Colloidal Structure of Rubber in Solution. Colloidal Aspects of Vulcanization

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Abstract
Colloidal changes in solutions of purified rubber due to a vulcanizing system consisting of piperidinium pentamethylenedithiocarbamate, sulfur, and zinc propionate have been followed by means of measurements of the depolarization and intensity of the transversely scattered light and by viscosity measurements. A study was made of the time required for vulcanization of benzene solutions of rubber with the above vulcanizing agents. The temperature coefficient of vulcanization was approximately the same as that for cures of solid stocks. The light scattering results are interpreted as showing that, upon the addition of the vulcanizing agents to the solutions, the colloidal units become larger. The decrease in viscosity is explained as being due to a diminished “interlocking” of the units. In the vulcanization of the solutions, an equilibrium of colloidal processes occurs which results in a constant viscosity for the larger part of the time required for vulcanization, although the light scattering measurements show a continuous change. The magnitude of the light scattering changes indicates that the molecular clusters in the gelled solution are probably not very different from those in the original solution. The viscosity measurements show that the forces between the clusters have been radically strengthened.

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