Polyurethanes Based on Unmodified and Refined Technical Lignins: Correlation between Molecular Structure and Material Properties

Abstract

The structural complexity and robust intermolecular interactions have challenged the incorporation of technical lignin into value-added polymeric materials for decades. To study the correlation between lignin molecular structure and material properties of lignin-based polyurethanes, we applied co-solvent enhanced lignocellulosic fractionation pretreatment followed by sequential precipitation to produce three distinct lignin preparations with narrowly distributed (molecular weight dispersity <2) and comparatively low molecular weight (<1500 g/mol) from poplar biomass. Structural characterization indicated that these lignin preparations differed in average molecular chain length and stiffness as well as hydroxyl group distribution. Secondary hydroxyl group providers such as aliphatic diols and polyethers were incorporated as building blocks into the lignin-based polyurethanes to provide additional hydrogen capacity to improve the dispersion of lignin in the polyurethane network. The selected aliphatic diols and polyethers interacted with lignin molecules at different levels of strength depending on their molecular structure, and their impacts were ultimately reflected in the mechanical and thermal properties of the resulting lignin-based polyurethanes. The copolymerization of technical lignin with tailored structure and secondary hydroxyl providers could provide new strategies in formulating lignin-based/containing polyurethanes for various functional applications.

Molecular Engineering of Biorefining Lignin Waste for Solid-State Electrolyte

“…Current technologies to use lignin waste mainly include (1) catalytic conversion of lignin into aromatic compounds and platform chemicals, (2) chemical conversion of lignin into functional polymeric materials such as resin, polyurethane, and plastic alternatives, , (3) biological funneling of lignin into commodity chemicals or platform chemicals, and (4) thermal conversion of lignin into carbon materials like carbon fibers , and carbonaceous electrodes. , However, these conversions need notable catalysts, require elaborate chemical design or biological engineering, or are energy consuming, all of which have hindered the commercialization of these lignin-derived products. Therefore, a facile, cost-effective, and energy-efficient technology to valorize lignin into a high-value-added product still represents a significant challenge.…”

“…15 In another word, the valorization of lignin by converting it into high-value-added products will return economics, enhance carbon efficiency, improve sustainability, and finally promote development of the bioeconomy. 16 Current technologies to use lignin waste mainly include (1) catalytic conversion of lignin into aromatic compounds and platform chemicals, 17 (2) chemical conversion of lignin into functional polymeric materials such as resin, 18 polyurethane, 19 and plastic alternatives, 20,21 (3) biological funneling of lignin into commodity chemicals 22 or platform chemicals, 23 and (4) thermal conversion of lignin into carbon materials like carbon fibers 24,25 and carbonaceous electrodes. 26,27 However, these conversions need notable catalysts, require elaborate chemical design or biological engineering, or are energy consuming, all of which have hindered the commercialization of these ligninderived products.…”

Exploring the reactivity of aliphatic and phenolic hydroxyl groups in lignin hydrogenolysis oil towards urethane bond formation

“…An in-depth kinetic study showing the rate at which hydroxyl moieties in lignin (aliphatic, phenolic) react with different commercial isocyanates moieties (aliphatic or aromatic) is still missing in the literature. Besides recent work (Antonino et al, 2021) in which the difference in reactivity of the aromatic hydroxyl group between S, G, and H units in lignin is described, very little comparable and comprehensive data is available on the reactivity of the different hydroxyl moieties of lignin when treated with both aliphatic and aromatic isocyanates (Cateto et al, 2011;Chauhan et al, 2014;Gómez-Fernández et al, 2017;Li et al, 2020;Wang et al, 2021;Zieglowski et al, 2019).…”

The Effect of Acidic Ternary Deep Eutectic Solvent Treatment on Native Lignin

“…29,31−35 This endows lignin with tunable properties and higher recalcitrance toward harsh reaction condition for more applications such as directly serving as building blocks or filling material for the production of functional polymers and composites. 36 In addition, the normal aryl ether linking motif can be recovered from the alkoxylated lignin via a mild acidic hydrolysis. 29,32 For further application, fundamental understanding of the consequences of such modifications on lignin isolation is required to understand where different modified lignin fragments end up in the process and to improve fractionation.…”

“…Benzylic alkoxylation of lignin with EG occurs during this fractionation (Figure c), which can significantly suppress repolymerization, providing lignin with enhanced chemical stability and new functionality. − Furthermore, the modification leads to increased solubility of such fully or partially modified lignin in common (organic) solvents, making it particularly suitable for further processing and upgrading. ,− This endows lignin with tunable properties and higher recalcitrance toward harsh reaction condition for more applications such as directly serving as building blocks or filling material for the production of functional polymers and composites . In addition, the normal aryl ether linking motif can be recovered from the alkoxylated lignin via a mild acidic hydrolysis. , For further application, fundamental understanding of the consequences of such modifications on lignin isolation is required to understand where different modified lignin fragments end up in the process and to improve fractionation.…”