Flame-retardant and UV-shielding poly (lactic acid) composites with preserved mechanical properties by incorporating cyclophosphazene derivative and phosphorus-modified lignin

•Epoxidized cyclotriphosphazene and modified lignin for PLA flame retardants.•High flame retardancy was achieved with low loadings of HCCP-HEP and Lignin(P).•The flame-retardant mechanism of HCCP-HEP and lignin(P) was described.•The incorporation of lignin(P) greatly improves the UV shielding properties of PLA.•PLA/H/L composites maintain superior mechanical properties. Poly(lactic acid) (PLA) is one of the most promising sustainable bioplastics for its superior processibility and mechanical strength. However, the inherent flammability and poor UV shielding severely inhibit its widespread application. Traditional solutions usually require a high content of additives, which results in the sacrifice of mechanical properties. In this work, we propose an efficient strategy to overcome these challenges by incorporating epoxy-functionalized hexa-cyclotriphosphazene (HCCP-HEP) and diphenylphosphinyl chloride modified lignin (Lignin(P)) into PLA. The synergistic effect of HCCP-HEP and Lignin(P) through free radical quenching, non-flammable gas dilution and charring promotion significantly impedes combustion and enhances the flame retardance of PLA/HCCP-HEP/Lignin(P) (PLA/H/L) composites. Consequently, the PLA/H/L composite with 1 wt% HCCP-HEP and 1 wt% Lignin(P) loading exhibits a limiting oxygen index of 28.3 % and achieves UL-94 V-0 rating. Moreover, the composite provides over 97 % shielding against UV-A and UV-B radiation with an increased ultraviolet protection factor (UPF) from 1 to 700, while maintaining superior tensile strength (59 MPa). This work presents a new approach to prepare high-performance and multi-functional PLA composites, which is expected to broaden the application of PLA.