Migration and Blooming of Waxes to the Surface of Rubber Vulcanizates

Abstract

Abstract The model proposed in this paper appears to give an adequate explanation for the magnitude of the blooming rates observed. The driving force is due to elastic stresses set up around the precipitated wax particles and thus the blooming rate is influenced quite strongly by the modulus of the rubber. On the basis of this mechanism it would be expected that unvulcanized rubber would show little blooming, and this is in accord with general observations on such materials. The solubility of the wax is an important parameter and, because of its sensitivity to temperature, the ambient temperature and the melting point of the wax will be important factors influencing the blooming in practical applications. The precipitation of the wax has been assumed to occur at imperfections in the material. The source of these is not yet clear, although impurities could clearly be important. The values that have to be assumed for the volume fraction of these seeding sites, about 10−3, is not unreasonable in general magnitude for impurity concentrations.