Structural Regulation And Properties Of Polytetrafluoroethylene Propylene Hollow Fiber Membranes

With the application of membrane separation technology getting more and more widely,the demanding for high-performance membrane materials is also getting higher and higher.In the chlor-alkali industry,paper-making wastewater treatment,high-temperature liquid feed treatment,chemical and pharmaceutical processing area,most of the existing organic membrane materials have the disadvantages of poor tolerance and to a certain extent,limit the further development of the membrane separation technology.The selection of suitable membrane materials to prepare high-performance separation membranes with acid and alkali resistant,heat-resistant and organic reagents resistant has become a hot spot of membrane science.In this topic,we choose a kind of perfluoropolymer-Poly(tetrafluoroethylene-hexafluoropropylene)(FEP),which has better acid and alkali resistance,organic solvent resistance and can stay stable at low or high temperatures,as the polymer material,to prepare FEP hollow fiber membranes and FEP/PPy composite hollow fiber membranes respectively,the structure and properties of the membranes were analyzed and discussed,the tolerance change and mechanism of the membranes after strong acid/alkali treatment were also explored.FEP hollow fiber membranes were prepared by melt-spinning-cold stretching method with FEP as polymer matrix,composite powder as pore-forming agent and dioctyl phthalate(DOP)as the diluent.The results shown that the prepared FEP hollow fiber membranes have a microporous structure with stretched pores,interface microporous and dissolved micropores,the sponge-like structure evenly distributed on the cross-section.The pure water flux of the membrane is high,initial flux can up to 4000 L m-2 ·h-1.Compared with the membranes before and after treated with 25wt%sulfuric acid solution and 25wt%sodium hydroxide solution respectively for 60 days,no significant changes in the morphology,structure and mechanical properties of the membranes,the breaking strength can still be maintained at 4?5MPa.The average pore size slightly increased,the pore size distribution became narrower,but the membranes still shown good stability.A functional layer of polypyrrole(PPy)was deposited on the surface of FEP hollow fiber membranes by a chemical vapor deposition method(CVD)with ferric trichloride(FeCl3)as the catalyst,and then FEP/PPy hollow fiber composite membranes with flat surface morphology were prepared,the microstructures and property of FEP/PPy hollow fiber composite membranes were investigated.The results shown that with the increase of deposition time,the pore diameter of the composite membrane decreased gradually and the pore size distribution became narrower,pure water flux decreased and the carbon ink retention increased,the water contact angle decreased mean that the hydrophilicity of the FEP/PPy hollow fiber composite membranes improved.Combined with scanning electron microscopy(SEM)and fourier transform infrared spectroscopy(FTIR)analysis,it was found that for the composite membrane deposited for 30 min,showed good performance and acid resistance after treated with 30wt%sulfuric acid solution and 30wt%sodium hydroxide solution for 60 days.