Abstract
Conversion of technical lignin into performance biopolymers such as polyurethane offers environmental and economic advantages when combined with production of biofuels from biomass sugars, presenting significant interest toward studying the role of pretreatment on lignin structure and functionality. Co-solvent enhanced lignocellulosic fractionation (CELF) pretreatment, employing acidic aqueous tetrahydrofuran (THF) mixtures, was developed to effectively break down the lignin-carbohydrate matrix and promote extraction of lignin from lignocellulosic biomass with desirable purity and yield. In this study, we report the effects of CELF pretreatment reaction severity on the molecular structure of CELF-extracted lignin and its impact toward the mechanical properties of the resulting lignin-based polyurethanes. Reaction temperature was found to play the most significant role, compared to reaction time and acidity, in manipulating structural features such as molecular weight, functionality and intra-polymer structure. At the severe reaction conditions at 180°C, the order of reactivity for primary lignin interlinkages characterized by semiquantitative HSQC NMR analysis were found to be β-ether > phenylcoumaran (β−5′) > resinol (β−β′) facilitating a high degree of depolymerization and yielding a high frequency of free phenolics and reduced aliphatic hydroxyl groups. All side-chain interlinkages were depleted converting guaiacyl subunits into condensed forms, while still retaining uncondensed syringyl subunits. Under the mild 150°C temperature reaction, CELF lignin had higher molecular weight and retained more β-ether interlinkages. The results from CELF lignin-based polyurethane synthesis indicated that the tensile properties depended on the miscibility of CELF lignin with other components and low molecular weight cuts improved the dispersion of lignin in the polyurethane network. Pre-mixing of CELF with poly(ethylene glycol) (PEG) reduced the brittleness and improved the ductility of the CELF lignin-PEG polyurethanes.
| Original language | English |
|---|---|
| Article number | 149 |
| Journal | Frontiers in Energy Research |
| Volume | 8 |
| DOIs | |
| State | Published - Jul 8 2020 |
Funding
Funding. We acknowledge the support through the U.S.D.A. National Institute of Food and Agriculture Grant 9008-004957 titled “Integrated Biorefinery to Produce Ethanol, High-Value Polymers, and Chemicals from Lignocellulosic Biomass.” Oak Ridge National Laboratory is managed by UT-Battelle, LLC under Contract DE-AC05-00OR22725 with the U.S. Department of Energy (DOE). This study was supported, in part, by the Center for Bioenergy Innovation (CBI), a U.S. Department of Energy Bioenergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science.
| Funders | Funder number |
|---|---|
| U.S. Department of Energy Bioenergy Research Center | |
| U.S. Department of Energy | |
| National Institute of Food and Agriculture | 9008-004957 |
| Office of Science | |
| Biological and Environmental Research | |
| Oak Ridge National Laboratory | |
| Center for Bioenergy Innovation | |
| UT-Battelle | DE-AC05-00OR22725 |
Keywords
- NMR
- lignin-based polyurethanes
- mechanical properties
- poplar lignin
- pretreatment conditions
