Abstract: Influence of ammonium polyphosphate (APP) on flame retardancy, mechanical properties, and thermal degradation of polylactic acid (PLA)/wheat straw composites was investigated. It showed that limited oxygen index of the composites improved by 33 %, and UL 94 flammability rating was V-0, and char yield was increased by 330 % when APP’s loading reached 20 %. Unnotched Izod impact strength was reduced and the stiffness was improved with the addition of APP, while flexural strength and density were not affected. TGA test indicated that the thermal degradation behavior was changed when adding APP, which made the decomposition temperature lower and PLA matrix stable. Expansion layer after burning served an important role in against heat and oxygen.

Key words: ammonium polyphosphate, wheat straw, polylactic acid, flame retardancy, mechanical property, thermal degradation behavior