A facile and green approach for the surface coating of phosphorus-silicon functionalized graphene oxide to improve flame retardancy of polyurethane foam

Polyurethane foam (PUF) is the most widely used polymeric foam due to its excellent thermal insulation properties, low cost, and low density. However, its applications are limited by fire performance concerns and associated safety issues. This study describes the synthesis of a novel flame retardant and an environmentally friendly coating method aimed at enhancing the fire safety and mechanical integrity of PUF using a water-based polyethyleneimine (PEI) binder. A phosphorus/silicon-containing functionalized graphene oxide (FGO) was successfully synthesized by grafting graphene oxide (GO) with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 3-glycidoxypropyltrimethoxysilane (GPTMS). The chemical structure of FGO was confirmed by XPS, FTIR, and Raman spectroscopy. FGO and GO were subsequently coated onto PUF surfaces via a layer-by-layer assembly method. Combustion tests of the PUF/FGO (5 wt%) revealed a Limiting Oxygen Index (LOI) of 34.2% and a V-0 rating in the UL-94 test. Furthermore, real-time TGA-FTIR analysis demonstrated a 46% reduction in CO₂ evolution and a high char residue of 52%, indicating significant suppression of volatile fuel and smoke hazards. This fire protection is attributed to the formation of a dense phosphosilicate protective layer, which provides a robust barrier effect in both gas and condensed phases. Additionally, the coating treatment remarkably enhanced the mechanical performance of the foam. The compressive strength of PUF/FGO increased by 152% (1.34 MPa) compared to pristine PUF, as the FGO effectively infiltrated structural defects and reinforced the cellular framework. Consequently, FGO demonstrates superior efficacy over GO in providing a multifunctional solution for high-performance, fire-safe PUF.