Preparation of poly(vinyl alcohol)-based membranes with controllable surface composition and bulk structures and their pervaporation performance

Poly(vinyl alcohol)-based membranes with controllable surface structures and bulk characteristics were prepared by casting PVA/poly(acrylic acid) (PAA) solutions onto different substrates. Four kinds of surfaces, namely the air-side 1 and glass-side surface (a glass plate used as substrate), the air-side 2 and PTFE-side surface (a polytetrafluoroethylene (PTFE) plate used as substrate), were formed. At any a given content of PAA in PVA casting solution, the air-side 1 and PTFE-side surfaces of the resulting membranes were less hydrophilic than the corresponding glass-side and air-side 2. Interestingly, there was similar surface composition between the air-side 1 and PTFE-side, and between the glass-side and air-side 2. Furthermore, the membranes prepared on a PTFE plate exhibited higher crystallinity than those formed on a glass plate. By an induction of the underlying substrates, the surface composition and bulk characteristics of those PVA-based membranes could be tuned. Pervaporation experiments for separating acetic acid/water mixtures through those membranes were carried out, and the results indicated that the permselectivity was mainly dependent on membrane surface composition, whereas the permeability was more significantly governed by membrane bulk characteristics. This provides a feasible method for the structure optimization of a high-efficient membrane and mechanism exploration in pervaporation separation.