Low combustible polypropylene/flax/magnesium hydroxide composites: mechanical, flame retardation characterization and recycling effect

Natural fibre-reinforced polymer composites are nowadays receiving considerable attention, especially in the automobile and civil engineering industries. Reduction in flammability characteristics besides retention of their excellent mechanical properties will ensure wider market for these composites. Polypropylene matrix was reinforced with 30 and 50 wt% of flax fibres. Magnesium hydroxide was added at different levels of 0, 20 and 30 wt% in order to investigate the flammability resistance behaviour. Thermal and thermomechanical tests were carried out in order to evaluate new and recycled composites. Limited oxygen index was improved to more than 27 with 50 wt% flax/30% magnesium hydroxide, although very slow burning rate in the horizontal test condition was achieved with 30/30, 50/20 and 50/30 wt% for flax/magnesium hydroxides. Regarding the UL94 test, no sample passed vertical burn test. Recycling of these composites was investigated and showed 4 and 10% decrease in strength and stiffness, respectively. Recycling experiments on 50/30 system showed an effect of 5% limited oxygen index decrease after reprocessing for two cycles.