Biomass-derived polyelectrolyte fire retardant: Synergistic phosphorus-nitrogen doping for enhanced epoxy resin flame retardancy and smoke suppression

A bio-based polyelectrolyte based on chitosan (CS) and sodium pyrophosphate (TSPP) was synthesized (TSPP-CS) by coprecipitation method. The resulting flame retardant was then incorporated into epoxy resin (EP) composites to improve their flame retardant properties. The structure, morphology and composition of the flame retardant were analyzed by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and Inductive Coupled Plasma Emission Spectrometer (ICP). The flame retardancy of EP composites was evaluated using cone calorimeter (CCT) testing. The results showed that the addition of only 0.68 % P content to the system resulted in a significant reduction in the flame retardancy of the composites compared to neat EP. After combustion, the expansion height of the residual char is higher and more compact, and the degree of graphitization is improved, which provides better substrate protection. Additionally, the addition of TSPP-CS had a positive impact on the mechanical properties of EP.