THE INDIA RUBBER WORLD 



[August 1, 1920. 



iesses comparable values for mixings with and without an arti- 

 ficial catalyst, appears from other results in our possession to be 

 a general one for all catalysts. This facilitates the representation 

 of the relative effectiveness of different catalysts by means of a 

 numerical factor. A factor representing the ratio of the respec- 

 tive periods cf vulcanization required for the attainment of a 

 definite state of vulcanization in a rubber-sulphur mixing, with 

 and without a definite proportion of accelerator, will be inde- 

 pendent of the temperature; it will be essential that this com- 

 parison be made at a stage of the vulcanization process when the 

 mixture still contains a considerable proportion of uncombined 

 sulphur. The resulting "acceleration factor" may differ accord- 

 ing to which of the three possible criteria — percentage of com- 

 bined sulphur, maximum tensile strength and extensibility at defi- 

 nite load — is taken as fixing a definite state of vulcanization. In 

 the case of the accelerator used in the experiments now quoted, 

 the behavior may be described as normal, all three methods giv- 

 ing comparable results. The efifectiveness calculated in this way 

 for the accelerator at various concentrations and at different tem- 

 peratures is given in the following table ; the figures in each case 

 represent the mean of the values obtained by the three different 

 methods for the comparison of rate of vulcanization. 



Stated otherwise, the presence of %, J4, V2 and 1 per cent, 

 respectively, of the accelerator increases the rate of vulcanization 

 at any ordinary vulcanizing temperature to 1.7, 3, 5 and IVz times 

 the normal. 



ACCELERATION FACTOE. 

 Percentage ^s ,'4 J^ 1 



Temperature C. 



118-J28 degrees 1." 2.8 5.1 7.5 



128-138 ■• 1.7 3.0 5.4 7.6 



138-148 " 1.7 3.0 4.8 7.1 



A graphic representation of this result as to the relation be- 

 tween the proportion of the accelerator in question and the 

 effect produced is given in Figure 3. The slight divergency from 

 the course of the smooth curve of the points for the lower per- 

 centages is doubtless due to the relatively greater effect of the 

 inevitable small loss of accelerator by vaporization during the 

 mixing operation. 



Comparison of the relative effectiveness of isomeric substances, 

 namely m- and /'-phenylenediamine as accelerators shows that 

 the meta-compound is notably less active than its para-isomeride. 

 It is of interest to note that the effectiveness of these two sub- 

 stances towards vulcanization falls in the same order as their 

 affinity constants as determined by Bredig in 1894. The low- 

 value of the coefficient of vulcanization at the maximum tensile 

 strength of the /i-phenylenediamine will also be noticed. 



The "acceleration factor" for »i-phenylenediamine, calculated 

 from the results in Fig. 3, has a mean value of approximately 1.5 ; 

 for /i-phenylenediamine judged by the physical methods the factor 

 is approximately i.i, whereas the rate of combination with sul- 

 phur indicates a value of only 3.0. 



HIXED CATALYSIS. 



The effectiveness of a mixture of catalysts in an ordinary chemi- 

 cal reaction is 'well known not to coincide invariably with the 

 sum of the effects produced by each independently. This pecu- 

 liarity is also observable with vulcanization catalysts." Lead 

 oxide with magnesium oxide, and />-nitrosodimethylaniline with 

 aniline or one of its homologs, are cases which have already 

 been quoted in the literature. A related phenomenon probably is 

 also the power of zinc oxide, which alone does not accelerate 

 vulcanization, to increase considerably the effectiveness of other 

 organic catalysts such as hexamethylenetetramine and thiocar- 

 banilide. As the latter by itself is practically inert, we have the 

 interesting case of a mixture of two inactive substances exerting 

 a distinct accelerating effect. In other cases we have found two 

 vulcanization catalysts to be "incompatible" in the sense that the 

 effectiveness of the more active catalyst is actually decreased by 

 the presence of the other. 



As has been intimated already, no acceptable general explanation 

 is yet possible as to the mode of action of vulcanization catalysts. 

 In addition to the theories already mentioned, others have also 

 been proposed. An observation of considerable interest in this 

 connection is that rubber in solution or wetted with benzene be- 

 comes vulcanized by successive treatment with sulphur dioxide 

 and hydrogen sulphide at the ordinary temperature." This reac- 

 tion appears to be very suggestive in connection with the action 

 of vulcanization catalysts. None of the three modifications, S^, 

 S*', and SJf present in liquid sulphur appears to be in possession 

 of exceptional chemical activity towards rubber (see above), but 

 there is evidently a possibility that there is capable of existence 

 yet another form of sulphur of much greater vulcanizing power. 

 Such a view, needing considerable modification however, has al- 

 ready been tendered" but the scope for investigation in this direc- 

 tion is enormous ; indeed, the evidence available as yet is insuffi- 

 cient even to exclude the possibility that vulcanization accelerators 

 may activate the rubber and not the sulphur. 



CHEMICAL PATENTS. 



UNITED STATES. 



METHOD OF COLORING riBROus M.\TERi.-\L. — The process of color- 

 ing and rubberizing fibrous material, which comprises dip- 

 ping the material into a solution of potassium antimonyl tartrate 

 and a solution of a sulphide of ammonium, whereby antimony 

 sulphide is formed directly in or upon the fibers of said material, 

 and coating the material with a vulcanizable plastic compound. 

 (Willis A. Gibbons, Flushing, New York, assignor to American 

 Rubber Co., Boston, Massachusetts. United States patent No. 

 1,332,982.) 



Artificial Rubber. — An elastic composition comprising gly- 

 cerin, two and one-fourth pounds ; glue, five and five-eighths 

 pounds ; water, nine pounds ; tannic acid, two and one-fourth 

 ounces; and a solution of formaldehyde, four ounces. (Ernest E. 

 Cathcart, Tecumseh, Nebraska. United States patent No. 1,335,- 

 657.) 



Process for Vulcanizing Rubber and Product Obtained 

 Thereby. — A process for treating rubber or similar material 

 which comprises adding thereto a dye, a vulcanizing agent nor- 

 mally tending to injure the coloring material under vulcanizing 

 conditions and an agent itself having no injurious effect upon 

 the coloring material and adapted to prevent injury by said 

 vulcanizing material and inducing vulcanization to take place. 

 (I wan Ostromislensky, Petrograd. Russia, assignor, by mesne 

 assignments, to New York Belting & Packing Co., New York. 

 United States patent No. 1,342,457.) 



Process for Vulcanizing Rubber and Product Obtained 

 Thereby. — A process for treating rubber or similar material, 

 which comprises subjecting the rubber to the action of sulphur 

 and an organic vulcanizing agent containing oxygen and induc- 

 ing vulcanization to take place under the action thereof. (Iwan 

 Ostromislensky, Petrograd, Russia, assignor, by mesne assign- 

 ments, to New York Belting & Packing Co., New York. United 

 States patent No. 1,342,458.) 



Rubber Vulcanization and the Product. — 'The process of ac- 

 celerating the vulcanization of rubber, which consists in vulcaniz- 

 ing the rubber in the presence of a compound of the amine bases 

 produced from beet sugar residue combined with carbon disul- 

 phide. (Stuart Benton Molony, Wellesley Hills, Mass., as- 

 signor to Michigan Chemical Co., Michigan. United States 

 patent No. 1,343,224.) 



fDitmar, "CHmmi-ZfitKBg," 1915, 29, 424. 



"Peachey, "Journal of the Society of Chemical fndustry," 1919, 688a. 



•■Dubasc. The India Rubber World, 1918. November I, 78; 1919. Feb- 



