Solubilities and diffusion coefficients of carbon dioxide and nitrogen in polypropylene, high-density polyethylene, and polystyrene under high pressures and temperatures

Solubilities of carbon dioxide and nitrogen in molten polypropylene (PP) an d high-density polyethylene (HDPE) were measured at temperatures 433.2, 453 .2, and 473.2 K and pressures up to 17 MPa. The solubilities increased almo st linearly with pressure. While the solubilities of carbon dioxide decreas ed with increasing temperature, those of nitrogen increased in the temperat ure range examined. The solubility of nitrogen in glassy polystyrene (PS) w as measured at 313.2, 333.2, and 353.2 K and pressures up to 17 MPa. Temper ature dependence on the solubility in this system was distinctive, where mi nimal solubility of 310 cm(3)(STP)/(kg MPa) was observed around 350 K, by t aking into account of our previous data above 373.2 K. Henry's constants, K ,, and their temperature dependence were determined from the experimental d ata. A linear relationship between In(1/K-p) and (T-C/T)(2) was obtained fo r each system. Diffusion coefficients of gases in molten polymers were dete rmined for the nitrogen + PP, nitrogen + HDPE, and carbon dioxide + HDPE sy stems at 453.2 K. The diffusion coefficients showed weak concentration depe ndence and had an order of magnitude of 10(-9) m(2)/s. (C) 1999 Elsevier Sc ience B.V. All rights reserved.