November 1. 1919.1 



THE INDIA RUBBER WORLD 



An Examination of German Synthetic Rubber. 



By Lothar E. Weber, Ph. D. 



THE SYNTHESIS OF RLBBEK lias always been a topic of interest 

 to the rubber industry. This interest probably reached a 

 maximum in the summer of 1912, when the experimental 

 results of Drs. Perkin and Hofmann were laid before the chemical 

 world. Rubber had been synthesized as a test tube experiment 

 by numerous investigators in the course of the previous twenty 

 years, but these two men, the respective leaders of independent 

 groups of English and German scientists, were undoubtedly the 

 lirst to produce synthetic rubber on something more than an 

 academic scale. 



The coming of the war had a marked influence on these investi- 

 gations. The possibilities of a rubber shortage in England being 

 remote, her scientists naturally turned to the s'olution of more 

 pressing problems. In Germany, however, the rubber situation 

 became acute, even in the early months of the war. Realizing as 

 she did the importance of rubber as a secondary instrument of 

 warfare, it was but natural that she should make a great effort 

 to effect its synthesis, being amply provided with the greatest 

 incentive for inventive research, namely, necessity. One has only 

 to recall the almost humorous methods of petty smuggling to 

 which she resorted, to realize her pressing needs for crude rubber. 

 It is to be expected, then, thai she should have made great strides 

 m the commercial development of the synthetic product. 



The four samples of synthetic rubber, which the Editor of 

 The Indi.\ Rubber World obtained from Germany and submitted 

 to the writer, exhibited a striking resemblance to natural crude 

 rubber. Three of the samples were intended for the manufac- 

 ture of soft rubber goods and the fourth for hard rubber. The 

 first three named took the form of crepe, about one-half-inch in 



less fibrous, and could be disintegrated without great difficulty. 

 The dark sample was highly resistant in this respect, much more 

 so than an average brown crepe, in fact, its behavior was almost 

 characteristic of an admixture of crude and reclaimed rubber. 



The light-colored sample showed scarcely any indication of 

 tackiness. This condition was somewhat more apparent in the 

 case of the pinkish sample, chiefly on account of some small 

 viscid globules on the surface of the rubber. 



The fourth sample, which was intended for hard rubber, re- 

 sembled a soft art-gum eraser in color and texture. -Mthough 

 the sample was somewhat spongy, it returned lo its original 

 shape rather slowly after compression. It was a iriflle sticky X.O 

 the touch, but by no means tacky. Black combs said to have 

 been made from this rubber had the characteristic black finish 

 and high gloss, which is observed in the highest grade of hard 

 rubber. 



Little is known as to the method of preparation of the samples. 

 It is reasonable to suppose, however, that they were produced at 

 the large dye works of Bayer, at Leverkusen. The method em- 

 ployed at this factory for synthetic rubber is to use acetone as a 

 raw material, and by means of aluminum to convert it into a 

 product known as pinacone. The pinacone is then converted into 

 methyl-butadiene, a substance bearing a very close chemical 

 relationship to is,oprene. This substance will be recognized as 

 having always been prominently mentioned in connection with 

 the synthesis of rubber. The methyl-butadiene is a thin liquid of 

 low boiling-point, and by the chemical process of polymerization, 

 is converted into synthetic rubber. According to Lieutenant- 

 Colonel J. F. Norris,' the polymerization process requires from 



LicHr Sv.vTHt 



Crepe For Soft Rubber Goods. 



thickness. Their color ranged from a reddish-orange, through a 

 pinkish-brown, to that of the characteristic dark-brown. In fact, 

 the last-named sample bore a striking resemblance to a thick 

 Iirown crepe. The sample of pinkish-brown color had very much 

 the appearance of w^ashcd Massai. The light sample was some- 

 what more reddish than first crepe, as we know it ; but otlierwisc 

 it was of excellent appearance. 



All of these rubbers possessed considerable toughness and elas- 

 ticity. The lightest and the darkest were apparently the strongest, 

 and after stretching resumed more equally their normal shape 

 and size. The pinkish sample had considerable strength, but was 



Medium Synthetic Crepe for Soft Rubber Goods 



idur lo six months. It is carried out al a temperature of 60 

 degrees C. The product thus obtained is technically referred to 

 as methyl rubber. 



The chemical analyses of the four samples were as follows : 



No. 1 .No. 2 No. i Xo 4 



Per Cent. Per Cent. Per Cent. Per Cent. 



Acetone extract 2.56 1.95 J.8> 1.59 



Mineral matter 0.02 0.15 0.09 09 



.N'itrogen 0.12 0.06 0.16 0.07 



The acetone extracts are all surprisingly low. They were of a 

 brownish color and of a hard resinous appearance. The nitrogen 

 values are interesting and without doubt signify the presence of 



'"Journal of Industrial Engineering Chemistry," Volume 11. page 81St 



