A new bio-based waterborne polyurethane/silica coating efficient against common and marine bacteria

Abstract

A new antibacterial waterborne polyurethane (WPU)/silica film was synthesized from the silane-functionalized hydroxyl telechelic natural rubber (SiHTNR) as bio-polyol, dimethylolpropionic acid (DMPA), and hexamethylene diisocyanate (HDI) by emulsion polymerization, then blended with nanosilica particles and antibacterial agents. The SiHTNR was prepared by grafting (3-mercaptopropyl) trimethoxysilane (MPTMS) to the hydroxyl telechelic natural rubber oligomers backbone (HTNR) issued from natural rubber, by thio-ene click reaction. The chemical structure of SiHTNR was confirmed by ¹HNMR and ²⁹SiNMR spectroscopy. The SiHTNR was used to successfully synthesize silane-functionalized WPU(SiWPU). The effect of nanosilica (SiO₂) content was studied on the morphology of SiWPU/SiO₂ particles and the mechanical properties, wettability and thermal properties of films. The TEM image indicated that siloxane functional group was successfully incorporated into the SiHTNR and showed interactions in silica-silica particles and the silica-SiWPU matrix, leading to a larger particle size with increasing nanosilica content. In addition, SiWPU/SiO₂ could form films and gave a more opaque yellow film with increasing nanosilica content. The tensile strength and thermal stability of SiWPU/SiO₂ films was improved and showed that single Tg and shifted toward higher temperature indicating the compatibility of nanosilica particles and confirmed stiffness characteristics of films with increasing nanosilica content. Finally, it was found that the efficacy of silver nanoparticles, chitosan, and sorbic acid to inhibit growth of E. coli, S. aureus and V. parahaemolyticus depends on the type and content of antibacterial agent. The minimum content of silver nanoparticles, chitosan, and sorbic acid to efficiently inhibit at least of 70 % of bacteria growth was 500 ppm, 200 ppm and 4800 ppm, respectively. However, the inhibition of E. coli growth required high contents of chitosan (600 ppm), while the inhibition of S. aureus required 8000 ppm of sorbic acid. Additionally, the release of these three types of antibacterial agents was investigated in the artificial seawater for 28 days. The behavior of silver nanoparticles and chitosan release showed increasing slope lines until day 14 while sorbic acid release showed increasing slope lines until day 7. After 28 days, the ratio of releasing content to antibacterial agent were 0.438:500Ag, 0.277:1600SB and 0.504:200CS. Comparatively, chitosan exhibits effective inhibiting E. coli, V. parahaemolyticus and S. aureus bacteria growth with a lower dose content, which is suitable for coating. This study offers an opportunity to use SiHTNR as bio-polyol to develop green antibacterial WPU film for coating in marine applications.