Development of layer-by-layer assembled carbon nanofiber-filled coatings to reduce polyurethane foam flammability

Layer-by-layer (LbL) assemblies made with carbon nanofibers (CNFs) are shown to reduce the flammability of polyurethane foam. The 359 ± 36 nm thick four bilayer coating of polyethyleneimine/CNF (cationic layer) and poly(acrylic acid) (anionic layer) contains 51 ± 1 mass fraction % CNF. This coating completely covers the entire internal and external surfaces of the porous foam. Even though the microscopic CNF distribution was non-uniform, the macroscopic CNF network armor that was generated from this LbL process significantly reduced the flammability of the foam (e.g., 40% ± 3% reduction in peak heat release rate). Normalized by flame retardant concentration, the reduction in foam peak heat release due to these CNF coatings is 38% larger than CNF embedded in the foam and as high as 1138% greater than other commercial technologies used to reduce foam flammability.