Greener method to prepare porous polymer membranes by combining thermally induced phase separation and crosslinking of poly(vinyl alcohol) in water

This paper presents a new technique for making porous polymer membrane without using organic solvent from a nontoxic and biodegradable polymer, polyvinyl alcohol (PVA). This method consists first in inducing a phase separation in water – 10 wt% PVA solution, by increasing the temperature above the polymer cloud point temperature. A PVA with a degree of hydrolysis of 72% was selected according to its low cloud point temperature (47 °C for 10 wt% polymer) allowing saving energy. The second step of the preparation procedure corresponds to the stabilization of the structure by jointly cross-linking the polymer to stabilize the porous morphology and drying to evaporate the dilute phase. A chemical cross-linking reaction was performed using glutaraldehyde with a molar proportion (GA/monomer alcohol) of 0.04. Results showed that the cross-linking control was the key step to obtain porous membrane morphology. Consequently, the temperature and the catalyst volatility of the cross-linking reaction act directly on the final membrane morphology. Additionally, it was shown that the control of the relative humidity during the elaboration process had an effect on the porosity of the membrane skin layer as depicted by SEM pictures and filtration tests.