Solubility of gases in molten polymers at high pressures

Supercritical fluids (SCFs) have unique transport properties, which makes them suitable as polymer-processing agents. The enhanced solubility of SCFs in most thermoplastics is coupled with a viscosity reduction effect at normal processing conditions. SCFs such as CO₂ are environmentally benign alternatives to conventional solvents and plasticizers. SCFs pose a potential alternative as future polymer processing agents,; The power of an SCF can be harnessed effectively only if the solubility of SCF in polymer, the density of polymer-SCF mixture and other thermodynamical properties can be predicted and controlled accurately. An equation-of-state (EOS) model, which is suitable for polymer-gas systems, can predict these mixture properties. The EOS model has to be tuned with experimental solubility data before it can be put to use.; In this work the solubility of CO₂ was measured in molten poly(ethylene glycol) (PEG) and polystyrene at pressures up to 20 MPa. For each polymer the solubility was measured for three different molecular weights. A new experimental technique has been designed to measure in situ solubility of gases in polymer melts. The technique utilizes a high-pressure variable-volume view cell. The method is fast, accurate and produces an array of solubility data at various temperature and pressure conditions with a single polymer-gas loading.; The solubility data was analyzed by Sanchez-Lacombe (SL) EOS theory and by a hybrid model. The hybrid model was developed to account the non-idealities in the gas-phase. Combining SL EOS with another EOS suitable only for gases created the hybrid model. These models were optimized with experimental solubility data. The effectiveness of each model was analyzed. Both models had same systematic deviations from the experimental data. The hybrid model had no significant improvements over the pure SL model. Thus it was established that the non-idealities in the gas-phase were insignificant.; The experimental solubility data was also analyzed by applying Henry's law. By applying Henry's law, the non-idealities in the polymer-phase were selectively isolated. The EOS models were reexamined for the ideal-solution region, which obeys Henry's law. Both models were equally effective in the ideal-solution region. Thus the applicability of these models in the ideal and non-ideal region was established.; The Henry's law is applicable in the low-pressure region. The Krichevsky-Kasarnovsky equation extends the applicability of Henry's law into the high-pressure region by providing a correction factor to Henry's constant. The correction factor is an exponential function of pressure, temperature and partial molar volume of solute gas at infinite dilution (v˜ ∞). The KK equation was fitted to experimental solubility data and, Henry's constant and v˜∞ were evaluated for each solubility isotherm. The range of applicability KK corrected results was also analyzed.