To enhance the flame retardancy of polylactic acid (PLA), the exploration of bioderived flame retardants has captured the focus of researchers globally. Herein, a core–shell bioderived flame retardant is prepared through electrostatic self-assembly using ammonium polyphosphate (APP) as the core and chitosan (CS)/tannic acid (TA) bilayer as the shell. In addition, the Fe³⁺ ion is introduced into the outermost TA shell through coordination with the phenolic hydroxyl group, which can reduce the droplets during combustion. The prepared flame retardant, APP@CS@TA-nBL-Fe³⁺, has core–shell structure (where “nBL” represents the number of coating layers of CS and TA bilayer) and excellent flame retardancy for PLA. With 5 wt % flame retardant, PLA/5% APP@CS@TA-2BL-Fe³⁺ attains the highest LOI value (31.6%) and achieves UL-94 V-0 rating in vertical combustion tests with light melt droplets. Furthermore, cone calorimetry results reveal that a reduction of 17.6% in the peak heat release rate and a 22.3% decrease in total heat release were achieved. Meanwhile, the Fe³⁺ catalyzes the matrix to form a micro-cross-linked char layer blocking the heat and oxygen exchange. Moreover, PLA/5% APP@CS@TA-2BL-Fe³⁺ not only has a 99.98% reduction in UV transmittance but also has better mechanical properties after UV aging than that of neat PLA. This study presents a convenient and environmentally friendly approach for preparing efficient biobased flame retardants for PLA, aiming to broaden the application of PLA.

中文翻译：

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基于环保核壳阻燃剂的聚乳酸的阻燃、抗熔滴和抗紫外线性能

为了提高聚乳酸（PLA）的阻燃性能，生物源阻燃剂的探索引起了全球研究人员的关注。本文以聚磷酸铵（APP）为核，壳聚糖（CS）/单宁酸（TA）双层为壳，通过静电自组装制备了核壳生物源阻燃剂。此外，Fe ³⁺离子通过与酚羟基的配位被引入到最外层的TA壳中，可以减少燃烧过程中的液滴。所制备的阻燃剂APP@CS@TA-nBL-Fe ³⁺具有核壳结构（其中“ nBL ”代表CS和TA双层的包覆层数），对PLA具有优异的阻燃性能。阻燃剂含量为 5 wt% 的 PLA/5% APP@CS@TA-2BL-Fe ³⁺在轻熔滴垂直燃烧测试中获得了最高的 LOI 值 (31.6%) 并达到 UL-94 V-0 等级。此外，锥形量热法结果表明，峰值放热量降低了 17.6%，总放热量降低了 22.3%。同时，Fe ³⁺催化基体形成微交联炭层，阻止热和氧交换。此外，PLA/5% APP@CS@TA-2BL-Fe ³⁺不仅紫外透过率降低了99.98%，而且在紫外老化后具有比纯PLA更好的机械性能。本研究提出了一种便捷、环保的制备PLA高效生物基阻燃剂的方法，旨在拓宽PLA的应用。