Constructing polyphosphazene nanonetworks on ammonium polyphosphate to synchronously enhance the flame retardancy, mechanical and UV-shielding performances of polylactic acid

To address the applications of polylactic acid (PLA) in various environmental conditions, this study designed a novel additive, i.e. in-situ growing polyphosphazene nano-network on ammonium polyphosphate (APP) surface to construct the core-shell like structure through the bridging effect of chitosan. Such additive as a novel flame retardant exhibited superior flame retardant efficiency compared to the original APP, and the composite with only 15 wt% additive showed the limited oxygen index (LOI) of 31 % and V -0 flammability rating in UL-94 testing. The unique polyphosphazene nano-network structure on the surface of filler enhanced the interfacial interaction of composites and promoted the dispersion of filler in the PLA matrix, which improved the strength and modulus of composites to a certain extent, making up for the deterioration of mechanical properties induced by APP. Furthermore, the additive also endowed the composite with excellent ultraviolet (UV) shielding capability, and mechanical properties of the composite could be maintained at high level after long time UV irradiation. This work not only offers novel perspectives on the development of advanced multifunctional flame retardants, but also enhances the applicability of PLA across diverse industries.