Layer-by-Layer Assembly of TiO₂ Nanoparticle/Poly(acrylic acid)/Montmorillonite Trilayer Composite Films as Flame-Retardant Coatings

In order to create green nanocoatings with high fire resistance, titanium dioxide (TiO2), montmorillonite (MMT), and poly(acrylic acid) (PAA) are used as the flame-retardant (FR) system that is prepared by the layer-by-layer self-assembly technique. The thermal behaviors and FR performance of the coated fabrics and polyurethane foam (PUF) are determined by thermal gravimetric analysis, vertical/horizontal flame tests, and a cone calorimeter. The effect of layering polymers between metallic nanoparticles (NPs) and clay sheets on growth behavior and flame retardancy is investigated. The assembly of a TiO2/PAA/MMT trilayer (TL) system, incorporating a polyelectrolyte layer between the inorganic layers, results in a significantly thicker and heavier coating. This could be attributed to the infiltration of PAA chains into the interstitial spaces of the clay sheets and TiO2 NPs, which also introduce additional interactive sites. The addition of polymers in the multilayered composites greatly improves FR properties. Cone calorimeter analysis demonstrates that a 10 TL TiO2/PAA/MMT nanocomposite, approximately 160 nm in thickness, applied to PUF, completely suppresses the second peak heat release rate and enhances other fire-retardant properties relative to the TiO2/MMT system. The markedly enhanced flame retardancy observed in the TiO2/PAA/MMT system is attributed to the increased char yield facilitated by the incorporation of PAA. The addition of polymer layers promotes the deposition of a greater quantity of clay and TiO2 NPs while maintaining a tightly packed nanobrick wall structure.