Study on poly(tetrafluoroethylene-co-hexafluoropropylene) hollow fiber membranes with surface modification by a chemical vapor deposition method

Abstract

In this paper, poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) hollow fiber membranes, for applications in water purification, were prepared by a melt-spinning method with FEP as the polymer matrix, water-soluble composite powder as the pore-forming agent and dioctyl phthalate (DOP) as the diluent. Then, a layer of polypyrrole (PPy) was deposited on the surface of the FEP hollow fiber membranes by a chemical vapor deposition method. The microstructures and acid/alkali resistance properties of the FEP/PPy composite hollow fiber membranes were investigated. The results showed that the as-prepared FEP hollow fiber membranes had a multi-microporous structure of stretched pores, interfacial pores and dissolved pores. The sponge-like pore structure was distributed homogeneously over the cross-section of the membrane, which brought about a larger pure-water flux. The polymerization of the pyrrole deposit on the surface of the FEP hollow fiber membranes brought about the improvement of hydrophilicity while the reduction of membrane pore size further resulted in the increase of rejection. The acid/alkali resistance results indicated that the un-deposited FEP hollow fiber membranes had excellent acid and alkali resistance, whereas the alkali resistance was weak after PPy deposition.