Effect Of Additives On Morphology And Performance Of PVDF Hydrophobic Membranes

It is a effective method for preparation of high hydrophobic polyvinylidene fluoride(PVDF) porous membrane with rough substrate assisted phase separation at a high humidity. In this paper, hydrophobic polyvinylidene fluoride(PVDF) membranes were fabricated by one-step gel method to simplify the membrane technology and improve the performace of membrane based on PVDF/N,N-dimethylacetamide/ octanol/water system. Effects of single or composite additives of polymer and nano particle on the morphology and performance of PVDF membrane were researched.First of all, it was studied that the effects of additives on the thermodynamics and gel kinetics of the casting solution system by the analysis of themodynamic properties and the test of viscosity and gel test of casting solution.The results showed that the content of additicves in the casting solution increased, the thermodynamics stability of casting solution will be worse and phase separation will be strengthening.The effects of four single additives such as polymer, nano particles, inorganic salts and liquid non-solvent, on the membrane morphology and performance were explored by scanning electronic microscopy, contact angle, gas flux, mechanical performance and other analysis methods.It was found that the cross-section macroporous morophology developed fully and it is beneficial to increase gas flux of PVDF membrane, while hydrophhobic reduced because of the small amount of residual additives in PVDF membrane. Nanoparticles additives maked membrane generate more spherulite on the membrane bottom surface, and it is beneficial to maintain or even enhance hydrophobicity of membrane, but the gas flux decreased. Inogranic salt additives make the roughness of membrane bottom surface increase, and the hydrophobic,gasflux and mechanical performance were better. Non-solvenr additives make the membrane generate a certain thickness of spherulite stack structure, it is beneficial to increase the hydrophobic of PVDF membrane, the overall performance of membrane with phosphoric acid as additives was best, and it can keep the hydrophobic property and mechanical properties, in the meantime improved the gas flux of membrane obviously. Different kinds of additives can keep the mechanical of PVDF membrane well.On the basis of the above-mentioned study, different kinds of additives were choosed for mixing, and effect of composite additives on PVDF membrane morphology and performance was studied,and the result showed that, when the composite additives of H3PO4-SiO2 were added in the casting solution, the mass content of SiO2 is 1.5wt%, the mass content of H3PO4 is 2wt%, the comprehensive perfommance was best, contact angle is 142.6°,gas flux is 0.055 m3·m-2·s-1 at 0.06 MPa pressure,tensile strengle is 4.18 MPa. when the composite additives of PVP-SiO2 were added in the casting solution, the mass content of SiO2 is 1.5wt%, the mass content of PVP is 2wt%, the comprehensive perfommance was best, contact angle is 133.8°,gas flux is 0.208 m3·m-2·s-1 at 0.06 MPa pressure, tensile strengle is 4.24 MPa. The PVDF membranes of two methods of preparation have the optimum combination of properties.