Synthesis of a novel poly(amide-imide) (PAI) and preparation and characterization of PAI blended polyethersulfone (PES) membranes

In this study, firstly poly(amide-imide) (PAI) containing flexible groups was synthesized through polycondensation reactions of diimide-diacid with p-phenylene diamine (PPDA) via direct Yamazaki method. PES/PAI blend membranes were prepared with phase inversion induced by immersion precipitation technique. Polyvinylpirrolidone (PVP, 2 wt% concentration) was added in the casting solution as pore former. The PES/PAI blend membranes were characterized by contact angle, AFM, SEM, TGA, mechanical measurements and cross-flow filtration for milk concentration. The contact angle measurements indicate that the hydrophilicities of PES membrane are enhanced by increasing the PAI in the casting solution. The AFM and SEM images show that addition of synthesized PAI in the casting solution or blending with PES results in a membrane with high surface and sublayer porosity. The pure water flux and milk water permeation through the prepared membranes are increased by blending PES with PAI. Moreover, the protein rejection and anti-fouling properties of PES/PAI blend membranes are improved. TGA reveals that thermal stability of PES/PAI blend membranes is slightly decreased compared with PES membrane. Furthermore it was found that blending PES and PAI polymers results in membranes with higher mechanical strength.