The market is in great need of more environmentally friendly alternatives to fossil-based composite materials to obtain a more sustainable future. Lignin is the second most common biopolymer and is a byproduct in the pulping and paper industry. Fractionation of lignin has made it possible to receive lignin with narrow dispersity and low molecular weight, which is suitable for further applications. Modification of lignin structure yields new reactive sites that can be tailored for specific needs. Because of the aromatic structure of lignin, it is a promising renewable resource for production of thermosets. In this project Kraft lignin is sequentially solvent-fractionated and modified in an allylation process with allyl chloride. The allylated lignin is reacted with a cross-linking agent and used to impregnate carbon fibre mats. The resin-coated material is then cured at 125 oC to achieve a composite material. The project also encompasses characterization of the chemical structure of lignin in the different fractions. The morphology and adhesive properties of the lignin as well as the carbon fibres and the composite material was investigated. Although the production of composite material from lignin and carbon fibres were accomplished, bubble formation in the resin was a problem for all composite samples that were prepared, whether it was during solvent evaporation or during curing. By performing the addition of resin to carbon fibre mats in multiple steps, where pressure is added after the first applied layer, it is suggested that complete adhesion to the carbon fibre can be achieved, whilst maintaining adequate resin to carbon fibre ratio. / Marknaden är i stort behov av mer miljövänliga alternativ till fossilbaserade kompositmaterial för att kunna erhålla en mer hållbar framtid. Lignin är den näst vanligaste aromatiska biopolymeren och framställs som en biprodukt i pappersindustrin. Fraktionering av lignin har gjort det möjligt att erhålla lignin med låg dispersitet och molekylvikt vilket är lämpligt för vidare applikationer. Modifiering av lignins struktur ger upphov till nya reaktiva grupper som kan anpassas för ens behov. Den aromatiska strukturen som lignin besitter resulterar i en lovande förnybar resurs för produktion av härdplast. I detta projekt är Kraft lignin sekventiellt fraktionerat med lösningsmedel och modifierat med hjälp av en allyleringsprocess i närvaro av allylklorid. Det allylerade ligninet reagerar med en tvärbindare och används vidare för att impregnera kolfiber. De impregnerade kolfibermattorna härdades i ugn vid 125 oC för att erhålla kompositmaterial. Projektet omfattar även karaktärisering av den kemiska strukturen i lignin från de olika fraktionerna. Morfologin och vidhäftningsförmåga av lignin, kolfiber och likaså kompositmaterialet undersöktes. Ett kompositmaterial bestående av kolfiber och lignin erhölls med framgång under projektets gång, dock var bubbelbildning ett stort problem under förångningen av lösningsmedel och även under härdningsprocessen. Addition av harts till kolfibermattorna i flera steg, där tryck är adderat efter det första lagret har blivit applicerat, anses vara en lovande metod för att en hög vidhäftningsgrad ska kunna erhållas. Detta medan ett adekvat förhållande mellan harts och kolfiber upprätthålls.

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No description available.

Silicones elastomers are widely used all over the world due to their unusual properties when compared to their carbon-based counterparts. Synthetic methods for their synthesis are still quite limited and the traditional silicone products are not able to completely meet the requirement for modern materials. Silicone elastomers with customized structures and with higher levels of sustainability will be the research focus for the development of next generation materials. The element sulfur and its functional groups are growing players in modern polymer and materials science, since sulfur reactions are exceptionally versatile. The incorporation of sulfur reactions into the design and preparation of silicone materials can lead to silicones with unique properties for various research interests. Initial exploration was focused on the creation of general and simple methods for 3D printing silicone elastomers using thiol-ene chemistry. However, silicone inks suitable for 3D printing are still quite limited. Photo-initiated thiol-ene chemistry was proposed to design a rapid cure silicone ink for extrusion 3D printing. Unlike other radical reactions, the relatively oxygen insensitive thiol-ene was able to provide the necessary rapid reaction rate and build up the necessary viscosity for practical printing in less than 2 seconds in the presence of air. Various customized silicone structures with different moduli were obtained with a relative fast printing speed. The use of thiol oxidation reactions in the synthesis of silicone elastomers is also demonstrated in this thesis. Reductive cleavage of the resulting disulfide bridge was successfully performed with the presence of hydrosilane and B(C6F5)3 catalyst. Herein, a synthetic method to reversible silicone elastomers based on the disulfide linkage is described. This method could be extended to cleave the disulfide and polysulfide linkage in used automotive rubber materials. Various kinds of sulfur-cured rubbers were successfully devulcanized to polymeric oil. This simple and efficient method could potentially offer a solution for the huge amount of tire waste produced every year. Finally, a new method for preparing thermoplastic silicone elastomers with ionic linkages is reported. A novel dicarboxylic acid-modified silicone was synthesized though thiol-Michael additions. The resulting ionic crosslinked networks were built though the neutralization between carboxylic and amino silicone. Thermoplastic silicone elastomers with unique viscoelastic behavior can be obtained. In summary, the thesis demonstrates that sulfur chemistry is an exceptional synthetic tool for the silicone chemist. / Thesis / Doctor of Philosophy (PhD)

<p> Dimethylgermylene (GeMe2) has been generated by laser flash photolysis of 1,1dimethyl-3-phenylgermacyclopent-3-ene (23) and 1,1,3-trimethyl-4phenylgermacyclopent-3-ene (24) in hexanes at 25°C and its absorption maximum (λmax) has been unambiguously established to be 470 nm. GeMe2 decays with second-order kinetics under these conditions (2k/ε. = (10 ± 2) x 10^7 cm s^(-1)) to give Ge2Me4 (λmax = 370 nm). Kinetic studies of the reactions of GeMe2 and Ge2Me4 with typical germylene/digermene scavengers such as 1,3-dienes, olefins, alkynes, alkyl halides, group 14 metal hydrides, carboxylic acids, and amines have been carried out. </p> <p> GeMe2 reacts reversibly with MeOH, t-BuOH and THF to form Lewis acid-base complexes which exhibit relatively strong absorption bands that are blue-shifted with respect to GeMe2 (λmax ~ 295-310 nm). The decay of the Me2Ge-MeOH complex is accelerated in the presence of a Brnnsted acid (acetic acid or methanesulfonic acid) or base (MeONa). The reactions of the Me2Ge-THF complex with sodium methoxide, methanesulfonic acid, 4,4-dimethyl-1-pentene, 2,3-dimethyl-1-butadiene, acetic acid and CC4 have also been studied in THF. </p> <p> The photochemistry of two well-known precursors to GeMe2, namely dodecamethylcyclohexagermane (14) and dimethylphenyl(trimethylsilyl)germane (18) was reinvestigated. Laser flash photolysis of 14 in hexanes led to the formation of two transients, one with λmax= 490 nm (τ < & = 10 ns) and the second with λmax= 470 nm. The latter decays with second-order kinetics with concomitant formation of a new transient with λmax= 370 nm. The transient at 470 nm is assigned to GeMe2 and that at 370 nm to Ge2Me4, based on comparisons to the results obtained from laser flash photolysis of 23 and 24. Laser flash photolysis of 18-in hexane gives rise to two absorption bands centered at λmax = 300 nm and λmax = 430 nm, which are assigned to the dimethylphenylgerrnyl radical and the conjugated gerrnene derivative 38, respectively. GeMe2 cannot be detected in laser flash photolysis experiments with this compound. </p> / Thesis / Doctor of Philosophy (PhD)

Thesis (PhD (Chemistry and Polymer Science)--University of Stellenbosch, 2009. / The work presented in this dissertation describes the development of self-healing coatings based on thiol-ene chemistry. The approach was to synthesize capsules with thiol and ene compounds separately encapsulated. These capsules were embedded in various coating formulations and upon the formation of a crack with a razor blade, these capsules ruptured. This caused the healing agent to flow into the crack via capillary action and the thiol-ene healing mechanism was initiated. This resulted in recovery of the damaged coating and provided continued protection to the substrate. Pentaerythritol tetrakis(3-mercaptopropionate) (TetraThiol), 1,6-hexanediol diacrylate (DiAcrylate) and 1,6-hexanediol di-(endo, exo-norborn-2-ene-5-carboxylate) (DiNorbornene) are the thiol and ene compounds used in this study. Kinetic experiments indicated that both TetraThiol-DiAcrylate and TetraThiol-DiNorbornene monomer pairs undergo rapid polymerization and form a network within minutes upon exposure to UV radiation and with the addition of a photoinitiator. The TetraThiol-DiNorbornene monomer pair also showed a high rate of polymerization without the addition of a photoinitiator and/or exposure to UV radiation. Styrene-maleic anhydride (SMA) copolymers and chain-extended block copolymers with styrene (P[(Sty-alt-MAh)-b-Sty]) were synthesized via Reversible Addition-Fragmentation chain Transfer (RAFT)- mediated polymerization. These copolymers were used as surfactant in miniemulsification for the synthesis of core-shell particles with TetraThiol as the core material. It appeared that P[(Sty-alt-MAh)-b-Sty] block copolymers, sterically stabilized via the addition of formaldehyde, provide optimal stability to the core-shell particles. DiNorbornene is encapsulated via miniemulsion homopolymerization of styrene and well-defined, stable nanocapsules were obtained. TetraThiol and DiAcrylate microcapsules were synthesized via in-situ polymerization of urea and formaldehyde. Microcapsules with a particle size of one to ten micrometers and with a very smooth surface were obtained. These microcapsules and nanocapsules were embedded in poly(methyl acrylate) (PMA), styrene-acrylate and pure acrylic films and the self-healing ability of these coatings, after introduction of a crack with a razor blade, was assessed.

Lignocellulosic biomass is believed to serve a prominent role in tomorrow’s sustainable energy and material development. Among the polysaccharide fractions of lignocellulosic biomass, the potential of hemicelluloses as a valuable material resource is increasingly recognized. Thanks to their hydrophilic structure, hemicelluloses are suitable substrates for hydrogel design. The work summarized in this thesis aims to develop feasible strategies for the conversion of O-acetyl galactoglucomannan (AcGGM), an ample hemicellulose in softwood, into hydrogels. Within this framework, four synthetic pathways targeting the formation of crosslinked hydrogel networks from pure or unrefined AcGGM fractions were developed.   Aqueous AcGGM-rich and lignin-containing side-stream process liquors of forest industry, known as softwood hydrolysates (SWHs) were formulated into highly swellable hydrogels by: i) allyl-functionalization of AcGGM chains of crude SWH to obtain a viable precursor for hydrogel synthesis via free-radical crosslinking, ii) directly incorporating unmodified SWH fractions into semi-interpenetrating polymer networks (semi-IPNs). SWH hydrogels and semi-IPNs were characterized with appreciable maximum swelling ratios of Qeq = 170 and Qeq = 225, respectively.   Rapid crosslinking of AcGGM through thiol-click chemistry was addressed by first imparting thiol functionality onto pure AcGGM chains in a one-pot procedure. The thiolated AcGGM proved to be a suitable substrate for the synthesis of hemicellulose hydrogels via thiol-ene and thiol Michael addition reactions. Finally, sequential full IPNs were developed by subjecting single network hydrogels of pure AcGGM to a second network formation. IPNs obtained through either free radical crosslinking or thiol-ene crosslinking exhibited higher shear storage moduli than their single network counterparts. / <p>QC 20161102</p>

This thesis concerns the development of surface ligation techniques for the preparation of carbohydrate biosensors. Several methodologies were developed based on efficient photochemical insertion reactions which quickly functionalize polymeric materials, with either carbohydrates or functional groups such as alkynes or alkenes. The alkyne/alkene surfaces were then treated with carbohydrate azides or thiols and reacted under chemoselective Cu-catalyzed azide-alkyne cycloaddition (CuAAC) or photo-radical thiol-ene/yne click chemistry, thus creating a range of carbohydrate biosensor surfaces under ambient conditions. The methodologies were evaluated by quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) flow through instrumentations with recurring injections of a range of lectins, allowing for real-time analysis of the surface interactions. The developed methods were proven robust and versatile, and the generated carbohydrate biosensors showed high specificities and good capacities for lectin binding.  The methods were then used to investigate how varying the glycan linker length and/or a sulfur-linkage affect the subsequent protein binding. The survey was further explored by investigating the impact of sulfur in glycosidic linkages on protein binding, through competition assays with various O/S-linked disaccharides in solution interactions with lectins. / QC 20120309

This thesis presents technological advancements in microfluidics. The overall goals of the work are to develop new miniaturized tests for point-of-care diagnostics and robust super-lubricating surfaces for friction reduction. To achieve these goals, novel materials, surfaces and manufacturing methods in microfluidics have been developed. Point-of-care diagnostic tests are portable miniaturized instruments that downscale and automate medical tests previously performed in the central laboratories of hospitals. The instruments are used in the doctor’s office, in the emergency room or at home as self-tests. By bringing the analysis closer to the patient, the likelihood of an accurate diagnosis, or a quick therapy adjustment is increased. Already today, there are point-of-care tests available on the market, for example blood glucose tests, rapid streptococcus tests and pregnancy tests. However, for more advanced diagnostic tests, such as DNA-tests or antibody analysis, integration of microfluidic functions for mass transport and sample preparation is required. The problem is that the polymer materials used in academic development are not always suited for prototyping microfluidic components for sensitive biosensors. Despite the enormous work that has gone into the field, very few technical solutions have been implemented commercially. The first part of the work deals with the development of prototype point of-care tests. The research has focused on two major areas: developing new manufacturing methods to leverage the performance of existing materials and developing a novel polymer material platform, adapted for the extreme demands on surfaces and materials in miniaturized laboratories. The novel manufacturing methods allow complex 3D channel networks and the integration of materials with different surface properties. The novel material platform is based on a novel off-stoichiometry formulation of thiol-enes (OSTE) and has very attractive material and manufacturing properties from a lab-on-chip perspective, such as, chemically stable surfaces, low absorption of small molecules, facile and inexpensive manufacturing process and a biocompatible bonding method. As the OSTE-platform can mirror many of the properties of commercially used polymers, while at the same time having an inexpensive and facile manufacturing method, it has potential to bridge the gap between research and commercial production. Friction in liquid flows is a critical limiting factor in microfluidics, where friction is the dominant force, but also in marine applications where frictional losses are responsible for a large part of the total energy consumption of sea vessels. Microstructured surfaces can drastically reduce the frictional losses by trapping a layer of air bubbles on the surface that can act as an air bearing for the liquid flow. The problem is that these trapped air bubbles collapse at the liquid pressures encountered in practical applications. The last part of the thesis is devoted to the development of novel low fluidfriction surfaces with increased robustness but also with active control of the surface friction. The results show that the novel surfaces can resist up to three times higher liquid pressure than previous designs, while keeping the same friction reducing capacity. The novel designs represent the first step towards practical implementation of micro-structured surfaces for friction reduction. / <p>QC 20110907</p>