Molecularly engineered polyphosphazene-derived for advanced polylactide biocomposites with robust toughness, flame retardancy, and UV resistance

Polylactic acid (PLA) is inherent brittle, flammable, and susceptible to ultraviolet light irradiation, limiting its application in the field of engineering safety. Therefore, advanced PLA composites with toughness and flame retardancy as well as other exceptional engineering performance has garnered significant interest. In this work, a versatile additive (PAHP) was synthesized by nucleophilic substitution utilizing flexible chain (polyphosphazene) as the skeleton and rigid biomass compound (guanine) as a substituent, then fabricating all-in-one PLA composites. The PAHP plays a synergistic flame-retardant role in both the gaseous and condensed phases, improving the flame retardant performance of the composites while effectively enhancing the crystallization and mechanical properties of PLA. Only 5 wt% PAHP within PLA composite can meet the fire-safety requirements of engineering applications (V-0 rating of UL-94) and exhibits a ∼12-folds enhancement in toughness compared to neat PLA. Moreover, the PLA/5% PAHP composite shows excellent ultraviolet shielding effects, blocking approaching 100 % UV isolation under UV-B wavelengths. This work offers a scalable strategy for preparing multifunctional flame-retardant additives, opening up a great promise for the application of high-performance PLA engineering composites in packaging, electronic, and automotive.