High Performance PVDF/SMA Ultrafiltration Membrane And Structural Regulation Were Prepared By TIPS Method

Poly(vinylidene fluoride)(PVDF)is an excellent membrane material due to its high mechanical strength,good thermal stability and chemical resistance.However,natural hydrophobicity makes it prone to fouling in a water treatment.Most researches have been focusing on adjusting the membrane structure by selecting novel diluent or mixed diluent and few studies have been concentrating on the hydrophilic modification of PVDF fabricated by thermally induced phase separation(TIPS).Blending is an effect method to improve the hydrophilicity of the membrane.Thus.TIPS method and blending have been combined in this paper.First,amphiphilic poly(styrene-co-maleic anhydride)(SMA)has been used for the PVDF/ATBC solid-liquid phase separation system to adjust the membrane structure and to improve the hydrophilicity of the membrane.It has been indicated that high content of maleic anhydride had a positive effect on the change of the membrane structure.A suitable high boiling point organic reagent,acetyl tributyl citrate(ATBC),which can be used as both the solvent of SMA and the diluent of PVDF,was selected.PVDF would crystallize,but SMA would still solve in ATBC during the cooling process,and SMA would deposit on the surface and pore of the established PVDF matrix during the extraction process.Based on the results of the phase diagram,scanning electron microscopy(SEM),differential scanning calorimetry(DSC)and transmission electron microscopy(TEM).the membrane formation mechanism for SMA surface deposition and crystallization control was proposed,and the evolution of the membrane structure was investigated.The addition of SMA decreased the surface roughness and the BSA rejection ratio increased from 48%to 94.Thus,the TIPS-NIPS method can not only adjust the membrane structure but also form a layer as thin as 200 nm.Mixed diluent had been used to adjust the hollow fiber membrane structure.It can be indicated that the addition of non-diluent changed the system from solid-liquid phase separation to liquid-liquid phase separation.And also SMA sodium salt has been added to the system to affect the membrane formation process and to improve the hydrophilicity of the membrane.Post treatment had been used to improve the tensile strength and flux of the membrane.