Effect of lignin on the self-bonding of a natural fiber material in a hydrothermal environment: Lignin structure and characterization

Yinling Zhao; Jinquan Yue; Longchen Tao; Yusen Liu; Sheldon Q Shi; Liping Cai; Shengling Xiao

doi:10.1016/j.ijbiomac.2020.04.060

Effect of lignin on the self-bonding of a natural fiber material in a hydrothermal environment: Lignin structure and characterization

Int J Biol Macromol. 2020 Apr 29:158:1135-1140. doi: 10.1016/j.ijbiomac.2020.04.060. Online ahead of print.

Authors

Yinling Zhao¹, Jinquan Yue², Longchen Tao², Yusen Liu², Sheldon Q Shi³, Liping Cai³, Shengling Xiao⁴

Affiliations

¹ College of Engineering and Technology, Northeast Forestry University, Harbin 150040, China.
² College of Materials Science and Engineering, Northeast Forestry University, Harbin 150040, China.
³ Department of Mechanical and Energy Engineering, University of North Texas, Denton, TX 76203, USA.
⁴ College of Engineering and Technology, Northeast Forestry University, Harbin 150040, China. Electronic address: shenglingxiao@126.com.

PMID: 32360469
DOI: 10.1016/j.ijbiomac.2020.04.060

Abstract

Self-bonding natural fiber materials (SNFMs) were prepared at different initial moisture contents (IMCs) through a molding pressing process. The self-bonding mechanism of the SNFMs was deduced from the chemical and structural changes of lignin and their mechanical strengths. The structural transformations of milled wood lignin (MWL) in the SNFMs were investigated by two-dimensional heteronuclear single quantum coherence, quantitative ³¹P-nuclear magnetic resonance spectra, gelpermeation chromatography, and thermogravimetric analysis. As IMC increased from 0% to 80%, the tensile strength increased from 23.0 to 70.0 MPa and the density increased from 0.99 to 1.05 g/cm³. IMC affected the distribution and abundance of the typical lignin linkages (β-O-4', β-β, and β-5') and the S-OH/G-OH ratios of lignin. Moreover, as IMC increased, the aliphatic hydroxyl groups proportionally decreased, while the condensed phenolic and non-condensed phenolic hydroxyl groups increased, the molecular weight of MWL became larger, and the thermal stability of lignin improved. These findings indicate the simultaneous occurrence of depolymerization and condensation reactions of lignin. The condensation reaction dominated, improving the mechanical strength of the material. Our results explain (at least partly) the self-bonding mechanism of SNFMs.

Keywords: Initial moisture content; Lignin; Self-bonding.