Preparation And Characterization Of PVDF Composite Hollow Fiber UF Membranes

Poly(vinylidene fluoride) (PVDF)-inorganic particles composite hollow fiber ultrafiltration (UF) membranes were prepared by combination of Sol-Gel method with the non-solvent induced phase separation (NIPS) method. The structure and properties of membranes were systemically characterized by using various test methods (SEM, bubble point pressure,burst pressure, flux and rejection, pore-size distribution, etc.).Through a series of preparation and characterization of hollow fiber composite membranes, the optimal composition of membrane dope and the optimal spinning conditions were obtained.First, deployment of the best ratio of solvent.And using only pure TEP as organic solvents,the casting solution can not be homogeneously mixed, so adding DMAc was necessary, and the smallest proportion of MTEP:MDMAc=3:2.Secondly,selection of the bore liquid of different materials, PVDF-SiO2composite hollow fiber UF membranes were prepared by NIPS method.In order to obtaine more complete micropore structure, also larger permeation flux and rejection, lwt.% NH4Cl was chosen as the bore fluid solution.Selection of different casting solution temperature. With the increase of casting solution temperature, the membrane compressive strength was improved,and PEG20K rejection decreased significantly. Therefore, it is necessary to take into account the integration of permeation flux and rejection, as well as pore size distribution, and then choose a suitable temperature of casting solution.Then,different materials as additives has made a great difference on the structure and properties of the membrane. After added PTFE and PVP in the casting solution,membrane symmetry more evident, the finger-type pore structure of sub layeris gradually well versed in. At the same time, PVB could not improve the membrane flux, but join the hydrophilic materials PVP made a great improvement of the membrane flux, the defect of the membrane inner surface were also improved. Thenthis change rasied membrane flux, and tend to be stable.Subsequently, use the solution which was same as the casting solution as the liquid core, outer cortex followed the NIPs method, phase separation and mass transfer process jointly determine the structure of the outer cortex for the traditional finger holes. The cortex was removed and form a pore structure tends to foam support layer. After added 20% deionized water to the core solution, the inner surface of the structure has improvedand tend to round.Finally,FeCl3 particles is play a positive role to improve the performance of PVDF hollow fiber UF membrane. The membrane which was added 0.5wt.% FeCl3 particles and with 50% aqueous solution as the core solution tends to has a smooth inner cortex. And the overall structure is more complete, also tend to symmetrical, so that the intensity increases. After adding FeCl3 and LiCl particles, the inside cortex isn't as dense as the pure PVDF membrane and the middle layer is also tend to be more sponge-like structure, more conducive to the improvement of fluxwhich can reach 400 L·m-2·h-1·bar-1...