This thesis is intended to present a theoretical approach based on_ the thermodynamic models for a thorough understanding on the solubility of physical blowing agents in polymer melts under plastic foam processing conditions. The reliable solubility data of blowing agents in polymer melts are not only useful for the development of next generation blowing agents but also are critical parameters for the optimization of plastic foam fabrication process.

As a gravimetric method, the magnetic suspension balance (MSB) was used to measure the sorption of blowing agents in polymer melts under high temperature and pressure. The proposed theoretical approach based on thermodynamic models, i.e., SLEOS, SS-EOS, and SAFT-EOS, is applied to account for the volume swelling during the sorption and to determine the phase equilibrium or solubility afterwards.

A comprehensive investigation on solubility was conducted in this study. Various blowing agents (HFC 134a, HFC 152a, CO₂, N₂, n-Butane) are used in a large number of polymers (linear PP, branched PP, HDPE, LDPE, PS, Engage material, Nylon, polylactide). A novel research methodology is also setup for the investigation on the solubility of gas blends in a polymer melt. It is observed that the linear and branched molecular chain structure exhibits a different behavior in terms of swollen volume and solubility. It is believed that the branched molecular chain structure causes a higher amount of entanglement among the molecular chains which can generate a higher resistance to volume expansion. Therefore, the molecule with branched chain structure generates less accommodation for the small gas molecules to dissolve in the polymer melt and exhibit less swollen volume than molecule with linear chain structure does.

The phenomenon about the induced crystallization in PC by the high-pressure CO, is also studied. The kinetics of high-pressure-gas-induced crystallization in PC was investigated based on the sorption measurements. It was observed that either admitting a higher content of dissolved CO», or raising the crystallization temperature could successfully promote the increased mobility of the molecular chains. Consequently, the degree of crystallinity, the melting temperature, and the crystal growth rate were all increased.