Temperature-induced morphology control in the polymer- foaming process
Supercritical carbon dioxide (scCO2) is a promising foaming agent for the production of polymeric foams, representing an environmentally friendly alternative for the foaming agents currently used. During the expansion phase of the scCO2-foaming process, temperature plays an essential role. This study focuses on relating the effects of temperature and pressure profiles on the foaming process and the resulting foam morphology. Therefore, several experiments have been performed in a high pressure reaction calorimeter (RC1e) that can be set to three different modes: isothermal, adiabatic, and isoperibolic. It has been observed 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.