Nanostructured Flame-Retardant Coatings Containing Layered Double Hydroxides ^†

In this work, a coating approach for obtaining flame-retardant EVA (Ethylene–Vinyl Acetate) and EBA (Ethylene–Butyl Acrylate) copolymer-based materials is proposed. To achieve this aim, firstly nanocomposite films of EVA and EBA were produced by cast extrusion, by using as nanofillers two types of layered double hydroxides (introduced at 5 wt.%), which have the same chemical nature (magnesium–aluminum with intercalated oleate anions) but differ in aspect ratio. The morphology of the nanocomposite films, as well as their thermal characteristics, was preliminarily assessed through rheological, thermal, and morphological analyses.

The films were then applied as coating to the corresponding neat copolymer substrate by compression molding, and the so-obtained samples were tested using a cone calorimeter. Despite the small amount of nanofiller (0.5 wt.% considering the whole specimen), the application of the coating films significantly improved the Time to Ignition as compared to the pristine copolymers, while the shape of the HRR curves and the HRR peak values remained largely unchanged.

In all, the obtained results demonstrated the effectiveness of the coating approach, since it allowed us to concentrate the flame-retardant action on the surface of a polymer system, where combustion specifically takes place; consequently, the required amount of flame retardant is minimized. This has a beneficial effect on the final mechanical properties of the material, since the tensile characteristics of the bulk polymer are preserved. Furthermore, introducing such a small amount of flame retardant does not affect the future recyclability of the polymer, which can be treated as its pristine (non-flame-retardant) counterpart.