Dopamine-Based Interfacial Design for Enhancing Flame Retardancy and Fire-Warning Capability in Rigid Polyurethane Foam

Rigid polyurethane foam (RPUF) is widely used as a thermal insulation material in building energy conservation. Nevertheless, its inherent flammability severely limits its safe applications. Conventional flame-retardant strategies rely on the direct incorporation of flame retardants into the matrix. Although effective in improving fire safety, these strategies often disrupt the foam structure and lead to a marked deterioration of mechanical properties. In this work, a biomimetic interface modification strategy integrating active fire warning and passive fire protection was proposed to mitigate the fire hazards of RPUF. On the basis of the mussel adhesion mechanism, a biomimetic flame-retardant microcapsule (PDA@EG) was constructed by surface-modifying expandable graphite (EG) with polydopamine (PDA) and subsequently incorporated into RPUF to fabricate RPUF/PDA@EG foam composites. The abundant catechol and amine groups on the PDA surface significantly improved the interfacial compatibility between EG and the RPUF matrix, thereby promoting the uniform dispersion of PDA@EG. The resulting RPUF/PDA@EG foam composites exhibited an excellent flame retardancy. The RPUF/PDA@EG foam composites could achieve V-0 in UL-94 when the PDA@EG content reached 15 wt %. In particular, RPUF/25PDA@EG achieved a limiting oxygen index (LOI) of 42.6%. Meanwhile, PDA@EG significantly promoted the char formation. Compared with pristine RPUF, the peak heat release rate (pHRR), total heat release (THR), smoke production rate (SPR), total smoke release (TSR), and CO 2 production (CO 2 P) of RPUF/25PDA@EG were reduced by 63.9%, 69.4%, 77.8%, 95.1%, and 65.2%, respectively. Notably, the foam composites retained favorable compressive properties even with a high loading of flame retardants. More importantly, because of the uniform dispersion of PDA@EG, a continuous conductive network was formed upon thermal expansion. As a result, RPUF/25PDA@EG exhibited rapid and stable fire warning behavior, with a response time as short as 2.6 s and an alarm duration exceeding 6000 s. This biomimetic interface modification strategy offers a promising strategy for the design of multifunctional foam composites with flame retardancy and fire warning.