Comparison study of the effect of blending method on PVDF/PPTA blend membrane structure and performance

A novel hydrophilic poly (vinylidene fluoride)/poly (<i>p</i>-phenylene terephthalamide) (PVDF/PPTA) blend membrane was prepared by <i>in situ</i> polycondensation of <i>p</i>-phenylene diamine (PPD) and terephthaloyl chloride (TPC) in PVDF solution with subsequent nonsolvent induced phase separation (NIPS) process. For comparison, conventional solution blend membrane was prepared directly by adding PVDF powder into PPTA polycondensation solution. Blend membranes were characterized by means of viscometry, X-ray photoelectron spectroscopy (XPS), Field Emission Scanning Electron Microscopy (FESEM). The effects of different blending methods on membrane performance including water contact angle (WCA), mechanical strength, anti-fouling and anti-compression properties were investigated and compared. Stronger interactions between PVDF and PPTA in <i>in situ</i> blend membranes were verified by viscosity and XPS analysis. The incorporation of PPTA accelerated the demixing rate and caused the formation of a more porous structure in blend membranes. <i>In situ</i> blend membranes exhibited better hydrophilicity and higher tensile strength. The optimal values of WCA and tensile strength were 65&#176; and 34.1 MPa, which were reduced by 26.1% and increased by 26.3% compared with pure PVDF membrane. Additionally, antifouling properties of <i>in situ</i> blend membranes were greatly improved than pure PVDF membrane with an increasing of flux recovery ratio by 25%. Excellent anti-compression properties were obtained in <i>in situ</i> blend membranes with a stable pore morphology. The correlations among membrane formation mechanism, structure and performance were also discussed.