Study on the fabrication, characterization and performance of PVDF/calcium stearate composite nanofiltration membranes

In this study, hydrophobic nanofiltration membranes were fabricated by blending polyvinylidene fluoride (PVDF) and calcium stearate through nonsolvent induced phase inversion process. The prepared membranes were characterized by attenuated total reflectance infrared spectroscopy (FTIR-ATR), X-ray diffractometry (XRD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), field emission microscopy with energy dispersive X-ray spectroscopy (FESEM with EDX), scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle measurement, work of adhesion and mechanical strength analysis. The modified composite membranes were thermally and mechanically stable. The filtration performances of the membranes were examined by determining molecular weight cut off (MWCO), porosity, and water uptake rate. The highly hydrophobic character was confirmed by contact angle measurement, work of adhesion analysis and thickness parameters of the membranes. Low surface roughness was evident in AFM topography. The inorganic salts were highly rejected by these membranes in the following sequence Na2SO4 > MgSO4 > MgNO3 > LiCl > NaCl. Humic acid was used as the model foulant to testify the antifouling property. The flux recovery ratio (FRR) was high, ensuring excellent irreversible fouling. Membrane irreversible fouling was enhanced for its dominant charge effects, highly hydrophobic character and low surface roughness; diminishing the organic foulants to get deposited on the membrane surface and also acted with its self cleaning capacity. The modified membranes were good enough to withstand its stability and durability.