The effect of kinetic factors on the structure of the hydrophilic ethylene-acrylic acid copolymer microporous membranes prepared via thermally induced phase separtation

The effects of kinetic factors of phase separation, such as coarsening time and quenching temperature, on the hydrophilic microporous membranes were studied via thermally induced phase separation(TIPS) process using three hydrophilic ethylene-acrylic acid co-polymers(EAA) with different co-unit contents and diphenyl ether(DPE). The coarsening time and quenching temperature were used to influence the phase separation of the three different EAA/DPE systems, their diluent droplets growth, membrane cell size and crystalline structure. The mechanism of phase separation, liquid-liquid or solid-liquid made, was determined by the quenching temperature. For EAA/DPE systems liquid-liquid phase separation occurred when the quenching temperature was above the crystalline temperature of EAA, and solid-liquid phase separation occurred when the quenching temperature was below the crystalline temperature of EAA. The experimental results showed that the membrane pore size of the EAA/DPE systems was increased with increasing the quenching or cooling temperature. The average size of the cells was 1 ∼ 3 μm, 3 ∼ 5 μm and 6 ∼ 8 μm for samples with a same coarsening of time of 10 min, but differernt quenching temperatares 30°C, 60°C and 90°C, respectively. At the quenching temperature of 30°C, the droplet phase in EAA/DPE systems hardly grew because the temperature was below the crystalline temperature of EAA. The diluent droplet growth was restricted by the high viscosity of the system and the crystalline structure of EAA co-polymer. While at 90°C, it is above the crystalline temperature of EAA co-polymer, a dramatic increase of droplet size occurred with the coarsening time in the begining, and after 8 min the size kept almost unchanged.