Fabrication of low density microporous polymeric foams

By the general freezing-dry technology, low density, open-celled microporous polymeric foams, such as polystyrene, can be fabricated. The density of polystyrene foam is 0.02~0.1g/cm3, and the average cell size is 1~20μm. The factors that affect the cellular structure of foams, such as the process of phase separation between polymer and solvent, the system of polymer and solvent, and the freezing rate have been studied. In order to obtain the homogeneous defect-free foams, the technology must pick a system in which the theta temperature of solvent to polymer is higher than the solvent melting point temperature, and use unidirectional freezing whose quench rate exceeds 100℃/min．