Studies On The Preparation And Properties Of Poly (Vinylidene Fluoride) Hollow-Fiber Porous Composite Membranes

Poly(vinylidene fluoride) (PVDF) hollow-fiber porous membranes have excellent performances. But adsorption fouling will still be created on the hydrophobic surface when the membranes are used in aqueous solution separation systems. This can cause the decrease of the permeate flux and separation efficiency, thus the applications of the membranes are limited. The preparation of composite membranes in this dissertation can optimize the separation function and improve the antifouling ability of the membranes while not change the properties of the PVDF radicle membranes.The PVDF-g-PAMPS hollow-fiber grafted composite membrane was prepared through surface chemical grafting. First, the treatment with strong alkali and strong oxidant to PVDF hollow-fiber membrane was carried out to activate the surface. The reaction condition was: [KOH]=2.5mol/L, [KMnO4]=3wt%, [TBAB]= 500mg/150ml, T=60 C, t=10~30min. Second, grafting copolymerization reaction was carried out. AMPS was chosen as hydrophilic monomer. Reaction system was: [AMPS]=1.5mol/L, [FAS]=4.3 10-3mol/L, [CAN]=500mg/150ml, T=60 C, t=3hr. Grafted copolymers on the surface of composite membrane were verified by FTIR, XPS and SEM.The PVDF-g-PAMPS composite membrane is a kind of intelligent membrane with environment responsibilities. The structures of PAMPS molecule chains change along with the changes of solution environments (pH and ionic strength (I)) and thus affect the water flux and selective permeability of the composite membrane. The water flux decreases with increasing pH and increases with 1. The BSA rejection is highest at the isoelectric point (IEP) (4.8), while decreases on both sides of IEP. The BSA rejection increases as I decreases.PAMPS/PVDF hollow-fiber gel composite membrane was prepared through interfacial polymerization. First, the treatment with strong alkali to PVDF hollow-fiber membrane was carried out to create C=C bonds on the membrane surface. The treatment condition was: [KOH]=2.5mol/L, [TBAB]= 500mg/150ml, T=60 C,t=10min. Then the treated membrane was dipped in the AMPS monomer solution([1.5mol/L]) for 3hrs. Crosslinking copolymerization reaction was followed. The crosslinking system was: [MBAA]=0.03,0.06,0.09mol/L, [K2S2O8]=0.0075 mol/L, T=60 C, t=40~60min. The existence of PAMPS gel layer on the surface of composite membrane was confirmed by FTIR and SEM.PAMPS/PVDF hollow-fiber gel composite membrane also has environment responsibilities. The PAMPS gel layer swells-shrinks reversibly as the solution environments (pH and I) change. The water flux increases with decreasing pH and decreases with 7. The BSA rejection increases as /decreases.The hydrophilicity of the surface of PVDF hollow-fiber membranes has been greatly improved and the antifouling ability increased obviously. Adsorption fouling can not be created easily and the permeate flux decreases limitedly.