| Poly(vinylidence fluoride)(PVDF)membrane is often used as a membrane matrix because of its better chemical resistance,good thermal stability,excellent anti-ultraviolet capability and aging resistance.During the membrane separation process,high hydrophobic nature of PVDF would induce a low fouling resistance,as a result,its application in wastewater treatment was restricted.Therefore,the hydrophilic modification for PVDF is extremely essential.Blending is not only a convenient method to improve hydrophilicity,but also a simple way to influence the membrane formation process and regulate the microstructure of the membrane,which is often applied to the study of membrane modification.Poly(ethylene-co-vinyl alcohol)(EVOH)is a semicrystalline random copolymer with hydrophilic vinyl alcohol and hydrophobic ethylene segments,which has excellent hydrophilicity,higher mechanical strength,good thermal stability and chemical resistance.In this paper,the PVDF/EVOH blend membrane was prepared by both blend and thermally induced phase separation(TIPS)with excellent hydrophilicity,higher mechanical strength and better anti-fouling capacity.The blend membrane was prepared with glyceryl triacetate(GTA)and high boiling point organic reagent M as mixture diluent,water and ethanol as extraction agent,and water as coagulation bath.In addition,the preparation of hollow fiber membrane is on the basis of the flat membrane with different composition.The membrane structure is easily in control by means of changing EVOH content and the mass ratio of mixture diluent,finally,the evolution mechanism of the structure and performance of membranes is obtained.The compatibility between PVDF and EVOH was poor,compared with the pristine membrane,it was seen that little change could be found for the structure of the membrane and the fibrous-shaped materials parallel to the draft direction gradually appeared and the number was increased with the addition of EVOH.The distribution of EVOH in the PVDF membranes was relatively homogeneous,and the hydroxyl content of the membrane surface was gradually increased,besides the water contact angle was obviously decreased(down to 43°),therefore,the hydrophilicity of the membrane was improved.The addition of EVOH had no influence on the crystal form of PVDF,but the crystallinity of PVDF was first increased and then decreased.The mechanical strength of the membrane was increased(up to 13.63 MPa)because of the function of EVOH in the stress field,and the toughness was improved due to the internal plasticization mechanism of water molecular.The blend membrane was prepared with water soluble diluent propylene carbonate(PC)and M,and water as coagulation bath and extraction agent.The addition of EVOH made the membrane structure changed from interconnected network pores to semi-closed cellular pores,and the permeability of the membrane was decreased,but the hydrophilicity was significantly improved.With the increase of EVOH,the tensile strength of the membrane was increased obviously(up to 10.27 MPa)but the breaking elongation was decreased.However,the influence of water molecular on the toughness of the membrane was not obvious compared with the PVDF/EVOH/GTA/M system.The content of EVOH had no effect on the crystal form of PVDF.In addition,with the increase of EVOH,the crystallinity of PVDF was first increased and then decreased due to the function of both hydroxyl and viscosity.Spinning parameters and post-treatment conditions had an important impact on the structure and performance of the membrane.Air gap,winding speed,spinning temperature,and bore fluid types would affect the structure of membrane,thereby the performance of membrane changed.Increasing heat setting temperature and time were beneficial to improve the mechanical properties and reduce the shrinkage degree of the membrane.The mechanical property of membrane was outstanding with glycerol-water solution as heat setting medium.In addition,stretching was helpful to improve the permeability of the membrane. |
PDF Full Text Request