The Synergistic Effect of Ammonium Polyphosphate and a N/P/Si‐Containing Intumescent Flame Retardant on the Flame‐Retardant Properties of Polylactic Acid

ABSTRACT Ammonium polyphosphate (APP) and intumescent flame‐retardant di‐(3‐amin‐opropyltriethoxysilane) spirocyclic pentaerythritol diphosphate (PDAP) were prepared as an intumescent flame retardant with synergistic effect, and polylactic acid (PLA) was modified by melt blending. The flame retardancy of PLA/PDAP/APP was evaluated by limiting oxygen index (LOI), vertical combustion test (UL‐94), and cone calorimetry test (CCT), and the thermal stability of PLA/PDAP/APP was studied by thermogravimetric analysis and thermogravimetry‐Fourier transform infrared spectroscopy (FTIR). The possible flame‐retardant mechanisms of PLA/PDAP/APP were analyzed based on the results of laser Raman spectroscopy and FTIR. When PDAP:APP = 2:1 and the addition amount of PDAP/APP is 20 wt%, the LOI value of PLA/IFR‐modified material is as high as 43%, and the UL‐94 test reaches V‐0 level, and in the CCT, the PHRR and THR of PLA/PDAP/APP (2:1)‐modified material are reduced by 80.7% and 76.8%, respectively, compared with pure PLA, and the carbon residue is as high as 62.01%. The results show that the compound APP/PDAP has an excellent flame‐retardant effect on PLA, which provides a good research case for PLA flame‐retardant‐modified plastic materials.