Synergistic Effect of POSS on Mechanical Properties, Flammability, and Thermal Degradation of Intumescent Flame Retardant Polylactide Composites

The intumescent flame retardant polylactide/polyhedral oligomeric silsesquioxane (IFR-PLA/POSS) composites were prepared via a melt blending method. The morphology of the PLA nanocomposites was assessed by transmission electron microscopy (TEM). Dynamic mechanical analysis (DMA) and tensile tests showed that the incorporation of POSS enhanced the mechanical properties of the PLA matrix. The limiting oxygen index (LOI) values increased from 20.0% for neat PLA to 40.0% for PLA based on 22.5 wt% IFR and 7.5 wt% POSS, and the latter could pass UL-94 V0 rating. Thermal gravimetric analysis (TGA) showed that the thermal stability of the residual char at the later stages of the thermal degradation was significantly improved. The dynamic Fourier transform infrared (FTIR) spectra suggested that the thermally stable poly(phosphoricacid) and polysiloxane derivatives were formed during the thermal degradation process of PLA/POSS composite. The scanning electron microscope (SEM) and X-ray photoelectron spectrography (XPS) indicated that the residual char of flame retardant PLA/POSS composite had a exterior layer with a compact and continual surface, while the interior had a porous structure, which was composed of cross-linked phosphorous oxynitride and carbonized aromatic networks.