THE INDIA RUBBER WORLD 



[jANl-ARV 1, 1916. 



What the Rubber Chemists Are Doing. 



A LEADING feature of the work of rubber cliemists in 1915 

 is the development of vulcanization accelerators. The re- 

 searches which resulted in the production of synthetic 

 rubber developed the value of certain organic chemical com- 

 pounds for improving the quality of synthetic rubber and hasten- 

 ing its vulcanization. Organic accelerators are not indispensable 

 to good manufacturing results and so far are practically pro- 

 hibitive in price. These are, however, decidedly interesting 

 from a chemical point of view, and have been noticed in the 

 patent literature and in special articles m The Indi.\ Rubber 

 World (December, 1914, March and June, 1915). 



Methods of reclaiming waste have been much studied the past 

 year and some results have been embodied in patented processes. 



The published methods of analysis of vulcanized rubber per- 

 fected and issued by the United States Bureau of Standards, 

 afford the best standard practical instructions on the subject for 

 the rubber works laboratory. The gain in this regard is very 

 great. 



Every phase of the rubber industry, from the plantation to the 

 finished product, is undergoing careful study and research, and 

 knowledge of rubber is steadily increasing in consequence. 

 Much of this new knowledge has been gathered and classified in 

 the columns of this paper. 



ISOPRENE FROM BETA-PINENE. 



AW. SCHORGER and R. Sayre, of the Forests Products 

 , Laboratory, Madison, Wisconsin, in the "Journal of En- 

 gineering Chemistry" (November, 1915), publish their 

 researches on the production of isoprene from beta-pinene. The 

 chemical relation between isoprene, the terpenes. and caoutchouc 

 may be represented by the following reversible reaction : 

 Dipentene ^^ 2-isoprene y*^ (Dimethyl-1,5 — Octadiene-1,5) x 

 (Caoutchouc) 



The authors used a modified form of the isoprene lamp of 

 Harries (See The India Rubber World, December, 1914, page 

 129) for conducting their experiments. Their results show 

 that turpentine and beta-pinene, under the same conditions, yield 

 about the same amount of isoprene, approximately 10 per cent. 

 They consider that the isoprene obtained from turpentine is not 

 due to the cracking of dipentene or limonene originally present 

 in the turpentine, but that the isoprene results indirectly from 

 dipentene. 



.\lpha-pinene can be converted into dipentene by heat ; the con- 

 dition in the apparatus would be favorable to such a transforma- 

 tion. The change may be represented thus : 



Pinene ^) > Dipentene m> > Isoprene. 



It is not probalile that either alpha-pinene or beta-pinene can 

 be made to yield directly sufficient isoprene for the commercial 

 production of rubber. Since good yields of isoprene are possible 

 from dipentene. an attempt to obtain an approximately quantita- 

 tive conversion of pinene into dipentene is worthy of further 

 consideration. 



RUBBER OF UNIFORM COLOR. 



Beadle and Stevens have shown that the darkening of raw 

 rubber is due to the presence of an oxydase. Pale rubber can be 

 produced by coagulating with an excess of acetic acid, creping, 

 and drying rapidly, preferably by heating in a vacuum, or by 

 placing freshly coagulated rubber in boiling water from 10 to IS 

 minutes ; but in both cases the product yields vulcanized rubber 

 of inferior quality. By adding to the latex small quantities (1 

 part per 500 to 1 part per 1,000, or even less) of substances such 

 as sodium bisulphate or formalin, which arrest enzyme action, 

 pale rubber of uniform color is obtained and the treatment has no 

 injurious effect on the vulcanized rubber. 



Tlie "Bulletin of .\gricultural Intelligence" (1915. page 1064) 

 recounts a simplined Scliadt's process for preparing rubber. It 

 consists in spreading a thin layer of latex over tin plates with re- 

 curved edges. When the latex has dried, the rubber films are 

 smoked in a revolving drum covered with perforated sheet iron, 

 and then compressed into blocks. The cost of the process is very 

 low, and the rubber is fit for transport two days after tapping. 



PREP.^R.\TION AND PROPERTIES OF PURE RUBBER. 

 Tlie investigations of F. Heim and R. Marquis on the prepara- 

 tion and properties of pure rubber have been published in the 

 ■'Bulletin of Agricultural Intelligence" (1915, page 874). Their 

 method was to coagulate wild Para rubber by smoke, and planta- 

 tion Para rubber by acetic acid. These were purified by macera- 

 tion, washing in cold water in a darkened tube and washing with 

 acetone. When the latter had evaporated, the rubber was dis- 

 solved in ether or benzene, the solution filtered through a Buch- 

 ner funnel, and precipitated with alcohol or acetone. After re- 

 moving traces of benzene by digesting with alcohol, the pure 

 caoutchouc was dried over sulphuric acid in the dark. The pure 

 substance is white, that obtained from smoked rubber slightly 

 yellow. Analysis confirmed the absence of resins and proteins, 

 and the fact that pure caoutchouc is a polymer of isoprene. Solu- 

 tions of it were less viscous than those of impure rubber, and the 

 pure substance oxidized more rapidly in air than the impure, 

 particularly when dissolved in chloroform. 



TACKINESS OF RUBBER. 



According to Spence, tackiness is caused by change in the ag- 

 gregation of the rubber molecule and is not due to chemical 

 change. K. Gorter finds that rubber exposed to light in sealed 

 tubes remains unchanged when the tubes are filled with hydrogen 

 or carbon dioxide, but becomes tacky in air or oxygen, and he 

 concludes that tackiness is due to oxidation. In one of his ex- 

 periments 3 per cent of oxygen was absorbed. Absorption of 

 oxygen proceeds slowly for the first 6 days ; it then increases and 

 attains its greatest rapidity in about thirty days. Oxidation does 

 not appear to be due to enzyme action, for it occurs in rubber 

 which has been boiled in water. Aldehydes were detected in 

 tacky rubber. 



METHODS OF ANALYSIS. 



Determination of Total Sulphur in Rubber. — The method 

 for determining the total sulphur in vulcanized rubber, as 

 given by A. Hutin, consists in decomposing from 1 to 2 grams 

 of rubber by means of 30 c.c. of fuming nitric acid, added 

 2 to 3 c.c. at a time.. The liquid is evaporated to a syrup, made 

 alkaline with caustic soda, and mixed with sufficient calcined mag- 

 nesia to form a stiff paste, which is dried, first on a water bath 

 and then in an air oven, at 140 degrees C, and finally ignited 

 cautiously over a small flame so as to avoid an explosion. After 

 ignition the mass is dissolved in hydrochloric acid and the sul- 

 phur determined by precipitation as barium sulphate in the usual 

 way. 



Drying Acetone Extract of Rubber. A. Hutin holds that the 

 acetone extract should be vacuum dried in order to obtain a resi- 

 due of constant weight. Unless this is done serious errors may 

 occur, owing to the increase in weight of the residue on drying 

 in the ordinary way ; even drying in carbon dioxide appears to 

 be unsatisfactory. 



Estimation of Mineral Matter in Vulcanized Rubber. — 

 .\ simple method for this purpose is given by H. W. Jones in 

 "Rubber Industry," London, 1914. Two grams of the sample are 

 heated with 40 to 50 c.c. of nitrobenzene in a 200 to 300 c.c. 

 flat-bottom flask, connected to a reflex air-condenser. When so- 

 lution of the rubber is complete, the flask is allowed to cool, the 



