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Polymers 2017, 9(9), 428; https://doi.org/10.3390/polym9090428

Fast Curing Bio-Based Phenolic Resins via Lignin Demethylated under Mild Reaction Condition

1
Ministry of Education (MOE) Key Laboratory of Wooden Material Science and Application, Beijing Key Laboratory of Wood Science and Engineering, School of Materials Science and Technology, Beijing Forestry University, Beijing 100083, China
2
Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (MOE), School of Materials Science and Engineering, Shandong University, Jinan 250061, China
*
Authors to whom correspondence should be addressed.
Received: 5 August 2017 / Revised: 2 September 2017 / Accepted: 5 September 2017 / Published: 7 September 2017
(This article belongs to the Special Issue Bio-Based Resins and Crosslinked Polymers from Renewable Resources)
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Abstract

Demethylation technique has been used to enhance lignin reactivity for preparation of phenolic resins. However, the demethylation efficiency and the demethylated lignin (DL) reactivity were still unsatisfactory. To improve the demethylation efficiency, alkali lignin was demethylated under different mild conditions using sodium sulfite as a catalyst. Lignin and DL were characterized by 1H-NMR (nuclear magnetic resonance) and Fourier transform infrared (FT-IR) spectroscopy to determine the demethylation mechanism. With the demethylation of lignin, the methoxyl group content decreased from 1.93 m mol/g to 1.09 m mol/g, and the phenolic hydroxyl group content increased from 0.56 m mol/g to 0.82 m mol/g. These results revealed that methoxyl groups were attacked by SO32, and some methoxyl groups were converted to phenolic hydroxyl groups by a nucleophilic substitution reaction, generating DL with high reactivity. The chemical properties of lignin-based phenolic resins were studied by 13C-NMR and FT-IR spectroscopy, and their physical properties were also investigated. The results indicated that lignin-based phenolic resins exhibited faster curing rate and shorter gel time. In addition, the bonding strength increased from 0.92 MPa to 1.07 MPa, and the formaldehyde emission decreased from 0.58 mg/L to 0.22 mg/L after lignin demethylated at the optimum condition. View Full-Text
Keywords: alkali lignin; demethylation efficiency; demethylation mechanism; bio-based phenolic resins alkali lignin; demethylation efficiency; demethylation mechanism; bio-based phenolic resins
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Li, J.; Zhang, J.; Zhang, S.; Gao, Q.; Li, J.; Zhang, W. Fast Curing Bio-Based Phenolic Resins via Lignin Demethylated under Mild Reaction Condition. Polymers 2017, 9, 428.

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