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Lignin Structure and Solvent Effects on the Selective Removal of Condensed Units and Enrichment of S-Type Lignin

Authors
  • Gao, Si1
  • Zhao, Ji
  • Wang, Xing1, 2
  • Guo, Yanzhu1
  • Han, Ying1
  • Zhou, Jinghui1
  • 1 (Y.H.)
  • 2 State Key Laboratory of Pulp and Papermaking Engineering, South China University of Technology, Guangzhou 510640, China
Type
Published Article
Journal
Polymers
Publisher
MDPI AG
Publication Date
Sep 01, 2018
Volume
10
Issue
9
Identifiers
DOI: 10.3390/polym10090967
PMID: 30960892
PMCID: PMC6403703
Source
PubMed Central
Keywords
License
Green

Abstract

This study focused on the structural differences of lignin after pyridine–acetic acid–water (PAW) and dioxane–acidic water (DAW) purification processes. These structural differences included the S/G ratio, condensed structure, weight-average (MW) molecular weights, β-O-4 linkages and sugar content. The chemical structure of the isolated crude lignin (CL), PAW purified lignin (PPL) and DAW purified lignin (DPL) was elucidated using quantitative 13C NMR, 2D-HSQC NMR spectra, thermogravimetric analysis (TGA), gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR). The results showed that the PPL fractions contain fewer condensed structures, higher S/G ratios, more β-O-4 linkages, higher average MW and lower thermal degradation properties compared to the CL and DPL fractions. Furthermore, the PAW process was more selective in removing condensed units and enriching S-type lignin from CL compared to the DAW process. These results provide valuable information for understanding which purification process is more suitable to be applied for lignin.

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