Preparation And Structural Regulation Of PVDF-based Blended Porous Membranes By Thermally Induced Phase Separation

Poly(vinylidene fluoride)(PVDF)has been widely used in microfiltration,ultrafiltration due to its outstanding properties such as high thermal stability,good chemical resistance.At presend,the PVDF membrane is usually prepared by immersion precipitation technology.Whereas,the PVDF membrane by this technology has many problems.For example,many factors can influence the membrane structure,and the membrane prepared by the technology is likely to obtain the fingerlike pores which usually lead to poor mechanical properties.In this study,thermal induced phase separation(TIPS)technology was used to prepare PVDF porous membrane.The effects of the species of the diluent and non diluent,the weight ratio and the content of ethylene acrylic acid(EAA)on the membrane formation process,structures and properties of membranes were studied.The hydrophilic modification of PVDF membrane was achieved by the addition of EAA which provided the theoretical basis and application foundation for the preparation and structural control of PVDF blend membranes with high strength and high flux.The solid content of PVDF remained unchanged.By adjusting the weight ratio of diluent ester 1 and non diluent dioctyl terephthalate(DOTP),the study found that with the addition of easter 1,the membrane hole held changed from honeycomb hole structure to the spherical particle structure.Meanwhile,the surface of spherical particles appeared porous structure and the pore size of honeycomb hole was gradually increased.Mixing polyethylene glycol 400(PEG400)into the "PVDF/ester 1/DOTP" system,the results showed that with the increase of PEG400 content,the diameter of spherical particles reduced and the spherical particles squeezed each other so that the arrangement of the spherical particles were closer.Doping nano calcium carbonate into "PVDF/ester 1/DOTP" system,it was found that the formation of the spherical particle structure of the casting solution system could effectively be inhibited by nano calcium carbonate.At the same time,the penetrating property of the PVDF plat membrane increased after immersed by the hydrochloric acid.For the "PVDF/ATBC(acetyl tributyl citrate)/DOTP" system,with the increase of the ATBC content,the porsity,water flux and mechanical properties of PVDF porous membrane all increased firstly and then decreased,while the rejection rate of the carbon ink decreased firstly and then increased.Mixing EAA into the "PVDF/ester 1/DOTP" system,to some extent,the generation of the spherical particle structure could be eliminated.With the increase of the EAA content,the cross section of membrane began to appear macroporous structure;Mix nano calcium carbonate into "PVDF/ester 1/DOTP/EAA" system,and with the increase of it,the diameter of the spherical particles became larger.When the weight ratio of ATBC and DOTP was 25/10,the diffterent content of EAA was added to "PVDF/ATBC/DOTP" system,and the section structure of the membrane all appeared spherical particle structure.When the weight ratio of EAA:PVDF was 5:100,the reticular pore structure of flat membrane was obtained.