Study On The Preparation Of Anti-pollution Ultrafiltration Membrane Based On Block Copolymer And Its Water Purification Mechanism

Water pollution and resources have been severely restricting our lives,society and economic development.Therefore,the pursuit of low-cost,low-energy,high-efficiency green water purification technology has become the focus of today's society.Most water treatment membrane materials are hydrophobic polymers,and organic pollutants in polluted water bodies are easily adsorbed on the surface of the membrane material,thereby reducing the service life of the membrane material.Therefore,this paper has promoted the hydrophilic modification of membrane materials in the field of water treatment.In this study,polyethylene glycol(PEG)and 4,4'-diphenylmethane diisocyanate(MDI)were used as raw materials to synthesize NCO-MDPH-PEG-MDPH-NCO prepolymer linked by isocyanates at both ends,and the content of NCO groups was determined by chemical titration.Subsequently,a novel amphiphilic block copolymer PPG-co-PEG-co-PPG was synthesized by polymerization chain extension reaction of polypropylene glycol(PPG)and synthetic NCO-MDPH-PEG-MDPH-NCO prepolymer.PVDF/PPG-co-PEG-co-PPG blend membranes were prepared by immersion precipitation phase inversion method,and the effects of different content of amphiphilic block copolymers on the structure and properties of modified membranes were investigated.The structure and molecular weight distribution of the amphiphilic block copolymer PPG-co-PEG-co-PPG were analyzed by nuclear magnetic resonance spectroscopy(~1H-NMR),infrared spectroscopy(FT-IR)and gel permeation chromatography(GPC).The structure,elemental composition and hydrophilicity of PVDF/PPG-co-PEG-co-PPG modified ultrafiltration membranes were characterized by total reflection fourier transform infrared spectroscopy(FTIR-ATR),X-ray photoelectron spectroscopy(XPS)and contact angle analysis.The surface morphology and cross-sectional pore structure of the membranes were investigated by scanning electron microscopy(SEM)and atomic force microscopy(AFM),and the pore size was measured between 12-17?m.The water-flux and membrane fouling degree of PVDF/PPG-co-PEG-co-PPG modified ultrafiltration membranes in the filtration process of bovine serum albumin,sodium alginate and yeast solution were evaluated by dead-end ultrafiltration experiment.The experimental result showed that with the increasing content of PPG-co-PEG-co-PPG additive,the water flux and anti-pollution of PVDF/PPG-co-PEG-co-PPG modified membranes were obviously improved.