Halogen-free Flame-Retardant and Smoke-Inhibiting Rigid Polyurethane Foam with Modified Expandable Graphite and Layered Double Hydroxides

Developing rigid polyurethane foam (RPUF) featuring well-balanced heat insulation, mechanical robustness, flame retardancy, and smoke inhibition properties through a halogen-free method is crucial for the advancement of building heat-isolated materials. In this study, a multi-component synergistic flame-retardant system was rationally constructed, consisting of Si/B ceramic precursors modified expandable graphite (EG-SB) and γ-aminopropyltriethoxysilane/phytic acid functionalized CeCoFe-LDH (LDH-SP), as well as ammonium polyphosphate (APP). Owing to the relatively low flame-retardant filler loading, the target RPUF composite retained an ordered pore structure with a low thermal conductivity of 0.028 W/(m·K). Besides, by virtue of the improved dispersibility of EG-SB and LDH-SP, the target RPUF composite exhibited desired compressive strength (0.21 MPa) and heat reliability (remaining char of 30.7 wt %). Benefiting from the remarkable cooperative flame-resistant effects of EG-SB, LDH-SP, and APP, the fire safety of the resultant RPUF composite was effectively enhanced (UL-94 V-0 grade; LOI value of 31.6%). Relative to pristine RPUF, the PHRR, THR, PSPR, and TSP parameters of the target RPUF composite decreased by 66.2%, 48.3%, 62.5%, and 92.9%, respectively, accompanied by significantly suppressed CO and HCN release. This work provides a feasible and viable route to fabricating high-performance RPUF thermal insulation materials with balanced comprehensive properties.