Measurement and prediction of diffusion coefficients of supercritical CO2 in molten polymers

The solubility and diffusivity of supercritical carbon dioxide (sc-CO2) in low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), ethyleneethylacrylate copolymer (EEA) and polystyrene (PS) were measured at temperatures from 150degreesC to 200degreesC and pressures up to 12 MPa by using the Magnetic Suspension Balance (MSB), a gravimetric technique for gas sorption measurements. The solubility Of CO2 in each polymer was expressed by Henry's constant. The interaction parameter between CO2 and polymer could be obtained from the solubility data, and it was used to estimate the Pressure-Volume-Temperature relationship and the specific free volume of polymer/CO2 mixtures. The diffusion coefficients were also measured by the MSB for each polymer. The resulting diffusion coefficients were correlated with the estimated free volume of polymer/CO2 mixture. Combining Fujita's and Maeda and Paul's diffusion models, a model was newly developed in order to predict diffusion coefficients for the polymers studied. (C) 2004 Society of Plastics Engineers.