Preparation And Performance Of Polyacrylonitrile Solvent-Resistant Nanofiltration Membrane

Polyacrylonitrile（PAN）has excellent chemical stability,good membrane formation and low price.It is one of the main raw materials for the preparation of organic polymer membranes.Asymmetric membranes prepared by the non-solvent phase inversion（NIPS）method have been extensively studied in the field of liquid separation（such as ultrafiltration,nanofiltration,and dialysis）.Among them,nanofiltration has attracted more and more attention in the application of non-aqueous systems in recent years,so solvent-resistant nanofiltration has become a research hotspot.The research on the preparation,modification,characterization and application of the whole asymmetric solvent-resistant nanofiltration membrane has attracted much attention.In order to improve the mechanical strength of PAN membranes,a flexible support PAN hybrid matrix thermal cross-linking membrane was prepared with high temperature resistant flexible porous material as the support,and the influence of thermal cross-linking process parameters on structure and properties was systematically investigated.The problem of low permeation flux of the membrane is modified by blending method,and the influence of the type and content of the polymer blend on the structure and properties of the membrane is systematically studied.The optimized formula is used to optimize the heat.The cross-linking process produces a large-flux flexible support blended modified mixed matrix thermally crosslinked membrane,and the following research results have been obtained:（1）The glass transition temperature of the TiO₂/PAN mixed matrix membrane is94-100℃.In the thermal crosslinking process conditions,the effect of thermal crosslinking temperature on the structure and properties of the membrane is critical.Above the glass transition temperature,the TiO₂/PAN mixed matrix membrane will undergo cross-linking reaction,and the pore size will shrink:100-150℃main physical shrinkage,this stage is mainly due to the accelerated thermal heat of the PAN macromolecular chain.The entropy shrinks,so that the pore structure appears to be hot-melted,and the higher the temperature,the higher the degree of hot-melting,resulting in a decrease in membrane flux;the intermolecular cross-linking reaction proceeds extremely slowly at this stage;chemical shrinkage occurs above 2150℃,ie The reasonable shrinkage of PAN linear molecular chain into a trapezoidal structure increases the degree of crosslinking with increasing temperature,the pore structure is further hot melted,and the flux continues to decrease.At the same time,the retention rate of Na₂SO₄ decreases with the increase of temperature.This may be due to the hot melt and most of the pores shrink or even disappear during the process.However,due to the presence of the support,the membrane shrinks with a small portion.big hole.Changing the constant temperature time during the low temperature phase has little effect on the membrane structure and properties.（2）The TiO₂/PAN mixed matrix membrane is blended and modified by two kinds of blended polymers of PMMA and PVAc,which can effectively cause pores in the mixed matrix membrane,thereby increasing the porosity and permeation flux of the membrane.The rejection rate of BSA does not change much.At the same time,by the method of blending modification,the thickness of the porous sublayer of the membrane can be effectively reduced,and a sponge hole having a large size appears in the film to improve the pore structure of the membranes.（3）The flux of the flexible support blended modified matrix membrane is larger than that of the unmodified membrane,and the rejection rate of BSA can be kept unchanged.After thermal crosslinking,the pure water flux is 13.71 and 4.13 times of the third cross-linked membrane flux under the same process conditions.However,the rejection rate of Na₂SO₄ is greatly reduced,and the rejection rates are about 15%and 20%,respectively.Due to the large pore size of the membrane,it has good performance for treating dye wastewater,and the rejection rate of Rose Bengalis about 93%and 98%,respectively.