Study On Pore-size Controlling Of Poly(vinylidene Fluoride) Membrane

Poly(vinylidene fluoride)(PVDF)is a kind of common membrane material,more and more researchers studied it because of its excellent chemical stability and thermal stability.Different PVDF membrane can be used for different purposes.In order to obtain PVDF membrane with different pore size,the methods the using double coagulation bath and blending modification are used in this research.The specific research contents and results are as follows:Firstly,the effect of different preparation conditions on the performance of PVDF membranes by NIPS was investigated.Studies indicated that the membrane which using DMSO(dimethyl sulfoxide)as solvent have the greatest pure water flux,using TED(triethyl phosphate)as solvent shows sponge-like cross-section structure.When ethanol was used as the first coagulation bath and 50%DMAC solution was used as the second coagulation bath,SEM(scanning electron microscope)test indicated that membrane shows different structure via different gel conditions.Experiments show that remaining in the ethanol will increase the water flux of membrane,decrease the thickness of surface layer,but with the increasing of residence time the strength of membrane will recede.Secondly,the methods that alkaline-treatment and UV grafting were used to prepare PVDF-g-AAC membrane.FTIR spectra indicated that the grafted membrane has an obvious absorption peak appeared at 1720cm-1,which is associated with the-COOH stretching.The emergence of O1s characteristic peaks in the XPS spectra demonstrated that the grafted monomer existed on the membrane surface.Experimental phenomena indicate that the grafting ratio can be effectively improved through alkaline-treatment.Through selecting proper solvent,monomer,initiator and light time,the hydrophilicity of the PVDF membrane has a siginificant improvement compared with PVDF membrane.Finally,PVDF-g-AAC membrane was fabricated via pH value-induced phase-inversion method.The results showed that with the increase of pH value of the coagulation baths,the modified PVDF membrane exhibited bigger pore size and better hydrophilicity.