Lignin-graphene oxide hybrid nanocoating for polymer foams: Dual functions of flame retardancy and toxic gas suppression

This study presents a fully water-based nanocoating that combines biomass-derived alkali lignin (AL) with graphene oxide (GO) to simultaneously achieve flame retardancy and effective suppression of toxic combustion gases in polyurethane (PU) foam. PU foam is widely used in construction but poses a serious fire hazard due to its high flammability and emission of toxic gases during combustion. To address this, an environmentally benign and scalable coating system was developed by exploiting the liquid-crystalline co-dispersion of GO and AL in water, forming a spontaneously aligned lamellar structure on the foam surface without the need for organic solvents or complex processing. At optimized loadings (10/10 wt%), the GO/AL coating reduced the peak heat release rate (pHRR) by 56.7 %, with further improvement up to 60.4 % at higher loadings. It also suppressed smoke density by 81 % and reduced emissions of reactive toxic gases (e.g., HCN, NO, HCHO) by up to 46 %. These enhancements are attributed to the synergistic interactions between GO and AL, where GO forms a thermally stable graphitic char barrier, and AL facilitates early-stage carbonization and scavenges combustion-derived radicals, thereby disrupting the emission pathways of toxic gases. By upcycling biomass-derived AL and leveraging the 2D-layered structure of GO, this system offers a sustainable, cost-effective, and industrially viable alternative to conventional FR approaches. The present findings highlight the broad applicability of GO/AL nanocoatings as next-generation fire safety solutions for enhancing the flame resistance of polymeric materials and reducing the risks of fire-related injury.