Thermally Induced Phase Separation Method P (VDC-co-VC) Copolymer Porous Membrane Preparation And Performance Study

Membrane separation technology was the key to solve the pollution problems in the current social development,and played an important role in the industrial production.With the development of membrane separation technology,people demanded more for the separation membrane.Poly(vinylidene chloride-co-vinyl chloride)[P(VDC-co-VC)]has good characteristics of high strength and toughness,chemical stability,flame retardance,hydrophobicity,acid and alkali resistance and harmless to the human body,and was widely used in various fields.However,there were few studies on separation membranes.P(VDC-co-VC)porous membrane was first prepared by thermally induced phase separation(TIPS)method with dimethyl phthalate(DMP)as the diluent.The microstructures of P(VDC-co-VC)porous membranes was observed by field emission scanning electron microscopy(FESEM),differential scanning calorimetry(DSC),X-ray diffraction(XRD),atomic force microscopy(AFM).The results showed that the membrane formation process of P(VDC-co-VC)-DMP binary system was dominated by liquid-liquid(L-L)phase separation.With the increase of the polymer concentration,the cross-sectional structure of the membrane came from petal-like structure to cavity structure.In the structural transformation,the pores connectivity of the membrane cross-section was reduced and the structure became denser.At the same time,the pore diameter and porosity of the membrane decreased and the roughness increased,and the bovine serum albumin retention and anti-pollution performance were improved.The changes of L-L phase separation time and the polymer concentration caused the crystallinity of the membrane decreased first and then increased.When the polymer concentration was 30wt.%,the prepared membrane had excellent permeability.P(VDC-co-VC)flat porous membrane was prepared by TIPS method with diphenyl ketone(DPK)and DMP as the mixed diluents.Based on the thermodynamic phase diagram,the membrane structure formation mechanism of the film-forming system was analyzed.The effects of the mixed diluents composition on the morphology and properties of P(VDC-co-VC)porous membranes were investigated by morphology observation,porosity,water contact angle,mechanical properties and permeability interception performance test etc.The results showed that the phase separation process of the film-forming system was mainly changed from L-L phase separation to S-L phase separation,and the membrane structure came from petal-like structure to flower bud shape structure and finally to a large size spherical stacked structure with the increase of DPK content in the mixed diluent.At the same time,the crystallinity of the membrane decreased first and then increased,the average pore size and distribution of the membrane were increased,and the tensile strength were decreased.The surface roughness and contact angle of the P(VDC-co-VC)membrane obtained by mixing the diluent were larger than those of the single diluent DMP.When the DPK content was 15 wt.%,the membrane protein has the best anti-pollution performance,and the comprehensive performance was superior.The membrane desalination rate reached 99.99%,and the permeation flux was 18.4 L/(m2·h).