Preparation And Hydrophilic Modification Of High Strength PVDF-PET Hollow Fiber Membrane

The main contents include:the use of applied research and development group-immersion phase inversion gel prepared hollow fiber membrane device inside make high strength PVDF-PET support hollow fiber membranes;Compared with the traditional hollow fiber membrane,the advantages of PVDF consumption,effective filtration area and strength of hollow fiber membrane were quantified;The effect of PVDF concentration on the coating effect and film properties was discussed;The effect of concentration on the properties of pure water flux,average pore size,porosity,and anti fouling of TiO₂ was evaluated;The removal efficiency of organic matter and turbidity in the high turbidity raw water and two grade effluent was investigated,and the optimum ratio of the nano TiO₂ particles in the modified film was determined.On this basis,the preparation of bovine serum protein（BSA）,humic acid（HA）, sodium alginate（SA） standard pollution solution,and urban two grade water（EfOM） as the simulation of pollutants in the macro filtration experiment.By using the change of flux in the process of continuous recording experiment,the flux attenuation curve was fitted,and the flux decay rate,membrane fouling rate and flux recovery rate were calculated.Using the quartz crystal micro balance（QCM-D） with dissipation factor function to monitor the adsorption behavior of BSA on the surface of the modified membrane in real time.Combining the two aspects of micro and macro,the improvement of membrane fouling mechanism was discussed,which provides a theoretical reference for the prevention and control of membrane fouling.The results of the study are as follows:（1）Using the high knitting machine to produce the low elastic polyester fiber braided tube with the inner diameter of 2.0mm,and the NaOH water solution with a concentration of 5% and the temperature of 80 degrees for the 30 min pretreatment.By coating the immersion precipitation phase inversion method in the casting solution and coagulation bath temperature for each 60 degrees, 20 degrees,casting solution for PVDF/LiCl/DMAC/TiO₂/PVP conditions,the casting film coating liquid to pretreatment of braided tube surface by using home-made spinning device.After the phase transformation production obtained the PVDF-PET high strength modified composite membranes.The outer coating layer of the composite film is closely adhered to the outer surface of the inner support layer,the composite film wall thickness is about 0.5mm,the coating layer is thin and dense structure,the thickness of the composite film is only about 1/5 of the whole composite film wall thickness.And because of the role of the braided tube reinforcement,the composite film has a very high radial intensity,which is beyond the scope of the current laboratory equipment（the maximum value of 5000cN）.（2）PVDF-PET hollow fiber membrane has more advantages than traditional hollow fiber membrane in PVDF consumption,filtration area and mechanical strength.With similar pure water flux and retention rate of hollow fiber membrane,as compared to pure hollow fiber membrane,in support of hollow fiber membrane in PVDF membrane substrate consumption,savings of about 40%;per 100 g casting membrane solution of the effective filtration area,the pressure filter support hollow fiber membrane is greater than the pressure filtration of traditional hollow fiber membrane;the only direction tensile strength higher than 50 MPa,in strength also far is superior to the traditional hollow fiber membrane.（3）The effect of PVDF concentration on the coating and film properties was significant.When the concentration of PVDF is less than 8% or more than 16%,the coating effect is very poor.When the concentration is 8%¹6%,the coating layer is uniform and smooth.With casting liquid membrane system in PVDF mass fraction increased from 8% to 16%,pure water flux of composite membrane decreased,mean pore size,porosity first increased and then decreased,the porosity between the 44.31%-61.72%.Access to improved water flux of composite membrane up to 1683.78 L?m-2 ?h-1;when W（PVDF）=12%,composite membrane porosity reached maximum 61.72%,the membrane surface is level and smooth.（4）The hydrophilic modification agent TiO₂ was added to the cast film liquid system for blending modification,and the modified composite membrane was used to filter the self mixing high turbidity raw water and municipal two grade water.The results showed that:1)with the increase of TiO₂ concentration,the solvent content decreased,the flux,average pore diameter and porosity of the composite membrane decreased gradually.When W（TiO₂）=1%,the composite membrane flux is promoted from 476.88L/（m2·h） to 683.8 L/（m2·h）,the porosity and flux is the largest,and the rejection rate is lowest.When W（TiO₂）≥2%,high TiO₂ content may cause inorganic nanoparticles random jam membrane pore and particle aggregation defects occurred,resulting in pure water flux decreases gradually,interception increases.2)improved composite membrane from particles with high turbidity raw water with excellent retention effect and effluent turbidity are much lower than 0.1NTU,And organic matter on the secondary effluent UV254 has a certain separation,removal in the 18.2%-43.7% range;when casting membrane solution system PVDF/PVP/LiCl/DMAC/TiO₂ group assignment than 12:6:2:79:1,composite membrane membrane morphology structure and separation performance optimal.（5）From QCM-D detection and analysis,after addition of BSA contaminated liquid, immediately drop frequency F,the maximum quantity of pure PVDF membrane adsorption,adsorption value △m=85.42ng/cm2,while the PVDF/TiO₂ film exhibits a lower the adsorption △ m=68.67ng/cm2;through the composite membrane protein（BSA）,humic acid（HA）,sodium alginate（SA） and the Secondary Treatment（EfOM） four pollutants macro filter experimental data show:flux attenuation and membrane fouling rate of the modified lower flux rate recovery and antifouling properties are to a certain extent to enhance;TiO₂ content is 1% of the composite membrane flux decay rate of the lowest,highest flux recovery rate The composite membrane is more excellent in overall performance.