Long-Time Exudation of Plasticizer from Swollen Rubber Vulcanizates: (I) Diffusivity during Swelling

Abstract

This series of two papers attempt to obtain appropriate estimates of diffusivity during extensive swelling/exudation of plasticizer in vulcanized rubbers and make clearer the difference in their behaviors in terms of diffusivity and time taken to reach equilibrium. Therefore, two mutually consistent kinetic models for extensive absorption/desorption are presented first. A particular treatment of the models is an incorporation of characteristic parameters into the theoretical diffusion coefficient, based on the Flory–Rehner theory. In this first paper, using the model for swelling (or absorption), we confirm that it can provide realistic diffusion coefficients by analyzing experimental data on the swelling of several standard rubber vulcanizates immersed in plasticizer (i.e., dioctyl phthalate), taken from the literature. In the second paper, the counterpart for exudation will provide both diffusivities during extensive exudation and time periods taken to reach equilibrium using the corresponding data. The results have a great difference from those of the swelling case, with the cause being explained.

Keywords:

• diffusion coefficient
• Fickian approach
• plasticizer
• swelling kinetics
• vulcanized rubber

Acknowledgments

The author thanks S&S Japan Company Ltd. for their support and cooperation. He also thanks Former Associate Professor K. Daiyasu of Shinshu University for helpful discussion on the solution of the nonlinear diffusion equation.