Self-extinguishing polypropylene with a mass fraction of 9% intumescent additive II – Influence of highly oriented fibres

Recently, noticeably enhanced flame retardancy of multilayered self-reinforced composites, flame retarded with common ammonium polyphosphate based intumescent system, was described. In this paper the observed novel flame retardant synergism between intumescent additive system and highly oriented polymer fibres is further studied. The ignitability and combustion behaviour of flame retarded multilayer self-reinforced composites were compared to flame retardant compounds, prepared by simple melt compounding, of identical low additive contents, both when the heat was applied parallel (UL-94 tests) and perpendicular (cone calorimetric tests) with the direction of the embedded oriented tapes in self-reinforced composites. SEM and EDS analyses supported the different foaming process of the two types of samples to be understood, while the structure and character of the finally (after combustion) obtained charred layers were examined by compression tests. Considering the results of all the applied testing methods, the complex picture of the mechanism behind the enhanced flame retardant efficiency of flame retarded self-reinforced composites could be clarified.