Synergistic effect of nano silicon dioxide and ammonium polyphosphate on flame retardancy of wood fiber–polyethylene composites

Wood fiber-high density polyethylene composites (WPCs) with nano silicon dioxide (nano-SiO2) and ammonium polyphosphate (APP) were prepared to investigate the synergistic effects on the thermal stability and flame retardancy of WPCs. APP/nano-SiO2 has significant improvement on heat release rate (HRR), total heat release (THR), time to ignition (TTI), mass loss rate (MLR), and limited oxygen index (LOI). The most efficiency was appeared in APP 8%/nano-SiO2 6%. It reduced the average and peak HRR by 42% and, 44% respectively, and increased the TTI by 78%. In WPCs containing APP/nano-SiO2, APP can interact with nano-SiO2, wood fiber, leading to promote the thermal degradation of WPC take place earlier, and stabilize the char residues. The presence of nano-SiO2 can further form an intercalated network in char structure, enhancing the physical integrity. This char layer with more thermal stability and physical integrity results in an effectively synergistic effect on flame retardancy of WPCs.