Fire safety and high mechanical strength epoxy resin enabled by a bis-benzimidazole-primed phenyl phosphonic acid

Preparation of fire safety and high mechanical strength epoxy resin (EP) has become a hot topic for its valuable applications in construction and other fields. Here, bis-2-aminobenzimidazole-modified phenyl phosphonates (PP-BMI) with symmetric structures were synthesized by a simple chemical modification strategy, and its fine structure and composition have been thoroughly characterized. Due to the multifaceted functions of PP-BMI in both gaseous and condensed phases, EP composite with 5 wt% PP-BMI reached a UL-94 V-0 rating and high LOI of 34.3 %. The excellent fire safety of EP/5PP-BMI was further verified with a significant reduction of 57 %, 52 % and 46 % in peak heat release rate (PHRR), total heat release (THR) and peak CO production (P-COP), respectively, compared to the original EP. The flame retardancy of PP-BMI on EP can be attributed to the dilution of non-combustion gases, free radical trapping and catalytic charring functions. More importantly, PP-BMI can further enhance the mechanical properties of EP, which is closely related to the interaction between PP-BMI and EP matrix. Furthermore, EP/PP-BMI composites have good resistance to acids and alkalis, ensuring long-lasting flame retardancy and mechanical properties. This work provides a new strategy for realizing epoxy composites with high fire safety and excellent mechanical properties in construction and multifaceted areas.