Formation of low density polyethylene microporous membrane via thermally induced phase separation-(II) the effects of kinetic factors on the structures of microporous membranes

Hydrophobic polyethylene microporous membranes were prepared via the thermally induced phase separation (TIPS) process using low density polyethylene (LDPE) and diphenyl ether (DPE). The effects of kinetic factors of phase separation, such as coarsening time and quenching temperature, on the microporous membranes were studied. The experimental results show that the membrane pore size of LDPE/DPE systems is increased with the increasing quenching or cooling temperature. The average size of the cells is 1 μm~1.7 μm when quenching at the temperature of 0°C, 30°C or 60°C and is approximately 5 μm when quenching at the temperature of 90°C with coarsening time of 10 min. At the quenching temperature of 60°C, the droplets phase in LDPE/DPE systems hardly grows because of the temperature is below the crystalline temperature of LDPE. The diluent droplet growth is restricted by high viscosity of the system and the crystalline structure of LDPE. While at 90°C cooling temperature, due to it is above the crystalline temperature of LDPE, a dramatic increase of droplets growth occurs with the increasing coarsening time.