EXPERIMENTAL-VERIFICATION OF A PREDICTIVE MODEL OF PENETRANT TRANSPORT IN GLASSY-POLYMERS

The validity of the Lustig et al. (Chem. Engng Sci. 47, 3037-3057, 199 2) model for penetrant transport in glassy polymers was investigated b y comparing experimental results of dodecane transport in crosslinked polystyrene samples with the model. All parameters of the model were m easured independently. The time-dependent concentration profiles at th e dodecane/polystyrene interface were predicted at various temperature s. The time-dependent concentration and the polymer stress profiles wi thin the dodecane/polystyrene system indicate a wide range of transpor t mechanisms at different temperatures. The dodecane transport kinetic s was affected by dodecane diffusion coefficient, the discrete viscoel astic relaxation time and the modulus of the dodecane/polystyrene syst em. The significance of the viscoelastic relaxation contribution on th e overall penetrant transport was evaluated by analyzing the temperatu re dependence of the diffusional exponent, n, of a simple exponential dependence of the dodecane uptake as a function of transport time. The diffusional exponent and the resulting penetrant transport kinetics w ere correlated to the mean diffusion Deborah number. In general, the t ransport process was closely characterized as Fickian diffusion far ab ove or far below the glass transition temperature of the system and as anomalous transport close to the glassy/rubbery transition Copyright (C) 1996 Elsevier Science Ltd