Study On The Effects Of Template And Non-solvent Additive On The Preparation Of High Hydrophobic Porous PVDF Membrane

It is a simple method for preparation of high hydrophobic polyvinylidene fluoride(PVDF) porous membrane with template assisted phase separation. In this paper,hydrophobic polyvinylidene fluoride (PVDF) membranes were fabricated by different roughtemplates used N,N-dimethylacetamide as solvent and water as non-solvent coagulation bath.Effects of templates and non-solvent additives (NSA) on the process of template assitedphase separation were researched.The effects of templates, such as forsted glass, corrodent alloy aluminum and corrodentstainless templates, on the membrane morphology and performance were explored byscanning electronic microscopy, water contact angle, N2flux and other analysis methods. Itwas found that the hydrophobicity, permeability and mechanical strength of PVDFmembrane prepared with rough templates were better than that with smooth glass. The watercontact angle of PVDF membrane fabricated by corrodent alloy aluminum template reachedas high as135°, and its comprehensive performance was optimal. Through the experimentaldesign and XRD analysis, the influence mechanisms of templates on the structure andhydrophobicity of the bottom surface of PVDF membrane were discussed. It was revealedthat the membrane could be anchored to the metal template, so that the mass transfer ratebetween solvent and nonsolvent decreased and liquid-solid demixing was promoted. Besides,the micrometer-sized morphology of etched metal substrate provided induced crystallization.In this paper, ethanol,2-propanol,1-butanol, n-pentanol, n-hexanol, heptanol, n-octanol,nonanol and decanol were used as NSA respectively. The effects of NSA and its content onthermodynamic variation, casting solution viscosity and the rate of gelation were studied bythe method of titration,viscometer and gelation kinetics experiment. The influence of speciesand contents of NSA on structure and performance of PVDF membrane prepared withtemplate assisted phase separation was studied.The results showed that the addition of NSAcould reduce the stability of casting solution thermodynamically, which made phaseseparation more easily. The viscosity increased, but the gelation rate was slower in the orderof ethanol—decanol as NSA so that crystallinity increased and hydrophobicity of the bottomsurface of PVDF membrane increased and then decreased slightly. With the increase ofNSA content, the hydrophobicity of the bottom surface of PVDF membrane increased. Both the rough template and non-solvent additive had important contribution toimprove the hydrophobicity of PVDF membrane. Anchoring effect and inducedcrystallization provided the microstructure and improved the crystalinity of the bottomsurface of membrane. The addition of non-solvent additives made the rate of phaseseparation slow down and promoted the polymer crystallization internally. Their synergismmade membrane hydrophobicity increase.