Synergistic effect of intumescent flame retardant and expandable graphite on mechanical and flame-retardant properties of wood flour-polypropylene composites

•The flame retardancy of the WPC were improved greatly when CFA was introduced.•The mechanical properties of WPC were improved greatly by adding m-TMI-g-PP.•The synergetic systems could reduce the HRR, SPR and mass loss of WPC.•The special microstructure was observed after burning of the expansion system by SEM. In this article, expandable graphite (EG) and intumescent flame retardant (IFR) that consist of a novel triazines char forming agent (CFA) and ammonium polyphosphate (APP) was chosen in wood flour-polypropylene composites. The synergistic effect between the EG and IFR on mechanical properties, flame retardancy, and thermal degradation of WPC were investigated. The WPC with 25wt% of EG/IFR (2:3) had the highest strength in the flexural, izod impact, and thermal stability. The ratio showed modest improvements in the Flame retardant performance as indicated by reductions in the heat release rate and the smoke production release rate. SEM results showed that a compact and thick char layer was formed in the ratio, which hindered the transfer of heat flow and combustible gases in the condensed phase. Thus, the combination of EG and IFR had been proved to be a promising flame retardant system for WPC.