January 1, 1921 



THE INDIA RUBBER WORLD 



251 



What the Rubber Chemists Are Doing 



Acceleration of ViJcanization — IV 



A DISCONTINUITY IN THE EFFECT OF VULCANIZATION 



IN THE previous paper on the above subject* the results were 

 given of comparative experiments with aldehyde ammonia, m- 

 and /"-phenylenediamine, thiocarbanilide, and hexamethylene 

 tetramine. 



The present paper contains the results of further tests. The 

 method of procedure was the same as that adopted earUer, the 

 most important feature being the use of a heated bath of oil for 

 vulcanization of the samples, whereby the periods of vulcanization 

 are rendered more definite than with steam heating. 



Fig. 1 represents the progress of vul- 

 canization of the standard mixing (pale 

 crepe rubber 90, sulphur 10) with and 

 without the addition of 1 per cent and 

 0.4 per cent of a high-grade, light cal- 

 cined magnesia. Judging the rate of 

 vulcanization by the period required 

 for the attainment of maximum tensile 

 strength, the acceleration factor* for 

 the magnesium o.xide in question is ap- 

 proximately 3.3 and 2.5 respectively for 

 1 per cent and 0.4 per cent ; the pres- 

 ence of the finely dispersed particles of 

 undissolved magnesium oxide somewhat 

 affects the extensibility of the rubber, 

 and the acceleration factor assessed by 

 the periods required for the reduction 

 of the extensibility at 0.5-kilogram per 

 square millimeter to 650 per cent 

 possesses a slightly exalted value. 



In Fig. 2 is represented the effectiveness of 0.5 per cent of 



Pot.is.^iiiin bydroxiil*'. 



M.igne>iiim oxide. 



Tf'/nt of Curt //» U-r'aCc3 



ffAra o^ Ct""* .*9 



k. 1% -MsO ; 



the same concentration and is approximately equal to the factor 

 for the magnesia in the preceding experiment at twice the con- 

 centration. 



The insistence of supporters of the use of thiocarbanilide that 

 this substance needs the simultaneous presence of zinc oxide for 

 the development of its catalytic effect, was suggestive of the possi- 

 bility that the active substance might really be carbodiphenylimide, 

 C(:N.CoH5)j, produced from the thiocarbanilide, CS(.NH.C.H5)2, 

 by the desulphurizing effect of the zinc oxide, and which is 

 known to be remarkably active chemically. An experiment made 

 with a sample of carbodiphenylimide 

 prepared by the action of mercuric ox- 

 ide on thiocarbanilide in benzene solu- 

 tion revealed no marked catalytic ac- 

 tivity, but on account of the easy 

 polymerization of carbodiphenylimide 

 this evidence could not be regarded as 

 final, and it was considered necessary 

 to produce the carbodiphenylimide in 

 situ by the interaction of the thio- 

 carbanilide and mercuric oxide in the 

 rubber mixing. 



Parallel vulcanization experiments 

 were therefore made, using (a) the 

 standard mixing of rubber 90, sulphur 

 10; (b) the standard mixing with the 

 addition of 1 per cent of thiocarbanilide 

 and 3 per cent of yellow mercuric 

 oxide; and (c) the same mixture as in 

 (h) but without the thiocarbanilide. The results given in Fig. 3 

 show that mixture (b) possesses no' marked advantage in rate of 



B,0.4"„ MgO; C blank (S 

 Fig. 1. 



/inc (Aitlc and hcNamclliylcnctctiaraine. 



35 69 

 r/'/ne of Cure /r> Mmutc^. 



Morrrric u\idc And' tliiocart>ai>ilidc. 



Fig. 2. 



potassium hydroxide introduced as a solution in three times its 

 weight of glycerol.' The acceleration factor, judged by the tensile 

 strength method or by the period' for the production of extensi- 

 bility of 650 per cent, has a value between 3 and 4, which com- 

 pares very favorably with many popular organic accelerators at 



OJVMJO /Ci'> "^o« r;j re oElonk 



Fig. 3. 



vulcanization relative to (c), and that any advantage in rate of 



G BlanM, -i^B/.*/'/,, H M T 



Fig. 4. 



> D. F. Twiss and C. W. Howson, Journal of Society of Chemical In- 

 dustry, August 31, 1920, pages 287-289T. 



' Part I, D. F. Twiss and S. A. Brazier, Journal of the Society of 

 Chemical Industry, May 15, 1920, pages 125t-132t; abstract, The 

 India Rubber World. August 1, 1920, pages 730-732. 



• See Twiss, Journal of the Society of Chemical Industry, 1917, page 1185. 



