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Open AccessArticle

Synthesis of Lignin-Based Polyacid Catalyst and Its Utilization to Improve Water Resistance of Urea–formaldehyde Resins

by Shishuai Gao 1,2,3, Yupeng Liu 1,3, Chunpeng Wang 1,3, Fuxiang Chu 1,3,*, Feng Xu 2,* and Daihui Zhang 1,3,*
1
National Engineering Laboratory for Biomass Chemical Utilization; Key Laboratory of Chemical Engineering of Forest Products, National Forestry and Grassland Administration, Key Laboratory of Biomass Energy and Material, Institute of Chemical Industry of Forest Products, Chinese Academy of Forestry, Nanjing 210042, China
2
College of Materials Science and Technology, Beijing Forestry University, Beijing 100083, China
3
Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, Nanjing Forestry University, Nanjing 210037, China
*
Authors to whom correspondence should be addressed.
Polymers 2020, 12(1), 175; https://doi.org/10.3390/polym12010175
Received: 10 December 2019 / Revised: 30 December 2019 / Accepted: 6 January 2020 / Published: 9 January 2020
(This article belongs to the Collection Fire and Polymers)
In this study, a lignin-based polyacid catalyst was synthesized via two steps to enhance water resistance of urea–formaldehyde (UF) resins. The first steps involved a hydroxymethylation reaction to increase the hydroxyl content in lignin. Then, hydroxymethylated lignins were reacted with maleic anhydride to form maleated lignin-based polyacids. The acid groups were expected to function as acid catalysts to catalyze the curing process of UF resin. In order to elucidate the structural variation, 3-methoxy-4-hydroxyphenylpropane as a typical guaiacol lignin structural unit was used as a model compound to observe the hydroxymethylation and the reaction with maleic anhydride analyzed by 1H and 13C NMR. After the structural analysis of synthesized lignin-based polyacid by FTIR and 13C NMR, it was used to produce UF resin as an adhesive in plywood and medium density fiberboard (MDF) production, respectively. The results showed that when the addition of lignin-based polyacid was 5% in plywood, it could effectively improve the water resistance of UF resins as compared to commercial additive NH4Cl. It also exhibited a lower formaldehyde emission. Like plywood, lignin-based catalysts used in medium density fiberboard production could not only maintain the mechanical properties, but also inhibit the water adsorption of fiberboards. View Full-Text
Keywords: lignin; catalyst; urea–formaldehyde resin; adhesive lignin; catalyst; urea–formaldehyde resin; adhesive
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MDPI and ACS Style

Gao, S.; Liu, Y.; Wang, C.; Chu, F.; Xu, F.; Zhang, D. Synthesis of Lignin-Based Polyacid Catalyst and Its Utilization to Improve Water Resistance of Urea–formaldehyde Resins. Polymers 2020, 12, 175.

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