It is in the nature of the human species to find solutions of complex technical problems and always strive for improvements. The development of new materials is not an exception. One of the many man-made materials is carbon fibre (CF). Its excellent mechanical properties and low density have made it attractive as the reinforcing agent in lightweight composites. However, the high price of CF originating from expensive production is currently limiting CF from wider utilisation, e.g. in the automotive sector.   The dominating raw material used in CF production is petroleum-based polyacrylonitrile (PAN). The usage of fossil-based precursors and the high price of CF explain the strong driving force of finding cheaper and renewable alternatives. Lignin and cellulose are renewable macromolecules available in high quantities. The high carbon content of lignin is an excellent property, while its structural heterogeneity yields in CF with poor mechanical properties. In contrast, cellulose has a beneficial molecular orientation, while its low carbon content gives a low processing yield and thus elevates processing costs.   This work shows that several challenges associated with CF processing of each macromolecule can be mastered by co-processing. Dry-jet wet spun precursor fibres (PFs) made of blends of softwood kraft lignin and kraft pulps were converted into CF. The corresponding CFs demonstrated significant improvement in processing yield with negligible loss in mechanical properties relative to cellulose-derived CFs. Unfractionated softwood kraft lignin and paper grade kraft pulp performed as good as more expensive retentate lignins and dissolving grade kraft pulp, which is beneficial from an economic point of view.   The stabilisation stage is considered the most time-consuming step in CF manufacturing. Here it was shown that the PFs could be oxidatively stabilised in less than 2 h or instantly carbonised without any fibre fusion, suggesting a time-efficient processing route. It was demonstrated that PF impregnation with ammonium dihydrogen phosphate significantly improves the yield but at the expense of mechanical properties.   A reduction in fibre diameter was beneficial for the mechanical properties of the CFs made from unfractionated softwood kraft lignin and paper grade kraft pulp. Short oxidative stabilisation (&lt;2 h) of thin PFs ultimately provided CFs with tensile modulus and strength of 76 GPa and 1070 MPa, respectively. Considering the high yield (39 wt%), short stabilisation time and promising mechanical properties, the concept of preparing CF from lignin:cellulose blends is a very promising route. / Det ligger i människans natur att hitta lösningar på komplexa tekniska problem, samt att alltid sträva efter förbättringar. Utvecklingen av nya material är inget undantag. Ett av flera material utvecklade av människan är kolfiber. Dess utmärkta mekaniska egenskaper samt låga densitet har gjort det attraktivt som förstärkningsmaterial i lättviktskompositer. Det höga priset på kolfiber, vilket härstammar ur en kostsam framställningsprocess, har förhindrat en mer utbredd användning i exempelvis bilindustrin.   Det dominerande råmaterialet för kolfiberframställning är petroleumbaserad polyacrylonitril (PAN). Användandet av fossila råvaror och det höga priset på kolfiber förklarar den starka drivkraften att hitta billigare och förnyelsebara alternativ. Lignin och cellulosa är förnyelsebara makromolekyler som finns tillgängliga i stora kvantiteter. Det höga kolinnehållet i lignin gör det mycket attraktivt som råvara för kolfiberframställning, men dess heterogena struktur ger en kolfiber med otillräckliga mekaniska egenskaper. Däremot har cellulosa en molekylär orientering som är önskvärd vid framställning av kolfiber, men dess låga kolinehåll ger ett lågt processutbyte som i sin tur bidrar till höga produktionskostnader.             Det här arbetet visar att många av de problem som uppstår med kolfiber från respektive råvara kan kringgås genom att utgå från blandningar av desamma. Prekursorfibrer från blandningar av kraftlignin och kraftmassa från barrved tillverkade med luftgapsspinning konverterades till kolfiber. Utbytet för kolfibrerna som framställdes var mycket högre än vid framställning från endast cellulosa. Ofraktionerat barrvedslignin och kraftmassa av papperskvalitet presterade lika bra som de dyrare retentatligninen och dissolvingmassan, vilket är fördelaktigt ur ett ekonomiskt perspektiv.   Stabilisering är det mest tidskrävande processteget i kolfibertillverkning. I det här arbetet visades det att prekursorfibrerna kunde stabiliseras på kortare än två timmar, eller direktkarboniseras utan någon sammansmältning av fibrerna. Detta indikerar att en tidseffektiv produktion kan vara möjligt. Impregnering av prekursorfibrerna med ammoniumdivätefosfat ökade utbytet avsevärt, men med lägre mekaniska egenskaper som bieffekt.           Kolfibrernas mekaniska egenskaper ökade vid en diameterreduktion. En kort oxidativ stabilisering under två timmar i kombination med tunna prekursorfibrer gav kolfiber med en elasticitetsmodul på 76 GPa och dragstyrka på 1070 MPa. Att göra kolfiber från blandningar av lignin och cellulosa är ett lovande koncept om det höga utbytet (39%), den korta stabiliseringstiden samt de lovande mekaniska egenskaperna tas i beaktande. / <p>QC 20190226</p>

This thesis examines the manufacturing process of a novel flax fibre polypropylene composite material, focusing on understanding the process and its influencing factors. The composite was manufactured using pre-impregnated twill-woven flax fibre sheets (AmpliTex 5040 – PP) as outer layers and two core layers of pre-impregnated polypropylene sheets reinforced with short, randomly oriented natural fibres (NfPP). The manufacturing process involved preheating the material to core temperatures of 180°C, 190°C, or 200°C, followed by compression moulding with tool gaps of 3.0 mm, 3.2 mm, and 3.4 mm. The study found that the core temperature after preheating did not significantly affect the composite's thickness or layer compaction. However, the tool gap exhibited a significant effect, with an increase in thickness with larger tool gaps. The lowest deviation from the tool gap size was observed at 3.2 mm. The compaction of the AmpliTex 5040 – PP layers demonstrated no dependency on the tool gap, while the NfPP layers exhibited the highest compaction at a gap size of 3.0 mm. Thermal degradation analysis indicated that flax fibre is the most critical component, with higher core temperatures reducing the ultimate tensile strength and fracture strain of the composite material. The maximum tensile properties were observed for materials preheated to 180°C during manufacturing. The manufacturing process demonstrated an improvement in reproducibility compared to previous methods, although substantial variance in thickness remained.

Cemented carbide tools are subjected to high loads and temperatures during use. Long before any significant wear can occur on the tool, the material will experience plastic deformation. The purpose of this master thesis was to investigate how Kernel Average Misorientation (KAM) can be utilised to analyse plastic deformation within the microstructure or grains of cemented carbides. Six different cemented carbides were investigated. The materials were plastically deformed by utilizing cutting tests with a feed rate staircase method to induce the plastic deformation. Each material was characterised by using Scanning Electron Microscopy (SEM) either equipped with a secondary electron detector or an Electron Backscatter Diffraction detector (EBSD). This made it possible to investigate the WC grain size, Co infiltration, step formation, cavities and pores, KAM and the average grain size. It was concluded that KAM showed to be a valuable tool to visualise the plastic deformation in the materials. There were some limitations to KAM regarding materials with similar amounts of plastic deformation. Additionally, the data from KAM could be used to create graphs to more easily display the misorientation. However, KAM cannot showcase the mechanisms that lead to plastic deformation. Other characterisation methods are needed as a compliment to completely understand what is happening in the material on a microstructural level.

Nanocomposites of polyethylene and metal oxide nanoparticles have shown to be a feasible approachto the next generation of insulation in high voltage direct current cables. In order to reach an operationvoltage of 1 MV new insulation materials with reduced conductivity and increased breakdown strengthas compared to modern low-density polyethylene (LDPE) is needed.In this work polyethylene MgO nanocomposites for electrical insulation has been produced andcharacterized both from an electrical and material perspective. The MgO nanoparticles weresynthesized into polycrystalline nanoparticles with a large specific surface area (167 m2 g–1). Meltprocessing by extrusion resulted in evenly dispersed MgO nanoparticles in LDPE for the silane surfacemodified MgO as compared to the unmodified MgO. All systems showed a reduction in conductivityby up to two orders of magnitude at low loading levels (1–3 wt.%), but where the surface modifiedsystems were able to retain reduced conductivity even at loading levels of 9 wt.%. A maximuminteraction radius to influence the conductivity of the MgO nanoparticles was theoretically determinedto ca. 800 nm. The interaction radius was in turn experimentally observed around Al2O3 nanoparticlesembedded in LDPE using Intermodulation electrostatic force microscopy. By applying a voltage on theAFM-tip charge injection and extraction around the Al2O3 nanoparticles was observed, visualizing theexistence of additional localized energy states on, and around, the nanoparticles. Ptychography wasused to reveal nanometre features in 3D of electrical trees formed under DC-conditions. Thevisualization showed that the electrical tree grows by pre-step voids in front of the propagatingchannels, facilitating further growth, much in analogy to mechanical crack propagation (Griffithconcept). An electromechanical effect was attributed as possible mechanism for the formation of the voids. / Nanokompositer av polyeten och metalloxidpartiklar anses vara möjliga material att använda i morgondagens isolationshölje till högspänningskablar för likström. För att nå en transmissionsspänning på 1 MV behövs isolationsmaterial som i jämförelse med dagens polyeten har lägre elektrisk ledningsförmåga, högre styrka mot elektriskt genomslag och som kan kontrollera ansamling av rymdladdningar. De senaste årens forskning har visat att kompositer av polyeten med nanopartiklar av metalloxider har potential att nå dessa egenskaper. I det här arbetet har kompositer av polyeten och nanopartiklar av MgO för elektrisk isolation producerats och karaktäriserats. Nanopartiklar av MgO har framställts från en vattenbaserad utfällning med efterföljande calcinering, vilket resulterade i polykristallina partiklar med en mycket stor specifik ytarea (167m2 g-1). MgO-nanopartiklarna ytmodifierades i n-heptan genom att kovalent binda oktyl(trietoxi)silan och oktadekyl(trimetoxi)silan till partiklarna för att skapa en hydrofob och skyddande yta. Extrudering av de ytmodifierade MgO nanopartiklarna tillsammans med polyeten resulterade i en utmärkt dispergering med jämnt fördelad partiklar i hela kompositen, vilket ska jämföras med de omodifierade partiklarna som till stor utsträckning bildade agglomerat i polymeren. Alla kompositer med låg fyllnadsgrad (1–3 vikt% MgO) visade upp till 100 gånger lägre elektrisk konduktivitet jämfört med värdet för ofylld polyeten. Vid högre koncentrationer av omodifierade MgO förbättrades inte de isolerande egenskaperna på grund av för stor andel agglomerat, medan kompositerna med de ytmodifierade fyllmedlen som var väl dispergerade behöll en kraftig reducerad elektrisk konduktivitet upp till 9 vikt% fyllnadshalt. Den minsta interaktionsradien för MgO-nanopartiklarna för att minska den elektriska konduktiviten i kompositerna fastställdes med bildanalys och simuleringar till ca 800 nm. Den teoretiskt beräknade interaktionsradien kompletterades med observation av en experimentell interaktionsradie genom att mäta laddningsfördelningen över en Al2O3-nanopartikle i en polyetenfilm med intermodulation (frekvens-mixning) elektrostatisk kraftmikroskop (ImEFM), vilket är en ny AFM-metod för att mäta ytpotentialer. Genom att lägga på en spänning på AFM-kantilevern kunde det visualiseras hur laddningar, både injicerades och extraherades, från nanopartiklarna men inte från polyeten. Det tolkades som att extra energinivåer skapades på och runt nanopartiklarna som fungerar för att fånga in laddningar, ekvivalent med den gängse tolkningen att nanopartiklar introducera extra elektronfällor i den polymera matrisen i nanokompositer. Nanotomografi användes för att avbilda elektriska träd i tre dimensioner. Avbildningen av det elektriska trädet visade att tillväxten av trädet hade skett genom bildning av håligheter framför den framväxande trädstrukturen. Håligheterna leder till försvagning av materialet framför det propagerande trädet och förenklar på det sättet fortsatt tillväxt. Bildningen av håligheter framför trädstrukturen uppvisar en analogi till propagering av sprickor vid mekanisk belastning, i enlighet med Griffiths koncept. / <p>QC 20161006</p>

The relatively new and still growing field of 3D-printing has opened up the possibilities to manufacture patient-specific medical devices with high geometrical accuracy in a precise and quick manner. Additionally, biocompatible materials are a demand for all medical applications while biodegradability is of importance when developing scaffolds for tissue growth for instance. With respect to this, this project consisted of developing biocompatible and bioresorbable polymer blend and composite filaments, for fused deposition modeling (FDM) printing. Poly(lactic acid) (PLA) and polycaprolactone (PCL) were used as supporting polymer matrix while hydroxyapatite (HA), a calcium phosphate with similar chemical composition to the mineral phase of human bone, was added to the composites to enhance the biological activity. PLA and PCL content was varied between 90–70 wt% and 10-30 wt%, respectively, while the HA content was 15 wt% in all composites. All materials were characterized in terms of mechanical properties, thermal stability, chemical composition and morphology. An accelerated degradation study of the materials was also executed in order to investigate the degradation behavior as well as the impact of the degradation on the above mentioned properties. The results showed that all processed materials exhibited higher mechanical properties compared to the human trabecular bone, even after degradation with a mass loss of around 30% for the polymer blends and 60% for the composites. It was also apparent that the mineral accelerated the polymer degradation significantly, which can be advantageous for injuries with faster healing time, requiring only support for a shorter time period.

Food packaging should ensure the safety and quality of food, minimize spoilage and provide an easy way of storing and handling it. Barrier coatings are generally used to meet the demands placed on fibre-based food packages, as these have the ability to regulate the amount of gases that can enter them. Some gases are detrimental to food quality: oxygen, for example, initiates lipid oxidation in fatty foods. Using both experimental data and computer modelling, this thesis explains some aspects of how the structure of barrier coatings influences the mass transport of oxygen with the aim of obtaining essential knowledge that can be used to optimize the performance of barriers. Barrier coatings are produced from polyvinyl alcohol and kaolin blends that are coated onto a polymeric support. The chemical and physical structures of these barriers were characterized according to their influence on permeability in various climates. At a low concentration of kaolin, the crystallinity of polyvinyl alcohol decreased; in the thinner films, the kaolin particles were orientated in the basal plane of the barrier coating. The experimental results indicated a complex interplay between the polymer and the filler with respect to permeability. A computer model for permeability incorporating theories for the filled polymeric layer to include the polymer crystallinity, addition of filler, filler aspect ratio and surrounding moisture was developed. The model shows that mass transport was affected by the aspect ratio of the clay in combination with the clay concentration, as well as the polymer crystallinity. The combined model agreed with the experiments, showing that it is possible to combine different theories into one model that can be used to predict the mass transport. Four barrier coatings: polyethylene, ethylene vinyl alcohol + kaolin, latex + kaolin and starch were evaluated using the parameters of greenhouse gas emissions and product costs. After the production of the barrier material, the coating process and the end-of-life handling scenarios were analysed, it emerged that starch had the lowest environmental impact and latex + kaolin had the highest. / Food packaging is required to secure the safety and quality of food, as well as minimize spoilage and simplify handling. Barrier coatings are generally used to meet the demands placed on fibre-based food packages, as these have the ability to regulate the amount of gases that can enter them. Some gases are detrimental to food quality: oxygen, for example, initiates lipid oxidation in fatty foods. This thesis focuses on the mass transport of oxygen in order to gain deeper knowledge of, and thereby optimise, the performance of barrier coatings. This experimental study, together with computer modelling, characterized the structure of barrier materials with respect to the mass transport process. The performance of the barriers was evaluated based on the parameters of environmental impact and product costs. As the long-term aim is to use non-petroleum-based barrier coatings for packaging, these should be evaluated by assessing the properties of the material in question, its functionality and its environmental impact to provide more insight into which materials are desirable as well as to develop technology. The results from this study indicate that several parameters (the orientation, concentration and aspect ratio of the clay and the polymer crystallinity) influence the properties of a barrier. Using this knowledge, researchers and food packaging engineers can work toward improving and customising renewable barriers. / VIPP

Magnesium with two-thirds of the density compared to aluminium and one-quarter of steel, intrigues product developers and material scientists due to the light metal’s excellent combination of strength to weight ratio as well as their capability of being produced as a High Pressure Die Cast component compared to other ferrous or light metal alloys.   However, a magnesium alloy inherits some concerning drawbacks, limiting the exploitation in structural applications and mechanical design such as automotive, heavy machinery and aerospace components. The need for a magnesium alloy that could withstand a sufficient amount of wear, temperature and corrosive environment, leads towards the investigation and evaluation of a suitable, functional coating as a solution to exploit the evident advantages a magnesium alloy exhibits. A substantial amount of research is required in order to reduce an existing knowledge gap that is the ongoing development in the search for a sufficient functional coating and adherence capability to the highly reactive substrate that is a magnesium alloy.   This industrial master thesis is an early stage investigation to evaluate how the currently used aluminium substrate with an electrodeposited coating relate and compares to a heat-treated electroless deposited coating through tribological and thermophysical induced stresses. These properties are tested with proven industrial standard methods resulted in a comprehensive conclusion and discussion regarding the feasibility of applying the coating onto a commercial magnesium alloy closely related to the Mg-alloy developed by Husqvarna and thereby contributing to technological advances to the highly relevant topic within product development in materials engineering.

Replacement of cobalt in cemented carbides has gained in attention recently because threats of regulations due to health issues (cancerogenic effect), increased demand from the electric vehicle industry and the questionable extraction from countries like Democratic Republic of Congo. In this report the use of Ni-based binder as an alternative binder for cemented carbides has been explored. The design is based on producing a Ni-based superalloy binder which contains dispersed Ni3Al Gamma Prime (γ’) -phase precipitates in the binder matrix. The investigation focuses on the design of cemented carbide compositions and processes that ensures the formation of γ’- precipitates, the control of their morphology and distribution as well as the effect of heat treatment. To do this a Ni-Al master alloy has been designed that enables the formation of γ’-precipitates in WC-Ni-Al-X systems, produced by conventional powder metallurgy process including standard free sintering. Furthermore, the addition of usual elements in the cemented carbide industry (such as Ti, Cr, Ta, Nb) and their effect on the stability of γ’-precipitates has been investigated. A method to reveal the precipitates including ion-polishing and electro-etching has been developed. Basic mechanical properties such as hardness and toughness have been investigated, revealing particular crack propagation in Ni-based binder reinforced with γ’-precipitates. It was found that the common variables in cemented carbide manufacturing influence all aspects regarding the stability of γ’-phase. By varying the powder type, binder composition and content, the carbon balance, the WC grain size and the heating/cooling steps; the formation of γ’-precipitates (size, morphology, distribution, etc.) can be controlled to tailor the properties of the cemented carbide. / Att hitta en ersättning av kobolt i hårdmetall har nyligen uppmärksammats bl.a. eftersom regleringar hotar användning av ämnet pga. dess cancerogenitet, en ökande efterfrågan från elfordonsindustrin samt den moraliskt tvivelaktiga utvinningen som sker i länder som Demokratiska Republiken Kongo. I denna rapport har användningen av ett nickel-baserat bindemedel som ett alternativt bindemedel för hårdmetaller undersökts. Designen är baserad på att producera en nickel-baserad superlegering som bindemedel som innehåller dispergerad Ni3Al Gamma Prim (γ’) – fas utfälld i bindemedlet. Utredningen fokuserar på designen av hårdmetallskompositioner och processer som försäkrar formationen av γ’-utfällningar, kontroller av dess morfologi, distributionen samt hur värmebehandlingar påverkar. För att kunna göra detta har en Ni-Al masterlegering skapats som möjliggör γ’-utfällningar i ett WC-Ni-Al-X system, producerat med konventionell pulvermetallurgiprocess inkluderat standard fri sintring. Dessutom har tillsatsen av vanliga ämnen i hårdmetallindustrin (such as TI, Cr, Ta, Nb) samt deras effekt på stabiliteten hos γ’-utfällningarna undersökts. En metod för att upptäcka utfällningarna, som inkluderar jonpolering och elektroetsning har utvecklats. Grundläggande mekaniska egenskaper som hårdhet och seghet har undersökts, vilket har avslöjat en speciell sprickutbredning i den nickelbaserade bindaren förstärkt med γ’-utfällningar. Det visade sig att de vanliga variablerna förenade med tillverkning av hårdmetall påverkar samtliga aspekter gällande stabiliteten hos γ’-utfällningar. Genom att variera pulvertyp, bindemedelkomposition och innehåll, kolbalansen, WC-kornstorlek och uppvärmning samt kylningssteg så påverkas bildningen av γ’-utfällningar (storlek, morfologi, distribution, etc..) som kan kontrolleras för att skräddarsy egenskaperna för hårdmetallen.

Today there is growing interest within the construction sector to increase the proportion of biobased building materials made from renewable resources. By-products or residuals from wood processing could in this case be valuable resources for manufacturing new types of biocomposites. An important research question related to wood-based biocomposites is how to characterise molecular interactions between the different components in the composite. The hygroscopic character of wood and its water sorption properties are also crucial. Thermal modification (or heat treatment) of wood results in a number of enhanced properties such as reduced hygroscopicity and improved dimensional stability as well as increased resistance to microbiological decay. In this thesis, surface characteristics of thermally modified wood components (often called wood fibres or particles) and influencing effects from moisture sorption have been analysed using a number of material characterisation techniques. The aim is to increase the understanding in how to design efficient material combinations for the use of such wood components in biocomposites. The specific objective was to study surface energy characteristics of thermally modified spruce (Picea abies Karst.) under influences of water vapour sorption. An effort was also made to establish a link between surface energy and surface chemical composition. The surface energy of both thermally modified and unmodified wood components were studied at different surface coverages using inverse gas chromatography (IGC), providing information about the heterogeneity of the surface energy. The water vapour sorption behaviour of the wood components was studied using the dynamic vapour sorption (DVS) method, and their surface chemical composition was studied by means of X-ray photoelectron spectroscopy (XPS). Additionally, the morphology of the wood components was studied with scanning electron microscopy (SEM). The IGC analysis indicated a more heterogeneous surface energy character of the thermally modified wood compared with the unmodified wood. An increase of the dispersive surface energy due to exposure to an increased relative humidity (RH) from 0% to 75% RH at 30 ˚C was also indicated for the modified samples. The DVS analysis indicated an increase in equilibrium moisture content (EMC) in adsorption due to the exposure to 75% RH. Furthermore, the XPS results indicated a decrease of extractable and a relative increase of non-extractable compounds due to the exposure, valid for both the modified and the unmodified wood. The property changes due to the increased RH condition and also due to the thermal modification are suggested to be related to alterations in the amount of accessible hydroxyl groups in the wood surface. Recommendations for future work and implications of the results could be related to knowledge-based tailoring of new compatible and durable material combinations, for example when using thermally modified wood components in new types of biocomposites for outdoor applications. / <p>Forskningsfinansiärer och strategiska forskningsprojekt:</p><p>Nils och Dorthi Troëdssons forskningsfond (Projektnr 793/12 Hydro-termo-mekanisk modifiering av trä).</p><p> KTH Royal Institute of Technology.</p><p> COST Action FP0904.</p><p> KK-Stiftelsen.</p><p>Stiftelsen för strategiskt forskning (SSF). QC 20150908</p>

Increasing demand for structural health monitoring in space highlights the need to make the creation of these systems more accessible. This study investigates the potential of additive manufacturing to achieve this goal by characterizing a self-sensing material made of a commercially available 3D-printed continuous carbon fibre filament. The results demonstrate the feasibility of converting the filament into a strain sensor with improved sensitivity compared to conventional foil strain gauges. Mechanical and electromechanical properties of the self-sensing material were characterized, including an ultimate tensile strength of 45.09 ± 3.45 MPa, a failure strain of 38.93 ± 3.41%, and a base resistance of 759.11Ω. The tensile gauge factor was calculated to be 467.06 ± 375.90 within the strain range of 0% to 3.8% with a linearity (R2) of 0.93. For the first time, a systematic literature review compares mechanical and electromechanical properties to enable material selection for mechanical design incorporating self-sensing material. The study highlights that the spread of material properties in a group of materials indicates how well-developed a material is for self-sensing purposes. This study advances our understanding of the feasibility of using additive manufacturing to create self-sensing materials for structural health monitoring systems and opens up new avenues for further research.