Preparation And Hydrophilic Modification Of Polyvinylidene Fluoride Ultrafiltration Membrane

Polyvinylidene fluoride as an excellent polymer membrane material has high toughness,thermal stability and strong corrosion resistance,etc.However,because polyvinylidene fluoride material is a kind of hydrophobic material,there are some problems limlting the scope of its use,such as the high pressure,the membranes easy to be polluted,the short life of membranes.So,it is necessary to improve the hydrophilicity of polyvinylidene fluoride membrane materials to solve all above problems.This paper regarded polyvinylidene fluoride ultrafiltration membrane materials as the main object of study,and the preparation technology and the improvement of the hydrophilic were studied.The study prepared PVDF ultrafiltration membrane using the immersion precipitation phase inversion method.Then the water flux,the contact angle,the pollution index,retention,surface topography of the membranes were tested,and then the influence of factors on the membrane structure and performance were analysised.The experimental part was composed with the univariate tests,orthogonal experiment with four factors and five levels and strength optimization tests.In the univariate tests,the paper studied the effect of the PVDF concentration,LiCl concentration,PEG concentration on membrane structure and properties.The concentration of PVDF has small impact on the hydrophilicity,the increasing concentration of LiCl can increase the water flux of the membrane,but it cannot improve the hydrophilicity of the membrane.PEG can improve the hydrophilicity of PVDF membranes,and increase the water flux of the membrane.PEG is good to modify the membrane.and when its concentration is 6wt% the membrane’s hydrophilicity is best.In four factors and five levels orthogonal experiment,PEG concentration,PVP concentration,LiCl concentration,the first coagulation bath composition were factors.The experimental factors on membrane pore size affect the ability to sort as follows: LiCl’s concentration,PVP’s concentration,then the first coagulation bath composition,the PEG’s concentration.The experimental factors influence on the contact angle of membrane ability to sort as follows: PEG’s concentration,the first coagulation bath composition,then PVP’s concentration,the LiCl’s concentration.The experimental factors on membrane water flux affect the ability to sort as follows: the first coagulation bath composition,LiCl’s concentration followed,then PEG’s concentration,the PVP’s concentration.The influence of experimental factors on membrane’s interception rate as follows: LiCl’s concentration,the first coagulation bath composition,then PEG’s concentration,PVP’s concentration.The influence of experimental factors on membrane’s equilibrium water content as follows: LiCl’s concentration,PVP’s concentration followed,then the first coagulation bath composition,PEG’s concentration.The influence of experimental factors on membrane’s pollution index as follows:PEG’s concentration,PVP’s concentration followed,then the first coagulation bath composition,LiCl’s concentration.When the concentration of PVDF,PEG,PVP,LiCl is 18%,4%,8%,1%,and the first coagulation bath ratio of DMAC / H₂O is 60/40 the membranes have the best overall performance.The strength and toughness of the membranes were not very high,so the soluble polyurethane was used to optimize the membranes.The results shows that the strength and toughness of the membranes are greatly improved by adding 1.5% water soluble polyurethane without affecting the other properties.