Combination of a bio-based polyphosphonate and modified graphene oxide toward superior flame retardant polylactic acid

Superior flame retardant polylactic acid (PLA) composites were prepared using bio-based polyphosphonate (BPPT) and polyethyleneimine-modified graphene oxide (M-GO) to be used as a flame retardant, the total amount of which is only 3 wt%. With 2.4 wt% BPPT and 0.6 wt% M-GO in the polymer matrix, the as-prepared PLA composites can achieve the UL94 V0 grade and a LOI value of 36.0. Analysis of the residual char and pyrolytic products revealed that the conjunction of a gas-phase and condensed-phase mechanism contributes to the good flame retardant performance. Moreover, the tensile toughness of PLA was also enhanced. The PLA composite with 2.1 wt% BPPT and 0.9 wt% M-GO displayed an elongation at break of 13.1% and maintained a tensile strength of 39.1 MPa. The debonding between the M-GO and PLA matrix and the plastic deformation around the M-GO particles were responsible for the improved tensile toughness.