Thermal decomposition of fire-retarded wood flour/polypropylene composites

The influence of magnesium hydroxide (MH), expandable graphite (EG), and ammonium polyphosphate (APP) on the kinetic property and degradation mechanisms of wood flour/polypropylene composites (WPPC) was investigated using thermogravimetric (TG) analysis. The kinetic parameters were determined using Kissinger and Flynn-Wall-Ozawa (F-W-O) methods. Criado method was used to investigate the probable degradation mechanisms. Thermogravimetric results indicated that EG and APP accelerated the degradation process of wood flour and promoted an increase in the conversion value at low temperatures. The activation energy values obtained through Kissinger and F-W-O methods were 161-178 kJ mol(-1) (wood flour degradation stage) and 234-305 kJ mol(-1) (polypropylene degradation stage) for WPPC with or without fire retardants. The degradation mechanism of wood flour occurred by diffusion in three-dimensional processes when the conversion value was below 0.8. Polypropylene and fire retardants had no direct influence on the degradation mechanism of wood flour. In the polypropylene decomposition stage, the degradation of WPPC without fire retardant followed phase-boundary-controlled reaction mechanism. However, the behavior of WPPC incorporation of MH, EG, or APP was governed by nucleation and growth mechanism.