Optimal design of energy-saving foam with multifunctional characteristics: Superb flame retardancy, outstanding hydrophobic, excellent thermal insulation and robust mechanical performances

The adoption of rigid polyurethane foam (RPUF) in construction and rail transit offers energy conservation and emissions reduction benefits, but its inherent flammability presents challenges. Traditional fireproofing methods often disrupt foaming balance, ultimately compromising flame retardancy and mechanical properties. While flame retardant coatings preserve the bulk physical properties of materials, it tends to be sensitive to moisture. In this study, we propose to address the issues by employing a combined approach of nano-reinforcement and surface treatment. The results demonstrate that the addition of 3 wt.% bio-based Phosphorus-Nitrogen-containing nanosheet (HACP-PA) to RPUF increases its yield strength and compressive strength (at 60% strain) by 63% and 86%, respectively. Subsequently, the surface coating comprising of polydopamine-encased ammonium polyphosphate (APP@PDA), polyethyleneimine (PEI) and 1-octadecanethiol-wrapped polydopamine (PDA@ODT) imparts the RPUF nanocomposite with remarkable properties, including an LOI as high as 42.5%, a satisfactory V-0 rating in the UL94 test, 44% reduction in PHRR, 30% reduction in THR, 507% increase in residues, and a water contact angle of 137° More importantly, this method does not affect the excellent thermal insulation properties of the RPUF. In summary, this advancement tackles the challenges associated with RPUF's flammability and provides a bio-based, low-cost, and eco-friendly approach for developing multifunctional flame retardant RPUF with superior comprehensive properties.