Improvement on fire retardancy of wood flour/polypropylene composites using various fire retardants

The addition of wood flour improves the mechanical properties of thermoplastics, but also increases the burning rate of neat plastics profoundly. To modify the flammability of wood-plastic composites (WPCs), various additive-type fire retardants such as ammonium polyphosphate (APP), melamine polyphosphate (MPP), and aluminum hydroxide were added to improve the fire performance of WPCs. Both UL94 flame tests and cone calorimetry were used to evaluate the fire performance of WPCs, and the results proved that the addition of 10 wt% APP lead to enhanced self-extinguishing properties. On the other hand, polypropylene with 30 wt% of APP did not achieve self-extinguish properties. The effective parameters in the cone calorimetry test to give self-extinguishing properties were discussed by comparing the results of the burning tests. It was presumed that the most important parameters for self-extinguishing of WPCs was an average heat release rate at initial stage of burning. The effect of fire retardants on the mechanical properties of WPCs was also investigated. The tensile strength and modulus of the composites decreased with the addition of fire retardants.