Fabrication of Smart Flame-Retardant Epoxy Composites Modified by VO ₂ (M)-Based Microcapsules with Thermoelectric Response Performance

The development of high-performance flame-retardant materials with favorable thermal insulation properties is crucial for mitigating fire hazards and energy consumption in applications such as packaging and modern buildings. In this study, flame-retardant microcapsules (VUMF-APP) were synthesized via microencapsulation and electrostatic self-assembly with ammonium polyphosphate (APP) as the core, urea-melamine-formaldehyde (UMF) resin as the shell, and thermoelectric-responsive VO₂ (M) as the functional outer layer. These microcapsules were incorporated into epoxy resin (EP) to enhance the composite's (VUMF-APP-EP) thermal stability, flame retardancy, and intelligent early warning function. The VUMF-APP-EP composite exhibits notable thermal insulation performance with a thermal conductivity of 0.0117 W m⁻¹ K⁻¹. Compared to pristine EP, the composite shows reductions of 46.7% in peak heat release rate (pHRR) and 78.3% in total smoke production (TSP) and achieves a UL-94 V-0 rating, indicating its effective flame-retardant characteristics. Owing to the thermoelectric-responsive property of VO₂ (M) decorated onto the microcapsules, the epoxy resin composite demonstrates an intelligent early warning function, triggering alerts before fire ignition while maintaining flame retardancy. This dual functionality contributes to timely fire prevention and the reduction of potential property damage and casualties.