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Covalently bound humin-lignin hybrids as important novel substructures in organosolv spruce lignins
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.ORCID iD: 0000-0001-6011-6767
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. Department of Earth and Environmental Sciences, University of Milano-Bicocca, Piazza della Scienza 1, 20126 Milan, Italy; NBFC – National Biodiversity Future Center, 90133 Palermo, Italy.ORCID iD: 0000-0003-3845-7017
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.ORCID iD: 0000-0001-7500-2367
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.ORCID iD: 0000-0003-0079-5950
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2023 (English)In: International Journal of Biological Macromolecules, ISSN 0141-8130, E-ISSN 1879-0003, Vol. 233, article id 123471Article in journal (Refereed) Published
Abstract [en]

Organosolv lignins (OSLs) are important byproducts of the cellulose-centred biorefinery that need to be converted in high value-added products for economic viability. Yet, OSLs occasionally display characteristics that are unexpected looking at the lignin motifs present. Applying advanced NMR, GPC, and thermal analyses, isolated spruce lignins were analysed to correlate organosolv process severity to the structural details for delineating potential valorisations. Very mild conditions were found to not fractionate the biomass, causing a mix of sugars, lignin-carbohydrate complexes (LCCs), and corresponding dehydration/degradation products and including pseudo-lignins. Employing only slightly harsher conditions promote fractionation, but also formation of sugar degradation structures that covalently incorporate into the oligomeric and polymeric lignin structures, causing the isolated organosolv lignins to contain lignin-humin hybrid (HLH) structures not yet evidenced as such in organosolv lignins. These structures effortlessly explain observed unexpected solubility issues and unusual thermal responses, and their presence might have to be acknowledged in downstream lignin valorisation.

Place, publisher, year, edition, pages
Elsevier B.V. , 2023. Vol. 233, article id 123471
Keywords [en]
Humins, Organosolv lignin, Structure elucidation
National Category
Bioprocess Technology
Research subject
Biochemical Process Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-95765DOI: 10.1016/j.ijbiomac.2023.123471ISI: 000948804300001PubMedID: 36736515Scopus ID: 2-s2.0-85148062762OAI: oai:DiVA.org:ltu-95765DiVA, id: diva2:1741548
Funder
Swedish Research Council Formas, 2016-20022Bio4Energy
Note

Validerad;2023;Nivå 2;2023-03-06 (joosat);

Funder: COST (European Cooperation in Science and Technology), (CA17128); University of Milano-Bicocca; University of Naples ‘Federico II’

Available from: 2023-03-06 Created: 2023-03-06 Last updated: 2024-05-02Bibliographically approved
In thesis
1. Structure and property oriented organosolv lignin extraction
Open this publication in new window or tab >>Structure and property oriented organosolv lignin extraction
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this Thesis, organosolv fractionation of softwood (spruce), hardwood (birch and beech), and herbaceous crops (wheat straw) was performed by applying various organosolv process conditions. Among these were a novel steam-explosion/organosolv hybrid mode, and two ternary solvent systems utilizing water/ethanol/acetone, and water/acetone/acetic acid. In addition, the effect of using inorganic acidic catalyst (H2SO4) was investigated for all raw material classes. Also, alkaline catalyst (NaOH) was investigated for wheat straw due to its reported high content of inorganics which presence adds additional structural complexity to the lignocellulosic recalcitrance. Following the organosolv fractionation, structural characterization was performed (content of cellulose, hemicellulose, lignin) in the isolated product fractions. Additionally, in-depth characterization of the isolated lignins was performed by combining Pyrolysis-Gas Chromatography Mass Spectroscopy (Pyr-GC/MS), Gel Permeation Chromatography (GPC), and different modes of Nuclear Magnetic Resonance (NMR; 13C, 1H-13C, 31P). Complementary analytics, such as content of monomeric/oligomeric sugars, dehydration products, total phenolics, and Size-Exclusion Chromatography (SEC) of the isolated product liquor, were performed to provide a comprehensive understanding of the process. Special attention was given the lignin structural changes occurring throughout the organosolv process. This was done as the use of lignin for higher-value application is considered crucial for the economic viability and development of a modern biorefinery. For this reason, significant focus was given to study how the lignin characteristics translate into physical properties such as solubility. The latter property was measured through solubility trials in binary aqueous acetone solutions, as well as solvent-based fractionation (acetone-water system). A coherent picture was aimed for, where structural motifs and lignin characteristics were correlated to reductions/enhancements in solubility at various water contents. To finally bridge this with a potential down-stream application, DPPH radical scavenging was performed in DMSO with and without intercalating Lithium Bromide (LiBr) for a selection of organosolv lignins, as well as their acetone/water fractionated lignins. This was complemented with a UV absorption study of the lignin solutions.The results provide a descriptive span of chemical characteristics related to organosolv lignins, where they range between highly native, to non-native. Whereas the former lignins are largely comprised of inter-unit motifs such as β-O-4’, β-β’ and β-5’, the non-native lignins are instead better characterized by a high content of oxidized sidechains, biaryls and bifurans, as well as showing strong indications of having quaternary cross-linkers originating from ketone functionalities. The ketones are also found to undergo aldol condensation with aldehydes formed throughout the process. Interestingly, these two extremes in lignin characteristics yield highly varying physical properties, where the predominantly native and non-native lignins for example display low and high solubility in pure acetone, respectively. Simultaneously, the latter is more prone towards water-induced precipitation, whereas the former instead require water to display complete (~100%) solubility at specific concentrations. These properties and findings are eventually consistent with recent literature where lignin aggregates also dominate their dissolved state, and the interunit motifs dictate the affinity on forming such aggregates which are important for both their dissolution, precipitation, but also their display of functionality such as antioxidant activity.                    

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2024
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Chemical Process Engineering
Research subject
Biochemical Process Engineering
Identifiers
urn:nbn:se:ltu:diva-105316 (URN)978-91-8048-564-7 (ISBN)978-91-8048-565-4 (ISBN)
Public defence
2024-09-20, C305, Luleå University of Technology, Luleå, 12:00 (English)
Opponent
Supervisors
Available from: 2024-05-02 Created: 2024-05-02 Last updated: 2024-06-10Bibliographically approved

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Paulsen Thoresen, PetterLange, HeikoRova, UlrikaChristakopoulos, PaulMatsakas, Leonidas

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