248 



THE INDIA RUBBER WORLD 



[Fff 



Application of Catalysis to Vulcanization.' 



specially Contributed by Andre Dubosc. 



THE part played by sulphydric acid, produced by the action 

 of resins during vulcanization, having been explained, 

 let us see what can be the part played by sulphocyanic 

 acid (CNjHS) which is formed by the action of the proteins, 

 of the glucosamine on the polymeric sulphur at the temperature 

 of vulcanization. 



The part it plays is ver>' simple, it is that of a condensator 

 which determines the polymerization and therefore the increase 

 of resistance to breaking of the caoutchouc. 

 — S— 

 The sulphocyanic acid, C_j^_^_ ^^^ {q^^ f^ee valences. 



It is therefore susceptible of saturating two double combi- 

 '.ations belonging to two dierent 



cHi 



CHr 



CHJ. 



CtJ^ 



CH, 



^^Uib^ 



Condensation of Two Molecules. 



molecules of caouthouc 

 molecules, the other 

 double combinations of 

 which have been satu- 

 rated by colloidal- 

 sulphur. 



We can therefore ap- 

 preciate the justice of 

 '''^^ the observations of Lock 

 and Bamber, who de- 

 clared that the purer a 

 gum is, the freer it is 

 from proteins, the less 

 (after vulcanization) is 

 its resistance to rupture 

 and, therefore, its poly- 

 merization. Nature has therefore placed in the gum the elements 

 necessary to its vulcanization and its polymerization, the resins 

 which act as accelerators, the proteins which, in the presence of 

 sulphur, form a condensator which determines the polymeriza- 

 tion. Can we reproduce at will, synthetically, by the aid of 

 simpler and more energetic products than the natural proteins 

 and resins, these conditions which analysis has revealed to us? 

 We cannot doubt it, for we know a certain number of nitro- 

 genous substances, which, when heated with sulphur and carbon, 

 are capable of producing abundantly sulphydric acid and sulpho- 

 cyanic acid. These reactions of formation are produced, for ex- 

 ample, in the distillation of coal which contains nitrogen, sul- 

 phur and carbon. 



This does not mean that coal can act in caoutchouc during 

 vulcanization, the same as proteins and resins act, for the simple 

 reason that the reactions which we have described take place 

 in the case of coal only at temperatures at which the gum 

 would be entirely destroyed. 



A substance cannot act as catalyzer during vulcanization, 

 substituting itself for the useful substances which the natural 

 gum contains, and producing effects which are similar, but more 

 rapid, more complete and extensive, unless it rigorously fulfils 

 certain conditions. 



It must contain, in proper proportions, the quantities of car- 

 bon, hydrogen, oxygen and nitrogen necessary to produce the 

 compounds reacting in the vulcanization, that is to say, the 

 sulphydric, sulphurous and sulphocyanic acids. It must be dis- 

 sociated at the temperature of vulcanization, 135 to 145 degrees 

 C, so that, in the presence of sulphur, the hydrogen, oxygen, 

 nitrogen or the cyanhydric acid necessary to the formation 

 of the bodies named, may be set free. It must, therefore, meet 

 both chemical and thermo-chemical requirements. 



^Continued from The India Rubber World, November 1, 1918, page 80. 



Further, the accessory products of the dissociation must have 

 no bad effect on the caoutchouc during the curing, must not 

 produce a disagreeable, persistent odor, and must cause no 

 change in the final product. 



Considering the varied results expected from these substances, 

 we can already see that, from the point of view of classification, 

 we must attribute two principal functions to them: (1) a 

 function of acceleration which, in the presence of sulphur, at 

 a proper temperature, will enable them to form sulphydric acid 

 and sulphurous acid ; (2) a function of vitaHzation which, in the 

 presence of sulphur, at the temperature of vulcanization, en- 

 ables them to form a condensator, the sulphocyanic acid, capa- 

 ble of producing the polymerization of the gum. 



.\ complete catalyzer must be at one and the same time: (1) 

 a sulphydric accelerator, (2) a sulphurous accelerator, (3) a 

 sulphocyanic condensator. 



Certain substances have two functions and three character- 

 istics, others have one function and two characteristics, while 

 others have two functions and two characteristics. Some have 

 only the function of sulphydric accelerators; they are the com- 

 pounds which in dissociating at 135 degrees C. furnish hydrogen 

 or acetylene, substances which, in the presence of sulphur, pro- 

 duce in their turn sulphydric acid. This is the case of the 

 resins and of a good many of the bases of the fat series. These 

 catalyzers are of only very little interest. 



Others have the function of sulphurous accelerators, such as 

 the metallic oxides, as litharge, and the part they play is so 

 well known as to render further explanation unnecessary. 

 There are others which have the full accelerating function; 

 they are sulphydric accelerators as well as sulphurous acceler- 

 ators, such as the easily decomposable organic hydroxide com- 

 pounds which, in the presence of sulphur, give sulphurous acid 

 and sulphydric acid. 



(R.OH),+2S=2R-f-SO,-|-H,S 



This is the case with certain alcohols and of most phenols. 

 Certain members of the terpene series, such as camphor, behave 

 in the same way and have two accelerating qualities. Other 

 compounds possess only the vitalizing function and can pro- 

 duce only sulphocyanic acid, for example, cyanhydric acid and 

 most of the cyanides; they yield their maximum effect only in 

 the presence of other compounds, such as sulphide of carbon, 

 which brings them a complement of carbonated elements. 



Finally certain substances, which are complete catalyzers, 

 have both functions and are at the same time sulphydric and 

 sulphurous accelerators and vitalizers ; such are the dinitrated 

 derivatives of the amines as paranitroso dimethylaniline. 



Besides these different catalyzers, we must mention a class 

 perhaps even more interesting, that of the nitrogenous thio- 

 compounds which can, besides acting as complete catalyzers, 

 furnish in a collodial state all the sulphur necessary for vul- 

 canization. Such, for example, is thio-carbanilide. 



It can be seen that, from the chemical point of view, the 

 number of compounds that can facilitate, hasten and improve 

 vulcanization, is considerable. Thermochemical reasons, based 

 on the necessity of their dissociation, show that the most in- 

 teresting ones are those whose dissociation constants are greater 

 than 1 x 10». 



Those which meet this last requirement are still rather nu- 

 merous and we have been able to test the results of about a 

 hundred of them. Bearing in mind the divisions which we have 



