Design of polymer-plasticizer-solvent films: Effects of initial and operating parameters on the residual solvent and film properties

The effects of wet film thickness, polymer content, polymer molar mass, drying temperature, and plasticizer content on the drying of polystyrene-p-xylene films are studied. The drying enhancer is plasticizer triphenyl phosphate (TPP) loaded over a wide range. Changing the initial wet thickness from 800 μm to 2400 μm renders a higher minimum residual solvent. Changing the initial polymer content from 7% to 14% yields a higher minimum residual solvent with a shift of optimum TPP content from 2.50 wt% to 5.00 wt%, attributed to higher solution viscosity. Lower PS molar mass of 35,000 gmol−1 yields significantly lower minimum residual solvent of 0.0110%, at 25 ± 2 °C and optimum TPP content of 2.50%. The diffusion parameters are computed after correlating the solvent evolutions with a one-dimensional semi-infinite medium model using nonlinear regression. Residual solvent increases with molar mass due to decreased segmental mobility and increased solution viscosity. SEM shows films prepared under optimum conditions to be dense and minimally-defective than the control. TGA, DSC, and UTM show higher molar mass films to be thermally and mechanically stronger.