Study On The PVDF Membrane Modified By Low-temperature Plasma And Electrokinetic Behaveor

An installment was designed to measure streaming potential of PVDF hollow fiber membranes in this paper,According to the relationship of streaming potential and zeta potentials,the zeta potentials the membrane were estimated on the basis of Helmholtz-Smoluchowski equation,PVDF membranes were modified by low-temperature plasma treatment and graft copolymerization.The acrylic acid(AA) and the acrylic amide(AM) grafting monomer were used,in order to change water affinity performance and adjust membranes' superficial electric charge,the results were showed that:(1) PVDF membranes were modified by low-temperature plasma treatment and graft copolymerization with Plasma modified equipment that was made by Lanzhou Jiaotong University.The acrylic acid(AA) and the acrylic amide(AM) grafting monomer were used. Considering the factors of monomer density,grafting voltage/power and pretreatment to the grafting rate and the best operating condition was determined,the electric current was 1.8A, the voltage was 2000V.FTIR was used to indicate that the effect of grafting copolymerization on the membrane surface.The absorption peaks of carboxyl and amino-group were appeared distinctly.(2) The electric charge of membranes in solution influenced by both membranes and solutions character,electrolyte solution.The streaming potentials of unmodified membranes and modified membranes were measured in electrolyte solutions of different concentration, Both unmodified membranes and modified membranes,the streaming potential increased when pressure difference increased,the absolute value of streaming potential decreased when electrolyte concentration increased,the streaming potentials of modified membranes were higher than unmodified membranes in the same measure conditions.(3) The streaming potentials were measured in electrolyte solutions of KCl,K₂SO₄,MgCl₂ and MgSO₄ that concentration was 10^-3 mol/L,the streaming potential in different electrolyte solutions is as follows:KCl＞K₂SO₄＞MgCl₂＞MgSO₄ The streaming potentials of membranes that were modified by AA and AM were higher than unmodified membranes.The zeta potentials were calculated by H-S equation showed that:the zeta potentials of membranes were modified by AA were decreased fast when the valence of cation was increased,but which were modified by AM were decreased slowly when the valence of cation was increased.(4) The Isoelectric point measured in ectrolyte solutions of KCl of different concentration was ahout 3.4,the IEP was nearly in solution of the same valence,the concentration was almost not affect it.The value of IEP in solution of NaCl,KCl,MgCl₂ and CaCl₂ as follows: 3.4,3.5,3.7 and 3.7,the trend of IEP in solution of same valence was similar,the IEP increased when the valence increased,the IEP of the membranes which were modified by AA and AM was improve little than unmodified ones. (5) Water flux of membrane modules that were made by myself was measured,the result showed that the flux of membranes were modified by AA and AM was more than unmodified ones 26%and 50%respectively,it indicated that modify can improve the hydrophilic of the PVDF membrane,through measuring the flux of the solution of BSA,the flux decreased fast in beginning stage,then decreased slowly,steady finally.