Effect of Additives on Hydrophobicity of PVDF Membrane in Two-stage Coagulation Baths for Desalination

This research aimed to improve the hydrophobic polyvinylidene fluoride (PVDF) membrane for direct contact membrane distillation (DCMD) desalination by mixing various additives (dibutyl phthalate and glycerol) in polymer solution via two-stage/dual coagulation bath (CB) system. The effect of each additive on the surface and cross-sectional morphology of PVDF membrane was investigated. The addition of additives showed increased in membranes porosity, but the water contact angle was less than 90 degrees when immersed in single CB (distilled water). Membrane prepared with two-stage CB system immersed into methanol CB for 20 min and transferred into distilled water CB for 24 h exhibited high water contact angle of 114.2 degrees, 142.6 degrees and 120.1 degrees for membrane M-3, M-4 and M-5, respectively. The porosity of membrane significantly increased when incorporated with additives. The membrane was further evaluated in DCMD operation for separation performance. The DCMD tested using distilled water and 35 g l(-1) of sodium chloride (NaCl) aqueous solution in feed showed M-4 achieved the highest flux among other membranes at 13.85 kg(-2) m(-2) h(-1) with 99% salt rejection under 70 degrees C of feed temperature.