I N D U S T R I A L A N D E N G I: N E E R I N G C H E M I S T R Y
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characteristics in this type of application seem ample for the conditions of service. An interesting development in the field of equipment has been that of high-frequency electrostatic heating devices (3). Although this type of equipment has not, to the best of our knowledge, been applied to the production of assembly bonds, use in this field is obviously indicated as it would permit the application of heat and pressure to thick assemblies and irregular shapes and forms.
Conclusions Despite the more impressive applications of phenolic resins
in the field of molding and coatings, they play an important part in the manufacture of plywood. The importance of plywood has grown tremendously in the last few years and is of great importance at the present time in our program of national defense. There seems little doubt that the importance of plywood in aircraft construction is just beginning to be appreciated in an industry which has heretofore devoted its attention almost exclusively to metals. With the availability of a fast curing, easily handled, powdered phenolic resin to supplement the phenolic resin film, the major adhesive problems seem already well on the way to solution.
Bibliography Anonymous, Modern Plastics, 17, 25 (1940). Anonymous, Modern Plastics Catalog, pp. 414-18 (1941). Berkness, I. R., Can. Wood Worker & M f r . , 40, 9-10, 24 (1940). Bernhard, R. K . , Perry, T. D., and Stern, E. G., Mech. Eng., 62, 189-94 and 748-51 (1940). Brenner, P., Aircraft Eng., 10, 129-34 (May, 1938). Brenner, P., and Kraemer, O., “Improvement of Wood by Synthetic Resin Gluing”, Mitt. d. Fachaussch. fur Holzfragen, Vol. 11. Berlin, 1935. Clark, V. E., Aero Digest, 35, 101-5 (1939).
Vol. 33, No. 8
(8) De Bruyne, N. A,, Aircraft Engineer (supplement to Flight), 18, 61-4 (1939). (9) Decat, R., Aero Digest, 38, 146, 149, 194 (1941). (10) Dike, T. D. ( t o Laminating Patents Corp.), U.S. Patent 1,922,668 (Aug. 15, 1935). (11) Ellis, C. L., “Chemistry of Synthetic Resins”, Vol. 1, p. 291, New York. Reinhold Publishing Coro.. 1936. (12) Haut, H . N.,’ Chem. Industries, 48; 26-9 (1941). (13) Hayward, C. H., W o o d , 4, 443-7 (1939). (14) Hulot and Mouninou-Doumichaud, French Patent 414,045 (1910). (15) Knight, E. V., and Wulpi, M., “Veneers and Plywood”, New York, Ronald Press, 1927. (16) Koch, R.. M o d ~ r nPlastics, 16, 264-5, 270 (1938). . . (17) Ibid., 17, 416-20 (1939). (18) Kollmann, F., “Technology of Wood”, p. 539, Berlin, Julius Springer, 1936. (19) Kuech, W., Jahrbuch der deutsche Luftfahr Forschung, pp. 4473 (1938). (20) Laucks, I. F., Modern Plastics, 15, 294-8 (1937). (21) McBain, J. W., and Lee, X7.B., J . SOC.Chem. Znd., 46, 321-4T (1927). (22) McClain, J. R. (to Westinghouse Electric & Mfg. Co.), U. S. Patent 1,299,747 (April 8, 1919). (23) Megson, N. J. L., “Phenomena of Condensation and Polymerization”, p. 336, London, Gurney & Jackson, 1935. (24) Moon, H. P., Auiation, 40, 44 (1941). (25) Mora, A , “Plywood, Its Production, Use and Properties”, London, Timber and Plywood, 1932. (26) Perry, T. D., J . A E T O ~ Sci., UU~ 8,.204-16 (1941). (27) Perry, T. D., and Bretl, 31. F., T ~ a n s Am. . SOC.Mech. Engrs., Wood Ind., 60, No. 3, 59-68, 682 (1938). (28) SOC.Derepas FrBres, Brit. Patent 17,327 (1901). (29) Sorensen, R., Trans. Am. SOC.lwech. E ~ T s .Wood , Ind., 56, NO.1, 37-48 (1934). (30) Sorensen, R., and Klein, L., Hardwood Record, 72, 15 (Oct., 1934). (31) Spencer, H. S., Modern Plastics, 14, 296 (1936). 132) Truax, T. R., Trans. Am. SOC.Afech. Engrs., Wood Ind., 54, N o . 1 (1932). (33) Weber, J., and Hengstebeck, E‘. (to Th. Goldschmidt Corp.), U. S . Patents 1,960,176-7 (May 22, 1934).
Cottonseed Hulls in Phenolic Plastics FRITZ ROSENTHAL University of Tennessee, Knoxville, Tenn.
HE processing of cottonseed results in the production of four primary commodities: cottonseed oil, an important edible vegetable oil; cottonseed meal, a cattle feed which is extremely high in protein content; cotton linters, a valuable source of alpha-cellulose; and cottonseed hulls. The hulls have been used so far as roughage for beef and dairy cattle, and whenever the price of hulls fell below a certain level they were burned as fuel by the oil mills. The applications of the four cottonseed oil mill commodities indicate that cottonseed hulls are the least profitable product of all of them. This fact has been the incentive for many diversified research efforts to find better uses for the hulls. 9 recent article by Musser and Nickerson (6) contains a complete review of research and development work devoted to the utilization of cottonseed hulls. Cottonseed hulls have been suggested as a filler for phenolic molding compounds. This is not surprising in view of the spectacular development of phenolics within the last twenty years. It is surprising, however, how little information is available on the utilization of cottonseed hulls as fillers in phenolic plastics. Hurst (4) obtained a patent on a lowcost molding compound comprising 70 to 80 per cent cotton-
T
seed hulls and 20 to 30 per cent phenolic resin. He called attention to the nonabsorbency of resin by cottonseed hulls and reduced the resin content by such amount as is ordinarily required to saturate the filler, and accordingly reduced the cost of the molding compound. Hurst’s claim with respect to nonabsorbency is of dubious value in the light of a publication by Meharg (6),who has given comprehensive thought to filler requirements. He discerns six primary and eight secondary requirements a material has to meet in order to be a satisfactory filler in thermosetting molding compounds. One of his primary requirements is the property of being easily wetted by resins, which he states is necessary to good bonding arid to good finish of the molded piece.
Absorbency The first problem to be solved was to decide whether cottonseed hulls are nonabsorbing, as claimed by Hurst, or whether they have a high absorbing power and therefore possess a primary requirement for a good filler. The absorbing power of any filler material, be it wood flour, cottonseed hulls, or cotton flock, is a function of the particle size of the
INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1941
filler. To illustrate this further, the surface of a given weight of filler increases in proportion to the smallness of particle size. Obviously, more resin is required to cover the greater surface of a filler of smaller size. It is further known that cottonseed hulls may be separated by various means into two components, hull bran and hull fiber, in a proportion dependent on the previous delinting operation in the oil mill. We have investigated the absorbing power of both cottonseed hull bran and hull fiber in all particle sizes in which they might be used as a filler and have obtained the corresponding data for wood flour (Figure 1). The test for absorbing power
Cottonseed hulls have been suggested as fillers in phenolic molding compositions, but little information has been available regarding the preparation of hulls for this application and the properties they lend to the plastic material. Hurst prepared a compound of low resin content based on the low absorbing power of cottonseed hulls. Our work reveals that the absorbing power is a function of the particle size and of the hull fiber content. Cottonseed hulls are a heterogeneous mixture of hull'bran and fiber, and the content of the latter may be controlled. Since hull fiber differs chemically and physically from hull bran, it was anticipated that the fiber content of hulls, when used as a filler, would have an influence on the characteristics of the resulting compound. Hull bran samples were prepared of controlled particle sizes of 40, 60, 100, 150, 200, and finer than ZOO-mesh screen, respectively. Compounds were made by impregnating each of the samples with the same amount of identical phenolic resin. Compounds were also prepared from bran of various particle sizes containing 5,10,15, and 20 per cent hull fiber, respectively. Tests were made for impact strength, modulus of rupture, and modulus of elasticity. The test results indicate the influence of particle size and fiber content of cottonseed hulls on the strength characteristics of phenolic compounds.
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FUNCTION OF PARTICLE
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< 200 mesh, no fiber D . < 200 mesh, 20% OF MOLDED MATERIALS (X40) FIGURE2. PHOTOMICROGRAPHS
fiber
was conducted according t o G a r d n e r a n d Coleman (d). Vegetable oil was added dropwise to a 10-gram sample of the filler material until the sample formed a coherent ball. This was considered the saturation point. The amount of vegetable oil used was taken as an indication of the absorbing power of the filler material. Our investigation has r e v e a1e d t h e following points: (a) The absorbing power of cottonseed hull bran is smaller than that of wood flour, while that of cottonseed hull fiber is considerably greater than wood flour. (b) The absorbing power rises with increasing fineness to a maximum, which lies at 8 particle size between 100and 200-mesh screen. It follows from these results that cottonseed hulls may be nonabsorbent, or may have high absorbing power according to their condition with respect to their particle size and their hull fiber content.
INDUSTRIAL AND ENGINEERING CHEMISTRY
982
parent in p h o t o m i c r o g r a p h s p r e p a r e d from polished cross sections of molded test bars (Figure 2 ) . Figure 2A shows how the coarse hull particles are surrounded by resin which obviously has not been absorbed. This s u p ports the results obtained in our oil absorption tests. However, in the other pictures (B, C, D) no excess phenolic resin is visible. It has been absorbed by the greater surface of finer hull particles or by the hull fibers, which have a much greater absorbing power. Photomicrographs have given other visible evidence of the interior structure of the material. All thirty samples of cottonseed hull fillers with various particle sizes and fiber contents were processed through a laboratory Banbury mixer to obtain compounds which could be compared to commercial phenolic materials. At random, the compound having a filler of 100-mesh screen and 5 per cent fiber content was selected to study the changes caused by the Banbury treatment (Figure 3). The Banbury promoted the impregnation of binder and filler, broke down coarse particles, increased the apparent density, and caused a much smoother texture in the molded article, as Figure 3 shows. The characteristics of the molded material were substantially improved. The impact strength rose from 0.14 to 0.27 foot-
Effect of Particle Size and Fiber Content The influence of particle size and fiber content of cottonseed hull fillers on the characteristics of phenolic molding compositions was the next point to be studied. Air-dry cottonseed hulls were ground in a hammer mill, and the hull fibers were separated from the bran. The bran was sifted into particle sizes of 40, 60, 100, 150, 200, and finer than 200 mesh. These samples were mixed with identical amount2 of a phenolic resinoid. Hull bran samples of the various particle sizes TTere then mixed with 5, 10, 15, and 20 per cent hull fibers, respectively, and were also mixed with the constant proportion by weight of phenolic resinoid. Thus, thirty compounds were prepared, which were identical in resin content and method of preparation but different in particle size and fiber content of the filler. This difference is ap-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
August, 1941
983
bend under stress seems to be a unique property of the cottonseed hulls filler, which will be investigated more thoroughly later.
Conclusions
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1. The absorbing power of cottonseed hulls is a function of their particle size and fiber content. 2. A maximum impact strength is obtained when the cottonseed hull filler has a particle size of 100 mesh and 10 per cent fiber content. 3. A maximum modulus of rupture is obtained in cottonseed hulls of 60 mesh and no fiber content. 4. The modulus of elasticity seems to vary in proportion to the modulus of rupture.
PARTICLE S I Z E CONSTANT 100 M E S H
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PERCENTFIBERCONTENT
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EFFECTOF PARTICLE SIZEAND FIBERCONTENT ON MODULUS OF ELASTICITY
pound per inch of notch Izod, the modulus of rupture increased from 6240 to 10,290 pounds per square inch, and the water absorption in 48 hours dropped from 0.89 to 0.48 per cent after the Banbury treatment. All thirty compounds were tested for impact strength, modulus of rupture, and modulus of elasticity, and the results were correlated to particle size and fiber content of the filler. Impact strength was tested in an Izod machine with a 0.1inch notch according to A. S. T. M. specifications (Figure 4). A maximum impact of 0.29 foot-pound was found a t a particle size of 100-mesh screen, and a 10 per cent fiber-90 per cent bran composition. Modulus of rupture was tested according to A. S. T. M. specifications (Figure 5). A maximum modulus of 10,480 pounds per square inch was obtained a t 60-mesh screen with no fibers. An increase in fiber content effected a decrease of breaking strength under a load in all ranges of particle size of the hulls. This would indicate that the hull fibers remaining after the delinting operation in the oil mill are too short to have a strengthening effect on the compound. The modulus of elasticity was determined according to Brother (1) and Hopkins (3) by measuring the deflections when loads were applied in the modulus of rupture tests (Figure 6 ) . Within the limitations of our testing equipment, the modulus of elasticity data were in close proportion to the values for modulus of rupture throughout the range of particle sizes and fiber contents. While a high modulus of rupture is desirable in plastic materials, we made some observations in a cottonseed hull compound of low modulus of elasticity. The smaller the modulus of elasticity, the greater the deflection where a given stress is applied. A practical demonstration of this low modulus of elasticity appears in Figure 7, an electric switch plate molded of a phenolic cottonseed hull compound. This switch plate was fastened tight to the surface of a rough cinder block wall. The switch plate bent and adjusted itself to the stress, while another switch plate, molded of wood-flour phenolic material, cracked when exposed to the same stress. The ability to
7. BENDELBCTRIC S W I T C HP L A T E UNDER STRESS(LOW MODULUS OF ELASTICITY)
FIGURE ING OF
5. The control of particle size and fiber content permits the preparation of phenolic cottonseed hull molding compounds whose strength characteristics compare favorably with commercial phenolic compounds. 6. Maximum strength characteristics are obtained a t specific particle sizes and fiber contents. This versatility with respect to particle size and fiber content is a unique characteristic of cottonseed hulls which tends to increase the scope of potential applications of cottonseed hulls as a filler in phenolic compounds.
Acknowledgment The author expresses thanks to the co-workers in the Experiment Station for their excellent collaboration, and to Reichhold Chemicals, Inc., for permission to use their laboratory facilities.
Literature Cited (1) Brother, G. H., IND. ENG.CHEM.,32, 1648 (1940).
(2) Gardner, H.A., and Coleman, R. E., Paint, Oil Drug Rev., 69. NO, 9,8,23-5 (1920). (3) HoDkins. I. L.. Am. 900. Testing- Materials, Bull.. 98, 29-30 (May, 1939). (4) Hurst, I. A.,U. S. Patent 1,863,540(June 14,1932). (6) Meharg, V.,Modern Plastics,16,30 (Oct., 1938). (6) Musser, D.M., and Nickerson, R.F., IND.ENO.CHEM., 31, 1229 (1939).
.,
End of Symposium
