Fire Retardancy Effects Of Ammonium Polyphosphate Complex Fire-retardant System On Wood Flour/Polyethylene Composite

As the wood-plastic composite is applied gradually from outdoor to the interior, it is necessary to carry out a fire-retarding treatment for the environmentally friendly material which is made from flammable materials. In this paper, the effects of ammonium polyphosphate (APP) complex fire retardant system on the fire retardancy, thermal degradation behavior and mechanical properties of wood flour/high density polyethylene (WF/HDPE) composite were studied using cone calorimetry (CONE), limited oxygen index (LOI), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and mechanical test.The results showed that the APP with high polymerization degree had good effects on improving the oxygen index, reducing the heat release and increasing the char residue of WF/HDPE composite, while made the smoke emission increased. The APP with low polymerization degree was conducive to reduce the smoke release of the composite and improve its thermal stability under nitrogen atmosphere. However, the heat release inhibition effect due to the APP with low polymerization degree was not obvious, besides the mechanical properties of the composite material were reduced significantly.When compounding GUP with APP by an appropriate ratio, there was a good synergistic effect on fire inhibition and smoke suppression so that the composite had a better performance of low heat release and low smoke release. Meanwhile, compounding GUP with APP also helped reducing the mass loss rate and increasing the char residue. The mixtures of APP and GUP made the flexural strength of the composite slightly decreased while the flexural elastic modulus and non-notched impact strength increased at some degree. The application of zinc oxide in the mixtures of APP and GUP could indicate a good synergistic fire retarding effect.The mixtures of APP and guanidine sulfamate helped catalyzing the charring process of wood flour, so that the char residue of the WF/HDPE composite was increased and both the heat release and smoke release were inhibited. Furthermore, the composite showed higher oxygen index. The synergistic effects on fire inhibition and smoke suppression of the mixtures of APP and guanidine sulfamate were more obvious than the mixtures of APP and GUP. The compounding of APP and guanidine dihydrogen phosphate could also indicate some synergistic effects on reducing the heat and smoke release of the composite, however, it couldn’t compared with the APP and guanidine sulfamate compounding system and had some adverse effects on the mechanical properties. Neither zinc oxide nor zinc borate showed synergistic effect in the system of APP and guanidine dihydrogen phosphate complex or APP and guanidine sulfamate complex, on the contrary, they made the fire retardancy and the mechanical properties of the composite decreased.