Influence of layer by layer coatings containing octapropylammonium polyhedral oligomeric silsesquioxane and ammonium polyphosphate on the thermal stability and flammability of acrylic fabrics

Abstract The use of Layer by Layer (LbL) assembly for modifying the thermal stability and flammability of acrylic fabrics is proposed. Many efforts have been devoted to improve the flame retardancy of acrylic materials that vigorously burn, releasing dense smoke when exposed to a flame or a heat flux. In spite of this, no one has still attempted LbL as new nanotechnological solution up to now. Here, nanostructured LbL coatings based on ammonium polyphosphate (APP) and octapropyl ammonium polyhedral oligomeric silsesquioxane (POSS) layer have been deposited on acrylic fabrics exploiting the LbL assembly. More specifically, the coatings consisting of 4 or 6 bi-layers have been found to homogeneously cover each fibre, creating an intimate interconnection between those adjacent. By this way, the acrylic fibres turned out to be efficiently protected the exposure to a 20 mm methane flame or 35 kW/m2 heat flux. As a result, the melt dripping phenomenon has been completely suppressed and the combustion rate significantly reduced. The success of the proposed treatments has been ascribed to (i) the char-former character of APP, (ii) the ceramic thermal insulating barrier created by POSS and (iii) the intimate contact between these two species, only occurring in a LbL assembly. These three aspects have proven to be responsible of a significant modification in the thermal degradation mechanism of acrylic fibres that discussed as key role in their combustion.