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Study on the Structure of Residual Lignin in Unbleached Kraft Pulp by 13C-2H Dual Isotope Tracer
Received:March 14, 2022  
DOI：DOI：10.11980/j.issn.0254-508X.2022.12.002
Key Words:ginkgo  dual isotope tracer  lignin  lignin-carbohydrate complex  kraft pulping
Fund Project:国家自然科学基金项目（21878070）；湖北省高等学校优秀中青年科技创新团队计划项目（T201205）。
Author NameAffiliationPostcode
LU Desheng Research Institute of Pulp & Paper Engineering， Hubei University of Technology， Wuhan， Hubei Province， 430068 430068
ZHANG Kai Research Institute of Pulp & Paper Engineering， Hubei University of Technology， Wuhan， Hubei Province， 430068 430068
CHEN Xudong Research Institute of Pulp & Paper Engineering， Hubei University of Technology， Wuhan， Hubei Province， 430068 430068
XIE Yimin* Research Institute of Pulp & Paper Engineering， Hubei University of Technology， Wuhan， Hubei Province， 430068 430068
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Abstract:The chemical structure of residual lignin in unbleached kraft pulp was investigated using 13C and 2H labeling of lignin and carbohydrates from gymnosperms， respectively. And then the chemical structure of the residual lignin in the unbleached kraft pulp was studied. Dual isotope labeled wood was obtained by putting the lignin precursor coniferin-［α-13C］， the polysaccharide precursor D-glucose-［6-2H2］ and the carboxymethoxyamine hemihydrochloride as the inhibitor of phenylalanine ammonialyas （PAL） into Ginkgo. After kraft cooking， the pulp was separated by enzymatic hydrolysis to obtain cellulolytic enzymatic lignin （CEL）， which was purified by alkali extraction to further obtain alkali-soluble CEL （CEL-Alk）. The 13C NMR was used to analyze its structure. It was found that the lignin substructural units in natural ginkgo xylem before cooking were mainly composed of β—1， β—5， β—O—4 structure， while a small amount of lignin units related to polysaccharides by acetal bond. The residual lignin of kraft pulp was mainly connected by β—5， β—1 and a part of lignin related to polysaccharides through acetal bond. The results of 1H NMR difference spectra showed that Cα of lignin units were also linked to glucose or mannose by benzyl ether bond， indicating that the acetal and benzyl ether linkages in ginkgo lignin-carbohydrate complexes were relatively stable during kraft pulping.
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