Abstract: Lignin is currently the second largest resource of biomass materials in the plant world. However, due to the complexity of the molecular structure of lignin, its thermal stability is relatively poor, and it does not contain flame retardant elements such as phosphorus and nitrogen. The direct use of lignin as a flame retardant shows limited effectiveness in enhancing the flame retardancy of materials, hindering its market prospects as a high-end flame retardant material. Physical synergy and chemical grafting treatment can improve the inherent defects of lignin fibers, resulting in low smoke release, low heat release rate, high flame retardancy and high thermal stability. At the same time, this treatment can better maintain the original performance of the fuel, such as softness, air permeability and so on. However, the traditional flame retardant preparation process involves the use of toxic substances, such as halogens and metals, resulting in processing difficulties. Finally, it tends to decompose easily at high temperatures, diminishing its flame retardant effectiveness. Safety problems seriously restrict the sustainable development of traditional flame retardants. In summary, the use of lignin flame retardant materials is the most environmentally friendly and easy-to-implement improvement method in the flame retardant industry.
Usually, lignin is compounded with other flame retardants, or flame retardant elements or groups are introduced into the chemical structure of lignin by chemical modification. In physical synergy, lignin can be used as a charring agent to make the char layer of the flame retardant material more compact after combustion. In composite flame retardant materials, the content of lignin has a certain impact on the flame retardant effect. As the lignin content increases, the limiting oxygen index of the combustible material rises, the total smoke production and the total heat release rate decrease. Chemical grafting modification can be roughly divided into nitrogen and phosphorus modification, nitrogen and phosphorus modification containing metal ions, organic silicon modification and nano modification. Among them, nitrogen and phosphorus modification is widely used. In terms of flame retardancy, most chemically modified lignin flame retardants can improve thermal stability and reduce smoke generation. In terms of flame retardancy, most chemically modified lignin flame retardants can improve thermal stability and reduce smoke generation. In the nitrogen and phosphorus modified lignin flame retardant, the phosphorus element plays a role in promoting the formation of carbon in the composite, making it form a dense carbon layer and flame retardant in the condensed phase. During the combustion process, nitrogen forms ammonia to dilute air, achieving the purpose of high efficiency flame retardant in the gas phase flame retardant mechanism. The introduction of metal ions can further improve the performance of nitrogen and phosphorus modified lignin flame retardant. Silicone lignin flame retardant has good heat resistance, oxidation resistance and smoke suppression. The introduction of organosilicon contributes to the formation of a uniform and dense carbon layer, aiding in the reduction of carbon emissions. The nano-modified lignin flame retardant, due to the presence of nanoscale, exhibits a higher specific surface area, facilitating contact with the material surface and enhancing flame retardant effectiveness. At the same time, the dispersion of lignin nanoparticles in the material can form a gas phase barrier effect, slow down the combustion spread and improve the flame retardancy.
Through physical synergy and chemical grafting modification, the flame retardant effect of lignin is improved. There are problems in the use of traditional flame retardants. Such as, high toxicity, serious environmental pollution and high energy consumption. These problems seriously restrict the sustainable development of flame retardant industry. The preparation of lignin flame retardant is an effective way to improve environmental protection and flame retardancy. Lignin flame retardants can carbonize combustibles at high temperatures to produce porous carbon materials and release some harmless gases. As a result, lignin flame retardant is more environmentally friendly and efficient. Therefore, lignin flame retardant become a research hotspot for the sustainable development of flame retardant industry.

Key words: lignin, physical collaboration, chemical modification, bio-based flame retardant, green environmental protection

摘要： 为解决传统阻燃剂引起的环境问题，提高产品的可持续性，研发绿色环保的阻燃剂具有重要意义。木质素因含有丰富的芳环结构、脂肪族和芳香族羟基等活性基团，广泛应用于制备多种生物基阻燃剂。文章首先分析了木质素的分子结构，介绍了木质素的阻燃机理及在阻燃领域的应用进展；然后总结了木质素在高分子复合材料中发挥阻燃作用的两种形式，即物理协同作用和化学改性作用；最后对未来木质素基阻燃剂研究进行了展望，分析了其发展趋势和面临挑战。

关键词: 木质素, 物理协同, 化学改性, 生物基阻燃剂, 绿色环保