Thermal degradation and flammability behavior of fire-retarded wood flour/polypropylene composites

Magnesium hydroxide, expandable graphite, and ammonium polyphosphate were used to enhance the thermal stability and fire retardant properties on wood flour/polypropylene composites. The thermal decompositions and flammability properties were investigated using modulated thermogravimetric analysis and cone calorimeter, and the activation energy of each decomposition process was also determined by modulated thermogravimetric analysis. The results showed that both expandable graphite and ammonium polyphosphate promoted thermal degradation of wood flour and char formulation, and magnesium hydroxide did not influence on the wood flour decomposition. Unlike in nitrogen atmosphere, magnesium hydroxide and ammonium polyphosphate increased the peak temperature of wood flour thermal degradation and diminished the decomposition peaks of polypropylene in air atmosphere. Cone calorimeter results showed that expandable graphite greatly reduced the heat and smoke release. A general activation energy range of 187–226 kJ mol⁻¹ (in nitrogen), 165–206 kJ mol⁻¹ (in air) at wood flour degradation stage, 237–262 kJ mol⁻¹ (in nitrogen), and 185–269 kJ mol⁻¹ (in air) at polypropylene degradation stage were proposed for wood flour/polypropylene composite with and without fire retardants.