Tailor-made zwitterionic polyurethane coatings: microstructure, mechanical property and their antimicrobial performance

Antimicrobial coating is of great important in leather finishing. Herein, we report a newly synthesized polyurethane with zwitterionic sulfobetaine side groups and evaluate their performance in the antifouling leather coatings. The microstructure of the synthesized zwitterionic polyurethane (iNPU) films has been examined by Fourier transform infrared (FTIR), X-ray diffraction (XRD) and atomic force microscopy (AFM) in order to understand how it influences the mechanical and surface properties. Our results show that introduction of zwitterionic groups into polyurethane can markedly increase the degree of microphase separation between the hard and soft segments of the PU chains since the incorporated zwitterionic group leads to more hydrogen bonding and polar interactions, making the hard components to be more thermodynamically incompatible with the soft segments. As the content of the incorporated zwitterionic content increases, the ordered structure in PU chains is reduced, and the micro-phase separation degree is increased. Therefore, the tensile strength and elongation at break of the iNPU films are significantly improved. Dynamic mechanical thermal analysis (DMTA) results further indicate that the Tg of the iNPU coatings decreases, and the deformability greatly increases at a higher content of zwitterionic group. Water contact angle (WCA) measurements reveal the improved surface wetting property due to the presence of zwitterionic group. The antibacterial testing shows that the iNPU coated leather surfaces exhibit reasonably good anti-mold adhesion performance, although the iNPU films do not show apparent contact-killing antibacterial property against E. coli and S. aureus. The present zwitterionic polyurethane is thus can be potentially used as antimicrobial adhesive leather coatingmaterials.