Polyvinylidene Fluoride (pvdf) Hollow Fiber Membrane Preparation And Chemical Reaming Study

Poly(vinylidene fluoride) (PVDF) is a kind of membrane material with excellent characteristics. In this thesis, hollow fiber PVDF membranes were prepared by phase inversion method. The effects of preparation conditions on the structures and properties of PVDF membranes were studied. Besides, PVDF hollow fiber membrane was modified by hypochlorite solution to expand pores and the modification effect on the property of membrane of was evaluted.It was found that with the increasing of PVDF concentration in spinning solution, the pore density and size at the upper surface of the membrane and water flux across membrane also decreased gradually, while the retention of the membrane for BSA increased. When hydrophilic substance including polyvinyl pyrrolidone (PVP) were used as additives in spinning solution, the water flux and porosity of the obtained membranes is higher than that of membranes prepared from additive-free spinning solution. The effect of PVP addictivs on the structures and properties of prepared membranes were studied . By fixing PVDF content in spinning solutions , the water flux decreased with the increase of PVP content, but the retention for BSA increased. The studies of the effect of temperature of spinning solution on the structures and properties of membrane showed that the pores on the upper surface of the membrane and the water flux increased with increasing temperature. The results were explained by kinetics of phase inversion process. Addition of DMAc into water coagulation bath would slow diffusion rate of non-solvent into spinning solution, and PVDF precipitation rate is reduced. The formation of the finger-like macrovoid is suppressed, and the finger-like structure near the upper surface changed to a sponge-like structure. While the temperature of spinningsolution was increased, the water flux and porosity of prepared membranes became higher.In chemical expansion of pores, by studying the effect of the concentraion and the treatment on the property of prepared membranes , it was showed that the water fluxes of all treated membranes were great than the initial ones. At the same time, the retention for BSA and mechanical property were not changed greatly by this treating process . The water flux of the treated membrane was increased to 750L/H. m2. 0. IMpa from 4321/h. m2. 0. IMpawith 16h treatment in 6g/L hypochlorite solution . So , concluded that this method is effective improve the flux of PVDF membrane, while the retention properties were not reduced greatly.