Study on the effect of air gap on physico-chemical and performance of PVDF hollow fibre membrane

Polyvinylidene fluoride (PVDF) was chosen in this study as the main material in fabricating membrane due to its excellent chemical resistance and good thermal stability. Combination of triethyl phosphate (TEP) with DMAc produce better structure of membrane which safer and provide high mechanical strength for membrane. Surface modified PVDF hollow fibre membrane (HFM) was prepared using dry-wet spinning technique by varying air gap namely 10 cm, 20 cm and 30 cm. The morphology was evaluated using scanning electron microscopy (SEM), atomic force microscopy (AFM), mercury intrusion porosimetry (MIP), contact angle, tensile test and performing water flux testing. From the characterization data, PVDF HFM with 3 wt.% PEG 400, HFM 3-10 and HFM 3-20 referred as microfiltration membrane with pore size range 0.1-0.8 µm. While, HFM 3-30 act as ultrafiltration membrane with pore size ranging 0.01-0.1 µm. Experimental results revealed that by increasing the air gap from 10 cm to 30 cm, the porosity and finger-like length decreased due to the higher elongational stress that shift the pores from broad to narrow. Thus, PVDF HFM at 10 cm air gap, HFM 3-10 achieve the highest water flux due to the higher porosity, longer finger-like length and hydrophilicity achieved. The modified HFM at shorter air gap was found to be a promising membrane structure for excellence water performance and eco-friendly to environment.