Structure Control And Properties Of Porous PVDF Membrane Modified With Amphiphilic Copolymers

As one of the most popular materials for microporous membranes, poly (vinylidene fluoride) (PVDF) has earned lots of attention due to its comparative molding properties, thermal and chemical stability, porous-controllability, et al. Whereas, inconvenience is in existence that PVDF membranes are inclined to be fouled by proteins, so high driving force for water to pass through exists which results from the obviously hydrophobic property of PVDF matrix. It is urgent to find effective methods to improve the hydrophilicity of PVDF membranes.From the modification of PEG and PVP on the membrane properties and the low reservation in membranes after the P-S process and simulated application, we bring forward that the linear soluble polymeric additives in membranes is inclined to be washed out of membranes easily in the P-S process and in application. It acts as the pore-inducing agent instead of the hydrophilic modification additive. To improve the reservation of additives, several amphiphilic polymers with various molecular structures are presented as the modification additives in preparation of hydrophilic porous PVDF membranes via phase inversion process.The linear three block amphiphilic poly-ether (EO_m-PO_n-EO_m, TBPE) was applied to achieve the hydrophilicity modification of poly (vinylidene fluoride) membrane through blending method. The introduction of TBPE increases the pores both on surface and inside the membranes, we found that the reservation of three TBPE polymers with different molecular weight (8,350 g/mol, 11,500 g/mol, 15,500 g/mol) were 34.0%, 36.2%和39.1% respectively, which is much larger than linear soluble polymers. The membrane properties were improved. Surface contact angle increased to 80.9°and water flux increased to 283.1 L/m~2·h.To increase the reservation of additive in membranes further, multi-block amphiphilic poly-ether with high molecular weight (UMF2) was synthesized. UMF2 was applied to prepare porous PVDF membrane via P-S process. SEM photos showed that UMF2 has better pore-inducing effect than F2. Element analysis data indicated that UMF2 has higher reservation in P-S process and simulated application than F2, 62.0 %和52.7 % respectively, which increase the hydrophilicity (contact angle is 87.0°) and water flux (535.6 L/m~2·h).To improve the transfer resistance of additives and decrease the lost, the amphiphilic comb-like polysiloxane (ACPS) containing polyether side chains was presented as the modification additive in preparation of hydrophilic pours PVDF membranes. The introduction of ACPS into membrane system increases the PVDF mechanical properties because of its good extending ability in PVDF matrix. The element analysis showed that the ACPS additive has high reservation in membrane formation process (84.0 %), higher than linear polymer systems. The XPS data proved the good enrichment of ACPS on surface (the ratio of ACPS content in membrane bulk to surface is 503.2 %).It is proved by previous researches from different molecular structure amphiphilic polymers that amphiphilic Copolymers have good modification effect on PVDF membrane because of their special properties. Between of these, multi-block amphiphilic poly-ether with larger molecular weight (UMF2) and amphiphilic comb-like polysiloxane (ACPS) containing polyether side chains have the best modification effect because of their higher reservation in membranes and enrichment on membrane surface.