Study On Preparation And Properties Of Composite Membrane For Filtration

Nonwoven material is widely used as a filtering material with low cost,simple processing technology,fast production speed and many changes in technology.It has three-dimensional reticular structure,which can capture and intercept particles.But the filtering accuracy of nonwoven materials is relatively low.Therefore,to improve its filtering accuracy,the PET nonwoven material is used as the base material,and the composite membrane with asymmetric structure is prepared by the hot-pressing composite method and the solidification coating method.The PTFE/PET composite membrane applied to gas filtration and the PES/PET composite membrane with liquid filtration respectively.To improve the filtration accuracy of nonwovens,composite membrane with asymmetric structure was prepared by combing PET nonwovens with PTFE microporous membrane through high temperature hot pressing process.The effects of high temperature hot pressing process parameter and the pore size of PTFE microporous membrane on the structure,the peeling performance and the air filtration efficiency of the composite membrane were studied.The results show that with the increase of hot pressing temperature and hot pressing pressure,the amount of PET melt penetrated into the PTFE microporous membrane increases,and the mechanical binding effect is enhanced,which leads to the increase of the peeling force of the composite membrane.With the increase of pore size of PTFE microporous membrane,the microporous osmotic pressure decreases,PET melt is more easily penetrated into the microporous membrane,resulting in the increase of the peeling force of the composite membrane;At the same time,the amount of PET melt penetration increased PTFE microporous membrane pore blockage,the surface pore of PTFE membrane decreases,causing the air permeate flux of the composite membrane decreases,and reduce the probability of penetration of particles,thereby improving the filtration efficiency of composite membrane.When the pore size of PTFE microporous membrane is 0.8?m,the hot pressing temperature is 290?and the hot pressing pressure is 6kg/cm²,the peeling performance of the composite membrane is best,and the air permeat flux is 51.52L·?m²·s?^-1,the filtration efficiency is 99.99%.In the solidification coating method,polyether sulfone?PES?and different proportions of polyethylene pyrrolidone?PVP?were dissolved in two methyl acetamide?DMAc?to prepare the casting fluid.Then the casting solution is coated on the surface of PET nonwovens by curettage.Finally,the PES/PET composite membrane was prepared by adding a layer of thin film on the surface of PET nonwovens by phase conversion in a solidification bath?deionized water?.By studying the content of PVP and the temperature of coagulation bath on PES/PET composite membrane structure,average pore size,hydrophilicity,pure water flux and BSA rejection rate,draw the following conclusions:the increase of PVP content caused the enhancement of the hydrogen bonding interaction during the amide groups of PVP and DMAc,the viscosity of the cast film is also increased;When PVP content is less than 4%,with the increase of PVP content,the pore forming effect is remarkable.The surface micropore density and the average pore size of the composite membrane increase,and the pure water flux of the composite membrane also increases.On the contrary,the rejection rate of the composite membrane to BSA decreases.When PVP content is higher than 4%,the viscosity of casting solution is larger,which result the delay of polymer phase separation,polymer agglomeration on the surface,the average pore size decreases,the pure water flux decreases and the retention rate of BSA is increased;in addition,PVP concentration on the membrane surface in the process of phase separation,therefore,with the increase of PVP content,the water contact angle of composite membrane decreases,the hydrophilicity improved.When the coagulation bath temperature increased from 25?to 45?,the speed of interdiffusion between PES and PVP increased,resulting in the average pore size of composite membrane,the pure water flux increases and the retention of BSA decreases.When the content of PVP in the casting solution was 4%,the bath temperature is 40?,the hydrophilicity of composite membrane is best,the average pore diameter is 2.54?m,the pure water flux is 1227.72 kg·m^-2 h^-1,BSA retention rate is 88.7%.