Chitosan/ZIF-8 interface-modified ammonium polyphosphate as core-shell additive for synergistically enhancing flame retardancy and degradation performance of polylactic acid.

Polylactic acid (PLA) is a promising renewable polymer material known for its excellent biodegradability and good mechanical properties. However, its easy flammability and slow natural degradation limit its further applications. In this work, we designed a multi-layer core-shell flame retardant (ZIF-8@CH@APP) with interfacial characteristics through organic-inorganic hybrid technology. The interfacial functionalization of inorganic flame retardant ammonium polyphosphate (APP) was carried out with bio-based chitosan (CH), and the three-dimensional network was constructed by in-situ growth of metal-organic framework (ZIF-8). With 7 wt% addition of ZIF-8@CH@APP, the PLA composite exhibited excellent flame retarded properties. It showed V-0 vertical burning (UL-94) grade, and reduced total smoke produce (TSP) (0.2 m). Additionally, the PLA/7 % ZIF-8@CH@APP composite exhibited higher degradation rate at mild condition. Additionally, the final degradation product of ZIF-8@CH@APP was confirmed to be DL-lactic acid. The design not only improves the interface compatibility between inorganic phase and polymer matrix, but also realizes the double breakthrough of flame retardant and catalytic degradation function through physical-chemical synergism, providing an innovative solution for the recycle of PLA material.