A GENERAL-MODEL FOR THE DIFFUSION AND SWELLING OF POLYMERS AND ITS APPLICATION TO ULTRA-HIGH MOLECULAR-MASS POLYETHYLENE

A numerical scheme is described that can predict the diffusion and swelling of solvents into a one-dimensional polymer slab. The work extends previous models of non-fickian diffusion and incorporates both generalized fickian diffusion and a concentration dependent viscoelastic response of the polymer. Depending on the relative magnitude of different parameters, both broad and sharp concentration profiles are predicted, together with linear or t1/2 mass uptake kinetics. The model is found to successfully predict the experimentally determined mass uptake kinetics of ultra-high molecular mass polyethylene exposed to an organic solvent at low and high temperatures. Significant solvent loadings are observed with linear kinetics at low temperature and t1/2 kinetics at higher temperatures.