Surface modification of membranes for the separation of volatile organic compounds from water by pervaporation

Surface modifying macromolecules (SMMs) are oligomeric fluoropolymers synthesized by urethane chemistry and tailored with fluorinated endgroups. Two novel SMM formulations were blended into polyvinylidene fluoride (PVDF) casting solutions containing N,N-dimethylacetamide. Based on the advancing and the receding contact angle measurements, it was found that the SMM modified membranes exhibited higher surface hydrophobicity than the unmodified membranes. The effect of solvent evaporation time and SMM concentration in the PVDF casting solution has been investigated. The membranes were characterized by scanning electron microscopy. Pervaporation experiments were carried out for dilute chloroform/water binary mixtures and the relationship between the membrane characteristics and the pervaporative performance of the membranes is discussed.

The PVDF flat-sheet membranes, modified by two types of surface modifying macromolecules (SMMs), showed chloroform selectivity in the separation of aqueous solutions containing a small amount of chloroform. The contact angle analysis demonstrated that the surface characteristics of PVDF/SMM blend membranes were dependent on the specific SMM formulation, solvent evaporation time and the concentration of SMM in the PVDF casting solution. The pervaporative membrane performance was improved with increasing SMM content in the PVDF casting solution and the solvent evaporation time up to 7 min. Morphology change occurred at 10 min of solvent evaporation time both for the modified and the unmodified PVDF membranes.