Formation of Compounding Ingredients in Rubber

Abstract

Abstract In 1923, dealing with compounding ingredients for rubber, one of the authors, with particular reference to compounding rubber with carbon black, commented on the attractiveness of the possibility of producing a compounding ingredient immediately inside the rubber colloid medium, to assure its formation in a state of uniform and intimate distribution with reinforcing effect, and with incidental avoidance of the economic and technical disadvantages attendant on mechanical mixing. Numerous experiments, however, with this aim, have given disappointing results. For instance, all attempts to produce amorphous carbon by means of chemical reaction in a rubber medium have been frustrated, either by the special conditions, so that the expected reaction proceeded in an unexpected and undesired direction, or by the carbon separating outside the rubber medium provided for it. A number of endeavors with the same aim, i.e., the improved compounding of rubber, but based on other possible compounding ingredients, was described in another paper in 1933, in which the ideal conditions for compounding in situ were reviewed. Two of the more important of these conditions were that the compounding ingredient must be formed in the rubber phase and must be as nearly insoluble therein as possible. More recent investigations into the mechanism by which carbon black exercises its beneficial influence on the mechanical qualities of rubber in which it is dispersed admittedly indicate that mere dispersion of ultrafine particles in the rubber phase may not be the only important factor. At present, however, such dispersion of fine particles appears to be an essential first step in the compounding process for eventual reinforcement, so that compounding by formation of reinforcing agents in situ may still provide a valuable or even essential step in methods for the production of rubber with exceptionally enhanced physical or mechanical characteristics.