Crosslinking effect in nanocrystalline cellulose reinforced sulfonated poly(aryl ether ketone) proton exchange membranes

Two novel series of poly(aryl ether ketone)s (PAEK) bearing pendant carboxylic acid groups have been synthesized, and subsequently sulfonated to obtain sulfonated poly(aryl ether ketone)s with carboxylic acid groups (SPAEK-COOH-x). The expected structures of the sulfonated copolymers were confirmed by FTIR. Modified nanocrystalline cellulose (NCC) was prepared and introduced into the SPAEK-COOH-x as the “performance-enhancing” filler and crosslinking agent. The nanocomposite proton exchange membranes were prepared via a solution-casting procedure. The composite membranes containing NCC presented the higher proton conductivity and better mechanical properties. After further crosslinking, the covalent crosslinked composite membranes showed even better mechanical properties while the proton conductivity and thermal stability were maintained. The hydrophilic/hydrophobic domains were observed from the TEM morphology investigation of COOH-10/NCC-y and C/COOH-10/NCC-y membranes. A balance of mechanical stabilities, proton conductivity, and thermal property could be designed by the incorporation of NCC and the crosslinking between NCC and SPAEK-COOH-10 to meet the requirements for the applications in the fuel cells. Suggested proton transfer mechanism in the crosslinked membranes. [Display omitted] •Two sulfonated poly(aryl ether ketone)s copolymers with different carboxylic acid group ratio were synthesized.•NCC was dispersed into SPAEK-COOH-x to prepare the nanocomposite for PEM, which showed excellent properties.•The covalent crosslinked membranes exhibited excellent mechanical properties compared to the physical crosslinked membranes.