Diffusion of reacting epoxy and amine monomers in polysulfone: a diffusivity model

In this work, a diffusivity model based on free volume theory is presented for the simultaneous diffusion of diglycidyl ether of bisphenol A (DGEBA) e poxy and bis(p-aminocyclohexyl) methane (PACM 20) amine monomers into amorp hous polysulfone (PSU). This model is expected to predict and explain the d iffusion behavior of the epoxy and amine monomers into PSU during the initi al time periods. The overall free volume of the polymer system is estimated using a Kelley-Bueche approximation for free volume in a binary mixture co nsisting of a non-reacting thermoplastic and the reacting thermoset. The fr actional free volume of the thermoset is estimated by the DiBenedetto equat ion. The model is valid only for low epoxy-amine concentrations and degrees of cure. The diffusivity model developed here suggests that reaction reduc es the species diffusivity with increasing cure from a loss of the overall fractional free volume for diffusion. Further, a model for increased epoxy diffusivity from amine-induced PSU swelling is presented and validated usin g data from previous studies on the single-component diffusion of epoxy int o amine-swollen PSU. By combining the reaction and swelling terms with the Arrhenius epoxy diffusivity, the epoxy diffusivity expression during the si multaneous diffusion and reaction of epoxy and amine into PSU for small tim es, is determined. Parametric studies on the nature of diffusivity are perf ormed to determine the influence of the various free volume parameters on t hermoset diffusion, and these studies show that the thermoset diffusivity, in general, decreases with time from reaction. (C) 2000 Elsevier Science Lt d. All rights reserved.