Cargando…

Bond Structures between Wood Components and Citric Acid in Wood-Based Molding

Citric acid-based wood adhesive is considered a chemical-bonding wood adhesive. However, the detailed structures of the bonds between wood components and citric acid remain unknown. Here, we examine the chemical bonding structures between citric acid and wood by heteronuclear single quantum coherenc...

Descripción completa

Detalles Bibliográficos
Autores principales: Ando, Daisuke, Umemura, Kenji
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7794866/
https://www.ncbi.nlm.nih.gov/pubmed/33375746
http://dx.doi.org/10.3390/polym13010058
_version_ 1783634309420154880
author Ando, Daisuke
Umemura, Kenji
author_facet Ando, Daisuke
Umemura, Kenji
author_sort Ando, Daisuke
collection PubMed
description Citric acid-based wood adhesive is considered a chemical-bonding wood adhesive. However, the detailed structures of the bonds between wood components and citric acid remain unknown. Here, we examine the chemical bonding structures between citric acid and wood by heteronuclear single quantum coherence-nuclear magnetic resonance (HSQC-NMR) analysis of wood-based molding using Japanese cedar (Cryptomeria japonica) and citric acid. In the HSQC-NMR spectrum of the wood molding, some esterified C/H correlation peaks appeared. The primary hydroxyl groups of polysaccharides, such as cellulose and galactoglucomannan, and the primary hydroxyl groups of the β-O-4 and β-5 substructures in lignin were found to be esterified with citric acid. In contrast, the secondary hydroxyl groups, except for xylan, barely reacted because of the steric hindrance. Additionally, the C/H correlation peak volumes of the reducing ends of mannan and xylan in the anomeric region increased after molding. It was clarified that the glycosidic bonds in the hemicelluloses were cleaved under the acidic molding condition with citric acid. The HSQC-NMR analysis revealed that the esterification of hemicellulose and lignin, and degradation of hemicellulose, proceeded under the molding condition. These results will promote understanding of the adhesive mechanism of citric acid-based wood adhesive and of the properties of the molding.
format Online
Article
Text
id pubmed-7794866
institution National Center for Biotechnology Information
language English
publishDate 2020
publisher MDPI
record_format MEDLINE/PubMed
spelling pubmed-77948662021-01-10 Bond Structures between Wood Components and Citric Acid in Wood-Based Molding Ando, Daisuke Umemura, Kenji Polymers (Basel) Article Citric acid-based wood adhesive is considered a chemical-bonding wood adhesive. However, the detailed structures of the bonds between wood components and citric acid remain unknown. Here, we examine the chemical bonding structures between citric acid and wood by heteronuclear single quantum coherence-nuclear magnetic resonance (HSQC-NMR) analysis of wood-based molding using Japanese cedar (Cryptomeria japonica) and citric acid. In the HSQC-NMR spectrum of the wood molding, some esterified C/H correlation peaks appeared. The primary hydroxyl groups of polysaccharides, such as cellulose and galactoglucomannan, and the primary hydroxyl groups of the β-O-4 and β-5 substructures in lignin were found to be esterified with citric acid. In contrast, the secondary hydroxyl groups, except for xylan, barely reacted because of the steric hindrance. Additionally, the C/H correlation peak volumes of the reducing ends of mannan and xylan in the anomeric region increased after molding. It was clarified that the glycosidic bonds in the hemicelluloses were cleaved under the acidic molding condition with citric acid. The HSQC-NMR analysis revealed that the esterification of hemicellulose and lignin, and degradation of hemicellulose, proceeded under the molding condition. These results will promote understanding of the adhesive mechanism of citric acid-based wood adhesive and of the properties of the molding. MDPI 2020-12-25 /pmc/articles/PMC7794866/ /pubmed/33375746 http://dx.doi.org/10.3390/polym13010058 Text en © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Ando, Daisuke
Umemura, Kenji
Bond Structures between Wood Components and Citric Acid in Wood-Based Molding
title Bond Structures between Wood Components and Citric Acid in Wood-Based Molding
title_full Bond Structures between Wood Components and Citric Acid in Wood-Based Molding
title_fullStr Bond Structures between Wood Components and Citric Acid in Wood-Based Molding
title_full_unstemmed Bond Structures between Wood Components and Citric Acid in Wood-Based Molding
title_short Bond Structures between Wood Components and Citric Acid in Wood-Based Molding
title_sort bond structures between wood components and citric acid in wood-based molding
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7794866/
https://www.ncbi.nlm.nih.gov/pubmed/33375746
http://dx.doi.org/10.3390/polym13010058
work_keys_str_mv AT andodaisuke bondstructuresbetweenwoodcomponentsandcitricacidinwoodbasedmolding
AT umemurakenji bondstructuresbetweenwoodcomponentsandcitricacidinwoodbasedmolding