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INDUSTRIAL AND ENGINEERING CHEMISTRY
be wholly attributed to the resulting close packing and cementing of the cellulose fibers, for the orientation effects alone would decrease the tensile strength. The observed decrease in relative orientation for wood which has been subjected t o high compression is in agreement with previous studies (4, 24). Compression wood growing on the leaning side of a tree was shown to have a less perfect preferred orientation than the normal wood, which grows in a portion of the tree relatively free from strain. Figure 5 presents distribution curves for normal maple and maple which has been heated at 400” F. for 4.5 hours. The half maximum anglesfor these specimen; are 10.65’ and 9.85’, respectively. The distribution curves and the smaller half maximum angle for the heated specimen indicate that the cellulose crystallites are more nearly parallel to the fiber axis in the heated wood than in the normal wood. .is a result of this more perfect preferred orientation, the tensile strength should increase; it does to the extent of a t least 10%. The changes in orientation do not explain the incre mensional stability of vood treated by either heat or pressure. 111 compressed wood the increase in stability is probably a result of the decrease in size of the capillary channels anti the subsequent small moisture absorption. The dimensional stability induced by heating may be the result of chrmicnl chanffesbrought about by the partial pyrolysis of the lignin in the wood or of the cellulose itself. It was observed ( 5 ) that increase in preferrrd orientation results in reduced shrinknpe of wood but sufficient data arc not yet available for quantitative evaluation of this effect. It is doubtful that the small increase in orientation observed for the heated wood would greatly affect the dimensional s tabilit 57.. LITERATURE CITED
Vol. 38, No. 12
(3) Beinhard, R . K . , Perry, T. D., and Stern, E. G . , M e c h . Eng., 62, 189 (1940). (4) Clark, G . L., IKD.EXG.CHEIM.,22, 474 (1930). (5) Clark, G . L., and Gross, S.T., ISD. EXG.CHEM..ANAL.ED.. 14, 676 (1942). (6) Clark, G . L., and Parker, E. *L,J . Phys. Chem., 41, 777 (1937). (7) Clark, G . L., and Shafer, TI’. M.,Trans. Am SOC.Metals, 13, 732 11941). (8) F a r r , %’. K.’, and Clark, G. L., C‘ontTib. Boyce Thompson Inst., 4, 273 (1932). (9) Frey-Wyssling, A, Kolloid-Z., 85, 148 (1938). (10) Goby, P., Compt.rend., 156, 686 (1918). (11) Hermans, P. H . , Kolloid-Z., 97, 223 (1941). (12) Hermans, P. H . , and Booys, J. de, Ibid., 97, 229 (1941). (13) Hess, K . , and Trogus, C., 2.physik. Chem., B5, 161 (1929). (14) K a t z , J. R., Trans. Faraday Soc., 29, 279 (1933). (15) K a t z , J. R., and Hess, K., 2.physik Chem., 122, 126 (1926). (16) Koehler, A., Trans. Am. SOC.X e c h . Engrs., 53, 17 (1931). (17) K r a t k y , O., and M a r k , H . , Z. physik. Chem., B36,129 (1937). (18) Lokschin, F. L., Holzchem. I n d . . 2, 45 (1939). (19) l l e r r i t t , , K. TI’., and White, 4 A., ISD.ENG.CHEX., 35, 297 (1943). (20) illeyer, K., and Mark, H., Der d u f b a u der hochpolymeren organischen Naturstoffe, Leipzig, Akad. Verlagsges., 1930. (21) O t t , E., ”Cellulose and I t s Derivatives”, chapter by W. A. Sisson, pp. 203-85, Kew York, Interscience Publishers, 1943. (22) Schmidt, B., Z. Physik., 71, 696 (1931). (23) Schramek, W., and Gorp. H . , Kolloid Beihefte, 42, 302 (1935). (24) Sisson, W. A , , IND.EXG.CHEY.,27, 51 (1935). (25) Sisson, R. A , , Textile Research, 7, 425 (1937). (26) Sisson, W.A., and Clark, G. L., IND.Esc. CHEM.,Xx.4~.ED., 5, 296 (1933). (27) Sisson, u’.A , , a n d S a n e r , W. K., J . Phys. Chem., 43, 687 (1939). (28) Stamm, A. J., IND. ENG.CHEM.,27, 401 (1935). (29) Stainm, A. J., Trans. Am. Inst. C h t m . Engis., 37, 385 (1941). (30) Stamm, .A. J., and Sehorg, l i . >I., IND.EXG.CHEM.,28, 1184 (1936). (31) Ihid., 31, 897 (1939). (32) Stanim, A . J.. and Seborg, 11. A I . , “Resin-Treated, Laminated, Compressed Wood”, mimeograph, Forest Products Lab., 1941. (33) Trogus, C . , and Hem, K., 2 . pbysik (’hem., B11,387 (1931). (34) Ibid., B14, 387 (1931).
(1) Barry, A. J., Peterson, F. C., and King, A. J., paper presented before Division of Cellulose Chemistry of A.C.S. a t Pittsburgh, Pa., 1936. (2) Berkley, E. E., arid T o o d y a r d , 0. D., IND.>:NO. CHEM.,.IN.~I..PRESSTED on the program of the Division of Cellulose Chemisthy of the 1945 Meeting-in-Print, AMERICAS CHEUICAL SOCIETY. ED., 10, 451 (1938).
Control of pH of Neoprene Latex H. IC. LIVINGSTON k N D R . H. WALSH E. Z. du Pont de h’emours & Compcrny, Znc., Wilmington, Del.
0
i\;E of the major contributions to the development of the use of rubber latex in manufacturing processes has been the introduction of methods for regulating the pH of the latex compounds ( 5 ) . On the basis of this knowledge the coagulating dip process, the use of heat-sensitive latex mixes, and the use of gelling agents have become standardized and accepted methods of manufacturing rubber goods. Most of the techniques used in rubber latex manufacturing processes have been applied to the alkaline neoprene latices such NS Types 571 and 60. However, in the case of the gelling agents the methods normally used to control coagulation of natural rubber latex do not always apply to neoprene latex. An investigation was made of the effect of pH reduction on the reaction between neoprene latex and gelling agents, and also of methods for the control of this reaction. The effectiveness of the gelling agents as coagulants arises from the delayed formation of hydrogen ions or multivalent metallic ions in the latex which these agents produce under certain specified conditions. h good example of this phenomenon is thr reaction that takes place when sodium fluosilicate is added t o either natural rubber or neoprene latex. The sodium fluosilicate liydro-
lyzes in the latex forming sodium fluoride, hydrofluoric acid, and silic
