Heat-Induced Discoloration of Chromophore Structures in Eucalyptus Lignin

Peng Zhang; Yanxia Wei; Yang Liu; Jianmin Gao; Yao Chen; Yongming Fan

doi:10.3390/ma11091686

Heat-Induced Discoloration of Chromophore Structures in Eucalyptus Lignin

Materials (Basel). 2018 Sep 11;11(9):1686. doi: 10.3390/ma11091686.

Authors

Peng Zhang¹, Yanxia Wei², Yang Liu³, Jianmin Gao⁴, Yao Chen⁵, Yongming Fan⁶

Affiliations

¹ MOE Key Laboratory of Wooden Material Science and Application, College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, China. rulai9565@hotmail.com.
² MOE Key Laboratory of Wooden Material Science and Application, College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, China. wyx0408@bjfu.edu.cn.
³ MOE Key Laboratory of Wooden Material Science and Application, College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, China. nolekobe@sina.com.
⁴ MOE Key Laboratory of Wooden Material Science and Application, College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, China. jmgao@bjfu.edu.cn.
⁵ MOE Key Laboratory of Wooden Material Science and Application, College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, China. ychen@bjfu.edu.cn.
⁶ MOE Key Laboratory of Wooden Material Science and Application, College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, China. fanym@bjfu.edu.cn.

Abstract

The color changes corresponding to chromophore structures in lignin caused by exposure of Eucalyptus (Eucalyptus grandis and E. urophylla) to heat were investigated. Eucalyptus wood powders were heat treated under saturated steam atmospheres for 10 h at 110 °C, 130 °C and 150 °C. The lignin was isolated before and after heat treatment. The physicochemical properties of the lignin and changes in chromophore structures during heat treatment was evaluated through wet chemical analysis, Fourier transform infrared spectroscopy (FTIR), diffuse reflectance ultraviolet-visible spectroscopy (DRUV-Vis), gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS) and ¹³C Cross polarization magic angle spinning nuclear magnetic resonance (¹³C CPMAS NMR). Wood color darkened and reddened with the increase in pressure and temperature. Depolymerization and dehydration reactions occurred via demethoxylation with heat treatment in saturated steam at 110 °C or 130 °C. Lignin condensed to form insoluble compounds after heat treatment in saturated steam at 150 °C. G units increased and S units decreased through demethylation during heat treatment, as revealed by FTIR and ¹³C-NMR analysis.

Keywords: Eucalyptus; chromophore system; heat-induced; lignin; wood discoloration.

Grants and funding

31400498/National Natural Science Foundation of China