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THE INDIA RUBBER WORLD 



[May 1, 1914. 



WHAT THE RUBBER CHEMISTS ARE DOING. 



[Extracts from recent articles on the Chemistry of Kttbher u'hich 

 have appeared in some of the foreign publications.] 



IN the issue of "Le Caoutchouc ct la Guttapercha" of the ISth 

 of January, 1914, A. Dubosc contributes an article on the use 

 of formic acid for the reclaiming of rubber, lie points out the 

 drawbacks inherent in the sulphuric acid |)rocess, such draw- 

 backs consisting chiefly in the injurious action of the acid on 

 the rubber and the difficulty of completely washing out the last 

 traces of acid. While it is a fact that the mineral acids have, 

 under certain conditions, a pronounced action on rubber, the 

 organic acids, especially acetic and formic, have an action much 

 less pronounced, Hy the action of acetic acid on cotton fabric, 

 cellulose acetate is formed, which latter may be separated from 

 the rubber by means of acetone. It is more expedient, how- 

 ever, to continue the action of the acid on the fabric till the 

 acetate or formate of cellobiose is formed. 



It is preferable to use formic acid rather than acetic acid, 

 for the reason that the formic acid acts without the application 

 of heat. It is necessary to use twice the weight of 90 per cent, 

 formic acid on the weight of the scrap rubber. The formic 

 acid before being used must be saturated with hydrochloric acid 

 gas. In 12 hours the fabric is converted into water soluble 

 cellobiose formate. The mass is filtered and the rubber washed 

 and dried. By working at temperatures between 60 degs. and 

 70 degs. C. it is possible to bring about the conversion of the 

 fabric in abcnit 4 hours. 



In the "India Rubber Journal," Vol. 47, No. 9, H. P. Stevens 

 publishes an investigation on "The Influence of Various Nitro- 

 genous and Resinous Substances on the Vulcanizing Proper- 

 ties of Rubber." The author determines the effect which the 

 removal of the protein matter has on the vulcanization of rub- 

 ber, the effect of the removal of the resins, and the effect of the 

 combined removal of the protein and resins. He also carries out 

 experiments with a view to determining the influence which 

 added amounts of these substances have on the vulcanization of 

 rubber. 



It is found ihat the removal of the protein matter greatly 

 retards the coefficient of vulcanization, and produces a product 

 which exhibits very slight resistance to stretching. .Adding 

 Casein or Riedel's Peptone to rubber, from which tlie protein 

 matter has been removed, while aiding the coinbination of the 

 sulphur and rubber, does not materially aid in improving the 

 physical tests of the compound. The addition of starch to 

 protein-free rubber was found to be of no avail. When litharge 

 is used in the vulcanization of a rubber, from which the protein 

 matter has been removed, there results a product which exhibits 

 the normal coefficient of vulcanization, and gives highly satis- 

 factory physical tests. 



The removal of the resins does not effect the co-efficient of 

 vulcanization, and aids slightly in the resistance to stretching 

 of the vulcanized product. Reincorporating the extracted resins, 

 and subsequently vulcanizing, gives normal values. Instead of 

 incorporating the extracted resins, the same weight of Pontianak 

 resin may be used without affecting the results obtained. If, 

 however, colophony is used, there results a decrease in the re- 

 sistance to stretching. 



Rubber freed from resins and protein matter, on vulcanizing 

 behaves similarly to rubber from which only the protein matter 

 has been removed. 



In the "Colloid Zeitschrift," \'ol. 14, page 35, !•". Kirchhof con- 

 tributes an article on the ".Addition Products of Rubber." The 

 author observed that vulcanized rubber behaves differently from 

 unvulcanized rubber when allowed to oxidize either in the air 

 or in oxygen. In the case of the vulcanized product, it would 

 seem as if there were only one double bond for every CwH,a 

 complex. Furthermore, unvulcanized rubber I)ehaves similarly 

 to vulcanized rubber when acted upon by certain substances in 



the gaseous state, such as, lor instance, bromine or sulphur 

 chloride. .After the saturation of one double bond no further 

 addition of bromine or sulphur chloride results. It would there- 

 fore appear as if sulphur in the process of vulcanization acted 

 on ruljber in a siiuilar manner as do bromine and sulphur 

 chloride at ordinary temperatures. 



In view of the above oljservations, Kirchhof carried out a 

 scries of experiments in which he determined the increase in 

 weight in a filin of ruliber when exposed to oxygen, bromine 

 and sulphur chloride for definite periods of time. In addition 

 to determining the increase in weight when rubber was allowed 

 to react with the above named substances in the gaseous condi- 

 tion, the author also determined changes in viscosity as resulting 

 from the addition of small quantities of sulphur chloride, and 

 also from the addition of oxygen. 



.-\s the result of these experiments the author concludes that 

 the reactions which result in the formation of addition products 

 proceed, in the case of rubber in the solid state, as though there 

 were only one double bond for every C,oHi„ complex. This 

 might be explained on the supposition that the two double l)onds 

 in the octadicne ring, supposed to exist in rubber, had unequal 

 affinities, or the saturation of one of these double bonds results 

 in the weakening of the affinity of the other. There is no ex- 

 perimental evidence, however, in favor of either of these views. 

 It is more reasonable to explain this phenomenon from the 

 standpoint of Partial Valences, the more so, since the latter are 

 supposed to condition the colloidal state, in that they unite the 

 individual simple complexes to form the highly complicated 

 colloid. As the result of the formation of the addition product, 

 the Partial Valences are converted into saturated bonds, with 

 the simultaneous addition of the bromine or sulphur chloride. 



The addition of very small quantities of bromine or sulphur 

 chloride results, in the first place, in a marked decrease in 

 viscosity, though an increase in the viscosity soon results, 

 gelatinization finally taking place. The period of time necessary 

 before gelatinization results is dependent on the original viscosity 

 of the rubber solution, the solvent, and the concentration of the 

 sulphur chloride. In a naphtha solution the period of time is 

 shorter than in a benzol solution. This decrease in the viscosity 

 is to be regarded as a depolymerization of the rubber. After 

 such depolymerization the rubber becomes more reactive for the 

 formation of addition products. It behaves as if it had two 

 double bonds for every CioH.e complex. It will thus be seen 

 that rubber in solution behaves differently from rubber in the 

 solid state regarding the formation of addition products. In 

 cases where the rubber is reacted upon in the solid state, equilib- 

 riuin results, and this equilibrium tends to act in the direction 

 of repolymerization. 



There are many factors which contribute to the actual 

 equilibrium obtained, such as the original degree of polymeriza- 

 tion, the strength of the depolymerizing agent, temperature, etc. 

 Accordingly products are foriued which do not exhibit siinple 

 and stoichiometrical relationships. Reactions of this nature have 

 often been referred to as being examples of "absorption." The 

 author believes that these observations are applicable to the ex- 

 planation of the vulcanization of rubber. It has previously been 

 pointed out that in the vulcanization process a slight depolymeri- 

 zation, owing to the action of heat, takes place. Kirchhof be- 

 lieves that rubber thus slightly depolymerized becomes more re- 

 active, and is thus more susceptible to the catalytic condensing 

 action of the sulphur, which latter reaction is regarded as the 

 real cause of the vulcanization. 



The results of government encouragement are shown in the 

 increased area of 2,595 acres now under cotton in Bisanuloke, 

 the principal growing center of the Monthol province of Siam. 

 This I'esult is partially attributed to free distribution of seed and 

 the erection of a motor ginning plant. Receipts by rail at Bangkok 

 have increased since 1909 from 120.000 to 2,000.000 pounds. 



