Fourteen-year-old aging study of the effect of thickness on methanol transport in crosslinked poly(methyl methacrylate)

The effect of thickness on methanol transport in fourteen-year-old crosslinked poly(methyl methacrylate) was investigated. The samples studied here are from the same primary source of those used by a study made fourteen years earlier. The sample was encapsulated by a plastic bag and maintained in a desiccator at room temperature. Four thicknesses, 0.6, 1.0, 1.5, and 1.9 mm, were examined. Methanol sorption data were fit to a model in which the mass sorption is a combination of case I, case II, and anomalous sorption. The diffusion coefficient for case I transport increases with increasing thickness, but the velocity for case II transport does the opposite. The diffusion coefficient for case I transport and the velocity for case II transport exhibit the Arrhenius behavior. The activation energies for case II transport are 18.9, 16.3, 14.6, and 13.4 kcal/mole, corresponding to the thicknesses 0.6, 1.0, 1.5, and 1.9 mm, respectively. The activation energies for case I transport are 24.7, 24.2, 21.7, and 21.9 kcal/mole, corresponding to the thicknesses 0.6, 1.0, 1.5, and 1.9 mm, respectively. For thickness 1.5 mm the activation energies for case I and case II transport are 21.7 and 14.6 kcal/mole for this study and 24.9 and 17.3 kcal/mole obtained fourteen years ago.