Fabrication and characterization of modified PVDF hollow fiber membrane coated with hydrophobic surface modifying macromolecules for desalination application

Polymeric membrane distillation (MD) can be used as a desalination application. It is a promising technology owing to mechanical stability, flexibility, and chemical resistance. However, polymeric-based MD needs to improve further due to low flux permeation in rejecting salt from seawater feed. PVDF hollow fiber membrane consisted of the hydrophilic (LSMM) and hydrophobic (BSMM) surface modifying macromolecules was fabricated. LSMM structure is end-capped by OH bonds which show hydrophilic nature while BSMM consists of a hydrophobic CF bond. By determining the appropriate ratio of LSMM and BSSM loading in the PVDF substrate, it could enhance the MD performance. LSMM could improve the hydrophilic nature at the lumen of the PVDF hollow fiber membrane which can promote the water flux permeation. On the other hand, the positioning of BSMM at the shell layer of the PVDF hollow fiber membrane through dip coating could lead to greater vapor transport. The effect of BSMM loading on the hydrophobicity, morphology, average pore size, porosity, thermal, and membrane performance was investigated. The BSMM loading at 1.5 wt% exhibited the highest contact angle value of 118.76°. Meanwhile, SEM images revealed finger-like structures as well as the LSMM and BSMM structures at the inner and outer layers of the modified PVDF membranes, respectively. The hollow fiber coated with 1.5 wt% BSMM offered the highest salt rejection percentage of 99.99%. Meanwhile, 1.0 wt% BSMM coated PVDF/PEG/LSMM membrane showed a maximum flux of 20.74 kg/m2.h. Furthermore, the melting point of the resulting membranes was 161 °C with various BSMM loadings which is the typical condition range for membrane distillation operation. In conclusion, the BSMM coating agent has a huge potential to improve the membrane's hydrophobicity and performance.