Preparation Of PVDF Hollow Fiber Membrane Via Modified TIPS Method

PVDF membrane has been widely applied in the fields of water treatment. In thepreparation of PVDF hollow fiber membrane, thermal induced phase separation (TIPS)process is the most easy method to achieve the purpose of controlling membranestructure. By reading a large number of literatures and experiments,This paperrespectively chose the single diluent system and composite diluents system usingthermal induced phase separation method to prepare PVDF hollow fiber membrane, byadjusting the concentration of polymer, coagulation bath conditions, additives andthinner ratio to control the structure and properties of membrane, which provides thetheoretical foundation for its application.By thermal induced phase separation method, with the aid of differentialcalorimeter scanner (DSC), X-ray diffraction (XRD), scanning electron microscope(SEM) and mechanical tensile strength to test the membrane structure and performance,Respectively we studied the PVDF/triethyl phosphate (TEP) binary system polymerconcentration, coagulation conditions, and additives of PEG on the membrane structureand properties; PVDF/triethyl phosphate (TEP)/diethylene glycol monoethyl etheracetate esters (DCAC) ternary system changes in concentration of DCAC on membranestructure and performance.Studies have shown that using the TEP as single diluent, with the increase ofPVDF polymer concentration in the casting solution membrane surface structurechanged gradually from porous to dense, Pure water flux and the porosity are decreasedand retention capacity and mechanical strength are significantly enhanced; As the good solvent for the polymer in the coagulation bath TEP content increased, the structure andproperties of the film showed the same trend, Hydrophilic additive PEG was added tothe polymer casting solution concentration and viscosity was increased, the flux ofmembrane decreased, but the mechanical strength and retention performance have beenimproved significantly, the film overall performance improved significantly. TEP andDCAC mixture as a composite thinners, composite thinners DCAC has graduallyincreased, the crystallization temperature of the system increasing, the system in phaseseparation process by liquid-liquid phase separation behavior to solid-liquid phaseseparation, membrane structure by continuous mesh structure gradually shift to thespherulite structure, and the spherulite size and the gap is increased; with the increase ofDCAC content in diluent, membrane flux and the porosity showed a trend of increaseand mechanical strength decreased, when DCAC content is70%, the pure water flux ofthe membrane can be as high as7000L?/m2h?; Use the series of films to made withtheturbidity of the water filtration experiments, found that the film can be an effectivematerial removal of turbidity, water turbidity less than0.1NTU, by backwashing thehollow fiber membrane flux can be recovered to more than80%of the initial flux.The results showed that the polymer concentration, diluent ratio, coagulation bathconditions, and additives both have an important role for casting liquid phase separationbehavior of the system, so can change these conditions to control the phase separationbehavior, so as to achieve the purpose of controlling membrane structure.