Synergistic effect of graphene and an ionic liquid containing phosphonium on the thermal stability and flame retardancy of polylactide

A series of nanocomposites based on the biodegradable plastic, polylactide (PLA), have been prepared by melt-blending with graphene (Gra) and ionic liquid containing phosphonium ([PCMIM]PF6, IL) surface-functionalized graphene (GIL). The morphology, mechanical properties, thermal stability and burning behaviour of the composites were investigated by Field Emission Scanning Electron Microscopy (FESEM), tensile test, impact test, Thermogravimetric Analysis (TGA), Limiting Oxygen Index (LOI), UL-94 test and Cone Calorimeter Test (CCT), respectively. The surface morphology and chemical structure of the char residues were explored by FESEM and Raman spectroscopy. It is confirmed that the fire-retardant performance of the PLA/GIL composites was significantly improved compared to PLA/IL and PLA/Gra; the CCT data showed a reduction in heat release rate and total heat released with increase of the char residue from the TGA results. It revealed that the catalytic charring effect of the ionic liquid, the physical isolating effect of graphene, and the combined effect of both the ionic liquid and graphene (forming continuous and compact char layers) were very efficient in improving the flame retarding properties of PLA/GIL nanocomposites.