TAPPI proceedings of the 1988 pulping conference; 1988 October 30-November2; New Orleans, LA. Atlanta, GA: TAPPI Press; 1988: 641-648. Book 3.

HISTORY OF FPL COLD SODA CMP PROCESS: 1950 - PRESENT The purposes of this report are: 1. To record the circumstances of the origin and development of the J. N. McGovern E. L. Springer FPL cold soda CMP process; 2. To note the growth University of Wisconsin U.S. Forest Products Lab. and decline of commercial cold soda pulping in the Madison, WI 53706 Madison, WI 53705 U.S.; 3. To point out the short time �or transfer of the experimental technology into mill practice; ABSTRACT 4. To discuss the nature and mechanism of the cold soda process from new experimental information; and The first report on the so- called FPL cold soda 5. To review recent literature on the process. pulping process was published in 1950. The feasi­ bility of the process for commercial operation was Historical demonstrated by continuous production in a Wisconsin NSSC mill, making corrugating board, in 1951-52. A cold soda- type process was patented in Germany in This was the first application of chemimechanical 1919 by Erich Opferman for producing from straw, (CMP) pulping. In 1956 the first custom- designed reeds and ocher nonwood plant materials by simul­ mill started up in New York State. The product was taneous treatment with alkali at ambient temperature . This CMP process was developed to and mechanically fiberizing in a kollergang, stamp produce pulp at near- groundwood yield with strength, mill or other fiber separation means (4). In 1935 processing capability and potential for softwood Robert Woodhead patented in Australia a chemical- groundwood substitution. mechanical pulping process based on treatment of wood chips (specifically Australian eucalyptus) with Within 10 years (1960) there were nine CMP mills in an alkali or alkaline salt (specifically caustic the U.S. and an equal number in foreign countries. soda) with simultaneous or subsequent disintegration By 1969 however, alternative methods of hardwood of the chips in a rod or ball mill (including a pulping had been developed and only one U.S. mill kollergang) to produce a coarse pulp for wrappings remained in operation along with several foreign and news (using 2% NaOH) and a fine pulp for mills. Despite chis decline, a cold soda CMP mill and writings (using 8-10% NaOH) (5). started operation in Spain in early 1980's making Although the patent also mentions the beater and pulp for coated . jordan as Fiberizing equipment, the disk refiner, the heart of the modern semichemical- type processes, Research and development on the process continues was not recognized. As far as is Known, neither and certain results and a chronology of the rise the Opferman nor the Woodhead processes were ever and decline of cold soda CMP operations in the U.S. developed commercially (6). arc given. FPL Cold Soda Pulping Process Development Studies INTRODUCTION FPL publications on cold soda pulping in the period A research program directed toward utilization of of 1950-1958 involved extensive investigations of hardwoods by producing pulps at near the variables of the process as outlined below groundwood yields but with processing potential was (2, 7, 8, 9). undertaken at the Forest Products Laboratory (FPL) in the immediate post- WorldWar II period. This Independent Variables: program continued the FPL investigations that had led to the FPL semichemical pulping process. Wood - Aspen and 17 northern, southern and western hardwoods, spruce, northern fir; chip size; The first study in the program, begun in late 1947, chip moisture content. involved treatment of wood chips with water and Treatment - Presteaming; time, temperature, pressure steam followed by fiberizing in a disk refiner. The (including vacuum impregnation) and alkali pulps were suitable for application to corrugating concentration; liquor/wood. medium as reported in May, 1949 (1 ). A preliminary Fiberizing - Degree (freeness), disk refiner; roll- study of pulping with mineral acids at low tempera­ type fiberizer. tures started at the same time proved unpromising. Brightening - Brightening agents (calcium hypo- chlorite, sodium peroxide, sulfur dioxide in Another research project, which started in late water, sodium hydrosulfite, zinc hydrosulfite). 1948, considered the use of caustic soda of Paper Products - Printing and ; corrugating. moderate strength on wood chips at ambient tempera­ ture. This project resulted in the development of Dependent Variables: the so- called " cold soda semichemical" (CSSC) process, more properly designated as cold soda Pulp - Yield; chemical consumption; freeness; pulp chemimechanical process (cold soda CMP). The first strength properties; optical properties; fiber publication on this process appeared in August, classification; chemical composition. 1950 (2 ). This process was successfully demon­ Paper Products - Strength properties; optical strated in a trial at the NSSC mill of Green Bay properties; special use tests. Pulp & Paper Co., Green Bay, Wisconsin, and was subsequently used there commercially from 1951 to Mill Application of FPL Cold Soda CMP Process 1952 (3 ). The product was corrugating board. This was the first CMP operation. The FPL cold soda process moved into full commercial production about six years after the first publica­ tion in 1950 with the exception of the 1951-1952 temporary, partial production in the NSSC mill noted previously. The chronological order of the

1988 Pulping Conference / 641 establishmen: of the nine U.S. mills in the period Pressing in screw pressers for prefiberizing and of 1950-1960 is given in Table 1. Nine cold soda spent liquor recovery. mills were also started up and operated in foreign Fiberizing in vertical disk refiners in one to countries, including Australia (Tasmania), Japan, three stages. Argentina, Colombia and Italy (10). Screening and cleanings with standard equipment. Brightening hardwood cold soda pulps from the Increased utilization of hardwoods from a fiber brightness range of 40-45%, depending on the resource standpoint was an important factor in the wood species, to a brightness level of 60-70% U.S. industry during the 1950- 1960 period. This by the application of sodium chlorite (yield circumstance was favorable to considering the cold loss of 2-5%), peroxide, sodium or hydrogen soda process as a means for increasing :he use of with appropriate buffering, and sodium hydro hardwoods in northern and southern mills. sulfite in methods adapted from groundwood brightening. The U.S. and foreign mills differed considerably in Spent Liquor Recovery and Disposal. Cold soda their pulping systems, as described below, although pulping operations in 1960 generally fortified all involved the two- stage, semichemical- type con­ spent caustic treatment reagent for subsequent figuration of impregnation and fiberizing steps. reuse. Wash water was usually recycled as dilution water at the refiners, screens and Chronology. A chronology of the FPL publications on cleaners. The reactions products, once the cold soda pulping and the U.S. mill applications system was in equilibrium apparently passed out over the 1950-1960 period is given in Table 1. in the white water or, as discussed below, in the pulp itself. Since the mills mostly had The records of longevity of the cold soda operations low pulp capacity (Table 1), the environmental cannot completely be established, but it is known effect was ignored. An exception was a that by 1969 only one of the original U.S. cold soda relatively large mill of 200 tons per day, mills was still in operation (27 ) and this mill employing a cross recovery arrangement with its terminated its cold soda pulp production in 1986 associated kraft mill (36). The caustic spent (19). The three mills in Tasmania (the first in liquor and the necessary sulfuric acid were 1957 (29, 30, 31)) and others in Japan have con­ added to the concentrated black liquor as a

tinued operating to this day (32, 33, 34). A cold replacement for salt cake makeup. The BOD5 for soda pulping operation in Spain, making pulp for use cold soda pulping is reported as being 200 in coated papers, was patented in 1981 with lb/ton of pulp (26). operation in 1984 (35). Continuing Investigations of Cold Soda CMP Pulps Hardwood utilization, The FPL publications showed and Pulping that the cola soda process was flexible as to hard­ wood species (7). This facility was important to The cold soda CMP process is still under investi­ mills dependent on softwoods and wanting to gation after nearly 40 years since the initial diversify their fiber base into the hardwoods. studies. These investigations cover such aspects as Thus. the northern mills used aspen (poplar), beech, the chemical composition of the pulp, the morphology maple and birch and the southern mills pulped gum of its fibers and process developments. and oak. The Tasmanian mills used eucalyptus and the Japanese cold soda mills used indigenous mixed Chemical Composition of Pulps. The first FPL hardwoods. The new Spanish mill also uses publication on cold soda CMP pulping of aspen showed eucalyptus (35 ). the yield loss, which increased with increased alkali consumption, was concentrated in the hemi­ Pulping systems. The nine cold soda pulp mills as fraction (2 ). The solution of wood sub­ of 1960 (Table 1) used a variety of systems for stances by the cold soda reagent has also been special chip preparation, impregnation of the described as being small amounts, 5-10% of caustic reagent, pressing for pre- fiberizing and and carbohydrates, with a pulp yield of 90-93% spent liquor recovery and fiberizing in one to three (uncorrected for fiber fragments) (37). Another stages. This same variety extended to the reference claims the loss of a small amount of brightening of the pulp as required by the products. lignin but mostly hemicelluloses (other than The screening and cleaning and washing and extractives), largely acetyl groups; sodium ions thickening before papermaking used the screens and may exchange for calcium ions (38 ). Another source cleaners of the period. also indicates that acetyl groups, in addition to hemicellulose (pentosan), and some lignin are lost The pulping systems themselves were of the (10). following types: Recent tests show that the principal hemicellulose Chip fractionators in some mills to produce small lost is xylan (Table 2). Glucan and Klason lignin chips. showed no change; there was a slight loss in acid Caustic impregnation is globe digesters or live- soluble lignin. A commercial PMP pulp made from bottom bins; cyclic pressure in batch vessels; hot extracted aspen chips treated with a low per­ inclined and horizontal tube continuous centage of (2%) exhibited only a pressure impregnator; and spray application very small decrease in xylan content (Table 2). before chip fractionator, press and fiberizers with intermediate retention. An experimental aspen, well- washed cold soda pulp had a sodium content (determined by inductively copled plasma (ICP spectroscopy) of 318 ppm (39). This compares with the sodium content of the aspen 642 / TAPPl Proceedings wood used of 39 ppm. (An average hardwood figure By 1960 there were nine cold soda mills each in the is 70 ppm and softwoods 50 ppm (40)). In contrast U.S. and in foreign countries making ultra-high-yield

an unwashed Na2O 2- brightened CMP pulp had a sodium (85-95) hardwood pulps for use in printing papers content of 11, 114 ppm. (including newsprint) and . Nine years later, however, there was only one U.S. and two or Morphology of Cold Soda Pulp Fibers. The mechanism three foreign mills operating, the others having of cold soda pulping has been described as a been converted to other CMP or NSSC processes or differential swelling causing increases in middle terminated due to changing industry needs. lamella thickness and fiber section area and a greater decrease in lumen area which result in Investigations of cold soda CMP technology continue; stresses which, on mechanical fiberizing. result in a new eucalyptus cold soda CMP mill started up in failures between the middle lamella, primary and Spain in 1984. Up to 62% of the pulp is used in secondary walls causing exposures of fibrils for writing paper. bonding (10, 37, 41). Microscopic examination of cold soda pulp shows largely undamaged fibers with It is concluded that the cold soda CMP process exposed secondary walls and some fine materia; (38). served a useful purpose as a transition process in The amount of fine material increases with the the growth of U.S. and world production of hardwood degree of fiberization at the expense of long fibers. pulps. SEM shows microfibrils of irregular outline due to adhering non- cellulosic and lignin particles (41). LITERATURE CITED

Current SEM studies at the FPL of aspen cold soda CMP, groundwood and kraft pulps at low magnification (25X) show the cold soda pulp to be less macerated and fiberillated than the groundwood pulp and more like the delignified and fiber- separated kraft pulp except for the fiber bundles in the cold soda pulp (Figs. 1, 2, and 3). At a considerably higher magnification (5,000X) the cold soda pulp exhibits fractured inner fiber structures and exposed inner surfaces due to stresses of swelling released by fiberizing (Fig. 4). These exposed inner surfaces account for the enhanced fiber bonding character­ izing the pulp.

Cold Soda Process Developments. The early 1980's Spanish high- yield eucalyptus operation (stated as a chemithermo- mechanical process (CTMP) but in reality a CMP mill) employs a patented impregnation in several towers with caustic soda plus additives and fiberising of the treated chips in a two- stage disk refiner system; there is a great overall similarity to the FPL process (35 ).

A Wisconsin mill makes an ultra- high- yieldpulp from aspen in a system involving pressing steamed chips treated with surfactant and chelating reagents before refiner addition of caustic soda and hydrogen peroxide (2 and 15%, respectively) in making a pulp suitable for use in carbonless paper (42).

A U.S. patented hardwood CMP process employs a two- stage treatment with caustic soda and sulfite in making a pulp strong for its grade. This is yet another variation of the FPL procedure 43, 44).

A Russian patented CMP process (species is not given in abstract) includes sulonation of a well- treated cold soda pulp (6-9% caustic soda) to produce a pulp suitable for newsprint of improved properties

~ (45). Up to 59% is used with groundwood.

CONCLUSIONS

The FPL hardwood- based cold soda chemimechanical pulping process, as first published In 1950, had its first commercial application in 1951-52 in a modified NSSC corrugating mil1 and its first pro­ duction in a custom- designed CMP mill in 1956.

1988 Pulping Conference / 643 644 / TAPPI Proceedings ACKNOWLEDGEMENTS

The services of M. J. Effland and T. A. Kuster, Forest Products Laboratory, in providing chemical analyses and SEM photomicrographs, respectively, are greatly appreciated.

Table 1. Chronology of Cold Soda CMP Development and U.S. Commercialization.

1988 Pulping Conference / 645 Table 2. Chemical Compositions of Aspen Wood and CMP Pulps (39).

646 / TAPPI Proceedings Fig. 1. Aspen cols soda (25X).

Fig. 2. Aspen groundwood (25X)

1988 Pulping Conference / 64 7 Fig. 3. Aspen kraft (25X).

Fig. 4. Aspen cold soda (5,000X).

648 / TAPPl Proceedings