Key Role of Reinforcing Structures in the Flame Retardant Performance of Self-Reinforced Polypropylene Composites

Abstract

Abstract:The flame retardant synergism between highly stretched polymer fibres and intumescent flame retardant systems was investigated in self-reinforced polypropylene composites. It was found that the structure of reinforcement, such as degree of molecular orientation, fibre alignment and weave type, has a particular effect on the fire performance of the intumescent system. As little as 7.2 wt % additive content, one third of the amount needed in non-reinforced polypropylene matrix, was sufficient to reach a UL-94 V-0 rating. The best result was found in self-reinforced polypropylene composites reinforced with unidirectional fibres. In addition to the fire retardant performance, the mechanical properties were also evaluated. The maximum was found at optimal consolidation temperature, while the flame retardant additive in the matrix did not influence the mechanical performance up to the investigated 13 wt % concentration.

Flame retarded self‐reinforced polypropylene composites prepared by injection moulding

“…It was proposed earlier that the type (organic, inorganic, char‐forming, or non‐char forming polymer) and structure (degree of molecular orientation, fibre alignment, weave type) of reinforcement have particular effect on the effectiveness of an intumescent FR system in SR‐PPCs. In this work, this phenomenon is further investigated using a new structure, ie, in disordered, short fibre reinforced SR‐PPCs.…”

“…No significant difference could be evinced between the flammability behaviour of the non‐reinforced and the self‐reinforced samples of identical FR contents. Slightly better FR performance was observed for the composites during vertical burning tests; some of the 15 wt% FR containing specimens showed self‐extinguishing behaviour even after the second 10‐second long ignition, which could be ascribed to the beneficial effect of the presence of highly oriented hPP fibres, in accordance with our earlier findings . However, it has to be declared that the contribution of the short hPP fibres to the synergism with the IFR system is almost negligible compared with the winded hPP yarns or woven fabrics composed of highly stretched filaments.…”

“…Based on these results, it was concluded that the incorporation of conventional FR additives in the matrix of injection moulded SR‐PPCs has roughly the same effect on the flammability properties as in non‐reinforced PP compounds. In contrast to continuous hPP fibres or woven fabrics, randomly aligned, short hPP fibres do not influence noticeably the foam forming process and the combustion behaviour of an intumescent flame retarded PP system.…”

“…Best FR performance was found in SR‐PPCs reinforced with unidirectional fibres. These composites, when prepared at optimum consolidation temperature, pass UL94 V‐0 rating with additive content as little as 7.2 wt%, one third of the amount needed in non‐reinforced polypropylene matrix …”

Non-destructive characterisation of all-polypropylene composites using small angle X-ray scattering and polarized Raman spectroscopy

“…Therefore, the basis of all SRP techniques is to set a suitable processing window which enables the partial fusing of the fibres (hot-compaction technique) or exploits the difference between the melting temperatures (T m ) of the structurally similar reinforcement and matrix polymer. Nevertheless, the increased processing temperature leads to molecular relaxation of fibres and consequently to loss in reinforcing efficiency [8]. In case of allpoly(ethylene terephthalate) (all-PET) composites increased processing temperature and holding time have found to cause hydrolytic degradation, embrittlement and noticeable deterioration of the mechanical properties of the polyester components [9,10].…”