CELLULOSIC AGRICULTURAL BY-PRODUCTS Possibilities for Industrial Utilization D. F. J. LYNCH Agricultural By-products Laboratory, Ames, Iowa’
Straw Products
E F O R E considering the possibilities of industrial utilization of cellulose from agricultural products, one should have a clear picture of the present industrial utilization of these fibrous materials. The two industries which use fibrous farm wastesat present are the insulat i o n c o n s t r u c t ion board makers and the strawboard producers. Representative companies which account for nearly all of the insulation construction board are the Celotex Corporation of Chicago, with a plant at Marrero, La. (16),and the Hawaiian Cane Products Company, Hilo, Hawaii, T. H., which use bagasse as their principal raw material; the Maizewood Insulation Company, Dubuque, Iowa, which uses cornstalks and straw (Id); the Stewart Inso-Board Company now U. S. Gypsum Company, St. Joseph, Mo. (15), which uses wheat straw; and the MacAndrews & Forbes Company, Camden, N. J., which utilizes extracted licorice root (16). Most of these by-products arrive at the factory in bales. The bales are opened, and usually some form of shredding and cleaning takes place before the material is charged into the cooker. The cook is carried on under pressure with live steam for varying periods. The cooked or softened fibrous material is then usually fed through some form of swing hammer shredder, washed, diluted, and sent to storage chests. At this point the filler, newsprint pulp, is added, as well as the chemicals which impart to the board desired characteristics, such as water resistance, etc. From the chest the stock is fed to the board-forming machines. In the production of “Maizewood,” straw as well as newsprint is mixed with the cooked cornstalks. About 35,000 tons of licorice root are imported into the United States every year. The extracted licorice root, ground with paper pulp, is used by the MacAndrews & Forbes Company in making construction board under the name “Maftex” (16). Individual companies making these boards frequently bring out specialties in this industry, such as termite-resistant, fungi-robresistant, and fieproofed boards. Special lines enter the trade for roof insulation, plaster base, and refrigerator insulation, as well as structural insulation. 1 Estrbliahed by the Bureau of Chemistry and Soils, United States Department of Agrioulture, in oooperation with Iowa StsGe College.
In this country over forty plants utilize straw in the production of the trade article known as strawboard. It is a relatively thick sheet of paper (0.006 to 0.06 inch) and is made from cereal straws, with about 10 to 15 per cent waste paper or other fibrous material. In 1936, 557,500 tons of 9-point (0.009-inch) strawboard was manufactured for corrugating in the corrugated box industry. Most of this tonnage is manufactured in Ohio, Indiana, and Illinois, with a smaller portion in Iowa, Kansas, Wisconsin, and Michigan. Wheat straw is the main source of this material, although oat and rye straws are used to some extent. The straw is baled and carted to the mill by truck. Hauls up to 100 miles are not uncommon. About two thirds of the annual supply is received by the mill in the fall and the r e mainder in the spring. Upon arriving at the mill, the straw is sampled and the amount of moisture present determined. The mills purchase the straw on a dry basis. The straw is piled for one or two years in stacks (which may or may not be covered) measuring about 50 X 100 feet on the ground and 60 feet (36 bales) in height. $ome decomposition of the straw of the outside bales takes place during this storage; the loss depends upon weather conditions and is usually not great. Several investigators disagree with industry’s practice in this method of storage. They believe that the loss due to decomposition of the raw material is greater than is realized. The bales are taken from the straw pile, broken up in a way to get rid of the fine dust and foreign material, such as wire, etc., and charged into large cookers. The pulping action in the production of strawboard is carried farther than the cook of raw material in the manufacture of insulation board. The cooking liquor varies with different plants, but usually contains lime and sometimes caustic soda. The pressure used is about the same as that in the cooking process for the production of building board, but the time of the cooking is usually considerably longer. At the end of the cook, the straw is blown out and conveyed to beaters where it receives the desired degree of beating and washing. The beaten stock is dumped into the beater chest where it is mixed with waste paper or “broke.” It is usually sent through Jordans for final refining and then to the machine chest, from which it is pumped to the board-forming machine. Clayton’s report (9) of the straw pulping process in 1920 is still a good description of this industry. Some few changes have been made, especially in shortening the digestion and beating time. I n a later article Clayton (10) listed the equipment of a 100-ton straw millplant. According to reports of the Bureau of the Census, the total board production for 1934,1935, and 1936 was about 6 million tons. I n 1937 Whiting (35) broke down the 1935 board production according to type of board. He stated that the 1936 production averaged 149
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CORNSTALK BALER
17 per cent higher in all grades. Of these grades of board, straw enters into chip board for corrugated and solid fiber boxes, corrugated material, setup box board, and miscellaneous grades. In 1937 Clark (8) estimated that straw entered into about 20 per cent of the paperboard industry. Although the quantity of straw available for straw paper and board varies from year to year, the amount used for commercial purposes is only a small fraction of the possible production. The present concentration of grain production in several well-defined areas should make the collection simpler and less expensive. Table I records the estimated amounts of straw available to the industry. These figures were compiled from United States Department of Agriculture preliminary reports and yearbooks, averaging a period of eleven years (1926 to 1936, inclusive).
TABLEI.
Straw
ESTIMATED AMOUNTOF STRAWS AVAILABLE TO INDUSTRY
Principal Sources
Estd. Total U. S. Production
Probable Amount Available to Industry 1000
Estd. Amount Now Commerciall Utilize8
Tons
Cellulose and Paper Specialties I n considering the utilization of substantial amounts of these fibrous agricultural wastes, better grades of cellulose and paper specialties must be considered because the cheap lime and associated straw pulp processes have apparently reached their practical commercial limit. Careful research at many laboratories and pilot plants is being carried on in this field. Most of those interested in this research remember the work on cornstalks by the Dorner process (11)some years ago at Danville, Ill. In other countries the Pomilio process (2, 2'7) has been carried on to a commercial stage with straw, particularly in Italy and South America. Different types of paper desired in Europe favor the introduction of straw pulps. A considerable amount of work has been done with straw by the Mead Corporation, Chillicothe, Ohio, under patents taken out by Traquair (SO) and Traquair and Rawling (31).
In 1936 a report was made on investigations of the De la Rosa continuous digester process (S), and some investigators are working on the digestion of cereal straws with alkali sulfite bases and ammonia. About ten years ago Barbier (7) reported good results in making imitation kraft paper from straw with ammonia. Investigations are now being conducted a t the Agricultural By-products Laboratory, with the cooperation of a large straw pulp plant, on a modified kraft process (56). This work is now in the pilot-plant stage, and by varying cooking conditions the beating properties as well as the strength of the pulp can be greatly improved. On an experimental scale, straw pulp with bursting strength comparable to that of commercial Husum prime kraft paper has been attained. Those experienced in these fields agree that expansion along these lines can be expected. The main constituents of fibrous farm products are cellulose, lignin, and pentosans, the proportion of each varying according to the material. I n comparison with wood, the cellulose content is smaller but not very much smaller. The lignin content is usually smaller and the pentosan content is usually greater than it is in wood. Table I1 presents the cellulose, lignin, and pentosan contents of some of the natural fibrous materials. Utilization of the cellulose present in these materials requires the adaptation of some pulping procedure to the individual fibrous material. This means a comprehensive study of the optimum conditions for the most efficient pulping of these materials instead of the substitution of samples of any one of these wastes for wood in a regular wood pulping digestion. The story of wood pulping development was that of overcoming opposition and adversity in the face of the established use of flax, cotton rags, etc. The utilization of agricultural wastes for paper and paper products now faces competition with the well-established wood pulp processes developed by several decades of research and commercial practice. A number of investigators are now working with these cellulosic materials. For example, the Agricultural By-Products Laboratory plans to publish a comprehensive review of the nitric acid pulping process (4). Approximately 170 references are cited. This laboratory is now working on the nitric acid pulping of these materials. Some years ago cellulose of good quality was prepared experimentally in the laboratory from bagasse. The work on bagasse has reached a pilot-plant scale of 500 to 1,000 pounds of pulp per run in Hawaii and the Philippine Islands. The work in Louisiana and Puerto Rico is not so far advanced. The pilot plant a t Ames has a reaction tank with a capacity of 500 gallons. At
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be loaded into the cooker. Engineering work is being carried on with different types of digesters to overcome this difficulty, and preliminary results are somewhat encouraging. Although the investigators a t Ames do not contend that the nitric acid process is the panacea in the pulping of all these agricultural wastes, their results with this process have TABLE11. PERCENTAGE COMPOSITION OF NATURAL CELLULOSE been encouraging. Feldtmann (12) reported that the German work with this process has reached a commercial stage MATERIALS and that a 40-ton plant started production on August 1, 1937, .Material Cellulose Lignin Pentosans a t Wolfen, of nitric acid pulp from beechwood. Feldtmann Bagasse (6) 60.2 21.7 29.1 Cornstalks ($4) 38.4 34.3 27.6 stated that “the process dissolves the lignin without degradSeed flaw straw ( $ 8 ) 53.8 23.3 17.1 Rice straw (1) 45.5 10.9 21,5a ing the cellulose, and nitric acid pulp from spruce and pine Rye straw ( 1 7 ) 36.3 11.3 20.4 is equal to the kraft pulps for papermaking on account of its Oat straw (80) 43.8 18.5 22.8b Wheat straw ($8) 56.7 16.6 28. 4a high pentosan content.” In the alcoholic nitric acid pulping Barley straw ( B d ) 48.6 16.4 31.95 74.9 11.7 1s.l a of bagasse, it was noteworthy that a high-pentosan pulp was Jute (28) Hemp ($1) 79.3 5,2 5.5a obtained (6). 62.1 26.5 17.6 Aspen (5) Jack pine (4) 57.6 33.6 12.3 From the above results, as well as those of many other inSpruce (19) 60.9 30.2 12.6 vestigators, it is not believed that pulps from agricultural a The values given in the reference are for total furfural, and they are conwastes are inherently less desirable than pulps from wood. verted to pentosans. b Hemiuellulose. Many of the samples tested are less desirable than the wood pulp, but on the other hand many samples have been made on an experimental scale which compare favorably with commercial wood pulp samples. The poorer pulp samples are by the same laboratory a t a recent meeting of the Technical due, probably, to the fact that the process employed has not Association of the Pulp and Paper Industry. A description of been adapted to the production of good pulp from agricultural the alcoholic nitric acid pulping of bagasse (6) and a report wastes. With different pulping conditions the characteristics on the conductometric analysis of the used nitric acid pulpof cellulose from these wastes can undoubtedly be changed ing liquor (34) have recently been published. All this experidrastically. It was thought for a long time that a wood pulp mental work does not mean that new cellulose industries will spring up immediately and start using agricultural products. could never be produced with a viscosity comparable to that Many technical difficulties have been encountered. of cotton linters pulp. Last year Olsen (IS) described the preparation of a wood cellulose which gave a viscosity higher Most of these agricultural fibrous materials can be pulped than any with cotton linters pulp. under much less drastic conditions than those necessary in the pulping of wood. The pulping solutions are more dilute. Besides technical difficulties there are also economic conThis dilution increases the difficulties in the recovery work. ditions which generally hamper utilization of many of the.
present work is concentrated on the pulping solutions. A report metric analytical control method tions. A similar report on kraft
the efficient utilization of (18) describes a conductofor the soda pulping solupulping liquors was made
THRESHING
Another serious difficulty is due to the low density of these materials. Using the customary digester, smaller amounts of pulp are recovered per run with these materials than with wood. This is not due wholly to the smaller cellulose content but rather to the smaller weight of the material which can
agricultural products, although this is not true in the case of all agricultural wastes. Generally, these raw materials are available only during a brief harvest period and, therefore, must be collected during that time. Although farm wastes are intrinsically of little value, collection costs are generally
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the inclusion of these h e hull specks. This technical problem will probably be overcome eventually. There is, however, an economic difficulty which hampers the use of this cottonseed-hull fiber. When mixed in cattle feeds, the separated ground hiills give a dense product which is unacceptable a t present in the feed industry. The utilization of this fiber depends now on finding some nse for ground cottonseed hulls to replace the unground cottonseed hulls plus the fiber in cattle feed. Cellulose from a specific source is more easily adapted to a specific use than other eelluloses. However, constant changes in processing make it hazardous to prophesy that these other celluloses will not enter that field. The viscose process, for emmple, once depended entirely on cotton linters pulp. Purified wood pulp entered the field to he mixed with linters pulp, and today wood pulp supplies practically all the cellulose for the large viscose prodlietion. Cotton lintem supplies the cellulose for our rapidly growing acetate rayon industry and the nitrocelliilose industry. However, beautiful acetate rayon has been made experimentally from purified wood cellulose, and in the laboratory wood cellulose with a rather high alkali-soluble content has been safely and successfully nitrated. It is felt that t.here are no insurmountable technical obstacles to bar cellulose made from agricultursl fibrous wastes from the many cellulose utilizat.ion industries.
Plastics
PILOT-PLANT EQUIPMENT Fon NITRIC ACIDPULPING
high. Agricultural engineers recognize thiu and are actively engaged in atudying the problem of cutting down these costs. Once collected and brought to the piant, the problem arises of storage for a relatively long period. Work is progressing on losses in storage as well as its costs. In parts of the Philippines and Hawaii, where they harvest and grind sugar cane 10 to 11 months a year, bagasse utiliation does not have to face these difficulties. The pulp plant takes as niuch bagasse as desired from the bagasse conveyors, allowing the residue which should include all the “fines” to go to the furnace. At present about 150,OOO tons of cottonseed-hull fiber are available in this country. After the fust- and second-cut linters are removed from the cottonseeds, a considerable amount of short fiber still remains on these seeds. The cottonseed hulls are broken to remove the seed. This by-product is now used as a filler in cattle feeds. Processes are available for the removal of this fine fiber from the cottonseed hulls. In the removal of this fiber the hulls are ground, and in the separation fine specks of the hulls are embedded in the short lint. When mixed with linters, some of this hull fiber finds use in the production of chemical cellulose. The industries which have tried to utilize this cottonseed-hull fiber (the chemical cellulose and fine paper industries) complain because of
Nthough in a somewhat different field, inention should he made of the possible commercial utilization of agricultural fibrous by-products in the plastic field. A considerable amount of groundwood is used in the plastic industry. Finely ground fibrous farm waste material has been utilized hy some manufacturing companies. This is substituted for groundwood and is also employed as a diluent in the explosives industry. The Agricultural By-Products Laboratory is particularly interested in the Lignin plastics and the possibility of using considerahle amounts of agricultral fibrous wastes in the manufacture of these plastics. Through the work of Phillips and his co-workers (86, 86) o€ the Bureau of Chemistry and Soils, and Sherrard and his colleagues ($9, S8) in the Forest Products Laboratory a t Madison. Wis.. the orivi1eh.e of commercially manufacttiring this type of plastics-is given to anyone because the patents taken out by these workers are for the free use of the people of the United States. Through the cooperation of the Derived Products Division of the Forest Products Laboratory, the Agricultural By-Prbducts Laboratory has carried on at Madison, Wis., and a t Ames, Iowa, research work with agricultural by-products similar to the work the former laboratory has done with wood. The plastic is made in .6?u by a simple processing of the wood sawdust or fibrous farm waste. The research results are eneouraging. It is thought that because of ita very low cost this type of plastic may open up new fields in the plastic industry and thus utilize more agricultural fibrous by-products. Those who have worked in these fields recognize the d&culties to he overcome, but they feel that with the help of the constsnt contributions in these and related fields of research, the increased and more vaned industrial utilization of eeUulose from agricultural products is a matter of time and hard work.
Literature Cited (1) Aoharva. C . N..Biochem. J.. 29. 528 (1935)
(5) Aronovsk$. 5. I.; and Gor&r.
R. A.. IND.Exo.Caear.. 22.264 (1930). (6) Aronovsku, S. I., snd Lynoh, D. F.J.. Ibid.. 30, 790 (1938). (7)Barbie.. Emile, Popeterie, 49,538 (1927).
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INDUSTRIAL AND ENGINEERING CHEMISTRY
(8) Clark, H. L., Mjrs.’ Record, 106, No. 3, 30 (1937). (9) Clayton, R., Paper, 27, No. 5, 17 (1920); No. 8, 19 (1920). (IO) Ibid., 27, No. 10,162 (1920). (11) Dorner, B., U. S. Patent 1,038,730 (Sept. 17, 1912). (12) Feldtmann, G. A., ZeZZstof u. Papier, 18, 55 (1938). (13) Gibson, A. G., IND. ENG.CHEM.,22, 223 (1930). (14) Hartford, C. E., Zbid., 22, 1280 (1930). (15) Houseman, P. A., and Lacey, H. T., Ibid., 21, 915 (1929). (16) Lathrop, E. C., Ibid., 22, 449 (1930). (17) Lookett, J. L., Soil Sci., 44, 425 (1937).
.--,McElhinnerv. T. R.. Whittemore. E. R.. and Lvnch. D. F. J..
(18)
(19) (20) (21) (22) (23) (24)
paper Trade J., 106, No. 10, 37(1938). Monsson, W. H., and Chidester, G. H., Zbid., 94, No. 6 (1932). Norman, A. G., Biochem. J., 23, 1353 (1929). Zbid., 31, 1575 (1937). Ibid., 31, 1579 (1937). Olsen, Fred, IND.ENG.CHEM.,30, 524 (1938). Peterson, C. J., and Hixon, R. M., Ibid., Anal. Ed., 1, 65
153
(25) Phillips, Max, U. 8. Patent 1,750,903 (Maroh 18, 1930). (26) Phillips, Max, and Weihe, H. D., IND.ENG.CHBM.,23, 286 (1931). (27) Pomilio, Umberto, IND.ENG.CREM.,24, 1006 (1932). 128) Schafer. E. R.. and Brav. M. W.. Ibid.. 21. 278 (1929). (29j Sherrard, E. C., and Beglinger, E., U. S. Patents 1,923,756, (Aug. 22, 1933) and 1,932,255 (Oct. 24, 1933). (30) Traquair, J., U.S. Patents 1,843,464-6 (Feb. 2, 1932). (31) Traquair, J., and Rawling, F. G., Zbid., 1,880,587 (Oct. 4, 1932) and 1,942,622 (Jan. 9, 1934). (32) U. 5. Forest Products Lab., Mimeographed Bull. R1134 (April 16, 1937). (33) Whiting, G., Paper Trade J., 104, No. 8, 41 (Feb. 25, 1937). (34) Whittemore, E. R., Reid, J. D., and Lynch, D. F. J., IND.ENG. CAEM.,30, 1192 (1938). (36) Wingfield, B., Whittemore, E. R., etal., Natl. Bur. Standards, Misc. Pub. MI24 (1936).
RECEIVEDDecember 13, 1938.
(1929).
INDUSTRIAL USE OF STARCH PRODUCTS W. B. NEWKIRK Corn Products Refining Company, Argo, Ill.
corn wet-milling industry of today is developed entirely around the production and utilization of starch. Our knowledge of starch and starch products is still largely empirical, in spite of the numerous investigations on this material recorded in the scientific literature. However, the industry does know how to produce a large number of satisfactory commercial products by methods which may be called a highly trained art controlled by a few physical and chemical tests. Generally speaking, the origin of the starch is of minor importance to the industry, in spite of the fact that the physical characteristics of the starch are essentially typical to the origin of the starch. There are a few cases where starch products from one particular origin supply the requirements more satisfactorily for certain products, such as tapioca for postage stamp adhesives; but even in these cases acceptable products can be made from starch of any origin. Another typical example is the superiority of cornstarch of certain modifications as dusting agents in the rubber industry, where large tonnages are used. On the whole, therefore, we are interested in the cost of only a fairly well-refined starch. The Corn Products Refining Company, which has plants throughout the world, uses starch made from corn, k a f i corn, rice, rye, potato, and manioc or tapioca. The choice depends
upon the availability and price of starch in the country in which the plant in operating. Although 30 per cent of its markets have been taken by cheap, duty-free, tropical starches, the industry as a whole has not felt the ups and downs of depression and prosperity periods as much as have other industries. The reason for this is not accidental but is the result of an intensive and continued effort on the part of all producers to meet the ever-changing needs of the purchasing industries by changes and modifications in our products so as to meet these requirements exactly. The industry as a whole is rather old compared to other American industries, but its organizations are youthful, open-minded, energetic, and research-conscious. The general public or even the various industrial chemists probably do not realize the diversification that exists in starch products and the different types of uses to which they have been put.
Thick-Boiling Starch Let us first consider the old thick-boiling starch which was supposed to be the natural starch of the corn. No starch on the market is starch as it exists in the grain or in the tuber, but is starch which has been modified by the operating process and the enzymatic action of nature’s converting agents. Nevertheless, the industry has discovered how to treat these modified starches to bring back some of the desirable characteristics of nature’s starch. For example, some companies have developed a thick-boiling starch which is thicker than is customarily produced by the industry and retains its thickness and viscosity in spite of the hydrolyzing action to which it may be exposed in some of its uses. As an illustration, cream soups must contain starches which will undergo the converting at high temperatures with organic acids during the pasteurization period of the packed product without a
