Effect of polymer-solvent compatibility on polyamide hollow fiber membranes prepared via thermally induced phase separation

In this study, five different types of polyamide (PA) (PA6, PA610, PA612, PA1010, and PA12) hollow fiber membranes were fabricated via thermally induced phase separation (TIPS). During the TIPS process, binary solvents composed of sulfolane (SFL) and N-methyl-2-pyrrolidone (NMP) were used as dope diluents, bore fluids, and quenching baths. The membrane morphology and filtration performance of the developed hollow fiber membranes were evaluated. Moreover, the effects of polymer-solvent compatibility and mass transfer during TIPS were investigated. Phase diagrams showed that NMP is more compatible than SFL with all PA types, thus the dope diluent was found to affect membrane bulk structure and performance. The PA-SFL systems provided cellular structure membranes through liquid-liquid phase separation, whereas PA-NMP systems influenced the formation of spherulitic structure through solid-liquid phase separation. The optimum SFL:NMP ratio of dope diluent differed depending on PA type. SFL:NMP ratio of binary bore fluid and quenching bath also affected membrane surface structure and permeability. The results suggested that the compatibility among the polymer, dope diluent, bore fluid, and quenching bath is important to obtain polyamide membranes with outstanding performance.