Preparation And Performance Study Of Ethylene-tetrafluoroethylene Copolymer Microporous Membrane

Ethylene-tetrafluoroethylene copolymer（ETFE）was a copolymer of ethylene and tetrafluoroethylene.It combined the properties of poly（tetrafluoroethylene）（PTFE）with chemical resistance,high and low temperature resistance,weather resistance,pollution resistance,and the easy processing of polyethylene（PE）.It has been applied in many fields,however,the research of ETFE separation membranes has not been reported.In this paper,ETFE as membrane forming polymer,SiO₂ and its composite inorganic particle（CEP）hybrid ETFE flat-sheet membranes were prepared by melt hot pressing method.Moreover,the ETFE hollow fiber membranes were prepared by melt spinning stretching method.The feasibility of ETFE flat-sheet membrane used in membrane distillation experiment and the acid and alkali resistance of ETFE hollow fiber membrane were analyzed and discussed.ETFE/SiO₂ hybrid flat-sheet membranes were prepared by melt hot pressing method,with ETFE as membrane forming polymer,nano-sized SiO₂ particles as pore forming agent,and dibutyl phthalate（DBP）as plasticizer.The effect of SiO₂ particle contents on membrane structure and properties were studied.The results showed that the average pore size,the porosity and N2 flux of the membrane increased as the contents of SiO₂ particles increased.While,the liquid entrance pressure（LEP）,the static water contact angle,the elongation at break and break strength of the membrane decreased.The membranes have high flux and salt rejection rate during the vacuum membrane distillation（VMD）experiment under 90 ℃and vacuum degree 0.09 MPa.The membrane permeation flux increased as the contents of SiO₂ particles increased.During the long-term membrane distillation experiment,the flux was attenuated as operating time progressed,while the salt rejection rate was still above 99.90%.ETFE/CIP hybrid flat-sheet membranes were prepared by melt hot pressing method,with ETFE as membrane forming polymer,CIP as pore forming agent,and DBP as plasticizer.The effect of CIP contents on membrane structure and properties were studied.The results showed that the hybrid flat-sheet membranes with CIP as pore forming agent had similar structure and porosity as those with SiO₂ particles.However,the membrane have higher static water contact angle,porosity and N2 flux of ETFE/CIP hybrid flat-sheet membranes were higher.While the content of CIP was 40 wt%,the permeation flux of the membrane still reaching 18.9 L·m-2·h-1,the salt rejection rate was above 99.90%,showing that the ETFE membrane have stable permeation flux.ETFE hollow fiber membranes were prepared by melt-spinning stretching method,with ETFE as membrane forming polymer,CIP as pore forming agent,and DBP as a plasticizer.The effect of draw ratios on membrane structure and properties was studied.The results showed that as the draw ratios increased,more interfacial pores were formed on the inner surface of the membrane than on the outer surface,leading that the permeation flux,porosity and break strength increased significantly.While the elongation at break,the rejection of DB 19 dye and the static water contact angle of inner and outer surface was decreased.ETFE hollow fiber membrane still maintained excellent mechanical properties after acid and alkali treatment,which demonstrated that the membrane had excellent acid and alkali resistance.