452 



THE INDIA RUBBER WORLD 



[May 1, 1917. 



samples having approximately one-third the strength of a 

 similar rubber vulcanized with sulphur in the same heat. 

 Samples from mix B occupy an intermediate position. All the 

 vulcanized samples are very pale in color, quite as pale as the 

 original raw rubber. Those of mix C have a very attractive 

 appearance. They are quite transparent and resemble some 

 of the palest cold-cured sheet prepared from plantation crepe. 

 In benzene the vulcanized mix A dissolves in a few hours 

 in similar manner to raw crepe. Mix B swells enormously, 

 but does not dissolve. It remains a soft gelatinous lump in 

 the solvent. Mix C behaves the same as an ordinary vulcan- 

 ized rubber, swelling considerably, but retaining its original 

 form. It may therefore be said that the change brought 

 about by heating with benzoyl peroxide is exactly similar to 

 that produced by sulphur and that the products formed have 

 similar properties. The proportion of benzoyl peroxide re- 

 quired to give a fairly complete vulcanizing effect is similar to 

 the proportion of sulphur which would be required for the 

 same purpose, but the vulcanization with benzoyl pero.xide is 

 brought about in a much shorter time. Thus, in the above 

 experiments and also in those published by Ostromyslenski, 

 vulcanization is fairly complete in 10 or 15 minutes at 130 to 

 135 degrees C. with 4 to 6 per cent of benzoyl peroxide, whereas 

 vulcanization would hardly have begun with a mix containing 

 S to 6 per cent of sulphur and would require two to three 

 hours for completion. Attempts to obtain satisfactory vulcani- 

 zation with smaller proportions of benzoyl peroxide, but vul- 

 canizing for longer periods, have not been successful. Thus, 

 with 1.33 per cent of benzoyl peroxide better results were 

 obtained when vulcanizing for 30 minutes than for 60 minutes. 

 Further experiments are in progress. 



ORGANIC VTTLCANIZING ACCELERATORS. 



In a communication in the "Journal of the Society of 

 Qiemical Industry" (February 15, 1917), Dr. Spence says, re- 

 garding organic vulcanization accelerators, that, according to 

 Ditmar, Gottlob and King, the discovery of the principle of 

 vulcanization, whether of natural or of synthetic rubber, by 

 means of organic catalysts dates from tlie disclosures of the 

 Elberfeld Farbenfabrik in November, 1912. This is probably 

 true so far as Europe is concerned, but not so with regard 

 to America. Dr. Spence states that substantial proof of this 

 assertion is to be had from an analysis of his own previously 

 published work on the subject of vulcanization. 



In the '•Kolloid Zeitschrift" (volume 10, page 303-305. 1912), 

 more than six months before the Eberfeld Farbenfabrik made 

 application for their first patent on this subject. Dr. Spence 

 described certain experiments, the significance of which 

 passed apparently unobserved. The reference follows: 

 "More than a year ago we prepared samples of two care- 

 fully chosen mixings. Both mixings were made from par- 

 tially purified rubber with about 9 per cent of sulphur. In 

 order to make the investigation as comprehensive and com- 

 plete as possible, the two mixings were purposely chosen so 

 that two quite distinct types of compound as different as 

 possible in their properties were obtained. The first was a 

 slow-curing compound deteriorating rapidly; the second, on the 

 other hand, was a guick-curiitg mixing which we knew from ex- 

 perience would resist deterioration indefinitely .... Two com- 

 pounds of the same ^cncnil character as No. 2 were prepared,; 

 both these compounds contained about 9 per cent of sulphur and 

 were free from mineral compounds." 



Dr. Spence then stales: 



As a matter of fact, the first of these two compounds actu- 

 ally contained 1 per cent of piperidine, the very substance 

 referred to in the German patent of November 16, 1912. The 

 formula for the mixing was as follows: Plantation Para, 100 

 parts; sulphur, 10 parts; piperidine, 1 part. Without the use 

 of piperidine in this mixing the results given in the com- 

 munication referred to would have been utterly impossible. 



In regard to the discovery of vulcanization of synthetic 



rubber by means of organic accelerators, also credited to 

 Elberfeld Farbenfabrik, the vulcanization of these products 

 by this means was actually carried out and successfully ac- 

 complished by me both for isoprcne-caoutchouc and for the 

 dimethyl caoutchouc from pinacone at a time when the large 

 industrial concerns in Germany engaged in the study of the 

 synthesis of india rubber were in the dark as to their lack 

 of success in the vulcanization of their products. The proof 

 of this assertion and the complete vindication of my position 

 with reference to the subject in general I am content to leave 

 over until a later date. At that time I will also bring evidence 

 to show that even the reagents claimed by Peachey (English 

 patent 4,263 of 1914) were known to me and had been used 

 by me both scientifically and industrially several years before 

 his application was applied for. 



VTrLCANIZATlON. 



The following remarks on the chemistry of vulcanization are 

 condensed from a study of the subject by Andre Dubosc ("Le 

 Caoutchouc & la Gutta-Percha," January, 1917). In discussing 

 the work of Stevens, the author amplifies his views on vul- 

 canization, published two years ago. 



The early inventors and rubber workers practiced vulcaniz- 

 ation purely as an art, and were interested solely in the industrial 

 results. Parkes seems to have seen a little more clearly than 

 others the problem of vulcanization as a science. The first not- 

 able advance in the study of vulcanization was the theory of Dr. 

 Carl Otto Weber, who held that sulphur in saturating the double 

 bonds either of one molecule, in the case of ebonite, or of a more 

 or less extended polymer, in the case of different qualities of soft 

 rubber, determined and stabilized the physical properties of the 

 crude rubber complex. Although of the greatest interest, Weber's 

 theory was incomplete, because it did not take into account the 

 state of polymerization of sulphur used in vulcanization, nor did 

 it explain the function of litharge and magnesia in this connec- 

 tion. 



Subsequently, Oswald put forward this theory that vulcaniz- 

 ation is an absorption and not a chemical phenomenon. His 

 views have found many adherents, somewhat displacing the well- 

 founded chemical theory of Weber, although the latter gains con- 

 firmation by the latest work of Bysow, and of Stevens on the 

 influence of nitrogenous products and resinous substances in vul- 

 canization, indicating that the proteins contained in rubber are 

 very important factors in considering the properties that rubber 

 acquires when vulcanized. The work also of Baritt supports the 

 new ideas of beneficial influence exercised on rubber by the 

 proteins, hitherto erroneously considered as impurities. In fact, 

 the proteins are now known to play the part of a catalyst in the 

 process of vulcanization. 



The eflfect of the addition of foreign nitrogenous substances 

 to rubber has been studied, with positive results. 



The function of rubber resins in vulcanization is important, the 

 most striking result being the deterioration of the rubber after 

 vulcanization, when all the resinous elements have first been elim- 

 inated. This fact is explained as follows : 



It has only been possible to get the colloidal sulphur neces- 

 sary for vulcanization, in the absence of resins, by a partial de- 

 composition of the rubber which has been altered and depoly- 

 merized. 



The formation of water accompanying the production of col- 

 loidal sulphur explains the need for an absorbent, like whiting, 

 in mixtures, to prevent porous rubber. 



It has been demonstrated experimentally that when rubber 

 resins and the proteins, previously separated from the rubber, are 

 heated at temperatures approaching those of vulcanization (120 

 to 150 degrees C), it is possible completely to convert the sul- 

 phur added into sulphydric acid. 



When a mixture of litharge, magnesia, oxide of zinc and sul- 

 phur is heated either in air or under oxidizing influence, metallic 

 sulphur and sulphurous acid are constantly produced. When the 

 latter is made to react on sulphydric acid resulting from the pre- 

 ceding reaction, colloidal sulphur and water are formed. 



