needles would lower pulp yield because of their high moisture content and low fibrous content. Bark, however, could raise the pulp yield by absorbing chemical from the low alkali liquor employed in this study. In addition to the biological makeup of the raw material, the variation of ash percent in WTC material (40% about the mean) supports the concept of a highly variable raw 50 material. Screening would probably lower this variability a great deal by removing bark, foliage, and oversize chips. Keays (1975) has identified chip screening as an important research area. Screened yield, or fiber yield, is expressed by the following relationship: Total Yield - Screenings (undercooked chips) = Screened Yield. No significant between-group differences were observed for screened yield, probably because of the large variation in 75% WTC material. This may be concluded because a strong downward trend was observed for all groups, except the 75% WTC material (Fig. 3). This trend for screened yield is supported by the analysis of screening or undercooked chips percent (Fig. 3). Two significant divisions are shown, 0% and 25%, and 50, 75 and 100% WTC material, and the increase in screenings is constant. Most studies report similar results (Martin and Brown 1952; Samuels and Glennie 1958; Horn and Auchter 1972; Keays and Hatton 1974; Howard and Boon 1975). This increase in screenings was caused by oversize chips and branch- wood. The inclusion of topwood is not suspected as a cause here because almost all reports agree that topwood and bolewood are very similar in their pulping response. Bark particles were too small to be measured as screenings in this study. Branchwood and oversize chips increased screenings percent because of high density compression wood, low moisture content and chip size. Each of these factors decreased the penetration of cooking liquor and in turn reduced the rate of delignification relative to that of bolewood. Chip size may be more important in the pulping of branchwood than wood density. 51 It is interesting to note that in loblolly pine boles the density of latewood may be up to five times greater than the density of earlywood (Koch 1972). If pulp chips are properly cut, cooking liquors will penetrate the wood and delignification will proceed uniformly. Kappa Number and Pulp Color In the present study, kappa number (Fig. 4) increased as the percent of WTC material increased, indicating delignification was not proceeding uniformly in all cooks. Three ordered significant kappa groups were found, indicating a step-wise increase in pulp lignin content. Undercooked chips were excluded from the pulp samples used for kappa tests and consequently they could not affect the lignin content. Increased pulp lignin content was predicted by Keays (1974a) for mixtures of branchwood. Bark may also contribute to a rise in screening and kappa number. Bark absorbs alkali, as does branchwood (Eskilsson and Hartler 1973). Bark is also highly soluble in alkali and its phenols may be included as lignin in kappa tests. Since cooking conditions and total yield were constant, it is reasonable to expect lignin content to increase. This result agrees with the results of Bublitz (1971) for young Douglas-fir whole tree thinnings. The change in pulp color was another expected result (Howard and Boon 1975). The 0% and 25% WTC material groups had a normal light brown color. The 50%, 75% and 100% WTC material groups showed a gradual darkening to a very dark brown chocolate color. This 52 change in pulp color is illustrated by the results of G. E. Brightness tests (Fig. 5). Higher kappa number and darker color indicate these pulps would be significantly harder to bleach than conventional pulp. Two factors may have caused the dark color and the rise in kappa number of WTC material pulp: increased amounts of bark and reprecipitation of lignin on the pulp. All reports on southern pine bark indicate it yields a very dark pulp, probably from conjugated lignin degradation compounds and dissolved bark solids. The dissolution of bark appears to have been small in the present study because the amount of black liquor solids and ash did not change across the range of WTC material input. As previously mentioned, bark particles were numerous in the pulp, and they were approximately one square millimeter in area. Soluble lignin may have been reprecipitated onto the fiber in the high WTC % material if the pH of the liquor became low. Although black liquor pH was not measured, it is reasonable to assume it was low: active alkali in the white liquor was low (15%), bark and branchwood absorb chemical, and the liquor to wood ratio was low (3.4/1). Alkali and liquor were set low in order to approximate industry conditions. Black Liquor Black liquor density, solids and ash showed no significant between-group differences (as seen in Table VI) and this is reasonable when total yield is constant: there is no change in the amount of material dissolved in the liquor. This finding is 53 supported by the kappa test results and pulp color which indicate a large reprecipitation of dissolved compounds for the material groups high in WTC material. Most studies report an increase in these black liquor parameters, due to the increase in bark and a decrease in total yield. Instead of dissolving more lignin and bark, the cooking conditions in this study produced equal total yield as whole tree chips were added to the raw material. In addition, the low liquor volume could have limited bark dissolution. Group differences in ash percent were expected, independent of yield, because ash should be passed through the system. Since increased ash did not show up in the black liquor, it was expected to be found in the fiber. Paper ash tests showed this to be true: 100%WTC matErial was significantly higher (60%) than the other groups. It may be that ash should properly be tested in unbeaten pulp, instead of paper. Beating may tend to physically remove ash. Handsheet Properties Beating time to a freeness level is reduced by whole tree chips (Table VII) as reported in this and other studies (Keays 1974b, Howard and Boon 1975). The reduction may have been due to the large volume of small tracheids found in top and branchwood as suggested by Howard and Boon (1975). Of all tests performed in this study, paper testing showed the largest data variation. This is probably the major reason analysis of covariance showed no between-group differences in tear or tensile tests. However, Martin and Brown (1952) found no loss in strength 54 for pulp mixtures containing up to 16% southern pine bark. Howard and Boon (1975) also found no loss in pulp strength of pine bark mixture. These results tend to discourage the prorating of strength for wood and bark mixtures, as suggested by Keays and Hatton (1974), at least in the case of southern pines. In the present study, the average ~ensile strength of 25% and 50% WTC material was consistently above the 0% WTC material values. These results indicate that if pulp is to be beaten to develop tensile strength, the major effect of WTC material is to lower the time or force required to beat the pulp. Tearing resistance tests appear to be more reliable because the C. V. never reached 3%. However, no between-group differences were found in tearing resistance, indicating that the regression lines lie close together and cross each other (Fig. 8). It is worth noting that 75% and 100% WTC materials were the lowest in tearing resistance at high freeness levels, but beating tends to make the tearing resistance of all groups converge. These results on paper strength indicate that a mixture of various fiber type cells tend to supplement each other in strength, as suggested by Keays (1974b, 1974c) and Halliburton, Glasser and Byrne (1975). Halliburton et al. (1975) observed that small isodiametric cells filled interstices in the fiber web of paper, and that small quantities of short fibrous cells could substitute for longer wood tracheids in paper. The above-mentioned studies were performed by mixing individual pulps, and the present study indicates that this effect may be operating in mixed cook pulps as well. CONCLUSIONS In sunnnary, increasing the volume of southern pine whole tree chips material will increase the percent of screenings when total yield is held constant. Under these conditions whole tree chips increase the quantity of lignin in pulp and pulp color becomes darker, indicating reduced bleachability. If yield is held constant, the amount of black liquor solids will not increase. The amount of ash processed by the system is increased and this may be the major drawback to whole tree utilization. Screening the raw chip material is a required step for whole tree chips, and this will probably remove the majority of oversize chips, bark, needles, and soil. However, the inclusion of needles does not appear to adversely affect pulp yield or quality. Pulp strength of WTC material is not greatly reduced and in any case, strength may be improved by beating. Beating time to a freeness level is reduced. The difference between CC and WTC material is highly dependent on species, and the variability in the chip composition can be large. In loblolly pine, bark and dense branchwood probably cause the largest problems in pulping. The volume of these components in the raw material can vary greatly, and they lower yield and darken pulp. However, these two components, in mixed cooks, do not cause the large reduction in pulp quality and yield that has been predicted by individual cooks. This study indicates that significant changes in pulp mill operation will develop as the amount of WTC material utilized is 55 56 increased. The low packing density of unscreened WTC material will reduce digester capacity. If the objective of cooking is a fixed pulp lignin content, digester yield will be further reduced. The percent of knots will probably increase. It appears that a larger volume of liquor would pulp WTC material more uniformly. This adjustment would increase the volume of liquor-processed by the recovery system, and the overall water requirement of the mill would be increased. Future laboratory pulping experiments of loblolly pine WTC material should concentrate in the areas of: 1) the yield-kappa number relationship, and 2) bleaching experiments. Such future investigation would explain how the lignin content of pulp varies with the total yield, and optimum cooking conditions could be determined. The findings of the present study strongly indicate that the raw chips should be screened, and liquor and active alkali should be increased. The hardness of bleaching should be studied because industrial use of WTC material will probably not be limited to unbleached products. Because bark is part of the input material, it is reasonable to suspect that WTC pulps may bleach in a different fashion than normal pulps. LITERATURE CITED Anon. 1975. Status of whole tree chipping. Pulp and Paper. 49(6):126-129. Auchter, R. J. and R. A. Horn. 1973. Economics of kraft pulping of unbarked wood. Paper Trade J. 157(26):38-39. Barefoot, A. C., R. G. Hitchings, and E. L. Ellwood. 1964. Wood characteristics and kraft paper properties of four selected loblolly pines. Tappi. 47(6):343-356. Belluschi, P. G. 1974. The total tree concept and its effect on the pulp and paper industry. Tappi. 57(3):96-98. Blackford, J. M. 1961. Separating bark from wood chips. For. Prod. J. 11(11):515-519. Bublitz, W. J. 1971. Kraft pulping quality of thinnings from young Douglas-fir. Tappi. 54(6):928-932. Chang, Y. 1954. Anatomy of connnon North American pulpwood barks. Tappi Monograph Series No. 14. Tappi, New York, N. Y. 241 pp. Chase, A., J. F. Hayland, and H. E. Young. 1971. Puckerbrush pulping studies. Tech. Bull. 49. Life Science and Agricultural Experiment Station, Orono, Maine. Erickson, J. M. 1972. The status of methods for debarking wood chips. Tappi. 55(8):1216-1220. Eskilsson, S. 1972. Whole tree pulping I - fibre properties. Svensk Papperstidning. 73(10):397-402. Eskilsson, S. and N. Hartler. 1973. Whole tree pulping II - sulphate cooking. Svensk Papperstidning. 74(2):63-70. Gilmer, W. D. 1972. Smallwood harvesting, debarking and chipping. Tappi. 57(6):54-57. Gladstone, W. ~.,A. C. Barefoot Jr., and B. J. Zobel. 1970. Kraft pulping of early and latewood from loblolly pine. For. Prod. J. 29(2):17-24. Glasser, W. G., R.H. Slupski, and J.P. Clark. 1973. Pulp and papermaking potential of peanut hull waste in blends with softwood pulp. Wood and Fiber. 5(2):98-105. 57 58 Halliburton, B. W., W. G. Glasser, and J.M. Byrne. 1975. The anatomy of Arachis hypogea, with special emphasis on the sclereid layer. Bot. Gaz. 136(2):52-58. Harkin, J. M. and D. M. Crawford. 1972. Separation of wood and bark by gravatory screening. For. Prod. J. 22(5):25-30. Hatton, J, V. and J. L. Keays. 1971. Laboratory precision digester studies. Svensk Papperstidning. 74(3):128-(3). Hatton, J. V. and J. L. Keays. 1972. Complete tree utilization studies III - yield and quality of kraft pulp from the components of Pseudotsuga menziesii. Tappi. 55(10):1505-1508. Horn, R. A., and R. J, Auchter. 1972. Kraft pulping of pulpwood chips containing bark. Paper Trade J. 156(46):55-59. Howard, M. J. S., and B. W. Boon. 1975. Some aspects of whole tree utilization with New Zealand pines. APPITA. 28(4):246-251. Keays, J. L. 197la. Complete tree utilization. I. An analysis of the literature--unmerchantable top of bole. PB198043. For. Prod. Lab., Vancouver, British Columbia. Keays, J. L. 197lb. Complete tree utilization. II. An analysis of the literature--foliage. PB198315. For. Prod. Lab., ancouver, British Columbia. Keays, J. L. 197lc. Complete tree utilization. III. An analysis of the literature--branches. PB199174. For. Prod. Lab., Vancouver, British Columbia. Keays, J. L. 197ld. Complete tree utilization. IV. An analysis of the literature--crown and slash. PB201292. For. Prod. Lab., Vancouver, British Columbia. Keays, J. L. and J. V. Hatton. 197la. Complete tree utilization studies I - yield and quality of kraft pulp from Tsuga heter- ophylla. Tappi. 54(1):99-104. Keays, J. L. and J. V. Hatton. 197lb. Complete tree utilization studies II - yield and quality of kraft pulp from the components of Picea glauca. Tappi. 54(10):1721-1724. Keays, J. L. 1974a. Complete tree utilization of mature trees. A.I.Ch.E. Symposium Series. 70(139):67-75. Keays, J, L. 1974b. Full tree and complete tree utilization for pulp and paper. For. Prod. J, 24(11):13-16. 59 Keays, J. L. 1974c. Full tree chips for kraft - yield, quality, and economics. Pulp and Paper Canada. 75(9):43. Keays, J. L. 1975. Full fore~t harvesting. Am. Paper Ind. 57(3):14-18. Keays, J. L. and J. V. Hatton. 1974. The effect of bark on wood pulp yield and quality and on the economics of pulp production. VP-X-126. Dept. of the Environment, Canadian Forestry Service, Western For. Prod. Lab., Vancouver, B. C. Koch, P. 1972. Utilization of the southern pines. I. The raw material. U. s. Dept. of Agric. For. Serv., Southern Forest Experiment Station. 734 pp. Lowe, K. E. 1973. The complete tree. Pulp and Paper. 15(12):42-47. Martin, J. S., and K. J. Brown. 1952. Effect of bark on yield and quality of sulphate pulp from southern pine. Tappi. 35(2):7-10. Martin, R. E. 1969. Characterization of southern pine barks. For. Prod. J. 19(8):23-30. McKee, J. C. 1960. The kraft pulping of small diameter slash pines. Tappi. 43(6):202A-204A. Pakkman, D. F., and R. A. Laidlaw. 1967. Pulping of British grown softwoods. Holzforschung. 21(2):38-45. Panshin, A. J. and C. deZeeuw. 1964. Textbook of wood technology. Vol. 1. McGraw-Hill, New York, N. Y. 705 pp. Powell, L. N., J. D. Shoemaker, R. Lazar and R. G. Baker. 1975. Whole tree chips as a source of papermaking fiber. Tappi. 58(7):150-155. Samuels, R. M. and D. W. Glennie. 1958. Bark tolerance of Douglas- fir chips in kraft pulp manufacture. Tappi. 41(5):250-255. Southern Forest Resource Analysis Committee. 1969. The South's Third Forest. 111 pp. Sproull, R. C., R. B. Parker, and W. G. Belvin. 1957. Whole tree harvesting. For. Prod. J. 7(4):131-134. Tappi Standard Methods: Tl5os-58. Ash in wood. Tappi Standard Methods: T20lm-58. Testing pulp for moisture. 60 Tappi Standard Methods: T227os-58. Freeness of pulp. Tappi Standard Methods: T236-m-60. Kappa number of pulp. Tappi Standard Methods: Tl203os-61. Standard terms used in the sulphate process. Tappi Standard Methods: T625ts-64. Analysis of soda and sulphate black liquor. Tappi Standard Methods: T200os-70. Laboratory processing of pulp. Tappi Standard Methods: T205os-71. Forming handsheets for physical testing of pulp. Tappi Standard Methods: T220os-71. Physical testing of pulp handsheets. Wahlgren, H. E. 1974. Forest residues. Tappi. 57(10):65-67. Wilkinson, G. 1974 Personal communication. Young, H. E. 1973. Complete tree harvesting and utilization-- roots to branches. Paper Trade J. 157(51):38, 40. Young, H. E. and A. J. Chase. 1965. Fiber weight and pulping characteristics of the logging residues of seven tree species in Maine. Tech. Bull. 17. Maine Agric. Exp. Stn., Orono, Maine. Zobel, B. J. 1970. Developing trees in the southeastern U. S. with wood qualities most desirable for paper. Tappi. 53(12): 2320-2325. Zobel, B. J. 1971. Wood for forest industries. Am. Paper Ind. (1):26-36. Zobel, B. J. and R. C. Kellison. 1972. Short rotation forestry in the southeast. Tappi. 55(8):12-5-1208. Appendix Table I. Wood and Chemicals for Pulping. Raw Conventional Wbole tree NaOH Na Na Water 2s 2co3 material chips chips to group green oven green oven add dry dry .& .& .& .& I 1680 750 0 0 108.9 35.4 47 1429 II 1260 562.5 377 187.5 108.9 35.4 47 1477 III 840 375 754 375 108.9 35.4 47 1514 IV 420 187.5 1131 562.5 108.9 35.4 47 1558 v 0 0 1508 750 108.9 35.4 47 1601 61 62 Appendix Table II. Yield and Coefficient of Va~iation for Yield Determination of Each Cook. Cook Yield (%) c. v. (%) 1 54.58 6 2 55.94 4 3 56.00 3 4 54.46 2 5 54.63 6 6 52.55 9 7 54.68 10 8 53.42 6 9 50.85 5 10 55.14 2 11 55.54 4 12 57.24 9 13 65. 72 10 14 64.10 10 15 54.70 7 16 57.49 7 17 54.33 12 18 56.89 13 19 59.05 14 20 53.04 12 The vita has been removed from the scanned document ABSTRACT For a variety of reasons, the need for increased utilization of the world's pulpwood resource has become an important subject of discussion in the 1970's. Whole tree chipping, or the use of all above-ground portions of trees, is a feasible method of achieving this goal. Many reports have been published in the field of pulping whole tree chips, and articles pertinent to softwood pulping are discussed in the literature review of the present study. Because a noticeable lack of information on mixed component pulping of southern pines was observed in the literature, the present study was designed to investigate the following topics: 1) The chemical and biological differences between conventional chips and whole tree chips, and the nature of the variation in the composition of whole tree chips. 2) The results of pulping mixed whole tree components in a laboratory digester. 3) The nature of changes that could be expected to develop in a pulping system as the amount of whole tree chips was varied from 0 to 100% of chip input. Kraft pulping of loblolly pine (Pinus taeda, L) was chosen because it is the major pulping system and species in the southeastern U. S. Unscreened whole tree chips are highly variable in their composition, and age and species have a large effect on the chip composition. Mixed component cooks do not appear to have the poor qualities predicted by individual component cooks. When yield and pulping conditions are held constant and the percent of WTC material is increased, fibrous yield decreases, kappa number rises and pulp color darkens. This may be a result of liquor chemical exhaustion and precipitation of lignin onto pulp fibers. These results indicate that in a mill operation, WTC material should be pulped with increased chemical and liquor volume.