Hierarchical bio-based flame retardant BNNS@PA@Fe-MOFs: A nanomaterials self-assembly strategy towards reducing fire hazard of polylactic acid and improving its degradation.

As a substitute for petroleum-based polymers, polylactic acid (PLA) always attracts great interest due to its unique eco-friendly properties and versatile applications. However, the inherent high flammability and slow natural degradation are still challenging for its wide usage. In this study, a multi-level sushi roll structured flame retardant (B@(D + E)@P-Fe) composed of boron nitride nanosheets (BNNS), iron metal-organic frameworks (Fe-MOFs), and phytic acid (PA) was synthesized through self-assembly technology and create a flame retardant PLA system. Loading of 6 wt% B@(D + E)@P-Fe enabled the PLA composites reached UL-94 V-0 rating and increased the LOI value up to 30 %. Cone calorimetry tests revealed that, compared with pure PLA, PLA composite exhibited a 32.6 % reduction in peak heat release rate and a 17.5 % reduction in total heat release. In addition, the composite material increased its crystallinity up to 51.2 % and maintained excellent mechanical properties with the modulus increasing from 2704.16 to 3448.52 MPa. Meanwhile, the as-synthesized flame retardant could be recycled with a yield of up to 81 %, and the purity of recovered lactic acid was 85.2 %, realizing a full life cycle of biodegradable PLA materials. This work presents a facile and eco-friendly strategy to fabricate renewable plastic with both good flame retardancy and high degradation efficiency.