Influence of layer by layer coatings containing octapropylammoniumpolyhedral oligomeric silsesquioxane and ammonium polyphosphateon the thermal stability and flammability of acrylic fabrics

The use of Layer by Layer (LbL) assembly for modifying the thermal stability and flammability of acrylicfabrics is proposed. Many efforts have been devoted to improve the flame retardancy of acrylic materialsthat vigorously burn, releasing dense smoke when exposed to a flame or a heat flux. In spite of this, noone has still attempted LbL as new nanotechnological solution up to now.Here, nanostructured LbL coatings based on ammonium polyphosphate (APP) and octapropyl ammo-nium polyhedral oligomeric silsesquioxane (POSS) layer have been deposited on acrylic fabrics exploitingthe LbL assembly. More specifically, the coatings consisting of 4 or 6 bi-layers have been found to homo-geneously cover each fibre, creating an intimate interconnection between those adjacent. By this way, theacrylic fibres turned out to be efficiently protected the exposure to a 20 mm methane flame or 35 kW/m2heat flux. As a result, the melt dripping phenomenon has been completely suppressed and the com-bustion rate significantly reduced. The success of the proposed treatments has been ascribed to (i) thechar-former character of APP, (ii) the ceramic thermal insulating barrier created by POSS and (iii) theintimate contact between these two species, only occurring in a LbL assembly. These three aspects haveproven to be responsible of a significant modification in the thermal degradation mechanism of acrylicfibres that discussed as key role in their combustion.