Flammability and thermal properties of modified carbon nanotubes in poly(lactic acid)

The multi-walled carbon nanotubes (CNTs) were modified using phosphaphenanthrene compounds (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)) and vinyl triethoxy silane (VTES) by covalent bond. The DOPO- and VTES-treated CNTs were named DVCNT, and the structure was characterized by Fourier transform infrared, thermogravimetric analysis, and transmission electron microscopy. Nanocomposites were prepared by adding CNTs or DVCNT to poly(lactic acid) (PLA), and the flame retardancy was examined by determination of limiting oxygen index (LOI), vertical burning (UL94), and cone calorimetry. Results reveal that the LOI of PLA/DVCNT_4% composites was increased to 26.6 and prevents dripping of PLA in some level, and DVCNT can significantly reduce heat release rate and mass loss rate during combustion, which indicate that DVCNT can improve the dispersibility of the CNTs in the polymer composites and hence enhance the flame retardancy simultaneously.