Synthesis of phytic acid-layered zinc oxide hybrid nanoparticles and their flame-retardant applications in polyurethane coatings

Phytic acid (PA)-coated zinc oxide (ZnO) nanoparticles were developed to produce high-efficiency flame-retarding (FR) additives for coating formulations. These hybrid (organic/inorganic) additives were fabricated using a layer-by-layer (LBL) approach to harness the FR properties of PA and ZnO on a single-platform nanoscale scaffold. These nanoparticles can be uniformly dispersed in a polyurethane (PU) coating for applications on metal substrates. The incorporation of the PA/ZnO layer-by-layer nanoparticles at 20 wt% of the polymeric resin did not adversely affect the physico-mechanical properties of the coatings. Flame-retardant properties of PU samples containing nanomaterials, showed a 50% reduction in flame spread rate than that observed from the samples prepared with only ZnO nanoparticles. Cone calorimeter studies performed on the metal panels coated with 20 wt% PA/ZnO nanoparticles-infused PU resins showed a 25% reduction in peak heat release rate and a 50% reduction in total heat release (THR) compared to control coatings prepared without nanoparticles. Scanning electron microscopy images revealed the presence of bubble-like morphologies in the burnt samples containing the nanoparticles, indicating char formation and obstruction of escaping gases produced during the burning of the coating materials. This study clearly reveals that the coatings prepared with PA/ZnO hybrid nanoparticles can protect metal substrates against fire-related damage.