(95a) Temperature- and Pressure-Induced Morphology Control in Polymer Foaming Processes

Micro- and macrocellular foams are widely used materials in our society, mainly because of their interesting mechanical properties. Microcellular foams have a favorable stiffness-to-weight ratio and high impact strength. Macrocellular foams are mainly used as light-weight packaging, insulating and cushioning materials. However, in the production process of these foams large quantities of organic foaming agents such as pentane and HCFCs are used.

Since the early nineties, foaming using supercritical carbon dioxide (scCO₂) has received considerable attention as an alternative to the organic foaming agents currently used. This study focuses on relating the effects of temperature and pressure decay profiles on the nucleation and foaming process and the resulting foam morphology. Nucleation experiments have been performed in an isoperibolic set-up. The minimum pressure drop needed to induce homogeneous and heterogeneous has been investigated.

In order to determine the effect of temperature upon depressurization with the resulting foam morphology, several experiments have been performed in a high pressure reaction calorimeter (RC1e) that can be set to three different modes: isothermal, adiabatic and isoperibolic. These experiments have shown that that the foaming could be divided into four stages: nucleation, slow cell growth, fast cell growth and shrinkage. The degree of shrinking that occurs is for a great deal dependent on the exposure to higher temperatures at the end of the foaming process. Since shrinkage does not occur in the adiabatic mode, this mode gives the best control on the foam morphology.