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Materials 2018, 11(9), 1686;

Heat-Induced Discoloration of Chromophore Structures in Eucalyptus Lignin

MOE Key Laboratory of Wooden Material Science and Application, College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, China
Authors to whom correspondence should be addressed.
Received: 13 July 2018 / Revised: 9 August 2018 / Accepted: 22 August 2018 / Published: 11 September 2018
(This article belongs to the Section Structure Analysis and Characterization)
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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. View Full-Text
Keywords: heat-induced; wood discoloration; Eucalyptus; lignin; chromophore system heat-induced; wood discoloration; Eucalyptus; lignin; chromophore system

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Zhang, P.; Wei, Y.; Liu, Y.; Gao, J.; Chen, Y.; Fan, Y. Heat-Induced Discoloration of Chromophore Structures in Eucalyptus Lignin. Materials 2018, 11, 1686.

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