80 



THE INDIA RUBBER WORLD 



(November 1, 1918. 



and sulphurous acid art gases ; they therefore obey the laws of 

 Graham and diffuse through the mass of caoutchouc with a 

 rapidity which is inversely proportional to the square root of 

 their densities. 



The reaction of formation oi the colloidal sulphur, which re- 

 sults from their reciprocal action, is produced not on the sur- 

 face but in the whole mass of the caoutchouc. Now, the ad- 

 sorption, first phase of the vulcanization, is the more rapid the 

 better the sulphur is mixed in the mass. We can easily under- 

 stand that, under conditions similar to those which we have de- 

 scribed, the adsorption would take place very rapidly and an 



acceleration of vulcanization would lake place as a result. 



As has been shown by these summary notes, the presence of 

 resins in virgin caoutchouc results in rendering easier and more 

 rapid the formation of adsorbable colloidal sulphur, the for- 

 mation of which is very slow under the influence of heat alone. 



The resins accelerate vulcanization, as litharge does ; it trans- 

 forms polymeric sulphur into sulphurous acid, they transform 

 it into sulphydric acid, difTusable gases which, reacting one on 

 [he other in the interior of the mass of gum, produce adsorbable 

 colloidal sulphur, the only sulphur that can vulcanize caoutchouc. 

 (To be continued.) 



What the Rubber Chemists Are Doln^. 



DEVULCANIZATION OF CAOUTCHOUC BY HEXAMETHYLINE 

 TETRAMINE. 



AN' interesting e-\perimental demonstration of the devulcaniza- 

 tion of caoutchouc by formation of hexamethyline tetramine 

 in the gum is described by Andre Dubosc in "La Caout- 

 chouc et la Gutta-Percha," August 15, 1918, of which the fol- 

 lowing is an abstract. 



Previous experiments have shown that hexamethyline tetramine 

 is capable, under proper conditions of quantity and pressure, of 

 removing sulphur chemically combined with caoutchouc. 



In the present demonstration advantage was taken of the fact 

 that caoutchouc is easily penetrated by gases. 



A sample of vulcanized caoutchouc was reduced to 100 mesh 

 and by \)rolonged acetone extraction all free sulphur was re- 

 moved; extracted with cold ammonium sulphide and thoroughly 

 washed; extracted with chloroform and with alcoholic potash 

 followed by washing with 95 per cent alcohol so as to remove 

 all factices which contain combined sulphur. The sample thus 

 prepared being successively treated alternately with ammonia 

 gas and formaldehyde gas, the formation f^rst of trimethyline 

 triamine was effected with liberation of water vapor and heat. 

 This body having been formed, the caoutchouc was made to 

 absorb a fresh quantity of ammonia to the point of satura- 

 tion, followed by absorption of more formaldehyde gas. Pen- 

 tamethyline tetramine was thus formed, also a certain quantity of 

 water vapor and rise of temperature resulted. Then ammonia 

 gas was again absorbed in excess followed by formaldehyde. 

 The combination between the two gases and the pentamethyline 

 tetn^tnine produced by the preceding reaction took place almost 

 immediately with evolution of heat, and hexamethyline tetramme 

 was formed. The caoutchouc noticeably increased in volume. 

 and gained practically 12.75 per cent in weight. 



Tlie rubber was next subjected in an autoclave for six hours 

 to steam pressure at seven atmospheres. Following this the 

 rubber was washed and sheeted until perchloride of iron gave no 

 reaction of sulphocyanic acid. On a sample dried at 100 degrees 

 C. the combined sulphur was determined by the Henriques-Ber- 

 trand method. Before treatment the rubber showed 2.723 per 

 cent combined sulphur ; after treatment, 2.478 per cent, or a loss 

 of 92.104 per cent of the combined sulphur. 



VULCANIZATION RESEARCHES. 



Vulcanization experiments, carried out during the last quarter 

 of 1917 in the Department of Agriculture, Federated Malay 

 States, as reported by B. J. Eaton, resulted as follows : 



The retardation of vulcanization caused by an excess of acetic 

 acid in the case of slab is comparable with the results obtained 

 with crepe, namely, very little. , , , 



Sodium bisulphite slightly retards the rate of cure of both 

 crepe and slab. The use of sodium bisulphate in slab is to obtain 

 a pale-colored, rapidly curing rubber, superior in tensile prop- 

 erties to ordinary pale crepe. This cannot be effected by allowing 

 the coagulum to mature in the open, since darkening occurs, 



probably on account of the large amount of oxidizable substances 

 and the greater amount of oxidizing enzyme remaining in the .slab. 



Since the researches carried out by tlie writer have shown the 

 presence of vulcanization accelerators to be actually present in 

 late.x and retained in the raw rubber under certain conditions of 

 preparation, in addition to those formed by the decomposition of 

 the proteins in the maturation of slab and rolled up wet sheet, 

 etc., it was considered advisable to ascertain whether these 

 accelerators were removed to any extent when the matured slab 

 was subsequently creped and dried. Experiments were there- 

 fore carried out in which the matured slab was cut up into 

 thin worms and air-dried and subsequently mixed directly with 

 sulphur for vulcanization. Comparative samples of matured 

 slab were converted to crepe and dried. 



Little or no difference was obtained between the rate of cure 

 of the slab cut into worms and dried and that converted into 

 crepe, which shows that little or none of the vulcanizing accel- 

 erators is removed by the normal washing and creping of the 

 matured slab. In fact, the creped slab in each series of the ex- 

 periment vulcanized slightly more rapidly than the "wormed" 

 slab. It was observed that a certain development of "spot" dis- 

 ease occurred invariably in the "wormed" slab (after worming), 

 due to the exposure to the air combined with the slow drying of 

 the worms, and this may have been responsible for the slightly 

 retarded cure, since the writer has shown previously that the 

 organisrns causing "spot" disease retard the rate of cure of a 

 fast-curing rubber. 



The rates of cure of 16 specimens of sheet, known to have 

 been prepared by coagulation of the latex with alum, varied from 

 one and three-quarters to four and a half hours, which gives a 

 very good idea of the lack of uniformity of such rubber. 



COAGULATION WITHOUT CHEMICALS. 



In a recent lecture delivered before the Malang Agricultural 

 Society, reported in "De Indische Mercuur," G. J. ZuyderhofT 

 discussed a half dozen principal methods employed for the 

 coagulation of rubber latex, namely; (1) the wild Para method, 

 its imitation methods by (2) D. MacGillavry, (3) Sanders 

 Birnie, (4) Wickham, (5) Lash van Goenoeng Toengal, and (6) 

 Clignett's electrical method. The author considers that none of 

 these methods of coagulation are entirely satisfactory and has 

 devised a new method without the use of chemicals. His reasons 

 as stated for undertaking this work were : the high price of 

 acetic acid; the possibility of increasing the intrinsic value of 

 the rubber product, and the preservation of occluded serum 

 in the coagulum and its putrefaction into products of value 

 affecting the rate of cure and physical properties along the line 

 of research developed by Eaton and Grantham. 



ZuyderhofT's method as quoted from his lecture is as follows: 



The latex is heated in an enameled coagulating basin over a 

 charcoal fire until full evaporation has taken place. The cakes 

 thus produced are put into a long wooden case and air is blown 

 in over them. They are alternately submitted to heat and dry 

 -.old and then the mass is tested in the open air. 



With a heating appliance placed beneath the wooden case the 

 best results were obtained by (1) heating very moderately under- 

 neath and blowing dry air above the cakes, (2) by simply 

 sending heated air over the cakes. 



