Electrostatic Direct Writing Polyvinylidene Fluoride Porous Membrane Structure And Its Application

Membrane separation technology is applied to various separation fields due to its high separation efficiency,low energy consumption,no secondary pollution and wide application range.In recent years,conventional polymeric porous membrane preparation methods such as phase inversion?thermally induced phase separation/TIPS,non-solvent induced phase separation/NIPS?,melt spinning-stretching,all have been industrialized.However,there are some problems with these methods,such as the irregular pore structure,and difficulty of controlling the pore geometry precisely.Compared to conventional methods,electrostatic direct-writing makes engineering complex,large area 3D structures a reality without the need of expensive moulds and multi-steps process.By this technology,the spinning jet in an initial stable motion state could be controlled by reducing the spinning distance and the spinning voltage,achieving precisely control of the jet stream and accurate deposition and stacking of the cured fibers.The movement path of the collecting device on the two-dimensional motion platform is controlled by the Auto CAD program,and realizing the fixed deposition of a single fiber in a two-dimensional plane or deposition,and finally an ideal 3D structure is obtained.Therefore,electrostatic direct-writing technology has broad application prospects in the field of membrane separation.Firstly,PVDF porous fiber membranes with regular pore structure were fabricated by electrostatic direct-writing technique.Especially,the spinning solution was prepared by using polyvinylidene fluoride?PVDF?as membrane materials,and DMAc/acetone as mixed solvent.Pore structures with different geometric parameters?pore size?were designed by Auto CAD program.Effects of solvent composition on rheological properties and spinnability were investigated respectively.The effect of membrane pore size on the obtained membrane morphology,permeability,surface wettability and mechanical strength were characterized.Finally,the application of electrostatic direct-writing membrane in oil-water separation,membrane emulsification and microparticle filtration was investigated.Results showed that when the PVDF concentration was 14%,the DMAc/acetone mass ratio was 4:1.Ambient temperature was 40°C,relatively humidity was 30%.And the spinning process parameters as followed:the voltage was3.5 k V,the receiving distance was 10 mm,and the extrusion rate was 0.25 m L·h^-1,the obtained PVDF porous fiber membrane exhibited excellent membrane structure and morphology.Secondly,the effect of membrane pore size on the performance of PVDF membrane was investigated.The results show that the membrane had good morphology and comprehensive performance when the membrane pore size was 0.3mm.The prepared PVDF fiber membranes were applied to the oil-water separation and membrane emulsification,respectively.In the process of oil-water separation,the permeate flux of kerosene at a lower filtration pressure?-0.01 MPa?could reach 1193.66L·m^-2·h^-1.Meanwhile,PVDF porous fiber membrane had high performance of oil-water separation.After repeating the oil-water separation process 10 times,the separation efficiency was still maintained at about 98%,and the cycle performance was good.During the membrane emulsification,the aqueous phase was used as the dispersed phase,and the emulsified oil phase was used as the continuous phase.The results showed that PVDF porous fiber membranes with different membrane pore size could be used to prepare water-in-oil emulsions with different droplet sizes.Finally,in order to further explore the application of electrostatic direct writing technology in micro-particle filtration.By optimizing the pore size and aspect ratio of the membrane,the membrane permeability could be greatly improved while ensuring the selectivity of the membrane,thereby improving the membrane separation efficiency The results show that when the membrane pore size was 0.1mm and the membrane pore length to width ratio was 1:2,the PVDF porous fiber membrane flux was 1791.4L·m^-2·h^-1,and the rejection ratio was 95.8%.