Organic-inorganic hybrid functionalized chitosan/ammonium polyphosphate (APP): A synergistic strategy for flame-retardant and high-mechanical-strength epoxy thermosets

Epoxy resin (EP) is an industrially essential polymer widely used in electronic packaging , adhesives, and construction. Despite its utility, the high flammability of EP poses a significant safety risk. In this study, a novel chitosan-derived organic-inorganic hybrid flame retardant (CPMM) was synthesized, which was then combined with ammonium polyphosphate (APP) and added to epoxy resin (EP) to produce high-performance flame-retardant epoxy thermosets . Samples containing 7.5 wt% CPMM and 7.5 wt% APP reached a limiting oxygen index (LOI) of 30.5 % and a V-0 rating, along with a marked decrease in peak heat release rate from 1447.0 kW/m 2 to 267.1 kW/m 2 compared to pure EP. Thermogravimetric analysis indicated that the synergistic effect of CPMM and APP promotes the formation of more complete intumescent char structures, thereby enhancing the flame-retardant properties of the epoxy thermosets . Furthermore, mechanical performance tests showed improvements in both tensile and flexural strengths due to the robust interaction between CPMM and the matrix. This study provides a promising strategy for the design of bio-based organic-inorganic hybrid flame retardants and epoxy thermosets with enhanced performance.