Comparative study on the effects of silica size and dispersion mode on the fire retardancy of extruded wood fiber/HDPE composites

Abstract The inflammability of wood fiber/high‐density polyethylene composites (WPCs/HDPE) remains a limitation for its application. Here the authors sought to improve the flame retardancy of WPCs by incorporating uniformly dispersed SiO₂. Specifically, micron‐ and nano‐SiO₂ were incorporated into HDPE via dry blending (dry dispersion) or solution blending (wet dispersion), to prepare the compounded matrices for the WPCs. The effects of SiO₂ size and dispersion mode on the thermal stability and fire retardancy of WPCs were investigated. The results indicated that the nano‐SiO₂ was more beneficial to improve the thermal stability of WPCs than the micron‐SiO₂, especially incorporating via wet dispersion. The cone calorimetry tests revealed that incorporating 9 wt% micron‐SiO₂ slightly decreased the heat release and smoke production of the WPCs. The incorporation of nano‐SiO₂ in WPCs showed a moderate reduction in the heat release, while slightly increased the smoke production. The wet dispersion presented minor advantage over dry dispersion in improving the flame retardancy of WPCs. In addition, the dynamic thermal‐mechanical analysis revealed that the WPCs containing wet‐dispersed micron‐ or nano‐SiO₂ exhibited a higher storage modulus compared to that dry‐dispersed SiO₂.