Packing Cross-linked Aerogel Beads in Rigid Polyurethane Foam towards Exceptional Mechanical Stiffness, Superior Thermal Insulation and Flame Retardance

Rigid polyurethane foam (RPUF), a widely used building insulation material, is intrinsically flammable. Adding flame retardants or fillers can address this issue, yet the key challenge lies in improving flame retardancy without sacrificing thermal insulation and mechanical properties. Here, chemically cross-linked and self-intumescent aerogel beads were designed and incorporated into RPUF via an in-situ packing and foaming method. In this method, the RPUF matrix firmly bonds the aerogel beads, resulting in “sea-island” structures. Notably, enabled by rigid crosslinked aerogel beads with excellent compatibility, G 5 M 2 P 1 /RPUF achieves a compression modulus of 15.62 MPa and strength of 3.29 MPa. These values represent increases of 101.3% and 265.6% over neat RPUF, surpassing most flame-retardant RPUF. Besides, benefitting from the “sea-island” structures, the G 5 M 2 P 1 /RPUF exhibits a thermal conductivity value of 28.1 mW -1 -1 , which is 21.5% lower than that of the pure RPUF. Compared to neat RPUF, G 5 M 2 P 1 /RPUF exhibits superior heat and smoke suppression with a 36.2% reduction in peak heat release rate and a 43.2% reduction in smoke production rate. Even after 3 days at 100% relative humidity, the density, mechanical modulus, strength, and LOI of the composite show almost no change, demonstrating good performance durability. This simple packing foaming strategy effectively overcomes the trade-off between fire safety and thermal performance, holding great application potential.