Starch is a natural polymer occurring in the seeds, tubers and stems of many plants, including maize. It is a mixture of two polymers: linear amylose and highly branched amylopectin. The ratio and the molar masses of the two polymers depend on the starch source, giving rise to different starch properties. Thermoplastic starch (TPS) was obtained by gelatinising a dry-blend mixture of maize starch, water, plasticisers and additives in a single-screw laboratory extruder. The TPS formed is a translucent amorphous material that could be shaped into pellets and injection-moulded into a variety of articles, just like conventional plastics [Shogren et al., 1994]. The advantages of TPS are that it is cheap and fully biodegradable. However, because of its hydrophilic nature, its properties and dimensional stability are influenced by moisture (humidity). It is also not easily processed like conventional plastics and the freshly moulded material ages, i.e. its properties change over time. The latter is caused by retrogradational structural changes which include helix formation and the crystallisation that occurs above the glass transition temperature [Myllärinen et al., 2002]. The unacceptable physical and processing properties of TPS were improved by blending with other polymers. The objective of this work was to determine the effects of water and glycerol content and the starch source or type on the mechanical properties of maize-based TPS. In addition, the effect of gypsum filler and polyamides or polyvinyl butyral (PVB) as modifying agent was also investigated. The PVB was based on material recycled from automotive windscreens. As with the thermoplastic starch, the thermoplastic/polymer blends, e.g. polyvinyl butyral, were also prepared using a single-screw extruder. After pelletisation, the materials were conditioned at 30 °C and a relative humidity of 60%. Tensile test specimens were prepared by injection moulding. Samples were characterised using X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) and tensile testing. The effect of environmental conditions (temperature and humidity or water submersion) on the ageing of the samples was investigated using tensile properties as a measure. Initial extrusion and moulding trials revealed that the TPS compounds were very difficult to process. Difficulties were encountered with feeding the dry blends into the compounding extruder. The moulded samples adhered strongly to the mould walls, especially the sprue part. These problems were overcome by adding 2,5% precipitated silica to improve the flowability of the dry blends and stearyl alcohol at ca. 1,5% as a processing aid. The latter performed as an external lubricant and mould-release agent. Nevertheless, for some compositions it was also necessary to use ‘Spray-and-Cook’ as mould-release agent during injection moulding. The results show that HiMaizeTM, a high-amylose maize starch, provided the best properties in TPS and its blends. Further improvements in properties were obtained by blending with low-molecular-weight hot-melt adhesive-grade polyamides (Euremelt 2138 and 2140), engineering polyamide (EMS Grilon CF 62 BSE) or low amounts of PVB. The properties of all the compounds investigated were affected by moisture content and also by ageing. The TPS-PVB blends showed highly non-linear composition-dependence. SEM and DMA revealed a phase separation for all the TPS-PVB blend compositions investigated. The tensile properties were negatively affected by ageing in a high-humidity environment and they deteriorated rapidly when the samples were soaked in water. Synergistic property enhancement was observed for a compound containing 22% thermoplastic starch. It featured a higher tensile strength, showed better water resistance and was significantly less affected by ageing. At higher PVB levels, the property dropped to values that were lower than expected from the linear blending rule. / Thesis (PhD)--University of Pretoria, 2008. / Chemical Engineering / unrestricted

This dissertation describes the development and application of various mechanical characterization techniques to four types of polymer composite materials. The composite nature of these materials ranges from molecular to macro-scale, as do the size scales probed by the techniques chosen. The two main goals of this work are to evaluate the suitability of existing characterization methods to new composite materials (and augment the methods as needed), and to use these methods to determine optimal composite system parameters to maximize the desired mechanical response. Chapter 2 employs nondestructive ultrasonic spectroscopy for characterizing the stiffness response of both micron-scale woven composites and macro-scale glass-polymer-glass laminates. Both traditional wavespeed measurement as well as aspects of resonant ultrasonic spectroscopy are applied to determine material parameters. The laminates are also examined in Chapter 3, which utilizes both large-scale and small-scale quasi-static and dynamic puncture tests to elucidate the size- and rate-dependence of dynamic behavior. Because of limitations encountered with these methods, a smaller-scale, more fundamental test is developed and applied which focuses solely on the deformation and delamination of the polymer. These two processes, which account for the vast majority of energy absorbed during a puncture event, can be evaluated in terms of self-similar process zone propagation process models. Identifying and optimizing the relevant model parameters can promote the design of systems with maximum energy absorption. Exploratory work on nanocomposite systems is presented in Chapter 4. The polymer matrix from the laminated systems of the previous chapter is used to produce nanosilica composites. A range of techniques are employed to determine the level of dispersion and the mechanical reinforcement provided. The final project presented investigates copolycarbonates, or molecular composites, that have been developed to lessen the detrimental effect of aging on mechanical properties. Mechanical and thermal measurements can elucidate the effect of structure, specifically molecular mobility, on susceptibility to physical aging. The differences in molecular mobility contribute to differences in energy absorption by plastic deformation and damage, which is required for material toughness. Thus, understanding the molecular structure allows for determination of an optimal structure or copolymer concentration to maximize fracture toughness.

Este trabalho investigou a obtenção de filmes de TiO2 por sol-gel e dipcoating (SGDC) e sua caracterização microestrutural e como fotocatalisador para a produção de hidrogênio a partir da água. Os precursores e reagentes utilizados foram: propóxido de titânio, ácido acético, etanol anidro, acetilacetona, Triton X-100 e polivinilbutiral (PVB). Foram preparadas 2 soluções precursoras, uma com PVB e outra sem. Foram produzidos filmes com 1, 2 e 3 camadas através da técnica de dip-coating. Os filmes foram tratados termicamente a 400, 500 e 600ºC, com uma taxa de 100ºC/h e um patamar de 2 h. O TiO2 sintetizado e os filmes produzidos foram caracterizados por difração de raios X (DRX) quanto à cristalinidade, fases presentes e tamanho de cristalito; microscopia eletrônica de varredura (MEV), adsorção de nitrogênio (método BET), análises termogravimétricas (ATG) e termodiferenciais (ATD), elipsometria espectroscópica, perfilometria óptica, espectroscopia Raman e de reflectância difusa (determinação do band gap). Após o tratamento térmico os filmes apresentaram uma microestrutura bastante irregular e com muitas trincas, com a presença da fase anatase em todas as temperaturas de tratamento térmico, e um teor de 3,7% de rutilo à 600ºC. O band gap dos filmes aumentou com a quantidade de camadas adicionadas, com a elevação da temperatura de tratamento térmico e adição de PVB. As medidas de fotocorrente foram realizadas no escuro e sob iluminação de lâmpada de Xe com 250W (simulador de luz solar de 1,5AM). A maior fotocorrente medida foi de 12 μA a 0,5V. A produção de H2 aumentou linearmente com o tempo de exposição para ambas as amostras com PVB. Foi possível relacionar a adição do PVB com o favorecimento da fotoatividade dos filmes de TiO2. / This work has investigated the effect of polyvinyl butyral addition in the synthesis of TiO2 films by sol-gel and dip-coating, their microstructural features and their photoelectrochemical activity for water-splitting hydrogen production. The precursors and reagents used were: titanium propoxide, acetic acid, anhydrous ethanol, acetylacetone, Triton X-100 and polyvinyl butyral (PVB). Two precursor solutions were prepared: one with PVB and another without it. The dip-coating technique was used to produce films with 1, 2 and 3 layers. The films were heat treated at 400, 500 and 600ºC, at a rate of 100°C/h and dwelling time of 2h. Afterwards the synthesized films were characterized by X-ray diffraction (XRD); scanning electron microscopy (SEM), nitrogen adsorption (BET method), thermogravimetric (TGA) and differential thermal analysis (DTA), spectroscopic ellipsometry, optical profilometry, Raman and diffuse reflectance spectroscopy (determination of the band gap). The films after heat treatment showed a very irregular microstructure with many cracks. The anatase phase was presented in all temperatures and a small content of rutile at 600 °C (around 3.7%) was identified. The band gap of the films increased with the number of layers, heat treatment and addition of PVB. The photocurrent measurements were carried out in the dark and under illumination with 250W Xe, using a sunlight simulator (1,5AM). The highest photocurrent was 12A at 0.5V. The H2 production increased linearly with time of exposure for both samples with PVB. Therefore, it was possible to relate the addition of PVB with improvement the photoactivity of TiO2 films.

Este trabalho investigou a obtenção de filmes de TiO2 por sol-gel e dipcoating (SGDC) e sua caracterização microestrutural e como fotocatalisador para a produção de hidrogênio a partir da água. Os precursores e reagentes utilizados foram: propóxido de titânio, ácido acético, etanol anidro, acetilacetona, Triton X-100 e polivinilbutiral (PVB). Foram preparadas 2 soluções precursoras, uma com PVB e outra sem. Foram produzidos filmes com 1, 2 e 3 camadas através da técnica de dip-coating. Os filmes foram tratados termicamente a 400, 500 e 600ºC, com uma taxa de 100ºC/h e um patamar de 2 h. O TiO2 sintetizado e os filmes produzidos foram caracterizados por difração de raios X (DRX) quanto à cristalinidade, fases presentes e tamanho de cristalito; microscopia eletrônica de varredura (MEV), adsorção de nitrogênio (método BET), análises termogravimétricas (ATG) e termodiferenciais (ATD), elipsometria espectroscópica, perfilometria óptica, espectroscopia Raman e de reflectância difusa (determinação do band gap). Após o tratamento térmico os filmes apresentaram uma microestrutura bastante irregular e com muitas trincas, com a presença da fase anatase em todas as temperaturas de tratamento térmico, e um teor de 3,7% de rutilo à 600ºC. O band gap dos filmes aumentou com a quantidade de camadas adicionadas, com a elevação da temperatura de tratamento térmico e adição de PVB. As medidas de fotocorrente foram realizadas no escuro e sob iluminação de lâmpada de Xe com 250W (simulador de luz solar de 1,5AM). A maior fotocorrente medida foi de 12 μA a 0,5V. A produção de H2 aumentou linearmente com o tempo de exposição para ambas as amostras com PVB. Foi possível relacionar a adição do PVB com o favorecimento da fotoatividade dos filmes de TiO2. / This work has investigated the effect of polyvinyl butyral addition in the synthesis of TiO2 films by sol-gel and dip-coating, their microstructural features and their photoelectrochemical activity for water-splitting hydrogen production. The precursors and reagents used were: titanium propoxide, acetic acid, anhydrous ethanol, acetylacetone, Triton X-100 and polyvinyl butyral (PVB). Two precursor solutions were prepared: one with PVB and another without it. The dip-coating technique was used to produce films with 1, 2 and 3 layers. The films were heat treated at 400, 500 and 600ºC, at a rate of 100°C/h and dwelling time of 2h. Afterwards the synthesized films were characterized by X-ray diffraction (XRD); scanning electron microscopy (SEM), nitrogen adsorption (BET method), thermogravimetric (TGA) and differential thermal analysis (DTA), spectroscopic ellipsometry, optical profilometry, Raman and diffuse reflectance spectroscopy (determination of the band gap). The films after heat treatment showed a very irregular microstructure with many cracks. The anatase phase was presented in all temperatures and a small content of rutile at 600 °C (around 3.7%) was identified. The band gap of the films increased with the number of layers, heat treatment and addition of PVB. The photocurrent measurements were carried out in the dark and under illumination with 250W Xe, using a sunlight simulator (1,5AM). The highest photocurrent was 12A at 0.5V. The H2 production increased linearly with time of exposure for both samples with PVB. Therefore, it was possible to relate the addition of PVB with improvement the photoactivity of TiO2 films.

Este trabalho investigou a obtenção de filmes de TiO2 por sol-gel e dipcoating (SGDC) e sua caracterização microestrutural e como fotocatalisador para a produção de hidrogênio a partir da água. Os precursores e reagentes utilizados foram: propóxido de titânio, ácido acético, etanol anidro, acetilacetona, Triton X-100 e polivinilbutiral (PVB). Foram preparadas 2 soluções precursoras, uma com PVB e outra sem. Foram produzidos filmes com 1, 2 e 3 camadas através da técnica de dip-coating. Os filmes foram tratados termicamente a 400, 500 e 600ºC, com uma taxa de 100ºC/h e um patamar de 2 h. O TiO2 sintetizado e os filmes produzidos foram caracterizados por difração de raios X (DRX) quanto à cristalinidade, fases presentes e tamanho de cristalito; microscopia eletrônica de varredura (MEV), adsorção de nitrogênio (método BET), análises termogravimétricas (ATG) e termodiferenciais (ATD), elipsometria espectroscópica, perfilometria óptica, espectroscopia Raman e de reflectância difusa (determinação do band gap). Após o tratamento térmico os filmes apresentaram uma microestrutura bastante irregular e com muitas trincas, com a presença da fase anatase em todas as temperaturas de tratamento térmico, e um teor de 3,7% de rutilo à 600ºC. O band gap dos filmes aumentou com a quantidade de camadas adicionadas, com a elevação da temperatura de tratamento térmico e adição de PVB. As medidas de fotocorrente foram realizadas no escuro e sob iluminação de lâmpada de Xe com 250W (simulador de luz solar de 1,5AM). A maior fotocorrente medida foi de 12 μA a 0,5V. A produção de H2 aumentou linearmente com o tempo de exposição para ambas as amostras com PVB. Foi possível relacionar a adição do PVB com o favorecimento da fotoatividade dos filmes de TiO2. / This work has investigated the effect of polyvinyl butyral addition in the synthesis of TiO2 films by sol-gel and dip-coating, their microstructural features and their photoelectrochemical activity for water-splitting hydrogen production. The precursors and reagents used were: titanium propoxide, acetic acid, anhydrous ethanol, acetylacetone, Triton X-100 and polyvinyl butyral (PVB). Two precursor solutions were prepared: one with PVB and another without it. The dip-coating technique was used to produce films with 1, 2 and 3 layers. The films were heat treated at 400, 500 and 600ºC, at a rate of 100°C/h and dwelling time of 2h. Afterwards the synthesized films were characterized by X-ray diffraction (XRD); scanning electron microscopy (SEM), nitrogen adsorption (BET method), thermogravimetric (TGA) and differential thermal analysis (DTA), spectroscopic ellipsometry, optical profilometry, Raman and diffuse reflectance spectroscopy (determination of the band gap). The films after heat treatment showed a very irregular microstructure with many cracks. The anatase phase was presented in all temperatures and a small content of rutile at 600 °C (around 3.7%) was identified. The band gap of the films increased with the number of layers, heat treatment and addition of PVB. The photocurrent measurements were carried out in the dark and under illumination with 250W Xe, using a sunlight simulator (1,5AM). The highest photocurrent was 12A at 0.5V. The H2 production increased linearly with time of exposure for both samples with PVB. Therefore, it was possible to relate the addition of PVB with improvement the photoactivity of TiO2 films.

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