Investigation of mechanical property, flame retardancy and thermal degradation of LLDPE-wood-fibre composites

The mechanical properties, flame retardancy and thermal degradation of linear low density polyethylene (LLDPE)-wood-fibre composites have been investigated. LLDPE-wood-fibre composites were prepared on a two-roll machine. Maleated polyethylene (MPE) was used to improve the mechanical properties of LLDPE-wood-fibre composites. Ammonium polyphosphate (APP) and the mixtures of APP, melamine phosphate (MP) or pentaerythritol (PER) were used as flame retardants. The experimental results demonstrated that MPE enhanced tensile strength and Izod impact of LLDPE-wood-fibre composites, which is in agreement with literature. APP influenced Izod impact of LLDPE-wood-fibre composites, while it scarcely affected tensile strength. It was found that PER could clearly decrease both tensile strength and Izod impact of LLDPE-wood-fibre composites. This is attributed to PER being involved in esterification reactions between wood-fibre and MPE. According to LOI obtained from this work, APP is an effective flame retardant for LLDPE-wood-fibre composites. It was also found that wood-fibre obviously influenced the thermal degradation behaviour of LLDPE. Wood-fibre made the rapid thermal degradation of LLDPE take place earlier, while APP thermally stabilized LLDPE in LLDPE-wood-fibre composite based upon the temperature (T_max) at maximum peak of the thermal degradation. APP decreased initial temperature (T_initial) of thermal degradation, and promoted char formation of the composite. It is suggested that APP can catalyze esterification, dehydration and char formation of wood fibre.