Effects of substrates on the thermal stability of thin-film composite polyamide nanofiltration membranes

High-temperature nanofiltration (NF) technology is essential in various industrial applications. However, the thermal instability of thin-film composite (TFC) membranes remains inadequately addressed. As a crucial constituent of TFC NF membranes, substrate membrane is highly important to the thermal stability of TFC membranes. Herein, four commercial ultrafiltration membranes were used as substrates to fabricate TFC NF membranes via support-free interfacial polymerization, which generates polyamide selective layers with high crosslinking degree. Combining experimental characterizations and COMSOL Multiphysics® thermal-stress simulations, we decoupled the decisive roles of substrate glass transition temperature (T_g) and coefficient of thermal expansion (CTE) in determining membrane integrity at high temperature. Results show that TFC membranes supported by substrates with low T_g or high CTE exhibit a significant decline in MgSO₄ rejection at high temperature. In contrast, substrates with high T_g and suitable CTE induce TFC membranes with a superior water permeance (33.4 L m^-2 h^-1 bar^-1), a desirable MgSO₄ rejection (96.4%), and good operation stability at 85 °C. This work reveals the roles of substrate membranes and demonstrates the design of thermally stable TFC NF membranes for high temperature separation.