Preparation And Property Study Of PH Sensitive Fluoride Microporous Membrane

Polyvinylidene fluoride (PVDF) and poly(tetrafluoroethylene) (PTFE) possess excellent chemical stability and mechanical properties, they has good resistant to heat, cold, radiation and chemical corrosion and widely used as excellent membrane materials in industry for a long time, but they both have strong hydrophobicity which can cause the pollution of the membranes. These will decrease the permeate flux and separation efficiency. In order to prepare pH sensitive microporous membrane, we need to modify their hydrophilicity.In this thesis, we adopt surface chemical grafted method to prepare fluoride pH sensitive microporous membrane. In contrast with surface treating method, surface grafting method can provide a more steady and durable hydrophilicity; In contrast with other grafting methods, chemical grafting method don't need special equipments so more low-cost to be suitable for the industrial continues producing.First PVDF membranes were pretreated by strong alkaline solution of potassium permanganate and PTFE membranes were pretreated by sodium naphthalene solution, the pretreatment process can introduce some double bonds, hydroxide groups, carboxyl groups to the surface of the membrane. Then the pH sensitive membrane were prepared by grafting poly(methacrylic acid) (PMAA) from these active points using cetric ammonium nitra (CAN) as initiator. Through studying the infection of reaction conditions to the grafting ratio, appropriate reaction conditions were made based on the infection of grafting ratio to the pH sensitive ability and mechanical properties.It was proved that the PMAA grafting layer exists on the surface of the membrane through studying the surface compositions of the virgin and modified membrane were determined by FT-IR and EDS. Further more, SEM and AFM test showed that the number of pores of decreased, and the diameter of the pores minished and floccules were observed in the pores, which were the further evidence of the existence of PMMA. Since the pKa value of PMMA is 5.65, so flux test was carried our under pH=4 and pH=7. As a result, PVDF-g-PMAA and PTFE-g-PMAA showed excellent pH sensitive property. Considered all the infections, the best grafting ratio of PVDF-g-PMAA is 3%～6.1% and the best grafting ratio of PTFE-g-PMAA is 5%～6%.