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Effect of Molecular Organization on the Properties of Fractionated Lignin-Based Thiol-Ene Thermoset Materials
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology.ORCID iD: 0000-0002-8127-9183
Deutsches-Elektronen Synchrotron (DESY),.ORCID iD: 0000-0002-5772-8065
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology.ORCID iD: 0000-0002-6940-6012
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.ORCID iD: 0000-0002-8614-6291
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

In this study, the combination of sequential solvent fractionation of technical Kraft lignin were followed by allylation of most OH functionalities to give highly functional thermoset resins. All lignin fractions were highly functionalized on the phenolic (≥95%) and carboxylic acid OH (≥85%), and to a significant extent on the aliphatic OH moieties (between 43 and 75%). The resins were subsequently cross-linked using thiol-ene chemistry. The high amount of allyl functionalities resulted in a high cross-link density. DMA measurements showed that thioether content dominates the performance of these thermosets with a glass transition temperature (Tg) between 73 and 99 °C and with a storage modulus between 1.9 and 3.8 GPa for all thermosets. The lignin fractions and lignin-based thermosets morphology, at nanoscale, was studied by wide angle X-ray scattering measurements (WAXS). Two π-π stacking interactions were observed: sandwich (≈4.1–4.7 Å) and T-shaped (≈5.5–7.2 Å). The introduction of allyl functionalities weakens the T-shaped π-π stacking interactions. A new signal corresponding to a distance of ≈3.5 Å was observed in lignin-based thermosets, which was attributed to a thioether organized structure. At the same time, a lignin superstructure, was observed with a distance/size corresponding to 7.9-17.5 Å in all samples.

Keywords [en]
Softwood lignin, solvent fractionation, allylation, thiol-ene thermosets, thioether linkage, wide-angle X-ray scattering, π-π stacking interaction, superstructures
National Category
Organic Chemistry Polymer Chemistry Polymer Technologies Paper, Pulp and Fiber Technology
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-327224OAI: oai:DiVA.org:kth-327224DiVA, id: diva2:1758409
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20230524

Available from: 2023-05-22 Created: 2023-05-22 Last updated: 2023-05-24Bibliographically approved
In thesis
1. Lignin-Based Thermosets with Tunable Mechanical and Morphological Properties: A Study of Structure-Property Relationships
Open this publication in new window or tab >>Lignin-Based Thermosets with Tunable Mechanical and Morphological Properties: A Study of Structure-Property Relationships
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nowadays, there is an urgent need to decrease our dependence on fossilresources and shift towards the use of renewable resources for advancingsustainable development. Utilizing renewable and bio-based raw materials,such as lignocellulosic biomass, for designing new materials is a promisingapproach to promote this objective. The main components of lignocellulosicbiomass are cellulose, hemicellulose, and lignin. Lignin is the most abundantaromatic biopolymer in nature and it is produced on a large scale fromchemical pulping processes as technical lignin. Lignin has the potential as asustainable and renewable alternative to fossil-based aromatics in variousapplications, e.g. thermosetting resins.

Technical lignin has a complex and heterogeneous structure, with arelatively low chemical reactivity. It is characterized by a high dispersity, thepresence of various functional groups that are unevenly distributed along thelignin chains, and various interunit linkages between the monoaromatics. Toovercome the challenges associated with lignin heterogeneity, technicallignin can be fractionated and/or chemically modified.

In this work, LignoBoost Kraft lignin was used as a starting material toproduce lignin-based thiol-ene thermosets. Firstly, lignin was fractionatedusing two approaches: 1) sequential solvent fractionation, and 2) microwaveassistedextraction. These fractionation approaches enabled access to ligninfractions with unique and tunable properties. Subsequently, lignin waschemically modified, in particular through allylation. Two allylation reagentswere used: allyl chloride and diallyl carbonate. The use of allyl chlorideenables a selective allylation of the phenolic OH groups, leaving the aliphaticand carboxylic acid OH groups unmodified. On the other hand, diallylcarbonate can react with all the aforementioned OH groups, leading to ahigher degree of allylation. Subsequently, allylated lignin was thermallycross-linked with various polyfunctional thiols, leading to thiol-enethermosets. The structure-property relationships of the thermosets wereinvestigated by varying several parameters, including the lignin source,fractionation approach, chemical modification, and thiol cross-linker. Byadjusting these parameters, various thermosets with tunable mechanical andmorphological properties were produced. Understanding the structurepropertyrelationships of these bio-based materials is crucial for identifyingpotential applications.

Abstract [sv]

Nuförtiden finns det ett akut behov av att minska vårt beroende av fossilaresurser och övergå till användningen av förnybara resurser och därmedavancera den hållbara utvecklingen. Att använda förnybara och biobaseraderåvaror, såsom lignocellulosabiomassa, för att designa nya material är ettlovande tillvägagångssätt för att uppnå detta mål. Huvudkomponenterna ilignocellulosabiomassa är cellulosa, hemicellulosa och lignin. Lignin ärnaturens vanligaste aromatiska biopolymer och den produceras i stor skalafrån kemiska massaprocesser som tekniskt lignin. Lignin kan fungera som etthållbart och förnybart alternativ till fossilbaserade aromater i olikatillämpningar, t.ex. g. värmehärdande hartser.

Tekniskt lignin har en komplex och heterogen struktur, med en relativt lågkemisk reaktivitet. Det kännetecknas av en hög dispersitet, närvaron av olikafunktionella grupper som är ojämnt fördelade längs ligninkedjorna, och olikatyper av enhetsbindningar mellan monoaromaterna. För att övervinna deutmaningar som är förknippade med ligninets heterogenitet kan ligninfraktioneras och/eller kemiskt modifieras.

I detta arbete användes LignoBoost Kraft-lignin som utgångsmaterial föratt tillverka ligninbaserade tiol-en-härdplaster. Först har lignin fraktioneratsmed hjälp av två olika metoder: 1) sekventiell lösningsmedelsfraktionering,och 2) mikrovågsassisterad extraktion. Dessa fraktioneringsmetoder gjordedet möjligt att erhålla ligninfraktioner med unika och skräddarsyddaegenskaper. Därefter modifierades ligninet kemiskt genom allylering. Tvåallyleringsreagens användes: allylklorid och diallylkarbonat. Användningenav allylklorid möjliggör selektiv allylering av de fenoliska OH-grupperna,samtidigt som de alifatiska och karboxylsyra-OH-grupperna lämnasomodifierade. Diallylkarbonat kan å andra sidan reagera med alla de tidigarenämnda OH-grupperna, vilket leder till en högre grad av allylering. Däreftertvärbands härdades allylerat lignin termiskt med olika polyfunktionellatioler, för att ge härdplast med tiol-en-tvärbindingar. Strukturegenskapsförhållandenaför härdplasterna undersöktes genom att varieraflera parametrar, inklusive ligninkällan, fraktioneringsmetod, kemiskmodifiering och tioltvärbindare. Genom att justera dessa parametrarproducerades olika härdplaster med skräddarsydda mekaniska ochmorfologiska egenskaper. Att förstå relationerna mellan struktur ochegenskaper av dessa biobaserade material är avgörande för att identifierapotentiella tillämpningar.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2023. p. 66
Series
TRITA-CBH-FOU ; 2023:19
Keywords
Softwood, hardwood, technical lignin, solvent fractionation, allylation, thiol-ene thermosets, thioether linkage, wide-angle X-ray scattering, π-π stacking interactions, Barrträ, lövträ, tekniskt lignin, lösningsmedelsfraktionering, allylering, tiol-en-härdplaster, tioeterbindning, vidvinkelröntgenspridning, π-π staplingsinteraktioner
National Category
Organic Chemistry Polymer Chemistry Polymer Technologies Materials Chemistry
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-327306 (URN)978-91-8040-567-6 (ISBN)
Public defence
2023-06-15, F3, Lindstedtsvägen 26 & 28, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation
Note

QC 2023-05-23

Available from: 2023-05-23 Created: 2023-05-23 Last updated: 2023-05-25Bibliographically approved

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Ribca, IulianaRoth, Stephan V.Lawoko, MartinJohansson, Mats

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