Thesis (Ph. D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed May 6, 2009). Vita. Includes bibliographical references.

Dissertation (PhD)--University of Stellenbosch, 2006. / Bibliography. Also available via the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 96-100). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 96-100). Also available on the Internet.

M.Sc. / Water is often contaminated with organic and inorganic compounds by natural means and through human activities. Once contaminated, water of this nature has little or no use. However, water that is free from toxic chemicals is essential to both human health and the environment. Current water treatment techniques such as separation by membranes (reverse osmosis), adsorption (activated carbon) and ion exchange are not always very efficient at removing contaminants which may be present in parts per billion (ppb) levels. Techniques need to be developed that are reasonably inexpensive and easy to use, and yet effective at removing both organic and inorganic pollutants to acceptable levels. Adsorption is a technique that has the potential to meet these criteria. In our laboratories, insoluble beta cyclodextrin (β-CD) polymers have been used to remove pollutants from water at concentrations as low as ppb levels. However, they exhibited some disadvantages, such as poor structural integrity and difficulty in recovery. This project sought to deal with these limitations by incorporating functionalized multi-walled nanotubes (f-MWNTs) into the polymer, and then embedding polymer particles in an alginate matrix as small beads for ease of use. The polymer composites, 1% f-MWNTs with β-CD polyurethane, were synthesised and embedded in alginates to form alginate composite beads. Composite beads were tested against a model organic and heavy metal pollutants, namely p-nitrophenol and Pb2+, respectively. The composites were characterized using Fourier Transform Infra Red spectroscopy (FT-IR), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDXS), among other techniques. The absorption capacity of f-MWNTs, β-CD, and alginates combined proved to be effective and stable adsorbents. They showed an adsorption efficiency of at least 95% for p-nitrophenol at a concentration of 10 mg/L and 98% for Pb2+ at a concentration of 50 mg/L. vii The novel adsorbents show a good thermal stability and maintain their structural integrity after repeated (thirty times) use in recycling experiments. The recycled beads maintained a high average adsorption efficiency of 96%, indicating the potential cost benefit of these materials. As a comparison, the plain calcium alginate (CaAG) beads and plain β-CD polyurethane beads showed an average adsorption of 55% and 74%, respectively, but their structural integrity was significantly compromised during similar recycling. Brunauer Emmett Teller (BET) surface area analysis showed that incorporation of f-MWNTs (1% loading) increased the surface area of the composite beads, and adsorption isotherms showed a good fit with both Langmuir and Freundlich models. This project has demonstrated the use of f-MWNTs as copolymer which improves the structural stability of the polymers, and that the combination of these polymers and alginates provide a potentially useful material for water treatment applications.

M.Sc. / The disinfection of drinking water is an important step in the water treatment process. However, toxic (unwanted) disinfection by-products (DBPs) are often produced during the disinfection of drinking water. One such group of DBPs are the nitrosamines such as N-Nitrosodimethylamine (NDMA). Nitrosamines, particularly NDMA, are highly carcinogenic, mutagenic and teratogenic. The US Environmental Protection Agency (USEPA) placed these compounds into the group B2, which indicates compounds of probable human carcinogens. The USEPA integrated risk information system (IRIS) database lists an estimated 10-6 lifetime cancer risk level for NDMA in drinking water of 0.7 ng/L. The formation of NDMA during drinking water disinfection, particularly chloramination, has been linked to the formation of NDMA through a reaction between monochloramine and organic nitrogen precursors via unsymmetrical dialkylhydrazine intermediates, such as unsymmetrical dimethylhydrazine (UDMH). UDMH is oxidized by dissolved oxygen to form NDMA. Therefore, it is also crucial to remove NDMA precursors (UDMH and dimethylamine (DMA)), before disinfection is carried out. Also, the chlorination of secondary wastewater can result in the formation of NDMA. In this research project, determination of nitrosamines, especially NDMA was done at four different water treatment plants in South Africa. Water samples collected from Midvaal, Sedibeng, Magalies (Vaalkop and Klipdrift) and Rand Water treatment plants were qualitatively analysed for the presence of NDMA. Also, the determination of possible NDMA precursors such as dimethylamine and UDMH was investigated in water samples collected from Sedibeng water treatment plant. The water samples were collected before and after each drinking water treatment process (coagulation, sedimentation, filtration, chlorination and chloramination or ozonation). Solid phase microextraction (SPME) was employed in the extraction of the water samples. Polydimethylsiloxane/divinylbenzene (PDMS/DVB) proved to be the most efficient fibre for the SPME extraction procedure. The water samples vi were then qualitatively analysed using gas chromatography-mass spectrometry (GC-MS). Very small amounts of NDMA were detected in water samples collected from Sedibeng water treatment plant. There was no detectable presence of NDMA or other nitrosamines in water samples collected from the other treatment plants. Water-insoluble cyclodextrin (CD) polyurethanes were then used to ascertain how much of the NDMA they would remove. The CD polymers showed capacity to remove NDMA and dimethylamine (which is a known NDMA precursor) in the water samples with 80% removal efficiency for NDMA (when comparing peak area before and after treatment with CD polymers) and approximately 98% removal rate for DMA.

M.Sc. / Safe drinking water is an essential resource for human survival, health, dignity and development. However, this vital resource has become scarce mainly due to population growth, economic activity, climate change and pollution. Treatment of polluted water is expensive and does not always ensure delivery of safe drinking water to humans. Reports on the detection of pollutants such as organics, bacteria, inorganics and the occurrence of toxic disinfection byproducts in treated water in distribution systems have necessitated further research in improving water treatment methods. Metal impregnated carbon nanotube incorporated into cyclodextrin polyurethanes were synthesised by first functionalising carbon nanotubes and then impregnating them with metal nanoparticles. The resultant product was confirmed using Transmission electron microscopy (TEM). The metal nanoparticles were found to have a diameter range of 6 to 35 nm. The metal impregnated carbon nanotubes were then polymerised to produce cyclodextrin polyurethanes. The polymers were characterised using various techniques such as Scanning electron microscopy (SEM), Emission dispersive X-ray spectrometry (EDX) and Brunauer-Emmet-Teller analysis. The metal nanoparticles were found to be part of the polymers through EDX and the polymers’ surface areas were measured to be 0.78 and 0.3383 m2/g for silver and copper polymers, respectively. The synthesised polymers were tested for their efficacy at destroying pathogenic bacteria from water. The polymers were found to inactivate bacteria by up to 4 logs from spiked water samples. These metal impregnated polymers when compared to native carbon nanotubes and cyclodextrin polymers had an enhanced antibacterial property. In environmental samples, metal impregnated polymers destroyed up to 3 logs of bacteria. There was complete removal of bacteria from filtered environmental water samples. Factors affecting the polymers’ efficacy were turbidity, nature of sample and the ratio of bacterial cells removed per gram of polymer.

Biological fouling occurs everywhere in the marine environment and is a significant problem for marine vessels. Anti-fouling coatings have been used effectively to prevent fouling; however, these coatings harm non-targeted sea-life. Fouling-release coatings (FRC) appear to be an alternative way to combat fouling. FRC do not necessarily prevent the settlement of marine organisms but rather allow their easy removal with application of shear to the coatings surface. These coatings must be non-toxic, non-leaching, have low surface energy, low modulus, and durability to provide easy removal of marine organisms. Here the goal is to develop FRC based on thermosetting siloxane-polyurethane, amphiphilic polyurethane, and zwitterionic/amphiphilic polyurethane systems. A combinatorial high-throughput approach has been taken in order to explore the variables that may affect the performance of the final coatings. Libraries of acrylic polyols were synthesized using combinatorial high-throughput techniques by either batch or semi-batch processes. The design of the experiments for the batch and semi-batch processes were done combinatorially to explore a range of compositions and various reaction process variables that cannot be accomplished or are not suitable for single reaction experiments. Characterization of Rapid-GPC, high-throughput DSC, and gravimetrically calculated percent solids verified the effects of different reaction conditions on the MW, glass transition temperatures, and percent conversion of the different compositions of acrylic polyols. Coatings were characterized for their surface energy, pseudobarnacle pull-off adhesion, and were subjected to bioassays including marine bacteria, algae, and barnacles. From the performance properties results the acrylic polyol containing 20% hydroxyethyl acrylate and 80% butyl acrylate was selected for further siloxane-polyurethane formulations and were subjected to the same physical, mechanical, and performance testing. Amiphiphilic copolymers based on PDMS molecular weight and the addition of PEG based polymer blocks on the properties of acrylic-polyurethane coatings were explored. The key properties screened were surface energy, determined by contact angle measurements using water and methylene iodide, dynamic water contact angle, and pseudobarnacle adhesion properties. The data from all of the biological assays indicates that the novel coatings were able to resist fouling and have low fouling adhesion for the broad variety of fouling organisms tested.

Conventional melt transesterification successfully synthesized high molecular weight segmented copolyesters.  The cycloaliphatic monomers 2,2,4,4-tetramethyl-1,3-cyclobutanediol (CBDO) and dimethyl-1,4-cyclohexane dicarboxylate (DMCD) afforded sterically hindered, ester carbonyls in high-Tg polyester precursors.   Reaction between the polyester polyol precursor and a primary or secondary alcohol at melt polymerization temperatures revealed reduced transesterification of the polyester hard segment as a result of enhanced steric hindrance adjacent to the ester linkages.  Subsequent polymerization of a 4,000 g/mol polyol with monomers comprising the low-Tg block yielded high molecular weight polymers that exhibited enhanced mechanical properties compared to a non-segmented copolyester control.  Atomic force microscopy uncovered unique needle-like, interconnected, microphase separated surface morphologies, and small-angle X-ray scattering confirmed the presence of bulk microphase separation. This new synthetic strategy enabled selective control of ionic charge placement into the hard segment or soft segment block of segmented copolyesters using melt transesterification.  The ionic placement impacted the microphase-separated morphology, which influenced its thermomechanical properties and resulting mechanical performance.  Melt transesterification of low-Tg, sodium sulfonated copolyesters achieved up to 15 mol% ionic content.  The 10 and 15 mol% sodium sulfonated copolyesters exhibited water-dispersibility, which enabled cation dialysis exchanges to divalent metal cations.  The sulfonated copolyesters containing divalent metal cations exhibited enhanced rubbery plateau moduli to higher temperatures.   Novel trialkylphosphonium ionic liquids chain extenders enabled the successful synthesis of poly(ethylene glycol)-based, cationic polyurethanes with pendant phosphoniums in the hard segments (HS).  Aqueous size exclusion chromatography (SEC) confirmed the charged polyurethanes, which varied the phosphonium alkyl substituent length (ethyl and butyl) and cationic HS content (25, 50, 75 mol%), achieved high absolute molecular weights.  Dynamic mechanical analysis (DMA) demonstrated the triethylphosphonium (TEP) and tributylphosphonium (TBP) polyurethanes displayed similar thermomechanical properties, including increased rubbery plateau moduli and flow temperatures.  Fourier transform infrared spectroscopy (FTIR) emphasized the significance of ion-dipole interaction on hydrogen bonding. Atomic force microscopy (AFM), small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD) supported microphase separated morphologies in the trialkylphosphonium polyurethanes, despite the presence of ionic interactions. Sorption isotherm experiments revealed TBP polyurethanes displayed similar water sorption profiles to the noncharged analogue and lower water absorptivity compared to TEP.  The phosphonium polyurethanes displayed significantly improved tensile strain; however, lower tensile stress of the TEP polyurethane was presumably due to absorbed water.  In addition, we also explored applications of the trialkylphosphonium polyurethanes as nucleic acid delivery vectors and demonstrated their abilities to form colloidally stable polyplexes in salt-containing media. / Ph. D.

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