Morphology Control Of Microporous Poly (Vinyl Chloride) Membranes Prepared Via High Temperature Phase Inversion

In this paper flat sheet microporous Poly(vinyl chloride) (PVC) membranes were prepared via high temperature phase inversion; the thermodynamic and kinetics fators influenced the PVC membrane formation process were studied; the systematic solutions to controlling the membrane morphology were introduced; the hydrophilicity of microporous PVC membrane was also improved by adding different additives or blending PVB.Firstly, using y-Butyrolactone (GBL)-DMAc as the mixed solvents, we estimated thermodynamically stablility by calculating the solubility parameter difference△δs-p between the mixed diluent and PVC. With the increasing content of GBL,△δs-p increased which caused the casting dope less stable in thermodynamic. The higher mass ratio of DMAc/GBL leaded to the lower mechanical property with the sponge-like structure changing to the finger-like structure along the cross section.Secondly, the PVC membrane were prepared by using mixed diluent DMAc/GBL=1/1. The effects of PVC concentration dope temperature and addtitve PVPK90 on the PVC membrane morphology and the performances were discussed. The lower mass ratio of PVC leaded to the higher flux and porosity and the higher temperature leaded to the lower prosity but higher flux. The higher flux, rejection and porosity but lower mechanical property membranes can be prepared by the addition of the PVP, with the smaller pores on top surface and finger-like structure changing to the taper-like structure along the cross-section.Thirdly, setting PVC concentration at 20wt.%, using GBL as diluent and PEG 400 as additive, the effect of PEG content on the membrane morphology and the performances were investigated. With the PEG content increasing from 10wt.% to 30wt.%, the cross-section of the membrane changed from finger-like structure to sponge-like structure, there was no apparent micropores on the top surface of the membrane at the magnification×10000. As the PEG content increased, the hydrophilicity of the prepared membrane enhanced and the porosity increased, but the flux hardly increased. Based on the previous work, the congulation bath changed from pure water to 50wt.%GBL and 95wt.%GBL solution. The 95 wt.% congulation bath leaded to apparent micropores on the top surface of the membrane with the flux increasing evidently.At last, using 20wt.% PEG400 as additive and 60wt% GBL as diluent, the preparation of PVC/PVB blending membrane was investigated. The hydrophilicity of the prepared membrane enhanced with the introduction of PVB. As the PVB/PVC proportion increased, the structure of the cross-section changed from sponge-like structure to net-like structure, the flux reached to 31.8 and the rejection of BSA(Mw=67000) was about 95%. The membrane also showed an excellent break strength of more than 5 MPa.