Lignin is a biomass material that attracts more and more attention because of its extremely low utilization rate. In this paper, we have fabricated a lignin‐based flame retardant chemically grafted with PEI followed with polyphosphoric acid by a mild two‐step method. It is found that the nitrogen/phosphorus modified lignin exhibited a lower char forming temperature and enhanced thermal stability. After adding 7 wt% functionalized lignin, the maximum decomposition temperature of epoxy resin (EP) composite was reduced from 387°C to 364°C, while UL‐94 grade and limiting oxygen index was up to V‐0 grade and 31.4%, respectively, with excellent flame retardant effect. Moreover, the results of the characterization show that the carbon residue becomes much denser with the addition of multifunctional lignin‐based flame retardant. It is proposed that the phosphorus element acts to promote char formation in the EP composite, endowing the resin matrix with a dense char layer. And the dense char layer with released ammonia from the nitrogen element to block the entry of air during combustion achieves the purpose of high‐efficiency flame retardancy. This gentle and efficient multifunctional process enhances the driving force for a wide range of applications of lignin‐based flame retardants.

中文翻译：

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木质素阻燃剂的两步制造，可增强环氧树脂复合材料的耐热性和阻燃性

木质素由于其极低的利用率而引起了越来越多的关注。在本文中，我们通过温和的两步法制备了先将PEI化学接枝有多磷酸的木质素基阻燃剂。发现氮/磷改性的木质素表现出较低的炭形成温度和增强的热稳定性。加入7 wt％的官能化木质素后，环氧树脂（EP）复合材料的最高分解温度从387°C降至364°C，而UL-94级和极限氧指数分别达到V-0级和31.4％，分别具有优异的阻燃效果。此外，表征结果表明，添加多功能木质素基阻燃剂后，碳残留量变得更加稠密。提出磷元素起到促进EP复合物中的炭形成的作用，使树脂基质具有致密的炭层。燃烧过程中，氮元素释放出的氨致密的焦炭层阻止了空气的进入，从而达到了高效阻燃的目的。这种轻柔而高效的多功能工艺增强了木质素类阻燃剂在各种应用中的驱动力。