Simultaneously Enhancing the Fire Retardancy and Heat Resistance of Stereo-Complex-Type Polylactic Acid

Polylactic acid (PLA) is considered to be the material with great application potential in the 21st century which has aroused wide research interest. However, PLA is a highly flammable material and exhibits low heat distortion temperature, which greatly limits its application in many fields. In this work, aluminum diethyl phosphinate (ADP) and poly (d-lactic acid) (PDLA) are used to improve fire retardancy and heat resistance of poly (l-lactic acid) (PLLA). PLLA/PDLA with the presence of 15 wt % ADP exhibited the limiting oxygen index (LOI) value at 26%, and the peak heat release rate (pHRR) and total heat release decreased, respectively, by 14.03 and 24.42% from 500 to 429 kW/m² and 86 to 65 MJ/m². The melt dripping phenomenon was suppressed obviously. The addition of ADP realized the flame-retardant effect from both the condensed phase and gas phase. Moreover, the results showed that the addition of ADP promoted the formation of stereo crystals and increased the crystallization temperature to 175 °C. The heat distortion temperature (HDT) of the PLLA/PDLA sample with 15 wt % ADP can be as high as 170.4 °C, which marks significant improvement in the heat resistance of PLA. The mechanical property test results showed that ADP has little effect on the mechanical properties of the composites. This work opens a window to realize the heat-resistant and anti-dripping fire-retardant PLA.