Tailoring the micro-structure of PVC/SMA-g-PEG blend ultrafiltration membrane with simultaneously enhanced hydrophilicity and toughness by in situ reaction-controlled phase inversion

Abstract

An in-situ reaction controlled non-solvent induced phase separation (RC-NIPS) method was developed to tailor the morphology of polyvinyl chloride (PVC)/styrene-maleic anhydride (SMA) grafting polyethylene glycol (PEG) (SMA-g-PEG) blend ultrafiltration (UF) membrane. Herein, PVC and SMA was dissolved in dimethylacetamide (DMAc) solvent to prepare a casting solution (16 wt% polymer concentration) at 50 °C. Subsequently, PEG (20 kDa) as an additive and reactant was added to the casting solution at a mass ratio of PEG to the polymer 1/1 wt/wt. to enhance the hydrophilicity and mechanical elongation of the membrane. Results demonstrated that the casting solution with PVC/SMA = 3/1 wt/wt. was an entirely compatible system. The viscosity of the casting solution with adding PEG gradually increased from 692 mPa s to 1880 mPa s at the initial stage and 4780 mPa s at 42 h, then rose sharply to 27,320 mPa s at 84 h. This behavior was ascribed to the esterification reaction between PEG and SMA, leading to pre-gelation and gelation of the system. Whereafter, SMA-g-PEG graft polymers were obtained. Meanwhile, the degree of grafting (DG) increased from 0.40% at 12 h of the reaction to 2.61% at 42 h. Afterwards, a phase inversion using water as coagulation was used to prepare PVC/SMA-g-PEG blend membrane after a certain time of the esterification reaction. It was found that the morphology of resultant membranes systematically changed from asymmetric structure with a dense top layer and finger-like sublayer at the initial stage to a dense layer with a fully sponge-like structure after 18–42 h reaction. The PVC/SMA-g-PEG membrane obtained after the reaction of 42 h demonstrated better hydrophilicity, high pure water permeance and excellent toughness due to the internal plasticization of water molecules. The membrane also exhibited a high BSA rejection (>95%) and fouling recovery rate (FRR) (85.9%). Our work provides some insights on tailoring the UF membrane structure and simultaneously enhancing permeability, antifouling performance and toughness.