A new DOPO-derived P/N/S flame retardant: Synthesis and application in epoxy resin for imparting flame retardancy, enhanced mechanical performance and acid-alkali corrosion resistance

In this study, a novel DOPO-based phosphorus/nitrogen/sulfur-containing flame retardant, TPD, was successfully synthesized and incorporated into epoxy resin (EP) at a low loading of only 4 wt%. The results showed that EP/4% TPD achieved a UL-94 V-0 rating, and its limiting oxygen index (LOI) increased from 21.8% to 30.5%, demonstrating excellent flame-retardant efficiency. Cone calorimetry revealed that the peak heat release rate (pHRR), total heat release (THR), total smoke production (TSP), and peak CO 2 release were reduced by 29.2%, 37.5%, 19.8%, and 23.0%, respectively, compared with neat EP, indicating a reduced fire hazard. Meanwhile, the incorporation of TPD enhanced the tensile strength and impact strength of EP by 10.6% and 76.4%, respectively. Furthermore, EP/4% TPD exhibited outstanding ultraviolet shielding performance in the 200–420 nm range while maintaining a certain level of visible light transmittance, along with improved resistance to acid and alkali and enhanced electrical insulation properties. These results demonstrate that TPD is a highly efficient multifunctional additive that simultaneously provides flame retardancy, mechanical reinforcement and toughening, UV shielding, corrosion resistance, and improved electrical insulation, offering a promising new approach for the development of high-performance epoxy resin composites.