Surface modification of polyvinylidene fluoride-co-hexafluoropropylene (PVDF–HFP) hollow fiber membrane for membrane gas absorption

The outer surface of polyvinylidene-co-hexafluoropropylene (PVDF–HFP) asymmetric microporous hollow fiber membrane prepared by phase inversion process was activated by 10 wt.% of NaOH solution, and subsequently modified with the mixture solution of α,ω-triethoxysilane terminated perfluoropolyether or Fluorolink®S 10 (FS10) and tetraethoxysilane (TEOS) in order to enhance the hydrophobicity of the membrane. The chemical and physical changes of the membranes were investigated by attenuated total reflection infrared spectroscopy FTIR-ATR and scanning electron microscope (SEM). The characteristics of the modified membrane were examined in terms of liquid entry pressure of water (LEPw), pore size and pore size distribution, contact angle and mechanical properties. The modified fibers were also used in the membrane contactor system to evaluate their performance for CO2 absorption. FTIR-ATR result showed the enrichment of fluorine and ethoxysilane on the modified PVDF–HFP membranes leading to higher LEPw and contact angle than those of the unmodified membrane by 36% and 33%, respectively. The contact angle increased from 95.5° to 127.8°. Compared to the unmodified PVDF–HFP hollow fiber, the cross-sectional morphology and mechanical properties of the modified membrane changed insignificantly, while the membrane mean pore size was reduced from 32.7 nm to 25.2 nm. The CO2 physical absorption performance of the modified fibers was better than the unmodified fibers. The membrane mass transfer coefficients of the unmodified and modified PVDF–HFP hollow fiber were 5.69 × 10−5 and 7.56 × 10−5 m/s, respectively, indicating that the modified membranes have good potential for application in the gas absorption process.