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Polymers 2017, 9(7), 266; https://doi.org/10.3390/polym9070266

Catalyzed Synthesis and Characterization of a Novel Lignin-Based Curing Agent for the Curing of High-Performance Epoxy Resin

1
Department of Applied Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz 51666, Iran
2
Institute for Frontier Materials, Deakin University, Geelong VIC 3216, Victoria, Australia
3
Department of Organic Chemistry, Faculty of Chemistry, Isfahan University of Technology, Isfahan 8415683111, Iran
4
Department of Applied Chemistry, Faculty of Chemistry, Urmia University, Urmia 5756151818, Iran
*
Author to whom correspondence should be addressed.
Academic Editor: Antonio Pizzi
Received: 19 June 2017 / Revised: 1 July 2017 / Accepted: 2 July 2017 / Published: 4 July 2017
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Abstract

In this study, lignin, an aromatic compound from the forestry industry, was used as a renewable material to synthesize a new aromatic amine curing agent for epoxy resin. Firstly, lignin was separated from black liquor and hydroxyl groups were converted to tosyl groups as leaving groups. Then, primary amination was conducted using an ammonia solution at high pressure and temperature, in the presence of a nano-alumina-based catalyst. The structure of the nanocatalyst was confirmed by FT-IR, ICP, SEM, and XPS analyses. According to the FT-IR spectra, a demethylation reaction, the substitution of hydroxyl groups with tosyl groups, and then an amination reaction were successfully performed on lignin, which was further confirmed by the 13C NMR and CHNS analyses. The active hydrogen equivalent of aminated lignin was determined and three samples with 9.9 wt %, 12.9 wt %, and 15.9 wt % of aminated lignin, as curing agents, were prepared for curing the diglycidyl ether of bisphenol A (DGEBA). The thermal characteristics of the curing process of these epoxy samples were determined by DSC and TGA analyses. Moreover, the mechanical performance of the cured epoxy systems, e.g., the tensile strength and Izod impact strength, were measured, showing that in the presence of 12.9 wt % aminated lignin, the mechanical properties of the aminated lignin-epoxy system exhibited the best performance, which was competitive, compared to the epoxy systems cured by commercial aromatic curing agents. View Full-Text
Keywords: renewable epoxy resin; lignin; curing agent; nanocatalyst renewable epoxy resin; lignin; curing agent; nanocatalyst
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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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Nikafshar, S.; Zabihi, O.; Moradi, Y.; Ahmadi, M.; Amiri, S.; Naebe, M. Catalyzed Synthesis and Characterization of a Novel Lignin-Based Curing Agent for the Curing of High-Performance Epoxy Resin. Polymers 2017, 9, 266.

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