Effect of cooling bath on LLDPE microporous membrane structure in thermally induced phase separation

Thermally induced phase separation (TIPS) is versatile method for making microporous membranes. The purpose of this work is to investigate the cooling bath temperature and type effects on the membrane structure prepared via TIPS method. The morphology of the resulting membrane shows a typical bicontinuous structure. When quenching into water at different temperatures, a larger pore size was obtained at higher temperature. Pore sizes are about 0.7 μm, 1.2 μm, and 2.2 μm for the water cooling bath with 273K, 303K and 333K. Porosity and tensile tests confirm these results. When the composition of the coagulation bath is similar with the diluents, the chemical potential difference of diluents would be declined and the concentration of diluent in polymer lean phase would be kept constant in stagnant condition which leads the droplets to grow and the pore size of the system will be larger. However in water cooling bath, the concentration of diluent in polymer lean phase decreased rapidly and pore size growth is decelerated which result is lower porosity