Flame retarded self-reinforced polypropylene composites prepared by injection moulding

A method was elaborated to prepare flame retarded self-reinforced polypropylene composites by injection moulding. The effect of intumescent flame retardant (FR) loading was comprehensively investigated on the morphology, flammability, and mechanical properties of the self-reinforced polypropylene composites and compared with non-reinforced counterparts of identical additive contents. Homogeneous distribution of both the reinforcing polypropylene fibres and the FR additive was achieved endowing significantly improved strength and stiffness accompanied with increased fire resistance. At 10% FR content, 37% reduction of peak of heat release rate, UL94 V-2 rating, and LOI of 24.5vol% were achieved without compromising the improved mechanical performance of the injection moulded self-reinforced composites, ie, a 4-fold increase of tensile strength and a 7-fold increase of tensile modulus were reached compared with the non-reinforced counterpart. At higher loading (15% FR), the FR properties improved further (LOI of 29.5vol% was reached); however, due to the abrasive effect of the FR particles in the matrix, the structure of the reinforcing fibres tends to get damaged during the thermo-mechanical processing, and thus their reinforcing efficacy deteriorated. It is demonstrated that the combination of polymer fibre reinforcement with other fillers (such as FRs) is advantageous and feasible even by injection moulding, but the balance between the individual attributed properties needs to be found.