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

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. PEG (20kDa) was simultaneously utilized as an additive and a reactant to enhance the hydrophilicity and mechanical elongation of the membrane. Herein, PVC and SMA at a mass ratio of 3 to 1 in dimethylacetamide (DMAc) solvent were employed to prepare a casting solution (16 wt.% polymer concentration) at 50 °C. Subsequently, was PEG was added to the casting solution at a 1/1 wt./wt. mass ratio with the polymers. Results from Schneier theory and differential scanning calorimetry (DSC) analysis demonstrated that the casting solution containing PVC/SMA 3/1 wt./wt. was an entirely compatible system. The viscosity of this casting solution gradually increased from 692 mPa s to1880 mPa s at the initial stage after adding PEG to 4780 mPa s at 42 h, then rose sharply to 27320 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 after which SMA-g-PEG graft polymers were obtained. The degree of grafting (DG) confirmed by elemental analysis increased from 0.40% at 12 h of the esterification reaction to 2.61% at 42 h. 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 asymmetric structure of resultant membranes systematically changed from a dense top layer and finger-like sublayer at the initial stage of esterification reaction to a dense layer with a fully sponge-like structure at the range of 18-42 h of the esterification reaction. The morphological changes were typical to delayed liquid-solid phase inversion. The resultant PVC/SMA-g-PEG membrane obtained after 42 h reaction time (M1-42h) demonstrated better hydrophilicity and high pure water permeance (601.2 (LMH) bar-1). After immersion in water, M1-42h exhibited excellent toughness due to the internal plasticization of water molecules. The blend membrane also exhibited a high BSA rejection (>95%) and fouling recovery rate (FRR) (85.9%). Findings from this study expands the various avenues that can be explored towards tailoring the UF membrane structure and to simultaneously enhance permeability, antifouling performance and toughness using RC-NIPS