252 



THE INDIA RUBBER WORLD 



January 1, 1921 



YiiUanization imparted to a mixing by the introduction of tliio- 

 carbanilide cannot be ascribed to the formation of carbodiphenyl- 

 imide. It is noteworthy, however, that the curves for mixing (r) 

 indicate marked catalytic power on the part of the mercuric oxide, 

 which, indeed, might have been expected from the basic character 

 of thi« substance. 



Reference to the previous paper' reveals the remarkable fact 

 that, although the mixing containing the organic catalyst, together 

 with zinc oxide, vulcanizes much more rapidly than the blank 

 mixing, the slope of the extensihihty or elongation curve in the 

 lower part of the diagrams, instead of being steeper, fends to be 

 more gradual. Closer examination of the behavior of mixtures of 

 this composition reveals the fact that the extensibility curve in 

 question undergoes a remarkable change of direction at an early 

 stage of the vulcanization process. A similar phenomenon is ob- 

 servable with a rubber-sulphur mixing containing as accelerator 

 a mixture of triphenylguanidine and zinc oxide. The results are 

 reproduced in Figs. 4 and 5. In both cases the extensibility at 

 first decreases very rapidly with increasing vulcanization, but 

 finally assumes a much more gradual rate of change. 



The presence of zinc oxide appears to be favorable, if not con- 

 ditional, to the occurrence of the inflexion in the extensibility 

 curve within the usual range of vulcanization. From the results 



Jdchydc-.TmmODia .tnj zinc ONidc. 



TriphcDjigiianidiiiC .-ind zinc o\idc. 



C) I % T P c 



Curves show rates ot cure as indi- 

 rated by (A) tensile strength, (B) 

 clongattoo. 



Fig. 6. 



^'/i'A f^f'. ■(p-y^ys.AA.-riy.zno. 

 Fig. &'. 



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

 ieal Industry, M,iy 15, 1920, pag<t 125t132t; abstract, The India Rubber 

 Wow-D, .\ugust 1. 1920, pages 730 732. 



• The effect, which is observable over only a small range of concentra- 

 tion, is probably to be attributed to the physical nature of the line oxide 

 as an exceedingly fine powder rather than to its chemical nature ; 1 per 

 cent of carbon black (gas black or lampblack) introduces a similar 

 irregularity. 



mine-zinc oxide mixing it is found that, in at least this case, the 

 curve in reality undergoes a double inflexion within a short in- 

 terval of time, Figs. 7 and 8.* This surprising result has been 



ncxaiiiethy.'cnctctraniiae'aDd iloc oxide. 



'<J\ TeTi plsa'C 





I © — CO 



I'/.H M T • I >. Z « O 



8V 



\ 



Tirtf* «/ Cur» m Mi^tutei 



g *0 ^O 60 lOO '»o 



T.mr of Cure m M,nu(c% 



\ V 



*90 too t*o 3*o j«< 



taO 20K J30 2^o ^Cc 



Curves show rates of cure as Indicated by (a) tensile strength, (b) 

 ei'->ngatron, (c) vulcanisation coelflcient. 



Fig. 7. 



confirmed by repeated reinvestigation with different mixings of 

 the same composition vulcanized at the same and different tem- 

 peratures. The results also indicate some concomitant discon- 



He\aniethylfne(ctramine .Tud zinc oxide. 



given in the previous paper it is evident that no indication of such 

 inflexion exists in the extensibility curves for the mixings, contain- 

 ing aldehyde ammonia. When the aldehyde ammonia is used in 

 conjunction with zinc oxide, however, an inflected extensibility 

 curve is obtained, as is demonstrated by the results in Fig. 6. 

 No such inflexion appears to occur in the progressive vulcaniza- 

 tion of the standard rubber-sulphur mixing with the addition of 

 thiocarbanilide and zinc oxide. It is possible, however, that when 

 the bend appears to be absent the extensibility curve undergoes 

 a change of direction at a stage of vulcanization beyond the range 

 of convenient testing. 



By concentrating the number of tests around the point of in- 

 flexion of the extensibility curve for the hexamethylene tetra- 



l%U.^ T' IV.ZnO Temp 118° C 



Curves show r.'vtcs of cure as Indicated by (a) ttireite strength, 

 IB) elongntloii. 



Fig. 9. 



tinuity in the tensile strength and combineti sulphur curves, but 

 the actual outline of the tensile strength curves in Figs. 7 and 8 

 is given with a certain amount of reserve on account of the 

 somewhat greater variability in the values obtainable. It is note- 



