Toward healthy and fire-safe building insulation: Multifunctional rigid polyurethane foams for simultaneous flame retardancy and formaldehyde removal

Indoor air pollution and fire safety are two major challenges in building insulation materials. In this work, a multifunctional rigid polyurethane foam (RPUF) was developed for healthy and fire-safe building insulation through the incorporation of alkali-activated graphite tailings geopolymer derived from industrial solid waste. A ternary halogen-free flame-retardant consisting of the geopolymer, chitosan oligosaccharide (COS), and melamine cyanurate (MCA) was explored to simultaneously improve the flame retardancy and formaldehyde adsorption performance. The results indicated that the incorporation of 2 wt.% geopolymer imparts RPUF with good flame retardancy, demonstrated by decreasing the peak of heat release rate (pHRR) from 178 to 84 kW·m -2 , and the Flame Retardancy Index (FRI) increasing to 8.26. The interaction between geopolymer catalytic charring and MCA decomposition promoted the formation of protective char structures and reduced the pyrolysis activation energy during thermal degradation. Moreover, an efficient formaldehyde adsorption around 61% while the thermal insulation performance of the foam was maintained. Adsorption kinetics and molecular dynamics simulations revealed that intraparticle diffusion played a dominant role in formaldehyde transport and capture. This study demonstrates a sustainable strategy and a new technical pathway to transform industrial solid waste to multifunctional building insulation materials with fire safety, indoor air purification, and thermal insulation functionalities.