Highly efficiency flame-retardant and anti-dripping performance with dual effect of phosphaphenanthrene-benzimidazole for poly (lactic acid) film

To improve the flammability and severe melt-dripping behavior of poly (lactic acid) (PLA), we designed and successfully synthesized a flame retardant structure (D-AB) based on phosphaphenanthrene and benzimidazole groups with hydrogen bonds and π-π stacking effect. Then, D-AB was blended with PLA in solution to prepare PLA/D-ABs films. The results showed that the incorporation of D-AB significantly enhances the viscoelasticity and complex viscosity of PLA due to the synergistic effect of hydrogen bonds and π-π stacking of D-AB. Meanwhile, with the good char formation ability of benzimidazole group, PLA/D-ABs exhibit excellent flame retardancy. With only a 5 wt % addition of D-AB, the PLA film with 0.15 mm thickness easily achieve UL-94 VTM-0 rating and high LOI value of 30.5%, while its melt-dripping behavior is improved. In addition, the flame retardant mechanism of D-AB in PLA is studied in detail. It is found that the release of PO· radicals and non-combustible gas in the gas phase, as well as the formation of a dense and intact carbon layers in the condensed phase contribute to the good flame retardant performance of D-AB. This work provides a method for designing highly efficient flame retardants for PLA.