Formaldehyde-Free Method for Incorporating Lignin into Epoxy Thermosets

Journal Article · Wed Jul 11 04:00:00 EDT 2018 · ACS Sustainable Chemistry & Engineering

DOI:https://doi.org/10.1021/acssuschemeng.8b01962· OSTI ID:1566360

Zhao, Shou ^[1]; Huang, Xiangning ^[2]; Whelton, Andrew J. ^[3]; Abu-Omar, Mahdi M. ^[4]

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1. Department of Chemistry &, Biochemistry, University of California, Santa Barbara, Building 232, Santa Barbara, California 93106, United States
2. Lyles School of Civil Engineering, Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907, United States
3. Lyles School of Civil Engineering, Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907, United States; Division of Environmental and Ecological Engineering, Purdue University, West Lafayette, Indiana 47907, United States
4. Department of Chemistry &, Biochemistry, University of California, Santa Barbara, Building 232, Santa Barbara, California 93106, United States; Department of Chemical Engineering, University of California, Santa Barbara, Engineering II Building, Santa Barbara, California 93106, United States

A series of liquid and curable lignin-containing epoxy prepolymers were prepared for making renewable epoxy thermosets. First, lignin was modified to phenolated lignin (PL) in a solvent-free reaction. PL was subsequently co-oligomerized with salicyl alcohol (SA) in water without the use of formaldehyde to obtain fully bio-based polyphenols (PL-SA). Glycidylation of lignin-based polyphenols yielded exclusively liquid epoxy prepolymers without production of solid co-products. The liquid epoxy prepolymers (with lignin content up to 21 wt %) were curable with amine hardener (diethylenetriamine) to generate homogeneous thermosets, which required no epoxy co-prepolymer. The structural evolution from starting monomers to epoxy thermosets was followed by nuclear magnetic resonance and Fourier transform infrared spectroscopy. Compared to common syntheses in which lignin is glycidylated prior to being blended with epoxy co-prepolymers, the herein reported methodology conferred networks with increased α-relaxation temperature (106–114 vs 96 °C), storage modulus (1843–2151 vs 1828 MPa), cross-link density (8.2–16.0 vs 5.4 mmol/cm3) and tensile properties (stress of 66.9–68.1 vs 28.7 MPa, and strain of 3.3–3.7 vs 1.4%). Moreover, bio-based thermosets exhibited comparable or superior thermomechanical properties to conventional bisphenol A (BPA)-based counterpart. By producing liquid-phase lignin-containing epoxy prepolymers, this study provides a formaldehyde-free method for incorporating lignin into epoxy thermosets without the need for additional co-prepolymers.

• Research Organization: Energy Frontier Research Centers (EFRC) (United States). Center for Direct Catalytic Conversion of Biomass to Biofuels (C3Bio); Purdue Univ., West Lafayette, IN (United States)
• Sponsoring Organization: USDOE SC Office of Basic Energy Sciences (SC-22)
• DOE Contract Number: SC0000997
• OSTI ID: 1566360
• Journal Information: ACS Sustainable Chemistry & Engineering, Journal Name: ACS Sustainable Chemistry & Engineering Journal Issue: 8 Vol. 6; ISSN 2168-0485
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

catalysis (homogeneous)
catalysis (heterogeneous)
biofuels (including algae and biomass)
bio-inspired
materials and chemistry by design
synthesis (self-assembly)
synthesis (scalable processing)