Biomimetic synthesis of sea urchin-Like MOFs-LDH and ternary synergistic flame retardants to improve the flame retardancy and UV resistance of Polylactic acid

In this work, a novel single molecule flame retardant (DT-S) was synthesized through the self-assembly of diethyltriamine penta-(methylphosphonic) acid and sulfanilamide. Additionally, the three-dimensional sea urchin-like layered double hydroxide hollow dodecahedral structure (MOFs-LDH) was etched from a MOF to increase specific surface area and reaction sites. The chemical structures of DT-S and MOFs-LDH were comprehensively characterized. Subsequently, the obtained flame retardants were molten-compounding into PLA matrix. The fire performance of PLA composites was evaluated by limiting oxygen index (LOI), vertical combustion (UL-94), and cone calorimeter tests. Compared with neat PLA sample, the inclusion of 3 % DT-S and 2 % MOFs-LDH led to an increase in the LOI value from 19.9 to 35.0 %, an upgrade in the UL-94 rating from none to V-0, and a reduction in the peak heat release rate from 524.4 to 401.2 kW m⁻². Analysis of the decomposition products of the PLA composites and the observation of char morphology suggested that DT-S and MOFs-LDH took effects in both condensed phase and gas phase. Furthermore, the evaluation of the UV protection performance using a UV–visible near-infrared spectrophotometer indicated an enhancement in the UV protection performance of PLA, achieving an "excellent" level in evaluating UV protection performance (UPF 50+).