Intumescent, flame-retarding wood-flour/polypropylene composites (WPCs) having different ammonium polyphosphate/pentaerythritol (APP/PER) ratios (4/1, 3/1, and 2/1) were prepared in this study. The thermal degradation behavior, flame retardancy, and mechanical properties of the composites were tested. Moreover, the residues of the WPCs were observed by scanning electron microscopy, and the flame retardancy mechanism was investigated. The results showed that WPC/APP/PER exhibited higher thermal

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... tability in the high temperature region and left much more char residue than WPC/APP, according to thermogravimetric analysis. Limiting oxygen index and cone calorimetry tests showed that the addition of PER improved the flame retardancy of the WPCs, especially when APP/PER ratio was 3/1. However, because of the poor compatibility with the composite matrix and uneven dispersion in the WPCs, the incorporation of PER decreased the mechanical performance of WPCs obviously.