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Article

Effect of Heat Treatment on the Chemical Structure and Thermal Properties of Softwood-Derived Glycol Lignin

by
Thi Thi Nge
1,*,
Yuki Tobimatsu
2,
Masaomi Yamamura
2,
Shiho Takahashi
1,
Eri Takata
1,
Toshiaki Umezawa
2,3 and
Tatsuhiko Yamada
1,*
1
Center for Advanced Materials, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki 305-8687, Japan
2
Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
3
Research Unit for Development and Global Sustainability, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
*
Authors to whom correspondence should be addressed.
Molecules 2020, 25(5), 1167; https://doi.org/10.3390/molecules25051167
Submission received: 15 February 2020 / Revised: 3 March 2020 / Accepted: 3 March 2020 / Published: 5 March 2020
(This article belongs to the Special Issue Lignin – A Natural Resource with Huge Potential)
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Abstract

A large-scale glycol lignin (GL) production process (50 kg wood meal per batch) based on acid-catalyzed polyethylene glycol (PEG) solvolysis of Japanese cedar (JC) was developed at the Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Japan. JC wood meal with various particle size distributions (JC-S < JC-M < JC-L) (average meal size, JC-S (0.4 mm) < JC-M (0.8 mm) < JC-L (1.6 mm)) and liquid PEG with various molecular masses are used as starting materials to produce PEG-modified lignin derivatives, namely, GLs, with various physicochemical and thermal properties. Because GLs are considered a potential feedstock for industrial applications, the effect of heat treatment on GL properties is an important issue for GL-based material production. In this study, GLs obtained from PEG400 solvolysis of JC-S, JC-M, and JC-L were subjected to heating in a constant-temperature drying oven at temperatures ranging from 100 to 220 °C for 1 h. All heat-treated GL series were thermally stable, as determined from the Klason lignin content, TMA, and TGA analyses. SEC analysis suggests the possibility of condensation among lignin fragments during heat treatment. ATR-FTIR spectroscopy, thioacidolysis, and 2D HSQC NMR demonstrated that a structural rearrangement occurs in the heat-treated GL400 samples, in which the content of α–PEG-β–O-4 linkages decreases along with the proportional enrichments of β–5 and β–β linkages, particularly at treatment temperatures above 160 °C.
Keywords: glycol lignin; polyethylene glycol (PEG) solvolysis; wood meal size; heat treatment; 2D HSQC NMR; thioacidolysis; thermal flow property glycol lignin; polyethylene glycol (PEG) solvolysis; wood meal size; heat treatment; 2D HSQC NMR; thioacidolysis; thermal flow property
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MDPI and ACS Style

Nge, T.T.; Tobimatsu, Y.; Yamamura, M.; Takahashi, S.; Takata, E.; Umezawa, T.; Yamada, T. Effect of Heat Treatment on the Chemical Structure and Thermal Properties of Softwood-Derived Glycol Lignin. Molecules 2020, 25, 1167. https://doi.org/10.3390/molecules25051167

AMA Style

Nge TT, Tobimatsu Y, Yamamura M, Takahashi S, Takata E, Umezawa T, Yamada T. Effect of Heat Treatment on the Chemical Structure and Thermal Properties of Softwood-Derived Glycol Lignin. Molecules. 2020; 25(5):1167. https://doi.org/10.3390/molecules25051167

Chicago/Turabian Style

Nge, Thi Thi, Yuki Tobimatsu, Masaomi Yamamura, Shiho Takahashi, Eri Takata, Toshiaki Umezawa, and Tatsuhiko Yamada. 2020. "Effect of Heat Treatment on the Chemical Structure and Thermal Properties of Softwood-Derived Glycol Lignin" Molecules 25, no. 5: 1167. https://doi.org/10.3390/molecules25051167

APA Style

Nge, T. T., Tobimatsu, Y., Yamamura, M., Takahashi, S., Takata, E., Umezawa, T., & Yamada, T. (2020). Effect of Heat Treatment on the Chemical Structure and Thermal Properties of Softwood-Derived Glycol Lignin. Molecules, 25(5), 1167. https://doi.org/10.3390/molecules25051167

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