478 



THE INDIA RUBBER WORLD 



ISeptember 1, 1911. 



pounds of starch should yield about 7.91 ounces of rubber at a 

 cost of about 20 cents per pound. The company also obtains, tiy 

 splitting up raw Russian oil of turpentine, isoprcne to the extent 

 of a yield of 15 per cent., the isoprene can then be transformed 

 into rubber with a yield of 50 per cent. As a by-product there 

 is obtained a highly valuable refined oil of turpentine." 



BARSOWS' KEVIEW ON SYNTHETIC BtTBBER. 



In a paper which recently appeared in the Armour Engineer, 

 the general question of synthetic rubber has been discussed 

 in the form of an able review of the technical literature on the 

 subject, by Mr. Frank E. Barrows, formerly of the Class of 1910 

 at the .Armour Institute of Technology, and now an assistant 

 examiner at the United States Patent Office, Washington, 

 District of Columbia. 



WHAT IS SYNTHETIC RUBBER? 



Synthetic rubber had been defined by the India Rubber Journal, 

 in 1907, as "a substance built up by chemical means and 



possessing all the physical and chemical properties of the natural 

 rubber." Mr. Barrows considers it necessary to modify this 

 definition. While retaining in its exact form the reference to 

 physical properties, he proposes enlarging the scope of the other 

 reference, so as to include chemical properties, either identical 

 with or analogous to those of natural rubber. These require- 

 ments would seem to be met by the four hydro-carbons intimately 

 connected with the production of synthetic rubber — isoprene, 

 diisopropenyl, erythrene and piperylene — between all of which 

 there is a close relation, as shown by Mr. Barrows's detailed 

 references. It would, however, seem that by reason of the closer 

 attention which has been paid to it by chemists, isoprene has be- 

 come the most familiar of these, and the problems of its pro- 

 duction and utili^.ation have, therefore, been most prominent in 

 the technical literature on the subject. 



ISOPRENE KNOWN FIFTY YEARS AGO. 



It had long been known to chemists, through experiment, that 

 isoprene (itself one of the products of the destructive distilla- 

 tion of rubber), could, under suitable conditions, be again con- 

 verted into rubber by polymerization. As early as 1860, both 

 these processes were described by Greville Williams (Journal of 

 the Cheinicai Society, vol. xv., p. 110). In 1879, Bouchardet also 

 described the polymerization of isoprene, the properties recorded 

 seeming to identify this isoprene polymer with the parent material 

 of the isoprene itself — rubber. 



In view, apparently, of the high cost involved by the produc- 

 tion of isoprene through the distillation of rubber, attention was 

 given to other sources from which that agent could be obtained. 

 Thus, Professor Tilden, in 1882 and 1884, recorded experiments 

 in the depolymerization of turpentine and the decomposition of 

 turpentine vapors by heat. In 1885 Wallach. a German chemist, 

 found that after the exposure of isoprene to the light and upon 

 the addition of alcohol, a rubber-like mass was developed, which 

 hardened on exposure to the air. In 1892, apparently unaware of 

 Wallach's observations, Tilden specifically reported the sponta- 

 neous polymerization of isoprene, which had been obtained from 

 turpentine. 



Harries, Pickles, and others have since described the polym- 

 erization of isoprene, claiming that the trials made identified the 

 prfjdtict as the same in composition and properties as natural 

 rubber. Other extracts from the technical literature on the sub- 

 ject deal with further researches by Pickles, Lebedoff and Wechs- 

 ler; as well as those of Henrichsen, affecting the ozone process. 



SAME FORMULA FOR SYNTHETIC AND NATURAL RUBBER. 



As Mr. Barrows remarks: "It is natural that the term, 'syn- 

 thetic rubber,' should first suggest the product made from iso- 

 prcne . . It is known that the rubber from isoprene has 

 the same percentage, composition, and hence empirical formula, as 

 natural rubber (C,„H„). It should follow that the rubbers from 



erythrene, piperylene and diisopropenyl should also have the 

 same empirical formula as the hydro-carbons from which 

 derived." 



PATENT LITERATURE ON SYNTHETIC RUBBER. 



Turning from periodical to patent literature, Mr. Barrows 

 (juotcs the priniipal features of the following patents referring to 

 synthetic rubber : 



(a) British patent to St. George, No. 15,544, of 1892; conden- 

 sation of turpentine by means of hydro-chloric acid. 



(b) Heinemann patents, British, No. 21,772, of 1907, and 

 French, No. 394,795; condensation of isoprene to caoutchouc by 

 concentrated hydro-chloric acid. 



(f) French patent. No. 417,170, to Badische Amlin and Soda 

 Fabrik ; the caoutchouc being separated by precipitation with al- 

 cohol, or by steam distillation of the unchanged isoprene. 



(rf) The polymerisation of diisopropenyl, described in British 

 patent No. 14,281, of 1910, and French patent No. 417,768, of 

 1911, to the Badische Anilin and Soda Fabrik. 



(f) The polymerisation of erythrene, according to the British 

 patent No. 15,254, of 1909, to the Farben Fabriken, of Elberfeld, 

 is also specially mentioned by Mr. Barrows, who remarks that 

 erythrene is the mother substance of both isoprene and diisopro- 

 penyl (two of the four hydro-carbons named). 



Such are the salient parts of Mr. Barrows' review of the syn- 

 thetic rubber question, as reflected in the technical literature on 

 the subject. This review is not offered as a final solution, but 

 for the purpose of making clearer the various issues under dis- 

 cussion. 



A I'R.\CTICAL MANUFACTURER ON SYNTHETIC RUBBER. 



In a recent issue of "Kunststoffe," Dr. Gerlach, of the Continen- 

 tal Caoutchouc and Gutta-Percha Company, Hannover, Germany, 

 makes the following statement : 



"The problem of producing caoutchouc synthetically has been 

 solved. But just as in the case of indigo, twenty years lapsed 

 before the synthetic product was successfully launched, it will 

 take perhaps longer with caoutchouc because the physical prop- 

 erties of this material are not as well known as those of indigo. 

 The high price of the natural product, stimulated research, and 

 after the pioneering experiments of Harries, the Elberfeld Far- 

 benfabriken have finally succeeded in producing larger quanti- 

 ties of a product derived from a material closely related to iso- 

 prene. At this stage of the development it was found out that 

 there exist many sorts of rubber which are near relatives, but 

 still possess different characteristics. 



"The first synthetic caoutchouc which was placed at my dis-* 

 posal, for example, did not unite with sulphur and had a 

 leathery appearance. This was not to be wondered at, as 

 there are known some varieties of natural caoutchouc which 

 cannot be vulcanized. Soon another sort of rubber came to my 

 notice which showed better affinity for sulphur, but still could 

 not be perfectly vulcanized. Above all, it lacked elasticity. Soon, 

 however, larger quantities of a third sort were submitted to me 

 which, to my great astonishment, showed all the excellent 

 properties of natural rubber. 



"But now the question arises whether this material of the 

 Elberfelden can be economically produced on a large scale and 

 may thus become a danger for natural rubber. It cannot be 

 denied that the substance, which possesses good qualities, can be 

 utilized for practical purposes. Its price is not high, but it is a 

 complex question to decide whether this synthetical product 

 will become a danger to natural rubber. All kinds of economi- 

 cal and commercial conditions must be taken into considera- 

 tion. One thing, however, is certain, that synthetic rubber will 

 soon be a comnrercial article." 



The accepted authority on South American rubber — "The 

 Rubber Country of the Amazon," by Henry C. Pearson. 



