Phytic acid–based flame retardant and its application to poly(lactic acid) composites

White pollution substantially impairs people's quality of life nowadays. Bio-based polymers that are environmentally friendly and biodegradable have garnered interest. Among them, polylactic acid (PLA) has attracted wide attention due to its excellent biodegradability, high transparency, and easy processing. However, its inherent flammability, low toughness, and poor compatibility with flame retardants severely limit its application scope. In this paper, a phytic acid-based flame retardant glycidyl methacrylate phytate (GPA) was prepared by epoxy ring-opening and phosphate transesterification. GPA was grafted onto PLA through free radical polymerization, and the introduction of GPA improved both the mechanical properties and flame retardancy of PLA. The LOI of PLA composite rose to 28% after adding a 6 wt% GPA. A reduction of 11.7% in the total heat release of the PLA-GPAX was observed in comparison to neat PLA, demonstrating that the prepared PLA composite exhibits high flame retardancy. Due to the improved dispersion and compatibility of GPA in the matrix after grafting onto PLA, the mechanical strength of PLA increased by 19.9%. This study provides a feasible method for improving the compatibility between flame retardants and bio-based polymers, achieving a mutually beneficial situation in flame retardancy and mechanical strength, and further expanding the application range of bio-based materials.