Mechanical and gas-transport behavior of poly(methyl methacrylate) dense films at elevated temperatures

The present study utilized 88-mum thick poly(methyl methacrylate) (PMMA) dense films that were fabricated via a dry-casting method. Mechanical and transport properties of these films were measured simultaneously using a unique apparatus designed in our laboratory. Tests were conducted over ≈20 hours with nitrogen and carbon dioxide gases at pressures of 4.1 and 3.1 MPa, respectively, and temperatures ranging from 35--125°C. Whereas nitrogen is relatively non-reactive, carbon dioxide is highly plasticizing.; Results obtained indicate that under nitrogen, PMMA shows time-dependent creep only at temperatures greater than 85°C with a maximum creep strain of 5% at 125°C. Permeability values follow an Arrhenius dependence on temperature with an activation energy of 20 kJ/mol. Carbon dioxide studies indicate the predominance of swelling at the lower temperatures (<75°C), and the dominance of creep at higher temperatures (>75°C). Permeability values for CO2 also show Arrhenius dependence with an activation energy of 12kJ/mol, the lower value reflecting the effects of plasticization. Time-temperature superposition is used to create a master curve for characterizing creep compliance over enhanced time scales. In a novel application, time-temperature superposition is also employed to provide a PMMA master curve that predicts long-term dense film permeability of nitrogen and CO2. (Abstract shortened by UMI.)...