Orientador: Elidiane Cipriano Rangel / Banca: Aldo Eloizo Job / Banca: Sandra Andrea Cruz / Resumo: Os elastômeros termoplásticos (TPE) têm sido bastante empregados em substituição às borrachas tradicionais, por terem custo reduzido de matéria prima, facilidade no processamento e serem recicláveis. Apresentam propriedades mecânicas semelhantes, porém quando utilizados em componentes de vedação apresentam limitada resistência à corrosão em água clorada. Assim, o desenvolvimento de tratamento superficial que não modifique as características originais, mas tornem o material mais resistente são desejáveis. Para tanto, este trabalho pretende desenvolver uma metodologia a plasma para melhorar esse quesito. O elastômero termoplástico de copoliéster (COPE) foi escolhido por ser o mais empregado em componentes de vedação. O tratamento a plasma de baixa pressão com hexafluoreto de enxofre (SF6) foi empregado visando tornar a superfície do COPE hidrofóbica através da incorporação de grupos fluorados. A implantação iônica por imersão em plasmas (IIIP) de argônio foi utilizada para criar uma camada superficial mais coesa e entrelaçada, além da possibilidade de torná-la hidrofóbica após envelhecimento. Para o tratamento com SF6, os parâmetros de excitação do plasma (12 Pa e 80 W) foram mantidos, variando-se o tempo do tratamento entre 2 e 180 minutos de modo a encontrar uma condição ótima para esse processo. Para a IIIP de Ar os parâmetros de excitação do plasma (5 Pa e 60 min) foram mantidos e a potência da radiofrequência foi variada entre 10 e 150 W. A energia de superfície e ângulo d... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Thermoplastic elastomers have been widely used in substitution for conventional rubber, given that the feedstock is cheaper, easier to process and recyclable. Its mechanical properties are similar, but when applied to sealing components its resistance is limited due to the chlorine present in water, therefore, it is interesting to develop a surface treatment that do not alter the original characteristics, but make the material more robust. To achieve such result, we chose to submit the copolyester thermoplastic elastomer (COPE) to plasma. This material was naturally chosen, once it is widely used for sealing purposes in this specific industry. By using low pressure plasma with sulfur hexafluoride, we expect to alter COPEs surface by incorporating fluorine groups, thus making it hydrophobic. We also submitted the sample to a second treatment, by submersion to argon plasma, making the outer layer less defective and more entangled with aging, as observed in previous experiments. For SF6 treatment, the exiting plasma parameters (12Pa and 80W) were kept and the treatment time was varied between 2 to 180 minutes in order to find the optimal treatment time. For Argon IIIP, the plasma exciting parameters (5Pa and 60 min) were maintained, while the radio frequency variation was between 10 to 150W. Surface energy and contact angle were obtained by and automatic goniometer, through the sessile drop method ... (Complete abstract click electronic access below) / Mestre

Neste trabalho foi desenvolvido um estudo com o poliéster biodegradável P[3HB] (poli[R-3-hidroxibutirato]) e seu copolímero P[3HB-co-3HV] (poli[R-3-hidroxibutirato-co-3- hidroxivalerato]). Esses materiais são conhecidos por seu grande potencial de biodegradabilidade, porém sua utilização pela indústria ainda é limitada em função de seu baixo desempenho mecânico. Visando a tenacificação desses materiais, optou-se por misturá-los com os elastômeros EPDM (terpolímero de etileno-propileno-dieno) e PVB (Poli(vinil butiral)). Foram estudados quatro grupos de blendas: P[3HB]/EPDM e P[3HB-co- 3HV]/EPDM processados em misturadores internos e posteriormente prensadas em filmes; P[3HB]/EPDM e P[3HB]/PVB extrudados e posteriormente injetados. As blendas foram obtidas nas concentrações de 10, 20 e 30% em peso de elastômeros. Inicialmente, estudou-se efeito da incorporação de elastômeros na cristalinidade, estrutura cristalina, propriedades térmicas e dinâmico-mecânicas das matrizes, e o efeito do tipo de processamento utilizado. Observou-se que a adição dos elastômeros às matrizes semicristalinas aumentou a nucleação de esferulitos, resultando em um aumento da cristalinidade das mesmas. O PVB apresentou um efeito plastificante na estrutura do PHB. Os filmes apresentaram uma degradação térmica maior que as amostras injetadas, resultando em uma cristalização mais lenta e um grau de cristalinidade maior. Em um outro estudo, avaliou-se a morfologia, tensão interfacial, comportamento reológico, propriedades mecânicas e a biodegradabilidade das amostras estudadas. Foi observada uma morfologia de dispersão de gotas para todas as misturas, exceto para a mistura P[3HB]/EPDM obtida por injeção que apresentou um certo grau de co-continuidade. No caso das misturas injetadas foi visto que o fator que parece influenciar mais fortemente em sua morfologia final são as razões de viscosidade observadas entre a matriz e a fase dispersa das mesmas. A adição de elastômeros aumentou a resistência ao impacto do P[3HB], principalmente no caso da mistura P[3HB]/EPDM, o que pode estar relacionado à morfologia co-contínua observada nesta blenda. A incorporação dos elastômeros resultou em uma redução do módulo de elasticidade e da resistência à tração do P[3HB], e aumento do alongamento, principalmente no caso da mistura com PVB. Foi visto que a biodegradação do P[3HB] e P[3HB-co-3HV] aumentou com a adição de elastômeros, devido à morfologia de dispersão e a diminuição do tamanho dos esferulitos que aumentam a área interfacial para a ação das enzimas, facilitando a biodegradação. / In this work a study with the biodegradable polyester P[3HB] (poly[R-3- hydroxybutyrate]) and its copolymer P[3HB-co-3HV] (poly[R-3-hydroxybutyrate-co-3- hydroxyvalerate]) was conducted. These materials are known for their high biodegradability but their use is still limited because of their poor mechanical properties. In order to improve these properties it was chosen to blend these biodegradable polymers with EPDM (Ethylene propylene diene monomer) and PVB (Polyvinyl butyral). Four groups of blends were obtained: P[3HB]/EPDM and P[3HB-co-3HV]/EPDM blends were prepared using an internal mixer and then compressed molded; P[3HB]/PVB and P[3HB]/EPDM blends were prepared using an extruder and further injected. The blend concentrations ranged from 10 to 30 wt. % of the rubbery phase. Initially, the effect of rubber type on the crystallinity, the crystalline structure, thermal and dynamic-mechanical properties of the matrices and the effect of processing method to obtain the blends were investigated. The addition of elastomers on P[3HB] (and P[3HB-co- 3HV]) increases the nucleation, resulting in an increase of matrix crystallinity. PVB showed a plasticizing effect on the P[3HB] structure. Film samples showed a higher thermal degradation than injected ones, resulting in a slower crystallization and higher crystallinity. The morphology, interfacial tension, rheological behavior, mechanical properties (tensile and impact) and biodegradability of samples were also studied. A droplet dispersion morphology type was obtained for all the blends except for P[3HB]/EPDM injected samples which presented some extent of degree of continuity. The experimental results indicated that the final morphology observed for the blends was controlled by the viscosity ratio between the matrix and dispersed phase. Elastomer addition increased P[3HB] impact strength mainly for P[3HB]/EPDM blends, probably due to its co-continuous morphology. Moreover, elastomer incorporation resulted in a decrease of P[3HB] elastic moduli and tensile strength and increase of elongation of break, mainly for P[3HB]/PVB blends. It was observed that P[3HB] and P[3HB-co-3HV] biodegradation increased with elastomer addition due to the droplet dispersion morphology and decrease of spherulites size witch causes an increase of interfacial area for enzymes, facilitating biodegradation.

Ferroelectric ceramics are broadly used in applications including actuators, sensors and information storage. An understanding of the microstructual evolution and domain dynamics is vital for predicting the performance and reliability of such devices. The underlying mechanism responsible for ferroelectric constitutive response is ferroelectric domain wall motion, domain switching and the interactions of domain walls with other material defects. In this work, a combined theoretical and numerical modeling framework is developed to investigate the nucleation and growth of domains in a single crystal of ferroelectric material. The phase-field approach, applying the material electrical polarization as the order parameter, is used as the theoretical modeling framework to allow for a detailed accounting of the electromechanical processes. The finite element method is used for the numerical solution technique. In order to obtain a better understanding of the energetics of fracture within the phase-field setting, the J-integral is modified to include the energies associated with the order parameter. Also, the J- integral is applied to determine the crack-tip energy release rate for common sets of electromechanical crack-face boundary conditions. The calculations confirm that only true equilibrium states exhibit path-independence of J, and that domain structures near crack tips may be responsible for allowing positive energy release rate during purely electrical loading. The small deformation assumption is prevalent in the phase-field modeling approach, and is used in the previously described calculations. The analysis of large deformations will introduce the concept of Maxwell stresses, which are assumed to be higher order effects that can be neglected in the small deformation theory. However, in order to investigate the material response of soft dielectric elastomers undergoing large mechanical deformation and electric field, which are employed in electrically driven actuator devices, manipulators and energy harvesters, a finite deformation theory is incorporated in the phase-field model. To describe the material free energy, compressible Neo-Hookean and Gent models are used. The Jaumann rate of the polarization is used as the objective polarization rate to make the description of the dissipation frame indifferent. To illustrate the theory, electromechanical instabilities in composite materials with different inclusions will be studied using the finite element methods. / text

Therapeutic angiogenesis is a promising technique to treat ischemia by creating new blood vessels. The aim of this thesis was to develop and characterize biodegradable elastomers for localized delivery of growth factors and to investigate the ability of released growth factors to induce angiogenesis. An osmotic delivery mechanism using photo-cross-linked elastomers based on trimethylene carbonate (TMC) was used to deliver vascular endothelial growth factor (VEGF165) and hepatocyte growth factor (HGF) alone or in combination at two different doses. It was hypothesized that elastomers made of TMC can provide an effective osmotic release using trehalose as a main osmotigen and that the use of TMC would eliminate the microenvironmental pH drop implicated in denaturing acid sensitive growth factors. To obtain an insight into the degrading zone in which growth factors will be released, the in vivo degradation mechanism and tissue response were investigated. The in vivo degradation of D,L-lactide/ε-caprolactone (DLLACL) elastomers that degrade by hydrolysis was investigated for comparison. Cross-link-density played a significant role in the degradation pattern of DLLACL elastomers. TMC and TMCCL elastomers degraded by surface erosion and oxidation played a significant role in their in vivo degradation. To obtain an efficient release, the mechanical properties of TMC elastomers were tailored by copolymerizing TMC with CL and DLLA and/or by controlling the cross-link density. The delivery device was able to provide a sustained release of growth factors for longer than two weeks with no initial burst. Cell based bioactivity assays indicated that released growth factors were highly bioactive over the entire release period. Microenvironmental pH studies using FITC-BSA indicated no significant drop in pH in TMC elastomers that contained small amounts of DLLA. Using 125I-VEGF165, it was found that the osmotic delivery can provide a direct in vivo-in vitro release correlation. Released growth factors were able to induce angiogenesis in rats when tested by subcutaneous implantation. Angiogenesis was dose dependent for both VEGF165 and HGF. Combined release of VEGF and HGF achieved the best results. The formed blood vessels were stable during the active release period, and they were normal looking and connected to the surrounding vasculature. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2009-09-03 14:54:28.709

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Polypropylene (PP) composites includ a mineral filler, though they can be enhanced by blending with an elastomer. Blending rigid fillers with PP increased strength while decreasing toughness. Blending soft elastomers with PP decreased strength while increasing toughness. PP-elastomer-filler ternary composites offer synergism because the increase of strength due to filler may compensate the loss of strength due to the elastomer. Two morphologies were identified, separated elastomer and filler particles in PP, and filler particles encapsulated by elastomer in PP. Interaction between filler and PP matrix are proposed to increase with the addition of polar elastomers when encapsulated morphology is formed, leading to enhanced mechanical properties. PP-elastomer-filler blended tapes were prepared via single-screw extrusion. Annealing was performed after cooling the tapes, and this combination proved to increase the modulus. Characterization of the composites was carri ed out using thermogravimetry, dynamic-force thermomechanometry, modulated-force thermomechanometry, and Fourier transform infrared imaging. Incorporation of polysiloxane elastomer increased the mobility of PP during extrusion. Elongation at break increased with increasing polysiloxane content, while the tensile modulus was slightly decreased. The silica core within the polysiloxane particles provided an additional strength enhancement. Polar elastomers aided binding between PP and fillers, while enhancing strength and toughness. Glass transition temperature and segmental motion activation energy was shifted to higher temperature with addition of elastomer and filler, including kaolin and talc.

Thesis (M.S.)--University of Nevada, Reno, 2005. / "December, 2005." Includes bibliographical references (leaves 41-42). Online version available on the World Wide Web.

Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: Michael A. Brook. Includes bibliographical references. Also available online.

Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2006. / McDowell, David, Committee Member ; Gokhale, Arun, Committee Member ; Saxena, Ashok, Committee Chair ; Johnson, Steven, Committee Member ; Sanders, Thomas, Committee Member.