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

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.