High flame retardancy enabled by dual clays-based multilayer nanocomposites

In an effort to develop environmentally-benign nanocomposites with high flame retardant (FR) performances, clays-based nanocoatings are prepared via layer-by-layer (LbL) assembly technique. Clays-based bilayer films, consisting of cationic boehmite (BMT) and anionic montmorillonite (MMT), exhibit good fire-resistant properties, as confirmed by vertical and horizontal flame testing. A BMT/poly(acrylic acid) (PAA)/MMT system, assembled by adding a polyelectrolyte layer between inorganic layers, produces a thicker and heavier coating, which can be explained by the fact that PAA chains fill the gaps of clay sheets and provide additional interactive sites. A polymer-clay trilayer film greatly improves flame retardant properties over the bilayer configuration. Cone calorimeter reveals that a 10 TL BMT/PAA/MMT nanocomposite (∼155 nm thick) coated on polyurethane foams completely eliminates the second peak heat release rate and reduces other FR performances, compared to those obtained from the BMT/MMT system. Improved flame retardancy in BMT/PAA/MMT is attributed to the enhanced char yield upon the addition of PAA that induces more clay particles to be deposited without altering a densely packed nanobrick wall structure, which effectively shields the underneath materials from the heat of the flame and acts as a protective barrier to heat and gas.