Preparation of Polyvinylchloride Membranes from Solvent Mixture by Immersion Precipitation

Abstract

In this study, polyvinylchloride (PVC) membranes were prepared through the immersion precipitation method using a mixture of two solvents (tetrahydrofuran (THF) and dimethyl formamide (DMF)), which had different affinities with the nonsolvent (water). Membranes prepared from PVC/THF/water system showed a sponge-like structure with isolated pores, which were impermeable to water even at a feed pressure of 20 bars, whereas those prepared from PVC/DMF/water exhibited a porous macrovoid ontaining morphology with a high water flux. The precipitation time and polymer concentration profiles were calculated by using a simple mathematical model and were in good agreement with the experimental findings on PVC/THF/water and PVC/DMF/water systems.<br><br>By using a mixture of DMF and THF as solvent and changing the mixed solvent composition, membranes with different morphologies from sponge-like to macrovoid containing were obtained. The membranes showed no water flux below a DMF concentration of 50 wt % and then became increasingly permeable with increasing DMF content in the casting solution. Measurement of the system cloud points showed a linear change of system thermodynamics with variation of the mixed solvent composition. The obtained<br><br>results showed that although the system thermodynamics could explain the overall behavior of the system, but the local changes such as change of membrane performance from impermeable to permeable at a certain mixed solvent composition could not be explained by the thermodynamics alone.