Study On Structure Control And Properties Of Microporous Membrane Of Ethylene-chlorotrifluoroethylene Copolymer

With the constant widening applications of membrane separation technology,the demand for membrane material and performance are also increasing.The development of new membrane materials with more excellent chemical and thermal resistance,high strength and high anti-pollution,has been a hot project.Poly(ethylene chlorotrifluoroethylene)(ECTFE)is a kind of thermoplastic,hemicrystalline fluoropolymer,which exhibits excellent thermal and chemical stability,wear resistance and mechanical strength,is a novel material with high potential in membrane separation processes.Due to the excessive forming temperature,the preparation of ECTFE microporous membrane is difficult,and the microstructure of prepared membrane is single.In view of the above problems,ECTFE microporous flat and hollow fiber membranes had been fabricated at a lower temperature via thermally induced phase separation(TIPS)by choosing the appropriate diluents in this paper.Then the structure and properties of prepared membranes were studied,and their application in the membrane separation processes of ultrafiltration,membrane distillation and oil-water separation was explored.ECTFE fibers were prepared by melt spinning.The crystal structure,thermal and mechanical properties,and creep resistance of the fibers were analyzed by X-ray diffraction(XRD),differential scanning calorimetry(DSC),mechanical and creep performance testing,etc.Results showed that the fibers had favourable crystallization property.Their crystalline structure belonged to hexagonal system,with the crystal cell parameters:a=b=0.57nm.The fibers exhibited excellent mechanical properties,themostability,creep resistance and chemical corrosion resistance(such as acid,alkali,strong oxidizing reagents,organic reagents,etc)below the temperature of 150?.ECTFE microporous membranes had been fabricated via TIPS by using dioctyl adipate(DOA)as the diluent,micro-scale Sip2 and composite inorganic particles(composed of soluble and insoluble inorganic particles)as the additives.The filtration performance of prepared membranes was characterized in terms of pure water flux,porosity,mean pore size,water contact angle,mechanical strength,and ultrafiltration tests.The results showed that,ECTFE membranes were a kind of homogeneous membrane,the addition of SiO2 and composite inorganic particles brought about interfacial microvoids(IFMs)and dissolved pore structure.The porosity,pure water and protein solution fluxes decreased,while the rejection ratio and mechanical strength increased with the increase of polymer content.With the addition of additives,the ultrafiltration performance improved obviously.Moreover,the membranes showed good resistance to the aggressive chemical corrosive solutions.ECTFE flat and hollow fiber microporous membranes with controllable structure were prepared via TIPS process using mixed diluents of DOA and diethyl phthalate(DEP).The formation mechanism of membranes was proposed with the assistance of a thermodynamic phase diagram of the ECTFE-diluent mixture system.Membranes'corresponding distillation performances were characterized in terms of porosity,contact angle,mechanical strength,permeability and rejection rate.The results showed that,the evolution of membrane microstructure ranged in honeycomb,bicontinuous and spherulitic with the increase of DOA ratio.The membranes prepared via L-L phase separation had excellent hydrophobicity,high permeate flux and salt rejection ratio,and excellent anti-fouling property,especially for the membrane with DOA/DEP mass ratio of 25wt.%/75wt.%.High-hydrophobic and super-oleophilic ECTFE/FEP blend microporous membranes were prepared via TIPS by blending poly(tetrafluoroethylene-co-hexafluoropropylene)(FEP).The blending of FEP increased the porosity and hydrophobicity of the membrane,made them show good hydrophobic and oleophilic properties,and realized an effective separation for the oil-water mixture.Superhydrophobic-superoleophilic ECTFE/SiO2 hybrid microporous membrane with hierarchical micro/nano-structural surface was successfully fabricated via TIPS using hydrophobic nanoscale SiO2 particles as the additive.Effects of SiO2 content on the morphology,pore size distribution,wettability and mechanical properties of prepared membranes were characterized by scanning electron microscope,automatic mercury porosimeter,static contact angle goniometer and tensile testing instrument,respectively.Results showed that,the prepared hybrid membranes' surface evolved into superoleophilic and superhydrophobic when the SiO2 content reached to 4wt.%.The separation experiments for different kinds of water-in-oil emulsions indicated that the prepared membranes had high oil/water separation efficiency.The antifouling performance of the membranes was also studied for multiple reuse in various pH conditions.This study provided a novel material and a facile method of fabricating superhydrophobic-superoleophilic membrane.The membrane was promising for numerous practical applications,such as produced wastewater treatment in industry and daily life,crude oil and fuel purification.