Performance study of modified ammonium polyphosphate/natural mineral synergistic flame retardant corn straw/polypropylene composites

In the present work, corn straw/polypropylene/modified ammonium polyphosphate composites (CS/PP/KAPP) were prepared by employing melt blending and hot-pressing methods. Due to the high production cost of KAPP and the fact that a large amount of KAPP can reduce the mechanical properties of wood plastic composite (WPC), natural minerals were used to replace some of KAPP to improve the flame retardancy. The results showed that, for all the studied groups, when the amount of ultrafine montmorillonite was 8.6 wt%, the flame retardancy of the co-effective flame retardant was better than that of the pure KAPP group. Meanwhile, the obtained oxygen index of the composite was 30.2%, with a vertical combustion class of V-0. In the other groups, the ultimate oxygen indices of the composites were lower than that of the pure KAPP group due to the reduced content of KAPP. The results showed that the three co-effective flame retardants formed a dense carbon layer during combustion. This enhanced the rate of formation of carbon and reduced the release of smoke and carbon monoxide. In addition, the three natural minerals were found to play a good filling role, enhancing the mechanical properties of the composites, improving their thermal stability, and reducing their rates of absorption of water.