Improving the flame retardancy of poly(lactic acid) using an efficient ternary hybrid flame retardant by dual modification of graphene oxide with phenylphosphinic acid and nano MOFs.

A novel ternary hybrid nanoflake (GPZ) based on graphene oxide (GO), phenylphosphinic acid (PPA) and nano metal-organic framework (nano ZIF-8) particles has been designed and synthesized via a simple two-step strategy. GPZ shows high thermal stability and good compatibility with PLA matrix. When GPZ nanoflakes are added into PLA, the tensile strength and toughness of the PLA-4 with 2.0 wt% of GPZ reach 44.1 MPa and 86.0 MPa compared with 30.0 MPa and 12.8 MPa of pure PLA owing to the good dispersion of GPZ in PLA matrix and their reinforcing effects. The incorporation of GPZ also dramatically enhances the flame retardancy of PLA and the PHRR of PLA-4 with 2.0 wt% of GPZ achieves about 316.2 W/g, which is decreased by 39.5% relative to 523.0 W/g of pure PLA, respectively. The LOI of PLA-4 is 27.0%, increasing about 31.7% compared to 20.5% of pure PLA. Meanwhile, the HRR and THR in the cone calorimeter test curves for the PLA nanocomposites have also been evidently reduced. The TG-IR is applied to characterize the pyrolysis gaseous products and volatile components are suppressed with addition of GPZ. The SEM, Raman and XPS results of char residues show that a protective graphitized char layer plays a major role in improving the flame retardancy, which mainly because of the catalytic and cross-linking effects of GO, nano ZIF-8 and PPA during combustion of PLA nanocomposites.