Enhanced Flame Retardancy and Mechanical Properties of Polylactic Acid Composites with Phytate-Chelated Nanotitanium Dioxide-Modified Bagasse Cellulose

Despite the potential of polylactic acid (PLA) as a biodegradable polymer, widespread applications have been limited by its inherent flammability and brittleness. To overcome these issues, PLA was combined with a composite-reinforced flame-retardant filler (A-MBC/PA/A-TiO2) consisting of γ-aminopropyl triethoxysilane (APTES)-grafted microcrystalline bagasse cellulose (A-MBC), phytic acid (PA), and APTES-silylated titanium dioxide nanoparticles (A-TiO2). When 10 wt % A-MBC/PA/A-TiO2 was incorporated, the tensile and impact strengths of the PLA composite increased by 15 and 22%, respectively, relative to those of pristine PLA. The addition of 10 wt % A-MBC/PA/A-TiO2 resulted in PLA composites with a UL-94 V-0 rating and a high limiting oxygen index of 29% owing to a synergistic flame-retardant mechanism in the gas and condensed phases. The presence of A-MBC/PA/A-TiO2 contributed to the formation of a solid carbon layer containing P and Ti in the condensed phase as well as the release of PO· free radicals and N-containing noncombustible gases in the gas phase, which reduced the flammable gas and oxygen concentrations, thus providing a synergistic flame-retardant effect. In addition, molecular dynamics simulations of the PLA/(A-MBC/PA/A-TiO2) composite system were performed. The numerical and analytical results showed that A-MBC and A-TiO2 in the filler interacted strongly with the PLA matrix, which was beneficial for distributing the flame retardant in PLA and improving its mechanical and flame-retardant properties. This work demonstrates a strategy for simultaneously improving the flame retardancy and mechanical properties of PLA composites using a biobased composite flame retardant.