Fabrication of a flame retardant, strong mechanical toughness and antimicrobial polylactic acid by chitosan Schiff base/ ammonium polyphosphate

Polylactic acid (PLA) has garnered global attention as a potential biomaterial thanks to its biodegradability and renewability. However, the drawbacks of its high flammability impede its broader application. In this work, two different types of all bio-based charring agents (named as CFU, CVA) were prepared in a green and environmentally friendly ethanol solvent by using chitosan derived from corn starch and sugarcane, as well as bio-based vanillin and furfural, as raw materials. The CFU (or CVA) in conjunction with ammonium polyphosphate (APP) were incorporated into PLA to prepare flame-retardant and high-performance composite materials. The addition of 3.75 wt% CFU (or CFA) and 11.25 wt% APP to PLA resulted in the attainment of the UL-94 V-0 rating, a nearly 28% of limiting oxygen index, as well as a decrease of ∼35 and ∼90% in total heat and smoke releases, respectively. Besides, the addition of mixed flame retardants significantly reduced the viscosity of PLA by an order of magnitude, which was greatly beneficial for processing and production. The mechanical performance testing results demonstrated an increase in the elongation at break and impact strength of PLA composites containing CFU (or CVA) and APP. Moreover, the heat resistance and crystallinity of the PLA composites were also improved.