Abstract: The effect of ammonium polyphosphate (APP) and wood flour (WF) content on the flame retardant and mechanical properties of high density polyethylene/wood flour composites (WPC) was investigated. The flammability and mechanical preperties of WPC were characterized by limiting oxygen index (LOI), UL94 vertical burning, cone calorimeter (CONE) tests, thermogravimetric analysis, Fourier transform infrared (FTIR) spectroscopy, and mechanical test. Loaded with 40 % WF, the LOI of the composites was increased to 30.5 % and UL 94 rating achieved V-0 level. CONE data revealed that heat release rate and total heatrelease were significantly decreased. The thermal stability of WPC was improved due to the protective char layer formed during certain chemical reaction occurring between WF and APP. The mechanical properties of WPC were also improved.

Key words: high density polyethylene, ammonium polysphate, wood flour, flame retardant, mechanical property