The TIPS Method Preparation And Structure Control Study Of PVDF/SMA Blend Functional Film

Because of its highly toxic of the diluents,high spinning temperature,dense cortex,etc.the traditional thermally induced phase separation(TIPS),as one of the most popular methods for membranes preparation,has earned lots of attention.Therefore,low toxic or non-toxic diluents are developed to reduce spinning temperature and to improve the surface porosity and the permeability of the membrane,which has become a hot research topic.Poly(vinylidene fluoride)(PVDF)has attracted wide attention due to its excellent mechanical strength,thermal stability and chemical resistance.However,the high hydrophobicity of PVDF membrane makes it easy to be contaminated in the process of water treatment,which greatly shortens the service life of PVDF membrane.Blending modification is not only simple,but also can realize the bulk modification of membrane,what more,it is a industrialized modification method.In this paper,the dope solution system of cast membrane was studied.Firstly,propylene carbonate(PC)and triethylene glycol(TEG),water-soluble diluent,were used as mixed diluents to prepare PVDF/SMA blend membrane by TIPS/NIPS coupled phase inversion method.The effects of SMA on the phase separation mechanism,membrane microstructure and the membrane properties were investigated.The results showed that the gelation temperature and crystallization temperature difference of dope solution were increased with the addition of SMA.Although the phase separation of solid liquid(S-L)occurred during the cooling process,the porous cellular structure formed by spherical stacking.In the process of PVDF/SMA formation,the combination of SMA and water molecules near the outer surface acts as a delayed phase separation effect in NIPS,resulting in the fonnation of a through reticular pore structure in the outer layer.The precipitation of the SMA on the membrane surface improves the hydrophilicity of the membrane surface.The pure water flux of the PVDF/SMA blend membrane was up to 465.24 L/(m2h).The antifouling mechanism of PVDF/SMA blend membrane was explained from the microstructure of the surface of SMA thickness and the ordered water layer on the surface of the blend membrane.When GTA was used as diluent,the regulation and modification process of SMA on the microstructure of PVDF membrane in non-water soluble diluent was studied.In the process of membrane formation,the NIPS process occurred at the same time of GTA extraction.The SEM figures show that SMA had a weak effect on the cross-section structure of the membrane,but when the content of SMA was 4 wt%,the SMA spherical structure appeared in the cross-section.As amphiphilic copolymers,SMA has the effect of surfactant,which will lead to the formation of micelles by combning with water.Owing to enhancement of the pore-forming effect of the combination of water and SMA,the outer layer structure gradually becomes looser.After the addition of SMA,the pure water flux of external pressure increases to 127.15 L/(m2h),and the retention of BS A increases to 94%.