The search for sustainable material solutions has put lignin as one of the prime candidates for aromatic building blocks in macromolecular materials. The present study aimed to demonstrate how lignin-based thermoset resins can be utilized in combination with different cross-linkers. Kraft lignin was used to produce thermosets with tunable mechanical and morphological properties. The lignin-based thermosets were obtained via a thermally induced thiol–ene reaction. The first part of this work was focused on Kraft lignin solvent fractionation and chemical modification of the ethanol soluble fraction. Chemical analysis indicated that the allylation process was selective toward phenolic hydroxyl groups. SAXS and SEM studies demonstrated that solvent fractionation and allylation processes affected the molecular and nanoscale morphological characteristics of lignin. The second part’s focus was on how the properties of thermosets can be tuned by using three different cross-linkers. The dynamic mechanical and morphological properties of three different thermosets were investigated via DMA, SAXS, and WAXS techniques. The three different thermosets exhibit similar molecular morphology but different storage modulus and glass transition temperature. In this work, it was shown that despite lignin’s heterogeneity it was possible to produce thermosetting materials with tunable properties.

The need for renewable alternatives for fossil-based aromatic material constituents is evident for a more sustainable society. Lignin is the largest source of naturally occurring aromatic compounds but has mainly been considered as waste material or energy source in the pulp and paper industry. Developments in extracting lignin from these processes provide a large source for renewable aromatic structures to be used in various applications. Producing thermosets out of lignin is a very promising route to utilize this raw material toward, for example, composite application. The buildup of the molecular network based on oligomeric lignin segments will be different from traditional thermoset analogues, where the constituents often are smaller molecules, and will have an effect on the material properties. In this work LignoBoost Kraft lignin is refined, chemically modified, and used to produce freestanding thermosets with different architectures and properties. These different thermosets are evaluated, and the possibilities to tailor the material properties through work-up and modification are demonstrated. Morphological studies on the formed thermosets using X-ray scattering show systematic differences in molecular stacking and aggregate sizes.

The need to find sustainable paths for our society is imminent to tackle environmental concerns of today. The majority of all plastic materials are produced from crude oil but in the future a much larger portion must originate from renewable resources to address some of these problems. Aromatic molecules are often used when producing rigid and thermally stable polymeric materials but there are few natural sources for them. One is, however, the wood component lignin that is produced on a large scale from chemical pulping processes of biomass. Lignins aromatic structures could be an alternative for non-renewable aromatics in e.g. thermoset applications.

The heterogeneity of lignin does however present some problems in terms of e.g. dispersity, solubility, diverse functionality, and varying polymer backbone structure. To tackle these challenges, work-up of lignin and thorough characterization are important to be able to produce materials with predetermined, predictable, properties. Technical lignins have functional groups that can be utilized as chemical handles for further modifications required for different material systems e.g. phenols, aliphatic hydroxyls, and carboxylic acids.

This thesis focuses on how to utilize solvent fractionated, relatively well-characterized, LignoBoost Kraft lignin to produce thermoset resins by chemical modification and a crosslinking procedure. An efficient procedure to selectively allylate the phenolics, the most abundant functionality, of the lignin fractions has been developed and evaluated as well as a curing procedure using a thiol crosslinker and a thiol-ene reaction. The produced materials were analysed with regards to material properties, density, and morphology. The resins based on the selectively allylated lignin fractions were furthermore evaluated as a potential matrix for carbon fibre composites. It was shown that the material samples could be processed by pre-impregnating carbon fibres and form composite materials. The molecules of the lignin fraction were also used as core substrates in a ring-opening polymerization to produce functional star co-polymers. The procedure was evaluated and it could be shown that the lignin backbone was subjected to substantial structural changes of lignin inter-unit linkages.

Lignin being one of the few large resources of naturally occurring aromatics has a big potential to be used for material applications where rigidity and thermal stability is important. This thesis attempts to add a few pieces towards such a goal.

Behovet av att hitta hållbara tillvägagångssätt för vårt samhälle ökar hela tiden för att bemöta dagens miljöutmaningar. Större delen av alla plastmaterial tillverkas idag av råolja men i framtiden måste en mycket större del produceras från förnyelsebara råvaror för att hantera några av dessa problem. Aromatiska molekyler används ofta vid tillverkning av styva och termiskt stabila material, dock finns det få naturliga källor för sådana. En är emellertid träkomponenten lignin som produceras i stor skala i kemisk massatillverkning. Lignins aromatiska strukturer kan vara ett alternativ för icke-förnyelsebara aromatiska molekylära byggstenar i t.ex. härdplastsapplikationer.

Lignins heterogenitet ger upphov till vissa problem i termer av t.ex. dispersitet, löslighet, olika funktionalitet och varierande polymerskelettstruktur. För att hantera dessa problem är upparbetning av lignin och noggrann karaktärisering viktigt för att material med förutbestämda och förutsägbara egenskaper ska kunna tillverkas. Tekniskt lignin har funktionella grupper som kan användas som kemiska handtag för modifieringar som krävs för användning i olika materialsystem.

Denna avhandling fokuserar på hur lösningsmedelsfraktionerad, relativt välkarakteriserad, LignoBoost Kraftlignin kan användas för att producera termiskt härdande hartser genom kemisk modifiering och tvärbindning. Ett effektivt sätt att selektivt allylera ligninfraktionernas fenol-grupper, den vanligaste av de funktionella grupperna, har utvecklats och utvärderats såväl som en härdningsprocedur med hjälp av en tiol-tvärbindare och tiol-en-kemi. De producerade materialen analyserades med avseende på materialegenskaper, densitet och morfologi. Harts baserad på en av de selektivt allylerade ligninfraktionen undersöktes även som en potentiell matris för kolfiberkompositer. Det kunde påvisas att genom för-impregnering av kolfibrer kunde kompositmaterial tillverkas. Molekylerna i de olika ligninfraktionerna användes även som kärnor för att producera funktionella sampolymerer genom ringöppningspolymerisation. Det kunde påvisas att ligninets molekylära uppbyggnad blev kraftigt påverkat av tekniken då intramolekylära bindningar bröts upp.  

Lignin som tillhör en av de mycket få stora naturligt förekommande råvarorna för aromatiska strukturer har stor potential för användning i materialapplikationer där hög styvhet och termisk stabilitet är viktiga egenskaper. Den här avhandlingen försöker bidra med några pusselbitar mot ett sådant mål. 

Transforming biomass derived components to materials with controlled and predictable properties is a major challenge. Current work describes the controlled synthesis of starcopolymers with functional and degradable arms from the Lignoboost (R) process. Macromolecular control is achieved by combining lignin fractionation and characterization with ring-opening copolymerization (ROCP). The cyclic monomers used are epsilon-caprolactone (epsilon CL) and a functional carbonate monomer, 2-allyloxymethyl-2-ethyltrimethylene carbonate (AOMEC). The synthesis is performed at ambient temperature, under bulk conditions, in an open flask, and the graft composition and allyl functionality distribution are controlled by the copolymerization kinetics. Emphasis is placed on understanding the initiation efficiency, structural changes to the lignin backbone and the final macromolecular architecture. The present approach provides a green, scalable and cost effective protocol to create well-defined functional macromolecules from technical lignins.

This study reports the development of nanocomposites based on poly(?-caprolactone) (PCL) and cellulose nanofibrils (CNF) modified with cationic latex nanoparticles. The physical adsorption of these water-based latexes on the surface of CNF was studied as an environment-friendly strategy to enhance the compatibility of CNF with a hydrophobic polymeric matrix. The latexes are composed of amphiphilic block copolymers based on cationic poly(N,N-dimethylaminoethyl methacrylate-co-methacrylic acid) as the hydrophilic block, and either poly(methyl methacrylate) or poly(n-butyl methacrylate) as the hydrophobic block. The simple and practical melt-mixing of PCL- and latex-modified CNF yielded white homogeneous nanocomposites with complete embedment of the nanofibrils in the thermoplastic matrix. All nanocomposites are semicrystalline materials with good mechanical properties (Young's modulus?=?43.6?52.3 MPa) and thermal stability up to 335?340°C. Degradation tests clearly showed that the nanocomposites slowly degrade in the presence of lipase-type enzyme. These PCL/CNF-latex nanocomposite materials show great promise as future environmentally friendly packaging materials. POLYM. COMPOS., 2018. ? 2018 Society of Plastics Engineers

Aromatic material constituents derived from renewable resources are attractive for new biobased polymer systems. Lignin, derived from lignocellulosic biomass, is the most abundant natural source of such structures. Technical lignins are, however, heterogeneous in both structure and polydispersity and require a refining to obtain a more reproducible material. In this paper the ethanol-soluble fraction of Lignoboost Kraft lignin is selectively allylated using allyl chloride by means of a mild and industrially scalable procedure. Analysis using 1H-, 31P-, and 2D HSQC NMR give a detailed structural description of lignin, providing evidence of its functionalization and that the suggested procedure is selective toward phenols with a conversion of at least 95%. The selectively modified lignin is subsequently cross-linked using thermally induced thiol-ene chemistry. FT-IR is utilized to confirm the cross-linking reaction, and DSC measurements determined the Tg of the thermosets to be 45-65 °C depending on reactive group stoichiometry. The potential of lignin as a constituent in a thermoset application is demonstrated and discussed.

The lack of aromatic material constituents derived from renewable resources poses a problem to meet the future demands of a more sustainable society. Lignin is the most abundant source of aromatic structures found in nature and is a highly interesting source for material applications. Development of controlled chemical modification routes of lignin structures are crucial in order to further develop this area. In this study allyl chloride is used to selectively modify a lignin phenol in the presence of other lignin functionalities, i.e. aliphatic hydroxyls and conjugated alkenes, under mild reaction conditions in quantitative yields. For this, coniferyl alcohol was used as a model compound in the present study. The modification was carried out in ethanol as the synthesis media. Studies on the effect of reaction time and temperature revealed optimum conditions allowing for a quantitative yield without any detectable levels of byproducts as studied with NMR, FT-IR and FT-Raman. The thermal stability of the formed product was determined to be up to at least 160 degrees C through DSC measurements. In addition, as a proof of concept, the use of the allylated monomer to form crosslinked films using free radical thiol-ene polymerization was demonstrated.