College of Light Industry Science and Engineering,State Key Laboratory of Pulp and Paper Engineering,South China University of Technology
設計合成并應用麥黃酮、阿魏酸、對香豆酸、芥子酸以及C5?C5連接 的二聚體等6種木質素模型物，結合稻草、麥草和燕麥三種堿木質素對秸稈類木質素中非常規特征結構的抗紫外輻射性能進行了研究。研究發現，分別將質量分數為2%的模型物或堿木質素添加至潤膚霜或低倍防曬霜后，添加麥黃酮后的霜體防曬指數（SPF值）增幅最高，阿魏酸次之，分別由基礎霜的SPF值 1.06(10.00)提升至4.67(38.49)和3.77(34.69)，增幅顯著；而添加對香豆酸和芥子酸后相應的SPF值增幅較少，揭示了甲氧基的存在形式對木質素紫外屏蔽性能的影響。將三種堿木質素添加至不同基礎霜后，相應的SPF值呈現不同程度的提升。結果表明，在木質素分離過程中保留麥黃酮有利于提升其紫外防護效果；同時，阿魏酸和對香豆酸的存在對秸稈類木質素的抗紫外輻射性能具有顯著影響。
As a natural aromatic polymer, lignin has been proven to be a natural broad-spectrum sunscreen agent due to its good UV protection properties. In general, lignin is a complex and heterogeneous macromolecule composed of guaiacyl (G), syringyl (S), and p-hydroxyphenyl (H) units. However, in addition to the three conventional structural units, some unconventional structures such as ferulates, p-coumaric acid, and tricin are also found in gramineous lignins, which leads to considerable impacts on the anti-UV radiation abilities of lignin. Herein six lignin model compounds, including tricin, ferulic acid, p-coumaric acid, sinapic acid, and C5-C5-linked dimers, were designed and applied to investigate the UV protection abilities of typical unconventional structures in straw-like lignin in combination with three different alkali lignins of rice straw, wheat straw, and oat straw. After the addition of different models or alkali lignins to the pure cream or commercial sunscreen, it was found that SPF values of the model-based or lignin-based sunscreens were increased but varied. The highest increase in SPF value was the sample of adding tricin (0.0558 mmol, about 2% by weight) into the low SPF commercial sunscreen, followed by ferulic acid, from 1.06(10.00) to 4.67(38.49) and 3.77(34.69), respectively, displaying the significant increment of the UV protection ability. In contrast, the increments of SPF values after adding p-coumaric acid or sinapic acid into the pure cream or sunscreens were much lower, which reveals, to some extent, the role of methoxy groups in lignin’s UV resistance ability. Considering lignin structural analysis, it was shown that lignin with the high retention of tricin was beneficial to the UV protection effect; meanwhile, the presence of ferulic acid and p-coumaric acid in lignin also significantly impacted the UV radiation resistance of gramineous lignin. Among the three different lignins, alkali lignin with higher tricin content has more apparent advantages as a sunscreen agent, which provides new insights and a theoretical basis for separating gramineous lignin and its following high-value utilization.