Yoshikage Ohmukai

Solidification Behavior of Polymer Solution during Membrane Preparation by Thermally Induced Phase Separation

The solidification behavior of poly(vinylidene fluoride) (PVDF) solution during membrane preparation by thermally induced phase separation (TIPS) was investigated. Apparatus newly developed in our laboratory was used to quantitatively measure membrane stiffness during phase separation. In this apparatus, a cooling polymer solution, placed on a stage, is moved upwards and the surface of the polymer solution contacts a sphere attached to the tip of a needle. The displacement of a blade spring attached to the needle is then measured by a laser displacement sensor. Different phase separation modes, such as liquid-liquid (L-L) phase separation and solid-liquid (S-L) phase separation (polymer crystallization) were investigated. In the case of S-L phase separation, the stiffness of the solution surface began to increase significantly just before termination of crystallization. In contrast, L-L phase separation delayed solidification of the solution. This was because mutual contact of the spherulites was obstructed by droplets of polymer-lean phase formed during L-L phase separation. Thus, the solidification rate was slower for the L-L phase separation system than for the S-L phase separation system.

Preparation of a PVDF hollow fiber blend membrane via thermally induced phase separation (TIPS) method using new synthesized zwitterionic copolymer

Antifouling properties of PVDF hollow fiber membrane were improved by the addition of a new synthesized zwitterionic copolymer. This copolymer was synthesized using methyl methacrylate and the zwitterionic monomer 3-(methacryloylamino)propyl-dimethyl(3-sulfopropyl) ammonium hydroxide) (MPDSAH). The copolymer was used as additive in the preparation of a poly(vinylidene fluoride) (PVDF) hollow fiber membrane via thermally induced phase separation. With addition of the copolymer, the crystallization temperature and spherulite growth rate of the polymeric solution decreased sharply. Quartz crystal microbalance with dissipation monitoring results showed that bovine serum albumin (BSA) interactions with the prepared PVDF/copolymer film sharply decreased with addition of the synthesized copolymer. BSA filtration results showed that the membrane had higher antifouling resistance than a membrane without the copolymer additive.

Poly(vinylidene difluoride)/poly(tetrafluoroethylene-co-vinylpyrrolidone) blend membranes with antifouling properties

To inhibit fouling phenomenon in membrane process, a new amphiphilic copolymer, poly(tetrafluoroethylene-co-vinylpyrrolidone) (P(TFE-VP)), was blended with poly(vinylidene difluoride) (PVDF) to fabricate a series of antifouling membranes via non solvent induced phase separation (NIPS) method. The effect of copolymer blend ratios and TFE/VP ratios on membrane properties were evaluated, and the stability of P(TFE-VP) in PVDF membrane was studied. The membrane morphology was controlled by adjusting polymer concentration in dope solution, such that all membranes have similar pore size and density, as well as pure water permeability. In evaluating the effect of TFE/VP ratios, the content of VP in dope solutions was also adjusted to allow a fair comparison. We found that for P(TFE-VP) with a higher VP content, adsorption of BSA on polymer film was negligible. Higher blend ratios of this copolymer resulted in higher surface VP content and better hydrophilicity, but antifouling performance ceased to improve when blend ratio was larger than 1:9 (copolymer:PVDF). Meanwhile, a lower VP content in copolymer resulted in inferior hydrophilicity and severe fouling of the blend membranes. It was also proved that comparing with PVP homopolymer, P(TFE-VP) had satisfying stability inside PVDF membrane.