Study On Polypropylene Microporous Membrane Via Thermally Induced Phase Separation

Polypropylene (PP) microporous membranes which were used in extensive fields (e.g., in battery separating membranes, biological filtration, chemical purification, artificial lungs, and clothing etc.), were studied in this dissertation via a novel method of membrane formation, thermally induced phase separation (TIPS). The effects of PP types, diluents, nucleating agents and membrane formation processes on structures of membranes were investigated. Then, ploy(4-methyl-l-pentene) (TPX) microporous membrane via TIPS process was also elementarily studied.As PP membranes are prepared via TIPS process, a diluent, which causes dissolution of PP at an elevated temperature and phase separation when cooling the homogeneous solution, is required. In this work, 12 single solvents were attempted as the diluents, as well as bicomponent diluents which inceasing the variety of diluents. The effects of diluents on membrane stucture were investigated. The results showed that homogeneous solutions were formed when dioctyl terephthalate (DOTP), dioctyl phthalate (DOP), paraffin oil, diphenyl ether (DPE), methyl benzoate, soybean oil, corn oil, peanut oil, gingeli oil and oleic acid were included in PP at 180°C respectively, but not for di-n-butyl-phthalate (DBP) and castor oil. Then, soybean oil, corn oil, peanut oil and gingeli oil respectively were mixed with DBP as bicomponent diluents, which can dissolve PP at 180°C. Small size and regular cellular structure were formed in the PP microporous membranes with diluents of DPE/soybean oil (7/3, mass ratio, as follow), DBP/soybean oil (7/3), DBP/gingeli oil (7/3) system, whose average pore sizes were 1.7, 1.1 and 1.0μmThe effects of PP concentration and quenching temperature were investigated. The monotectic point of PP/soybean oil(3/7) system was about PP concentration of 30wt%, cooling at this concentration caused only solid-liquid phase separation of solution and formed an irregular stucture. On the other hand, the monotectic point of PP/DBP/soybean oil(30/49/21) system was about PP concentration of 45wt%, so ragular cellular structure were formed at 30wt%. In this system the pore sizes...