496 



THE INDIA RUBBER WORLD 



[May 1, 1920. 



SUMUABY. 



1. Extraction for eight hours with acetone followed by four 

 hours' extraction with chloroform does not remove all soluble 

 material from some rubber compounds. 



2. .\fter a rubber sample has been extracted with acetone it 

 was found that : 



(a) Chloroform in every case extracted slightly more ma- 

 terial than carbon bisulphide. 



(b) Constant boiling mixtures such as 55 per cent carbon 

 bisulphide — 45 per cent acetone and 68 per cent chloroform— 32 

 per cent acetone extracted from many cheap compounds consid- 

 erably more material than either chloroform or carbon bisulphide. 



3. The constant boiling mixture of 68 per cent chloroform 

 and 32 per cent acetone exhibits a marked ability to dissolve 

 vulcanized rubber, as contrasted to the mixture of 55 per cent 

 carbon bisulphide 45 per cent acetone which hardly exhibits this 

 ability at all. 



4. It is recommended that the constant boiling mixture 55 

 per cent carbon bisulphide and 45 per cent acetone be used in 

 place of acetone and chloroform to extract rubber samples since : 



(A) It eliminates one extraction with the necessary weigh- 

 ings. 



(B) Extraction is complete in eight hours, while the ace- 

 tone and chlorofoim extractions require a total of twelve hours. 



(C) The extraction of free sulphur is complete. 



(D) A rubber analysis in which the mixed solvent is used 

 is more accurate than that in which acetone and chloroform are 

 used separately because : 



I. Little or no rubber is dissolved by this mixture, as com. 

 pared with chloroform which will in some cases dissolve con- 

 siderable quantities. 



II. The extraction of cheap rubber compounds is more 

 nearly complete, since the extracts obtained are greater than 

 the sum of the acetone and chloroform extracts. 



SYNTHETIC RUBBER OF GERMAN MANUFACTURE. 



.\ nimiber of different types of synthetic rubber have been 

 prepared, all of them by the gradual polymerization of butadiene, 

 mono-methyl butadiene (isoprene), or di-methyl butadiene 

 (methyl isoprene). Each of these three original substances 

 yields a different type of synthetic rubber of different compo- 

 sition and properties. Only that obtained from mono-methyl 

 butadiene or isoprene is supposed to give a product of the iden- 

 tical composition of natural rubber, but even this is very doubt- 

 ful. -Ml the products have properties in some way resembling 

 rubber, but that obtained from di-methyl butadiene, yielding the 

 so-called methyl rubber, was found by the Germans to be the 

 most useful as a substitute for natural rubber, particularly for 

 the manufacture of vulcanite plates for accumulator cells, be- 

 lieved to have been used in large numbers for U-boat eqiupment. 



In many ways these synthetic rubbers behave like a partly 

 vulcanized rubber. Probably oxidation sets in during prepara- 

 tion, and this would be sufficient to account for the semi-vul- 

 canized condition. Thus raw rubber, when mixed with power- 

 ful oxidizing agents such as "benzoyl peroxide" and heated, 

 yields a product resembling vulcanized rubber. For this reason 

 the specimens do not dissolve in benzene, cannot be rendered 

 properly plastic on the hot rolls without the addition of aids 

 to plasticity, and vulcanize badly It is also knovsm that syn- 

 thetic rubber tends to oxidize in the air, and that to obtain 

 satisfactory vulcanized products, it is necessary to use relatively 

 large quantities of powerful accelerators. 



There appears to be no doubt that Germany used large quan- 

 tities of synthetic rubber, particularly this methyl rubber, during 

 the war, but the product cannot compete with natural rubber 

 either in quality or price under normal conditions. ("The Bul- 

 letin of the Rubber Growers' Association," London, Volume 1, 

 No. 3. November, 1919.) 



CUMAR RESIN. 



Cumar, a synthetic resin produced from coal-tar distillates, is 

 gaining recognition in the rubber industry as a valuable com- 

 pounding ingredient. Chemically it is a mixture of para-couma- 

 rone, para-indene and the polymers of other hydrocarbons found 

 in coal-tar. In appearance cumar resembles ordinary resin, but 

 Its properties are radically different. It is uniform in quality, 

 neutral, non-saponifying and non-oxidizing. It is not affected by 

 water, acids, alkalies or salts. Exposure to the air or weather 

 will not change it. 



Cumar is soluble in all coal-tar solvents, turpentine, vegetable 

 oils, carbon bisulphide, carbon tetrachloride, ether, acetone and 

 most commercial solvents. It is insoluble in alcohol. Its spe- 

 cific gravity is 1.05-1.15. Nine different grades are available, 

 classified according to melting point, ranging from 50-60 to 145- 

 160 degrees C. and in color from clear light yellow to dark 

 imber, gaged by definite color standards. 



The softer grades, melting at 50-60 and 60-70 degrees C, are 

 good solvent? for rubber and are useful for softening the gum 

 in the breaking-down operation. The hard grades, melting at 

 90-100 degrees C, is used extensively as a substitute for Pontianak 

 and similar resins in rubber compounding. Cumar mills readily 

 into the rubber on the rolls and adds tackiness and plasticity to 

 the unvulcanized stock. It is of value also in the manufacture 

 if rubber cements and reclaimed rubber. 



VARIABILITY OF CURE OF SLAB RUBBER. 



Researches of Dr. H. P. Stevens on the variability of cure of 

 slab rubber show results which negative the conclusions of the 

 agricultural chemist of the Federated Malay States as to the 

 "remarkable uniformity" of slab rubber. 



Slab rubber has a repulsive appearance, especially on arrival 

 at destination. The surface is dark and slimy from the exuda- 

 tion of serum. It is usually moldy, and the smell is very of- 

 fensive. The slab can be washed and creped on the plantation 

 with a relatively small loss in the rate of cure. The rubber in 

 this form is much more presentable, but the color is dull and 

 tlie rubber frequently streaked. Experiments on a manufacturing 

 scale have resulted in the production of crepe from matured 

 coagulum of a uniform pale shade. The color was less bright 

 than that of ordinary crepe but sufficiently good to pass as 

 standard crepe. Of three sample cases of crepe tested, the first 

 cured 34 per cent faster than that prepared ordinarily, two other 

 cases cured 67 and 57 per cent faster, respectively. Hence, al- 

 though all sample cases contained more rapidly curing rubber 

 and were prepared in the same manner, the rate of cure showed 

 appreciable variation. 



SYNTHETIC ACETIC ACID AS A LATEX COAGULANT. 



Synthetic acetic acid produced from calcium carbide is not 

 of the purity of that obtained from pyroligneous acid, as the 

 synthetic acid is brown in color and has a distinct odor. It is, 

 however, free from copper and suitable for latex coagulation, 

 as the amounts or brown coloring matter in the acid are not 

 sufficient to affect the color of the finished rubber. 



Experimental data show that synthetic acid coagulated speci- 

 mens of both crepe and smoked sheet are practically identical 

 with the corresponding samples coagulated with ordinary acetic 

 acid. ("The Bulletin of the Rubber Growers' .Association." Lon- 

 don, Volume 2, No. 1, January, 1920.) 



LEAD OLEATE. 



.'\ preparation of lead oleate is now on the market for use as 

 a mild accelerator of vulcanization. It is marketed as an 

 oleaginous mass of wax-like consistency, fracture, and melting 

 point. It is non-poisonous, and gives off no fumes. It has no 

 tendency to cause scorching in mixing or calendering. It may 

 be used in conjunction with aniline or hexamethylene tetramine 

 but should not be used with thiocarbanilide. 



