Green and Facile Synthesis of Bio-Based, Flame-Retardant, Latent Imidazole Curing Agent for Single-Component Epoxy Resin

Developing bio-based flame retardants according to a green and simple strategy has drawn extensive attention recently. Hence, a biomass-derived, flame-retardant, latent curing agent (IMPA) was synthesized via the neutralization between imidazole and phytic acid in water at room temperature and was applied for single-component epoxy resin (EP). The results indicate that the shelf life of the resultant EP (EP/IMPA) increases from <1 day of the control single-component EP to 10 days at room temperature. Meanwhile, EP/IMPA features a fast curing rate at modest temperature (80–150 °C), and its gel time at 100 °C is only 14 min. Notably, EP/IMPA achieves superior flame retardancy with a limiting oxygen index of 34.7% and UL-94 V-0 rating. The peak heat release rate (PHRR), total heat release (THR), and total smoke production (TSP) of EP/IMPA are reduced by 43.0%, 31.9%, and 31.5% compared with the control sample. The enhanced fire safety is ascribed to the flame-retardant function of IMPA in both gaseous and condensed phases. Hence, this work provides a green and feasible method to create bio-based, flame-retardant, latent curing agents for one-component epoxy systems.