微波辅助羟甲基化改性木质素的制备及其结构表征

摘要

为提高木质素的反应活性及其利用效率，采用微波辅助加热对木质素进行羟甲基化改性研究。通过测定不同条件下木质素消耗甲醛的量，研究了反应温度、pH值、反应时间对木质素改性的影响，得到木质素羟甲基化的最佳反应条件为温度80℃、pH值10.5、反应时间30 min。通过对比常规加热和微波加热两种方式，发现微波加热能使反应时间显著缩短，提高木质素羟甲基化的反应效率。由傅里叶红外光谱( FT-IR)和核磁共振氢谱(1H NMR)表征木质素改性前后的结构，表明木质素经改性确实发生了羟甲基化反应，羟基含量增加，有利于反应活性增加。通过凝胶渗透色谱( GPC)分析表明相对于乙酰化木质素，乙酰化羟甲基木质素的数均相对分子质量(Mn)和重均相对分子质量(Mw)增加，分布系数(Mw/Mn)变大。%In order to improve the utilization efficiency and reactivity of lignin,the hydroxymethylate modification was carried out under microwave heating. The reaction conditions were optimized by measuring the amount of formaldehyde consumption. The optimal reaction conditions were 80℃,pH value 10.5 and reaction time 30 min.The reaction time of microwave heating could be shortened compared with the conventional method and the efficiency of the hydroxymethylate modification of lignin could be improved significantly.The lignin and modified lignin were characterized by Fourier transform infrared spectroscopy(FT-IR), nuclear magnetic resonance hydrogen spectrum(1H NMR) and gel permeation chromatograph(GPC).The results showed that the content of hydroxyl group and reactive activity of modified lignin increased. The number-average molecular weight ( Mn ) and weight-average molecular weight ( Mw ) of acetylated hydroxymethylation lignin increased, as well as the molecular weight distribution(Mw/Mn) tended to be wider compared with those of the acetylated lignin.