Novel chemical surface modification to enhance hydrophobicity of polyamide-imide (PAI) hollow fiber membranes

Membrane wetting is a major concern for the application of membrane contactors. In order to develop a novel hydrophobic membrane that can be used in membrane contactors, a hydrophobic surface modification method for Torlon^® polyamide-imide (PAI) membrane was explored, which has not been reported previously. Asymmetric microporous hollow fiber membranes were fabricated using PAI material followed by a simple surface modification using a silane coupling agent, 3-aminopropyltrimethoxysilane (APTMS), and a perfluro-compound (Fluorolink S10) to produce PAI hollow fiber membranes with a hydrophobic surface. The reactions between PAI and the modification reagents have been confirmed by experiments.Optimal modification conditions were investigated by varying the modification parameters, such as APTMS treatment temperature, APTMS concentration, APTMS treatment time, and Fluorolink S10 treatment time. The modified PAI membranes were, subsequently, characterized by a series of standard protocols in terms of membrane morphology, chemical structure, contact angle, porosity and critical water entry pressure. A preliminary study of using the modified membranes in a membrane contactor for CO₂ absorption was also carried out. The newly developed PAI hollow fiber membranes showed much higher hydrophobicity, the contact angle was improved from 76° to 108-117° and the critical water entry pressure was improved from 0.7-0.8bar to 2.1-4.0bar. Moreover, the modified PAI hollow fiber membranes showed reasonably high CO₂ flux by using water as a physical absorption liquid. The results indicate that the modified PAI membranes have great potential to be used in membrane contactor applications.