Preparation And Properties Of Poly (Ethylene - Ethylene - Propylene Oxide) Microporous Membrane

Hydrophobic membrane was a interface of vapor-liquid equilibrium and heat and mass transfer in the membrane distillation, plays an important role in the separation process. Due to its low surface energy of C-F structure, the fluoropolymer has outstanding hydrophobic properties. In this paper, poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) as membrane matrix was prepared FEP flat-sheet membrane, ultrafine fibrous FEP membrane, FEP hollow fiber membrane, respectively.FEP flat-sheet membranes were fabricated by the melt-pressed method. Effects of SiO2 content on the membrane morphologies and properties of FEP flat-sheet membranes were investigated respectively. Results showed that the porosity and permeability of FEP membranes increased obviously while the liquid entrance pressure (LEP) decreased with SiO2 content increasing. Furthermore, mechanical strength of FEP membranes decreased while elongation at break increased. The morphologies of FEP membranes showed that the increase in SiO2 content aided the formation of a larger and deeper pore structure. The salt rejections maintained above 99.0% by VMD process.Ultrafine fibrous poly(tetrafluoroethylene-co-hexafluoropropylene)(FEP) membrane was fabricated by electro-spinning process for the first time. Effects of FEP/polyvinyl alcohol (PVA) mass ratio and sintering temperature on the morphologies and properties were investigated. Results showed that a kind of dimensionally stable network structure was formed in the obtained ultrafine fibrous FEP porous membranes after sintering the nascent ultrafine fibrous FEP/PVA membranes. The optimal sintering conditions were obtained by comparing the performance in terms of membrane morphology, hydrophobicity, mechanical strength, and porosity. When the sintering temperature was 300℃ for 10 minutes, the porosity, static water contact angle (CA) and LEP of membrane was about 62.7%,124.2°, and 0.18MPa, respectively. Moreover, the ultrafine fibrous FEP porous membrane at the optimal sintering conditions was tested in vacuum membrane distillation (VMD) with a permeate flux of 15.1 L·m-2·h-1(-0.07MPa·80℃) and a salt rejection of 98.0%.FEP hollow fiber membrane was fabricated by melt-spinning stretching method. The nascent FEP hollow fiber membrane structure was compact, membrane permeability was weak. It was shown that porosity and N2 flux was small, the hydrophobic properties of the membrane, LEP and mechanical strength were higher. After stretching the FEP hollow fiber membrane, the porosity, and N2 flux improved significantly while the LEP decreased. Membrane morphologies observation showed that the quantity and pore size of the interfacial microvoids increased with the increase of draw ratio at the same treating temperature. Meanwhile, the FEP hollow fiber membrane was applied to the VMD process. The results showed that VMD flux brought about the higher valve with the feed temperature and vacuum increasing while the salt rejection maintained up to 99.0%.