Preparation And Properties Of PVDF Hollow Fiber Membranes By Melt Spinning

With the increasing level of global industrialization,water pollution and water shortage are becoming more and more serious.Membrane separation technology,with its advantages of convenience and efficiency,has been widely used in various industries of water treatment,but there is no more effective solution to the pollution problem in the process of membrane fabrication.Traditional membrane fabricating process often needs to add organic solvent or organic diluent,but it's difficult to recover,this has restricted the development of membrane separation industry.In this paper,PVDF hollow fiber membranes are prepared by using PVDF as membrane forming polymer,calcium chloride(CaCl₂)and polyethylene glycol(PEG10000)as pore forming agents,poly(tetrafluoroethylene-co-hexafluoropropylene)(FEP)as additives,and the structures and properties are studied.Based on PVDF as the membrane forming polymer,CaCl₂,PEG as the pore forming agents,through the melt spinning method and stretching process,PVDF hollow fiber membranes are prepared.Through the pore size distribution,porosity and permeation flux test to optimize the contents of PEG.The influence of different contents of PEG on the membranes'structures and properties are studied.The results show that there are no obvious dense cortices on the surface of the PVDF hollow fiber membranes.The primary hollow fiber membranes are washed with water,and the water-soluble pore-forming agents are successfully washed out,leaving relatively small round pores.With the increase of PEG contents,the porosities and the number of membrane pores increase,and the pore sizes of the membranes become larger.The continuities of membrane pores are improved effectively,the largest porosity can reach 73.7%,the largest average diameter is about 0.29?m.At the same time,the water contact angles and liquid entry pressures decrease,but the water contact angle are always more than90°,liquid entry pressures are always above 0.02 MPa.The fluxes of kerosene increase with the increase of PEG contents.M-3 with the largest flux has a good performance on oil-water separation.After ten cycles of use,the separation efficiency of oil-water emulsion reaches more than 95%.In order to further development the application of separation membrane in the direction of hydrophobic,and explore the properties of membranes,select hydrophobic FEP as additive,and make a blending modification for PVDF.The influence of stretching ratios on membrane structures and properties are investigated under the premise of constant stretching temperature.The results of fourier infrared spectroscopy,thermogravimetric analysis and other tests show that FEP still maintains its original structure in the spinning process,and the results of scanning electron microscopy shows that FEP is finally embedded in PVDF.Water contact angle test results show that compared with the membrane with none FEP,the hydrophobicity of PVDF hollow fiber membranes with FEP are improved,the water contact angle of the membrane increases about 15°.For oil-water emulsion,the separation efficiency is improved by about 2%.As the stretching ratio increases,the membrane pores become more and more narrow,and some of the pores are in the shape of micro capillary along the stretching direction.The porosities and pore size of the membranes increase,the liquid entry pressures decrease,and the fluxes of kerosene increase.Moreover,the breaking strength of the membrane increases with the stretching ratio,up to about 19.3 MPa at most.