High Flame Retardancy of Carbon Nanotubes Reinforced Polyelectrolyte Multilayered Nanocomposites

In pursuit of multifunctional flame-retardant coatings, a layer-by-layer (LbL) assembly was used to create hybrid nanocoatings by alternating the deposition of positively charged chitosan (CH) and negatively charged sodium lignosulfonate (Lg). Carbon nanotubes (CNT), dispersed in an Lg solution, were incorporated as robust reinforcements in polymer nanocomposites. Their high aspect ratio and dense network within the CH/CNT-Lg layers resulted in coatings that were notably thicker and heavier compared to those constructed without CNT. In horizontal flame tests, the presence of CNT led to superior fire resistance. Cone calorimetry further demonstrated that incorporating CNT into a single coating completely suppressed the second peak of heat release for polyurethane foam (PUF). Additionally, total smoke release, total smoke production, maximum average rate of heat emission, and effective heat of combustion were reduced by 68.9%, 72.7%, 47.7%, and 57.3%, respectively, compared to uncoated PUF. These improvements in flame retardancy are attributed to the enhanced thermal stability and high char yields provided by CNT. Overall, given the ease of applying LbL assembly, this strategy offers a promising halogen-free approach for improving fire safety in both natural and synthetic fibers.