乙二醇对低共熔溶剂改性木质素制酚醛树脂胶黏剂的影响

Effect of Ethylene Glycol on Preparation of Phenolic Resin Adhesive Using Modified Lignin via Deep Eutectic Solvent

采用氯化胆碱、甲酸和乙二醇(EG)合成三元酸性低共熔溶剂(TADES),利用傅里叶变换红外光谱(FT-IR)、二维核磁共振波谱(HSQC-NMR)和热重分析(TGA)等测试技术,分别考察TADES中EG质量分数对改性毛竹碱木质素(MBL)结构及其制木质素基酚醛树脂(LPF)胶黏剂性能的影响。结果表明:改性MBL保留了木质素特征结构,且出现羧基;当EG质量分数为15.0%时,改性MBL(DL-EG(15.0%))结构中紫丁香基结构单元摩尔分数减少,愈创木基和对羟基苯丙烷结构单元摩尔分数增加,其热稳定性得到提高;相较于MBL,EG质量分数对LPF胶黏剂黏度和pH值没有明显影响,但EG的加入提高了LPF胶黏剂的胶合强度,降低了游离甲醛含量;采用DL-EG(15.0%)制备LPF胶黏剂的固含量增加,且性能较优,其胶合强度高达3.25 MPa,游离甲醛含量仅为0.01%。

A ternary acidic deep eutectic solvent(TADES)was synthesized using choline chloride,formic acid and ethylene glycol(EG),and the effect of EG mass fraction in TADES on the structure of modified moso bamboo alkali lignin(MBL)and the properties of lignin-phenol-formaldehyde(LPF)adhesive was investigated respectively using Fourier transform infrared spectroscopy(FT-IR),two dimensional nuclear magnetic resonance(HSQC-NMR)spectroscopy,thermogravimetric analysis(TGA),et al.The results show that the modified MBL retains the characteristic structure of lignin,and the carboxyl groups appear.When EG mass fraction is 15.0%,the mole fraction of syringyl structure unit in modified MBL(DL-EG(15.0%))structure decreases,and the mole fractions of guaiacyl and p-hydroxyphenylpropane structure unit increase with improved thermal stability.Compared with MBL,EG mass fraction has no obvious influences on viscosity and pH value of LPF adhesive,but the addition of EG improves the bonding strength of LPF adhesive and reduces the free formaldehyde content.The solid content of LPF adhesive prepared by DL-EG(15.0%)increases and its performance is better with bonding strength as high as 3.25 MPa and free formaldehyde content only 0.01%.