A Research Of PVDF Membrane

In the condition of water shortage and serious environmental pollution, membrane separation technology as a new separation technology is widely used in the water treatment, material purification, enrichment, separation and so on. The separation process possesses merits of high efficiency, energy saving, easy to operate and control, without environmental pollution, etc. Poly(vinylidene fluoride)(PVDF) is widely considered as a promising materials for preparing separation membranes due to its attractive features such as chemical and mechanical stability, processability, etc. However, PVDF has low surface energy, strong hydrophobic properties, which lead a larger driving force for separation process, absorbing pollution easily and short life for PVDF membrane. This restricts the extensive application of PVDF membrane. One of the effective methods to improve membrane pollution and service life of the membrane is to prepare a PVDF membrane with good hydrophilic property. In this paper, hydrophily of PVDF macromolecule was improved by using alkali treatment and grafting with hydrophilic monomer. The obtained hydrophilic PVDF was further used to prepare a separation membrane.A hydrophilic PVDF separation membrane was prepared successfully by chemical grafting method in solution in this paper. Firstly, PVDF trains were treated by Na4SiO4 in order to import double bonds and hydroxyl groups. Then glycidyl methacrylate(GMA) was used as monomer and grafted onto PVDF trains to obtain the PVDF-g-PGMA macromolecule, which can further improve the hydrophily of PVDF macromolecule. Finally, a solution casting method was used to prepare PVDF-g-PGMA separation membrane with polypropylene non-woven fabric as support membrane. In this research, the factors affecting the characteristics of PVDF separation membrane have been examined, including the amount of initiator and monomer, the temperature of drying membrane and PVDF concentration and so on. At the same time, the PVDF separation membranes obtained under different conditions were measured to get the values of water flux, retention of polyethylene glycol(PEG)-20000, water uptake, inflation rate and porosity. The good parameters for preparing the membranes were concluded according to the values of water flux and retention of PEG-20000 mainly. The group changes of the upper and lower surfaces of the PVDF separation membrane were characterized by infrared spectrum(IR). The surface and cross-sectional morphology, thermal stability and crystalline state of the PVDF membranes were analyzed using scanning electron microscopy(SEM), thermogravimetry analysis(TGA) and X-ray diffraction spectrum(XRD), respectively. The results show that the PVDF separation membrane possesses good synthetic properties with pure water flux as 75.8L·m-2·h-1 and retention of PEG-20000 as high as 100% when the concentrations of GMA and BPO are 30.7g·L-1 and 12.9g·L–1, respectively; grafting temperature and time are 65℃and 4h, respectively; drying temperature and time of the membrane are 80℃ and 6h, respectively. The surface side of contacting glass is more smooth and compact than that of contacting air during preparation process of membranes. The former is also more uniform in pore distribution than the latter. The PVDF separation membrane is in semi-crystalline state and shows good chemical stability in water and HCl solutions, as well as anti-oxidation in hydrogen peroxide solution, but a little poor stability in NaOH solution.