VIRGIL S. HAM, JR., and GEORGE D. PALMER University of Alabama, University, Alabama
Swm lignin represents a cheap source of organic 80"-9O0C., i t is dried under reduced pressure and conmaterial (I), many processes have been developed for verted to a powder. By heating the powder, known as its utilization as a resin or plastic. Very few lignin Barkalite powder, from ZOO0 to 250°C. under 400 to plastics are produced commercially a t the present time, 1000 kg. per sq. om. of pressure for 5 or 6 minutes, the but many articles have been published and patents se- product lends itself to molding and is said to have good cured in this field. Lignin in its natural state is not in a mechanical properties. Bagdanov (6) ran a series of suitable condition for the manufacture of plastics and so experiments to study the reactions of plasticizers and after isolation it may be made more reactive through softeners such as phenol, furfural, a mixture of phenol and glucose, hexamethylenetetramine, sulfuric acid, chemical treatment. and phosphoric acid on the Barkalite powder. RESINS FROM HYDROLYZED WOOD AND AGRICULBy varying conditions and materials used, numerous TURAL WASTES other commercial molding products have been proSome natural plastic properties are found in Iignocel- duced by thermal hydrolysis. lulosic material which is taken from wood, straw, or Acid Hydrolysis: In several processes,, direct acid other agricultural wastes. If these natural properties hydrolysis is used as a pretreatment. When wood or could be developed, commercial products could be agricultural products are hydrolyzed by mineral acids, created from a vast amount of material which now has the ligneous residue has plastic properties after being low economic value. Wood and agricultural wastes are subjected to heat and pressure. A process patented by usually treated so that the lignin content is increased Sherrard (7, 8) involves the digestionof sawdust with and altered chemically and physically in order to de- dilute sulfuric acid. The resinous residue is then velop fusible and resinous properties. In most of the washed with water until neutral to litmus and dried, processes developed so far, this is accomplished by and a yield of approximately 62 per cent by weight of hydrolytic treatment-thermal or acid hydrolysis. the original wood is obtained. Higher yields are obThermal Hydrolysis: According to Boehm (Z), when tained if lower concentrations of acid are used. The lignocellulosic material is charged into guns which have strength of the product is decreased, but its water rea capacity of about 12 cu. ft. and treated with steam a t sistance is increased. After being ground to particle pressures up to 1200 p.s.i. for a matter of seconds, the size, this material may.be molded a t 190°C. using no hemicellulose is largely hydrolyzed and removed. The plasticizer except water. However, best results are cellulose is partially hydrated but otherwise substan- obtained by the addition of aniline and furfural which tially unchanged. The material is exploded by a sudden lower the required molding temperature to 150°C. and release of the high internal pressure and results in a causes marked modifications and improvements in the mass of fibers and fiber bundles still containing their properties of the product. The resulting product is natural coating of lignin. When subjected to tempera- hard and dense and shows many of the useful properties ture and pressure treatment, this fibrous mass can be common to the more expensive pressed materials. molded into a variety of boards. Olson and Plow (9) produced a thermosetting moldThe Masonite Corporation uses a process patented by ing compound which is similar to the products formed Mason, Boehm, and Koonce (3), which results in the in the above process patented by Sherrard. production of the well-known Masonite board. In this Bergius, Koch, and Faerber (10) patented a process procedure wood chips are subjected for several seconds whereby the pure liguin residue of hydrolyzed vegeto steam pressures up to 84 kg. per sq. cm. The pres- table material is pressed into a mold with a high consure is then released suddenly and causes the wood centration of hydrochloric acid. When taken from the chips to disintegrate into a fibrous mass which can be mold, the mass will retain the molded shape without dried, ground, or molded directly to form a dark, hard, the aid of any added binding agent. water-resistant product. This product can be machined The British Mead Corporation (11) a procand has very good mechanical strength and dielectric ess in which ligniu material is produced by the acid properties. process. The lignin is dissolved in phenol and the prodSome Russian investigators (4, 6 ) have described a uct is then reacted with formaldehyde. After being molding material obtained by thermal hydrolysis in dried, ground, and mixed with a filler, the product bewhich sawdust is heated under a pressure of 8 atm. a t comes a molding powder. . 170°C. for several hours. After the material is cooled to A Russian patent (12) claims that a molded product 8I7
88
can be obtained by incomplete hydrolysis of lignocellulose with acid. This material is mixed with 6 to 10 per cent of a plasticizer such as latex or benzyl cellulose. The above represents probably the most interesting of the many examples of resins produced by the acid process. WOOD SACCHARII'ICATION
There.have been many attempts to utilize the lignin remaining as a by-product from wood sacchariiication in the production of alcohol. The production of a plastic has been the primary object of the investigations. Burmeister (IS) has patented a method for making a plastic con~positionwhich involves mixing together by weight 100 parts of pulverized lignin from wood saccharification, 11 parts of phenol solution, and 132 parts of benzol. The mass is kneaded for 4 hours at 7S5"C., after which the solvent and unreacted phenol are removed. A German patent (14) claims to make a product that is useful as wall or floor coverin~materials from this much studied by-product. The jigneous residue from the saccharification of wood is deacidified and briquetted witbout the aid of a bider. Fillers can be added if desired. Grasser (16) converted this lignin into an alkali soluble product by treating it with an oxidizing agent. He then converted this into a water soluble resin by treating it with a sulfite or bisulphite. Karsch (16) has also produced a similar material. Farbenind (17) makes a plastic product by taking the lignin residue from the wood saccharification process and treating it with phenol, formaldehyde, and a catalyst. The mixture is heated a t a temperature above the boiling point of phenol, and the water which is formed is removed contmuously. The temperature is raised to 230°C. and condensation with formaldehvde is carried out. An investigation was made by Englert and Friedman (18) who found that a more desirable plastic product was made bv usine 41.5 Der cent of Schollers' lienin. 50 per cent of woo;d f l ~ u r , ~ a 8.5 n d per cent of p h t h i k anhydride. It has been found that Scholler's lignin does not lend itself for use as a molding powder unless chemically modified. Seiberlich has made thermosetting plastics (19) by treating Scholler lignin with zinc sulfate or zinc oxide and then reducing this mixture with hydrogen sulfide. He obtained a material suitable for molding a t 2000 p.s.i. a t 150%. for 3 minutes. The resulting product shows possibilities for use as a material for wallboards and other structural purposes. CHEMICAL CONDENSATION AND POLYMERIZATION
Sawdust, agricultural wastes, and free lignin will react and coidense with a number of chemicals to give moldable products. In the reaction of aniline ($0)with either sawdust, or agricultural waste the mixture is digested for 3 hours a t 11.25 kg. per sq. em. The result
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is an anilme lignin complex. In addition there is some hydrolysis of the.polysaccharides. The yield is about 95 per cent by weight of the original wood waste. The molded product obtained is hard and dense and has somewhat higher strength and water resistance than plastics prepared by the acid hydrolysis method. It has been known for many years that phenols will dissolve lignin a t about 200°C. (%I). The condensation of phenols with lignin causes this "solvent action" which is accelerated with the addition of small amounts of mineral acids. Champer and Christensen (22) have developed a method for preparing an infusible and insoluble resin by mixing 250 parts by weight of lignin which is substantially free of cellulosic constituents, 600 parts by weight of phenol, and 7.5 parts of sulfuric acid. The mixture is heated to a temperature of 150' to 160°C. and forms a fusible, soluble resin. The excess phenol and the water which is formed during condensation are removed. By adding an inert filler to this reaction product and subjecting the mixture to polymerization under pressure of 1000 p.s.i. a t a temperature of 160' to 180°C., an insoluble, infusible resin is formed. Peanut bulls, cottonseed hulls, and other cellulosic materials can be utilized according to a process developed by Jones ($8). One part of any of these substances is heated with less than one part of a phenol together with an inorganic acid such as hydrochloric acid. This mixture is heated-until a sticky, gummy, fusible, partially disintegrated mass is formed. Ushakov ($4) claims that the most favorable plastic masses can be obtained from lignin containing 10 per cent moisture, 4 per cent pentosans, and not more than 7.5 per cent resins, fats, and waxes. When lignin having this composition is mixed with phenol, the optimum condensation temperature is 115°-1200C. with a catalyst or 2 to 5 per cent sulfuric acid. The sulfuric acid is neutralized with calcium oxide after the condensation is complete. PHENOL-FORMALDEHYDE LIGNIN RESINS
D'Alelio (86) obtained a patent in which lignin is first dissolved in phenol and the solution treated with 0.5 to 0.95 mol formaldehyde per rnol of phenol in the presence of an acid catalyst. It is then refluxed for a period of time sufficient to react withmostof theformaldehyde and then made alkaline. After adding formaldehyde so that i t is in excess of one mol per mol phenol, the mixture is again refluxed. The introduction of a dispersion agent adjusts the hydrogen ion concentration to approximately 7.0. The addition of ammonia to react with the excess aldehyde contained in the neutral solution causes the mixture to form a dispersion of the resinous product. According to a British patent (26), phenol and lignin in a formaldehyde mixture with an alkali base reacted a t a temperature not exceeding 100°C. for 30 minutes. At this temperature and length of time, the mass will not separate into distinct layers. The most favorable resins are obtained by heating 130 parts of lignin, 100
FEBRUARY, 1949
parts of phenol, and 115 parts of formaldehyde for 5 to 20 minutes a t 110°C. Another British patent ($7) involves mixing phenol and lignin 5 to 1, respectively, by weight, This solution is treated with aldehyde in the presence of acid. Matveev, v , and Agashenko (28) claim in a Russian patent that hydrolyzed lignin is condensed with phenol in the presence of an acid catalyst. The acid is neutralized and the product is condensed with formaldehyde in the presence of 0.2 to 2.0 per cent of an organic base.
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RESINS FROM SULFITE WASTE LIQUOR LIGNIN
The disposal of waste sulfite liquors to avoid stream polution has been a problem for many years. This material is being utilized for the production of plastics by such companies as Marathon Corporation, Burgess Cellulose Company, Hammermill Paper Mills, and the Robeson Process Company (34), but the quantities used represent only minute fractions of the lignin which is available. The colloidal and adhesive pro~ertiesof sulfite waste liquorlignin have been knowfor-a long time, and it has RESINS FROM ALKALI LIGNIN frequently been recommended and used as a ~ , - l u.e adhesive, or cement. Various methods of converting alkali lignin into Since 1936 the Marathon Corporation's Rothschild resins have been attempted with different degrees of success. Plunguian (%?) claims to have made a com- mill has applied the Howard (56, 56) process for the mercial product from alkali pulp liquor which is suitable commercial utili~ation of sulfite waste liquor. The involves fractional precipitation with lime. l~ for plastics. By precipitating lignin from s ~ d a - ~ u Process liquor with the use of carbon dioxide, followed by In the first step, bisulfite and loosely bound sulfur in washing and drying, pure alkali lignin is obtained. the waste liquor are precipitated and recovered as calThis product, having the trade name "Meadol," can be cium mortosulfite. This recovered material is comused as a thermoplastic binder, phenolic extender, posed of 60 to 75 lb. of sulfur and 100 to 130 lb, of calmodifying agent for thermosetting resins, and as a base cium o d e per ton of pulp. The calcium monosulfite used in the preparation of sulfite cooking acid. In for other chemicals. The powder obtained has a good cure and flow, and the plastic which is produced from the second step, calcium lignosulfonate is recovered in it has only slightly less strengt,h and water absorption amounts from 1000 to 1200 lb. per ton of pulp. The basic calcium lignosulfonate can be coaverted into free than the straight phenol-formaldehyde powder. Crepaz and Bertolini (50) describe a process whereby acid or into other salts. Heating the sodium salt with acidifying alkali cook liquor nrith hydrochloric acid to a alkali results in the formation of.vanillin. The resulting pH of 6.5 to 6.7 and then washing until it is free of residue from this vanillin preparation is used for the chlorine ions, a reactive lignin can be obtained which production of plastics. The utilization of sulfite lignin for the production of remains "reactive." When heated $0 20O0C., this lignin forms a glossy, brittle solid with poor mechanical laminated products or boards seems more desirable properties. If mixed with phenol it forms a black resin than using it for molding powders because of the which can be combined with a filler and hexamethyl- greater quantities that may be utilized. Laminated enetetramine and molded in the same manner as a sheets or boards are produced from lignin "plastic phenol formaldehyde resin. Lignin-aniline and lipin- pulp" which have high strength, low water absorption, aniline-formaldehyde combinations are also mentioned and good electrical properties. The products can 'be machined and are suitable for use in the electrical, by Crepaz and Bertolini. Phillips and Weihe (81) were the first to condense mechanical, and decorative fields (57). Meiler (38)describes a "lignin-enriched filler" that alkali lignin with furfural and aromatic amines, obtaining in each case a brown or black, hard and brittle can be obtained by cooking waste wood and waste resin. These reactions were effected by heating one lignin solution taken from sulfite waste liquor. This part of lignin with one part of amine a t 150°C. for 1 material contains a higher proportion of lignin than hour. All of the resins were fusible and readily soluble the wood flour filler which is normally used in ~henolin mixtures of organic solvents. The amines which were formaldehyde resins. This "lignin-enriched filler" can used included aniline, ortho- and para-toluidine, cymi- be used as a satisfactory extender for phenolics. dine (1-methyl-2-amino4isopropyl benzene), orthoStresino (59) patented a process for making a molding and para-nitraniline, and dimethylaniline., Dimethyl- composition which involves impregnating wood with aniline-lignin resins are claimed to be useful in paper sulfite liquor. The product is then heated with phenyl laminates. According to Morrell (32), the use of lignin chloride to the optimum time and temperature to comfurfural resins should be of interest as a source of pre- plete a chemical reaction. A process has been patented by Hockwalt and fabricated bpilding materials. Scott (33) patented a process in which (meadol) Plunguian (40) for preparing a water-resistant, resinous alkali lipin is dissolved with ammonia in water and material suitable for moldmg. The method includes the then reacts with formaldehyde to form a resin with a reaction of sqlfite digestion liquor with an alkaline molding composition. material to remove the sulfonic acid compounds. This The above examples represent only a few of the many converts the lignin from the sulfite liquor to lignin investigations which have been made on the utilization having an alkaline reaction, which is condensed with a phenolic body and an aldehydit material in the presence of alkali lignin.
JOURNAL OF CHEMICAL EDUCATION
of a catalyst. A thermosetting resinous molding material is obtained. Despite the vast amount of study on sulfite waste liquor, its economic utilization is far from solved. RFSINS FROM AGRICULTURAL PRODUCTS
Much work has been done on wood plastics. However, the production of lignin plastics from agricultural by-products and surpluses also has been extensively investigated. Agricultural wastes have less potential value than wood wastes, but there is no fundamental reason why agricultural wastes could not be utilized just as wood wastes for the production of plastics
(40.
Johnson (42) claims that a plastic molding powder can be made by heating together 30 parts of furfuraldehyde, 24 parts of phenol, and 4 parts of ammonium hydroxide. The mixture is refluxed for 1 hour, and then 36 parts of soybean meal and 3 parts of lime are added. This is then heated with constant mixing for 4.5 hours a t 110"120°C. The product is dried and ground to pass a 60 mesh screen. Forty parts of tbis powder, 60 parts of asbestos, and 6 parts of hexamethylenetetramine are molded a t 200°C. under 1800 lb. of pressure per square inch. Plastics made by tbis process have strong mechanical strength and very low water absorption. Johnson also found that a plastic powder could be made by a similar process from corn cobs and corn stalks a t a very low cost of $0.028 to $0.10 per pound. , Harris (43) produced a plastic by heating to the boiling point in an autoclave 5 parts of zinc chloride, 5 parts of water, and 100 parts of cresol or phenol. To this mixture 30 parts of ground corn cobs or oat hulls were added with stirring. The autoclave was closed and kept a t 140°C. for 3 hours. The product obtained was vacuum distilled until the boiling point reached 260'-300°C. The resin can he ground and mixed with wood flour to produce a plastic. Another resin that lends itself to molding has been developed by Sorgato (44).In the manufacture of cellulose from sorgo bagasse by the soda process, lignin is precipitated by acidifying the spent alkaline lye. The yield is 15 per cent of the dry substance and contains 12 per cent methoxyl groups. Although many other lignin resins have been investigated, the above are representative and should indicate the possibilities in this field for the utilization of lignin.
(4) BARKALAI, G. E., Novosti Tckhnik, No. 19, 39-40 (1938). (5) Iv, B. T., AND 0. B. Iv, J. Applied Chem. (U.S.S.R.), 9, 322, (1936). (6) BOGDANOV, A. M., Trudy NauchJssledovatel. Lab., 110, (1935); Khim. Refem1 Zhur:, I, No. 7, 85 (1938). (7) S I I E ~ A R D E., C., rm E. BEGLINGER, U. 5. Patent 1,932,255, Oct. 24,1933. E. C., E. GEDLINGER,J. P. HOAP, AND E. (8) SAERRARD, U. S. Patent 2,153,316, April 4,1939. BATEMAN, (9) OLSON,E. T., AND R. H. PLOW,U..S. Patent 2,156,160. April 25, 1939. (10) BERGIUS, F., F. KOCH,AND E. FAERBER, U. S. Patent I,SSO,491, Dec. 13,1932, Britizh Patent 484.248., (11) BRITISH MEAD CORPORATION. May 3,1938. A. M., M. P. POLYAKOV, A N D KH. G. ENI(12) NASTYUKOV, HEEVA, Russian Patent 38,322, Aug. 31, 1934. HERMAN,U. S. Patent 2,192,030. Feb. 27, (13) BURMEISTER,
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(14) HOLZHYDROLYSE, A. G., German Patent 627.179, Maroh 10,1936. G., German Patent 729,343, Nov. 19, 1942. (15) GRASSEE, (16) KARSCFI, W., Gernmn Patent 729,344, Nov. 19, 1942. I. G., Belgian Patent 446,218, July 31, 1942. (17) FARBENIND., R. D., AND L. FRIEDMAN, Pae@ Plastics Mag.. (18) ENGLERT, 3, No. 10,38,40 (1945). J., C h m . Ind., 56, 53 (1945). (19) SEIBERLICH, (20) SHERRARD, E. C., E. BEGLINGER, AND J. P. HOAP, U. S. Patent 2,130,783, Sept. 29,1938. F. A.,Papier-Ztg., 25,3526 (1900); Chem. Ind.,26, (21) BUHLER, 138 (1903). 2,221,(22) CHMIPER,L. E., and L. M.CBRISTENSEN,U.S.P&~~~~ 282, Nav. 12, 1940. (23) JONES,L. R., U. S. Patent 1,917,038, July 4, 1933; U. 8. Patent 1,961,588,June 5,1934.
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(1931). R. S., Synthetic Resins and AlliedPlaslics, Oxford (32) MORRELG, Univemity Press, London (1943). (33) SCOTT, C. W., U. S. Patent 2,201,797, May 21, 1940. (34) ARIES,R. S., "Economic Consideration in the Productionof Wood Sugar and Alcohol," presented to the 108th Convention A. C. S. (1944). G. C., Paper Mill, 72 (Sept. 16, 1939). (35) HOWARD, G. C., Papw Industry, 628 (Sept. 1939). (36) HOWARD, (37) ModernPlastics, 19, No. 9,46 (1942). (38) MEILER,J. G., {bid., 20,64 (1942). C., U. S. Patent 2,026,106, Dec. 31, 1935. (39) STRESINO, LITERATURE CITED C. A., AND M. PLUNGUIAN, U. S. Patent 2,168,(40) HOCRWALT, 160, Aug. 1, I9.W. (1) SULLIVAN. V. A.. JR.. AND G. D. PALMER. J. CREM.EDUC., (41) ARIES,R. S., "Lignocellulose Residues, A Saga of Waste," 24,502 i1947): ' presented at the 108th convention A. C. S. (1944). (2) BOEHM,R M., Modern Plastics, 15, No. 2 , 2 6 7 , 56 (19373; J. A., Iowa State C&. J . S&., 1 9 , 2 6 4 (1944). (42) JOHNSON, ibzd., 17, No. 2,56 (1939). U. S. (43) HARRIS,W. D., ibid., 9,159-61 (1934). (3) MASON,W. H., R. M. BOEHM,AND W. E. KOONCE, IPPOLITO, 2nd. saccar. it& 32, 529-34 (1939). (44) SORGATO, Patent 2,080,078, May 11,1937.
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