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Microporous polyvinylidene fluoride (PVDF) membranes were synthesized from PVDF/N-methyl-2-pyrrolidinone (NMP) solutions using an immersion-precipitation method with a 2-propanol/water mixture as a soft coagulant. The effects of membrane thickness on pore size distribution and surface/cross-section morphology were studied using capillary flow porometry and scanning electron microscopy (SEM), respectively. All the synthesized membranes had a small range of pore size distribution, with the pore size decreasing with increasing casting thickness. The semicrystalline PVDF membranes demonstrated significant variations in morphology under SEM observation, with the existence of polymer agglomeration at a casting thickness of 500 lm and above. The protein binding capacity was observed to be highest at a casting thickness of 400 lm, where optimum pore morphology provided a large surface area for protein binding.

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Statistical experimental design was employed to optimize the preparation conditions of polyvinylidenefluoride (PVDF) membranes. Three variables considered were polymer concentration, dissolving temperature, and casting thickness, whereby the response variable was membrane-protein binding. The optimum preparation for the PVDF membrane was a polymer concentration of 16.55 wt%, a dissolving temperature of 27.5°C, and a casting thickness of 450 µm. The statistical model exhibits a deviation between the predicted and actual responses of less than 5%. Further characterization of the formed PVDF membrane showed that the morphology of the membrane was in line with the membrane-protein binding performance.

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