Fabrication of novel polyetherimide-fluorinated silica organic–inorganic composite hollow fiber membranes intended for membrane contactor application

Abstract

Hydrophobic surface can be produced by either lowering the surface free energy or enhancing the surface roughness or a combination of both. This study explored a novel method to form a highly hydrophobic organic–inorganic composite hollow fiber membrane by incorporating the fluorinated silica (fSiO2) inorganic layer on the polyetherimide (PEI) organic substrate. The formation of the composite membrane was examined and confirmed by ATR-FTIR, TGA and SEM. Ultrasonication test was conducted to examine the structural stability of the composite membrane. The experimental results revealed that the fSiO2 layer was tightly bonded to the PEI substrate through silane chemical reactions. The incorporation of the fSiO2 layer on the membrane surface could enhance the surface roughness and greatly reduce the surface free energy due to the hydrophobic compound perfluorodecyltriethoxysilane (PFTS). The hydrophobicity of the composite membrane surface was dramatically elevated, as evidenced by the dynamic contact angles increment, e.g. from original 66.7° to 124.8° for advancing values, and from 49.5° to 100.6° for receding values. In addition, it was observed the mechanical property of the composite membrane was better than some of the conventional polymeric membranes such as polyethersulfone (PES), and polyvinylidene fluoride (PVDF). The composite membrane was also not as brittle as the pure inorganic membrane.Highly hydrophobic membrane is the core element in gas–liquid membrane contactor and the newly developed PEI-fSiO2 composite hollow fiber membranes were intended for the use in such application. The CO2 absorption flux of the composite membranes was investigated in both physical and chemical absorptions in a gas–liquid membrane contactor system. Moreover, the membrane contactor showed a reasonably stable performance throughout the 31 days long-term operation using a 2M sodium taurinate aqueous solution as the liquid absorbent and pure CO2 as the feed gas. The chemical compatibility test indicated that after the long-term constant contact with the sodium taurinate, the hydrophobicity of the PEI-fSiO2 composite membrane still maintained and was much higher than that of original PEI substrate and conventional hydrophobic polymeric membranes such as PVDF. The incorporation of the fSiO2 inorganic layer not only offered high hydrophobicity, but also would protect the polymeric substrate from the attacks of chemical absorbents, making the membrane a longer lifespan.