Fabrication of Polyarylate-Based Porous Membranes from Nonsolvent-Induced Phase Separation Process and Related Permeability and Filterability Characterizations

Abstract

The stability demand of polymeric membrane separation systems used in harsh environments, including high temperature, high pressure, extreme acid, and high salinity, makes the role of polyarylate (PAR) porous membranes more and more crucial. Herein, the PAR ultrafiltration membrane is fabricated from the nonsolvent-induced phase separation (NIPS) method in a simple, high-efficiency way. In order to study the evolution mechanism of cross-sectional pore morphologies during the NIPS process, different coagulation conditions, including the PAR concentration in casting solution, the coagulation temperature, and the addition of different hydrophilic additives (PEG400, PEG4000, PEG20000, and PVP), are applied. Next, the morphologies and membrane performances of various PAR membranes are analyzed by scanning electron microscopy, porosity measurement, N2 isotherm adsorption–desorption measurement, water flux measurement, bovine serum albumin (BSA) separation measurement, and mechanical test. Based on these measurements, the formation rule of different pore morphologies in the cross section of PAR membrane was clarified, and the effects of different cross-sectional morphologies on the permeability, filterability, and mechanical properties of the resultant membranes are pointed out. The viscosity effect from a higher PAR concentration and a higher hydrophilic additive concentration in a casting solution can delay the formation of the outer layer and limit the nucleation growth process of the nonsolvent, then allowing the formation of near-surface sponge-like pores and fewer inner macropores. Moreover, not only the increase of the bath temperature but also the strengthening hydrophilicity of the casting solution can accelerate the double-diffusion rate and the growth process of nuclei, thereby promoting the formation of near-surface finger-like pores and more inner macropores. Combined with the enhancement of membrane hydrophilicity, these pores as channels can accelerate the passage of water through the PAR membrane. For the PAR16–PVP10-30 membrane, not only a 120 L·m–2·h–1·bar–1 of water flux but also a close to 100% of BSA rejection ratio is obtained. Although the formation of near-surface sponge-like pores and fewer inner macropores deteriorate the membrane’s permeability, the high BSA rejection ratio and the improved mechanical property can be maintained. Finally, the optimization component of the casting solution for fabricating a PAR ultrafiltration membrane with enough permeability, high selectivity, and suitable mechanical property adds 10 wt % PVP in the solution of 16 wt % PAR, ensuring the solid hydrophilic effect and moderate viscosity effect.