Environmentally Friendly Ionic Liquid: Synergistic Flame Retardation and Mechanical Reinforcement of Epoxy Resin

Epoxy resins are widely utilized owing to their excellent chemical resistance, favorable dimensional stability, and strong adhesion. However, their inherent flammability, high brittleness, and low impact strength significantly restrict their application in high-performance fields. In this study, a novel and environmentally friendly reactive ionic liquid, [PPyam]Ps, was designed and synthesized to modify epoxy resins, aiming to enhance both flame retardancy and mechanical properties. This ionic liquid is free of halogens and heavy metals, consistent with the principles of green and sustainable development. According to the study, after modification with [PPyam]Ps, the epoxy resin exhibits a limiting oxygen index (LOI) of up to 31.8% and achieves a V-0 rating in the UL-94 test. Furthermore, its peak heat release rate (PHRR) and total heat release (THR) are reduced by 35.3% and 38.9%, respectively. Notably, [PPyam]Ps remains in a liquid state during the epoxy curing stage, reducing the prepolymer viscosity, improving system flowability and wetting behavior, and acting as an internal plasticizer. Consequently, the tensile strength, flexural modulus, and impact strength of the resulting composite increase by 34.4%, 63.24%, and 68.95%, respectively. This work provides a new strategy for developing high-performance epoxy composites that integrate excellent flame retardancy and mechanical properties. Highlights A P, N, S reactive ionic liquid flame retardant was synthesized. It integrates multi-element flame retardancy, plasticization, and co-curing. It boosts epoxy flame retardancy via gas and condensed phase synergy. It improves epoxy mechanical properties via crosslinking and plasticization.