| 1. |
- Jain, Shubham, 1990-
(författare)
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Engineering 3D degradable pliable scaffolds for adipose tissue regeneration : Advancing cell-material interactions by understanding the influence from thermal, chemical, mechanical properties and scaffold design
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In soft tissue defects that arise due to trauma, tumor resections and complex burns, a significant loss in adipose tissue remains a considerable challenge due to the insufficient regenerative capacity of the tissue. This thesis focuses on assessing cell-material interactions between degradable 3D polymer scaffolds with different designs and adipose tissue-derived stem cells. This knowledge can be used to engineer 3D scaffolds with adequate physio-chemical and mechanical properties along with an appropriate design that augments adipose tissue regeneration.Salt-leaching 3D scaffolds were fabricated from various medical-grade polyesters, and cellular behavior was evaluated by correlating the physical, chemical, and mechanical properties of the scaffolds. The results showed that the glass transition temperature modulated the mechanical properties of the scaffolds, affecting stem cell proliferation and adipogenic differentiation. The same sets of polymers were further used in melt extrusion-based 3D printer and printability was established for the fabrication of customized 3D scaffolds. Based on printability and cell-scaffolds interaction results, poly (L-lactide-co-trimethylene carbonate) was used to print 3D scaffolds in different soft and pliable designs that promoted adipogenic differentiation. To fabricate even softer, and more hydrophilic 3D scaffolds, poly (ɛ-caprolactone-co-p-dioxanone) and a unique scaffold design were utilized within the research group. The copolymer 3D scaffolds were further combined with knitted mesh and electrospun nanofibers to develop scaffolds with multilayer architecture, modular scaffolds. The in vitro results asserted that the modular scaffold enhanced cell-material interactions by almost five times of those observed for the scaffold alone. Therefore, it can be concluded that softness and pliability are crucial and an appropriate scaffold design with adequate mechanical support is required for enhancing cell-material interaction. The in vitro results asserted that the modular scaffold enhanced cell-material interactions by almost five times of those observed for the scaffold alone. Therefore, it can be concluded that softness and pliability are crucial and an appropriate scaffold design with adequate mechanical support is required for enhancing cell-material interaction. The in vitro results asserted that the modular scaffold enhanced cell-material interactions by almost five times of those observed for the scaffold alone. Therefore, it can be concluded that softness and pliability are crucial and an appropriate scaffold design with adequate mechanical support is required for enhancing cell-material interaction.
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| 2. |
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| 3. |
- Liu, Dongming, 1987-
(författare)
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Polyethylene – metal oxide particle nanocomposites for future HVDC cable insulation : From interface tailoring to designed performance
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Low-density polyethylene (LDPE) nanocomposites containing metal oxide nanoparticles are considered as promising candidates for insulating materials in future high-voltage direct-current (HVDC) cables. The significant improvement in dielectric properties compared with unfilled polymer is attributed to the large and active interface between the nanoparticles and the polymer. The nanoparticles may also initiate cavitation under stress and potential accelerated aging risks due to the adsorption and inactivation of the protecting antioxidants. This study is focused on the possibilities of achieving well-balanced performances of the polyethylene nanocomposites for HVDC insulation via tailoring the particle interface in the nanocomposites.A facile and versatile surface coating method for metal oxide particles was developed based on silane chemistry. The developed method was successfully applied to 8.5 nm Fe3O4, 25 nm ZnO and 50 nm Al2O3 particles, with the aim to develop uniform coatings that universally could be applied on individual particles rather than aggregates of particles. The surface properties of the coatings were further tailored by applying silanes with terminal alkyl groups of different lengths, including methyl (C1-), octyl (C8-) and octadecyl (C18-) units. Transmission electron microscopy, infrared spectroscopy and thermal gravimetric analysis confirmed the presence of uniform coatings on the particle surface and importantly the coatings were found to be highly porous.The capacity of metal oxide particles to adsorb relevant polar species (e.g. moisture, acetophenone, cumyl alcohol and phenolic antioxidant) was further assessed due to its potential impact on electrical conductivity and long-term stability of the nanocomposites. The oxidative stability of the nanocomposites was affected by the adsorption of phenolic antioxidants on particles and transfer of catalytic impurities (ionic species) from metal oxide particles to polymer matrix. It was found that carefully coated metal oxide particles had much less tendency to adsorb antioxidants. They could, however, adsorb moisture, acetophenone and cumyl alcohol. The coated particles did not emit any destabilizing ionic species into the polymer matrix. The inter-particle distance of the nanocomposites based on C8-coated nanoparticles showed only a small deviation from the ideal, theoretical value, indicating a good particle dispersion in the polymer. Scanning electron microscopy of strained nanocomposite samples suggested the cavitation mainly occurred at the polymer/nanoparticles interface. The microstructural changes at polymer/nanoparticle interface were studied by small-angle X-ray scattering coupled with tensile testing. The polymer/nanoparticle interface was fractal before deformation due to the existence of the bound polymers at the nanoparticle surface. Extensive de-bonding of particles and cavitation were observed when the nanocomposites were stretched beyond a critical strain. It was found that the composites based on carefully coated particles showed higher strain at cavitation than the composites based on uncoated particles. The composites based on C8-coated nanoparticles showed the largest decrease in electrical conductivity and the lowest temperature coefficient of the electrical conductivity among the composite samples studied.
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| 4. |
- Nilsson, Fritjof, 1978-
(författare)
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Meso-scale modelling of composites and semi-crystalline polymers
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis covers the first few steps of a multi-scale computer simulation strategy for predicting physical properties of complex polymers like composites and semi-crystalline polymers. Meso-scale simulations of crystallization and solvent diffusion in polyethylene as well as simulations examining the geometrical impact on the effective permittivity of composites have been performed. These meso-scale models will in the near future be coupled to molecular dynamics models for increased realism and accuracy. The first paper was focused on solvent diffusion in spherulitic semi-crystalline polyethylene. Geometrical models of polyethylene spherulites were constructed and Monte-Carlo random walker simulations were used to estimate the geometrical impedance factor as function of volume crystallinity, mean free path and other geometry properties. Novel numerical off-lattice algorithms made it possible to increase the maximum volume crystallinity from 40 to 55%, to decrease the computation time a factor 100 and to use shorter and more realistic diffusion jump-lengths. The simulation results were in good agreement with experimental results and new analytical formulas were found that could be neatly fitted to both simulation data and experimental data. It was noticed that the geometrical impedance factor was proportional to the polymers mean free path length rather than its length/width aspect ratio and that the traditional Fricke formula for oblate spheroids was not able to correctly predict the diffusion behaviour in complex geometries like spherulites at medium-high volume crystal fractions. The second paper was focused on the electrostatics of composites. Geometrical models of layered composites were first obtained and the finite element method was then used to calculate the effective composite permittivity as function of particle content, particle shape, degree of mixing and other geometrical issues. Analytical lamellae formulas for 2- and 3-phase composites were formulated with clearly better correlation to corresponding finite element data than all other previously known analytical formulas. The analytical 3-phase formula was successfully compared with experimental data for mica/polyimide and it was noted that the influence of water and air was significant.
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| 5. |
- Blomfeldt, Thomas, 1982-
(författare)
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Gluten Protein-Based Microcellular Foams and Composites: Development and Functional Properties
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Most common foams are produced from non-renewable resources (e.g., synthetic plastics),with a number of environmental concerns, hence there is a demand for alternative bio-derivedfoam materials. Wheat gluten protein is widely known to have excellent foaming properties(e.g., in bread making) and is a possible alternative resource for making foam products.Gluten foams were produced using a lyophilization process (freeze-drying) and variousgluten/water-based mixtures were studied. Foams with varying properties were obtained bymixing various amounts of wheat gluten with glycerol (plasticizer) and bacterial cellulosefibers (reinforcement). The gluten foams looked like bread with a beige color and few visuallydetectable surface pores. They were generally characterized as having an open cell structurewith a porosity in the range 75-85% and pore sizes ranging between 20 and 73 μm. Differentmechanical properties were obtained by using varying gluten concentrations and the differentadditives. Plasticizing with glycerol lead to increased flexibility of the foams, with the abilityto recover up to 95% after being compressed by 80%. By reinforcing with bacterial cellulosefibers the material became stiffer, with an increased elastic modulus. Confocal lasermicroscopy revealed that the fibers and gluten interacted. Analyzing the protein structure ofthe foams revealed that the different additives resulted in structures with different proteinpatterns. The samples containing glycerol were more polymerized and less extractable in SDS,whereas the fiber containing samples were only polymerized in small regions and easilyextracted in SDS. Generally the gluten foams had low conductivity values, with some valuesbelow 0.05 W/(m K), which was found to be dependant on density and pore structure. Glutenfoams were also shown to be more difficult to ignite when compared to other conventionalfoams. It was further observed that the foams did not drip making it increasingly difficult forthe fire to spread.
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| 6. |
- Gustafsson, Emil, 1982-
(författare)
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Tailoring adhesion and wetting properties of cellulose fibers and model surfaces
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The layer-by-layer (LbL) technique was used to modify the surface of cellulose fibers by consecutive adsorption of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) followed by a final adsorbed layer of anionic paraffin wax colloids. Paper hand sheets made from the modified fibers were found to be highly hydrophobic with a contact angle of 150°. In addition to the significantly increased hydrophobicity, the sheets showed improved mechanical properties, such as a higher tensile strength. Heat treatment of the prepared sheets further enhanced both the mechanical properties and the hydrophobicity. These results demonstrate the flexibility and robustness of the LbL technique, which allows us to combine the known adhesive effect of PAH/PAA LbL films with the functionality of wax nanoparticles, creating a stronger and highly hydrophobic paper.It was further observed that LbL modified sheets without wax also displayed increased hydrophobicity when heat treated. The mechanism was studied through model experiments where LbL films of PAH/PAA were assembled on flat non-porous model cellulose surfaces. Contact angle measurements showed the same trend due to heat treatment of the model films, although, the absolute value of the contact angles were smaller. Analysis using the highly interfacial sensitive vibrational sum frequency spectroscopy technique showed an enrichment of CH3 groups (from the polymer chain ends) at the solid/air interface. These results indicate that during the heat treatment, a reorientation of polymer chains occurs to minimize the surface energy of the LbL film.In the second part of this work, the adhesive interactions between the main constituents of wood fibers were studied using high-resolution measuring techniques and well-defined model films of cellulose, hemicellulose and lignin. Successful surface modification of polydimethylsiloxane (PDMS) caps, needed in the Johnson-Kendall-Roberts (JKR) measuring methodology, by LbL deposition of nanofibrillated cellulose (NFC) and poly(ethylene imine) (PEI) allowed for the first known all-wood biopolymer JKR measurements of the adhesion between cellulose/cellulose, cellulose/lignin and the cellulose/glucomannan surfaces. The work of adhesion on loading and the adhesion hysteresis were similar for all three systems, suggesting that adhesion between the different wood biopolymers does not differ greatly.
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| 7. |
- Kallio, Kai J., 1967-
(författare)
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The Ageing of Fuel Lines Based on Polyamide-12
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Today, the use of bio-fuels for cars is increasing. There is a wide range of biofuelsavailable world wide, in Sweden ethanol containing fuels are favoured.For car manufacturers there is a need to be able to predict short and long termproperties of fuel lines subjected to ethanol containing fuels to ensure properlong term behaviour. The presented method for ageing in “close to real”environment involved circulating fuel inside the tubes and air on the outside attwo temperatures, 50°C and 110°C. The exposure time was extensive in the50°C case, almost 3 years, and the ageing at 110°C was conducted for 100days. Polyamide-12 was chosen as pipe material, which is also used in realparts. Tensile testing was used to assess the mechanical changes caused byageing. Long ageing times and high ethanol levels resulted in low extensibility.In the case of fuel with 25 vol.% ethanol at 110°C (100 days) the samplesshowed no macroscopic yielding. Even at 50°C a time induced loss ofextensibility was observed (80 vol.% ethanol). However, at ethanol levels of 0and 22 vol.% the extensibility was not reduced even after the 3 years of ageing.The changes at short times were interpreted as being due to loss of plasticizer.The changes at long ageing times were thoroughly investigated. The change incrystallinity, pipe swelling, leaching and the decrease in extensibility were allgreatest in the pipes subjected to ethanol. As expected, the molar massdecreased as the ethanol level increased and a good correlation between molarmass and extensibility was observed. A method for determining the fuelpermeation properties was developed. Fuel lines were subjected to circulatingfuels in the same manner as in the ageing tests and the surrounding air wasanalysed for fuel components with a flame ionisation detector. Higher level ofethanol increased the individual fuel component fluxes as well as the total fluxand also the temperature effect on the flux was significant. Finally it should bementioned, that ethanol was not always an unwanted ingredient; adding a smallamount of ethanol to the ethanol-free fuel prevented premature pipe failure at110°C.
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| 8. |
- Khosravi, Sara
(författare)
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Protein-Based Adhesives for Particleboards
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this study was to elucidate the possibilities to use wheat gluten (WG) as a binder for particleboards, as well as soy protein isolate (SPI). The focus was on the effect of the adhesive formulation and the processing conditions, while the press parameters were kept constant. Some aspects of the dispersion and the preparation of the dispersions that were investigated are: the time (1, 3 or 5h) to prepare the dispersion, the temperature (room temperature, 50 or 80°C) during the preparation of the dispersions and the effect of storing (1, 2.5 or 4 days) the dispersions. Furthermore, the utilization of green particles versus dried particles was examined. The concentration (12, 16, 20 or 24%) of WG dispersion and the process for applying it to the particles was studied. Two application methods were evaluated, in application method 1 (appl. 1) all the dispersion was added to the particles in one step before the particles were dried. When application method 2 (appl. 2) was employed the dispersion was added in two steps, some of the dispersion was added before the drying and some after the drying. The considered board properties were internal bond (IB), thickness swelling (TS) and water absorption (ABS). The results show that in the case of SPI dispersion the temperature seems to not be of significant importance and it appears as if longer time to prepare the dispersion is beneficial. On the other hand for WG dispersion it looks as if a lower temperature is preferable for the preparation of the dispersion and that the time to prepare the dispersion is of no importance. Furthermore, storing the dispersions for more than one day before it was used as an adhesive for particleboards (PB) resulted in poorer boards. According to this study it is beneficial to use dried particles instead of green particles. Additionally, the results show that the interaction between the concentration of WG dispersion and how it is applied is a significant factor, considering the IB value. However, in general the two step process (appl. 2) is preferable.
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| 9. |
- Pallon, Love, 1984-
(författare)
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Polyethylene/metal oxide nanocomposites for electrical insulation in future HVDC-cables : probing properties from nano to macro
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 10. |
- Wu, Qiong, 1987-
(författare)
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Biofoams and Biocomposites based on Wheat Gluten Proteins
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Novel uses of wheat gluten (WG) proteins, obtained e.g. as a coproduct from bio-ethanol production, are presented in this thesis. A flame-retardant foam was prepared via in-situ polymerization of hydrolyzed tetraethyl orthosilicate (TEOS) in a denatured WG matrix (Paper I). The TEOS formed a well-dispersed silica phase in the walls of the foam. With silica contents ≥ 6.7 wt%, the foams showed excellent fire resistance. An aspect of the bio-based foams was their high sensitivity to fungi and bacterial growth. This was addressed in Paper II using a natural antimicrobial agent Lanasol. In the same paper, a swelling of 32 times its initial weight in water was observed for the pristine WG foam and both capillary effects and cell wall absorption contributed to the high uptake. In Paper III, conductive and flexible foams were obtained using carbon-based nanofillers and plasticizer. It was found that the electrical resistance of the carbon nanotubes and carbon black filled foams were strain-independent, which makes them suitable for applications in electromagnetic shielding (EMI) and electrostatic discharge protection (ESD). Paper IV describes a ‘water-welding’ method where larger pieces of WG foams were made by wetting the sides of the smaller cubes before being assembled together. The flexural strength of welded foams was ca. 7 times higher than that of the same size WG foam prepared in one piece. The technique provides a strategy for using freeze-dried WG foams in applications where larger foams are required.Despite the versatile functionalities of the WG-based materials, the mechanical properties are often limited due to the brittleness of the dry solid WG. WG/flax composites were developed for improved mechanical properties of WG (Paper V). The results revealed that WG, reinforced with 19 wt% flax fibres, had a strength that was ca. 8 times higher than that of the pure WG matrix. Furthermore, the crack-resistance was also significantly improved in the presence of the flax.
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