Relationship between polymers compatibility and casting solution stability in fabricating PVDF/PVA membranes

- MLiSSP was employed to investigate solution stability for casting solutions.
- Compatibility of polymers has a strong correlation with casting solution stability.
- The critical TSI was determined to be 4.3 with an enthalpy≤10×10−3 cal/mol.
- Best antifouling performance was observed for PVDF/PVA membrane with 0.1 wt% PVA.

Antifouling membranes are of great importance to the applications of membrane technologies for water and wastewater treatment. Blending with hydrophilic polymer to provide enhanced antifouling properties for polymeric membranes is regarded as a facile method, while in preparation process the compatibility of membrane materials and blending agents may cause changes in casting solution stability, thus significantly affecting the physicochemical properties of modified membranes. However, the relationship of membrane materials compatibility and casting solution stabilities remains unanswered. In this study, for the first time, the relations of polymers compatibility and casting solution stability are disclosed in fabricating poly(vinylidene fluoride)/poly(vinyl alcohol) (PVDF/PVA) membranes. Results showed that there existed a strong correlation of compatibility with solution stability, and that the increase of incompatibility between PVDF and PVA resulted in deterioration of casting solution stability as revealed by multiple light scattering spectroscopy (MLiSSP). The critical Turbiscan stability index (TSI) was determined to be 4.3 based on the nexus of compatibility-stability (the enthalpy≤10×10−3 cal/mol); otherwise, a TSI value higher than 4.3 might cause the deterioration in properties of formed membrane. Casting solution with 0.1 wt% PVA showed favorable stability and compatibility of blend polymers, and the formed membrane exhibited better intrinsic membrane properties and enhanced antifouling behavior. The obtained results highlight the nexus of compatibility-stability to be an important factor in fabricating polymeric membranes via addition of hydrophilic polymer.

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