The effect of chitosan on the flammability and thermal stability of polylactic acid/ammonium polyphosphate biocomposites.

This work reports our recent efforts on introducing chitosan (CS) in association with ammonium polyphosphate (APP) into polylactic acid (PLA) by melt blending to improve the flame retardancy of the biocomposites. The flammability of the composites was characterized by limiting oxygen index (LOI), UL-94 vertical burning test and cone calorimetry test (CONE). The results showed that the PLA sample containing 2% CS and 5% APP achieved the maximal LOI value of 33.1, passed the UL-94 V-0 rating, and decreased the peak heat release rate to 425.6kW/m2 . The morphology characterization of char residue by scanning electron microscope indicated a dense, homogeneous and continuous residue char could be formed by the presence of APP and CS in PLA. Fourier transform infrared spectroscopy and thermal gravity analysis suggested that CS could act as a novel carbon agent owning to its high content of carbon atoms and multi-hydroxyl groups, and the interaction between CS and APP could provide synergistic effects in improving the flame retardancy of PLA biocomposites. X-ray diffraction and differential scanning calorimetry results demonstrated that the presence of APP and CS could promote the crystallization of PLA.