Flame Retardant Nanocoatings for the Protection of Polyurethane Foam

Abstract

Layer-by-layer (LbL) assembly is a simple technique capable of building multifunctional thin films on a variety of surfaces from dilute aqueous solutions. LbL coatings on polyurethane foam have been successful in reducing the flammability through environmentally friendly means. This technology provides a potential avenue for replacing halogenated flame retardants which are successfully used on foams, but present a toxic threat to health and the environment. A thin film nano-brick wall structure composed of chitosan and vermiculite clay was combined with an all-polymer film of chitosan and ammonium polyphosphate to form a stacked coating on polyurethane foam to reduce flammability. Individually, the coatings were able to reduce flammability of the foam, however the all-polymer coating was unable to prevent total degradation of the polyurethane due to inability to form char prior to the collapse of the foam. The nano-brick wall provided the necessary structure to allow the all-polymer coating to act and form an expanded insulating char layer that prevents flame spread across the surface of the polyurethane as well as reduce the peak heat release rate of the foam significantly. Incorporating carbon nanotubes into a LbL assembly allowed further reductions in polyurethane foam flammability. Only a few layers of nanotube-containing polymer layers were able to completely prevent flame propagation in both horizontal and vertical flame tests. Cone calorimetry revealed significant reductions in peak heat release rate as well as total smoke release. Reduction in heat release rates and smoke release are important factors towards extending escape time in a fire scenario. Barrier fabrics are commonly used to protect flammable materials. A polyelectrolyte complex was used to coat cotton fabric and prevented flame spread and ignition of underlying polyurethane foam. This study also highlights the importance of testing combined fabric and foam assemblies as pertaining to upholstered furniture. Cone calorimetry is a useful instrument to ascertain interactions between varying fabric and foam compositions and potentially will highlight an appropriate method for flame retarding the combination.