Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 41, 81, 130, 183, 270, 315, 336).

Sur la base de précédents travaux de l’unité INSERM 1148, sur des films à base d’alcool polyvinylique, nous avons implanté et évalué des prothèses de moins de 2mm de diamètre. L’ajout de gelatine in vitro a montré des capacités d’adhérence cellulaires, compatibles avec une endothelialisation in situ, des implants garant, d’une perméabilité à long terme. Notre modèle était le remplacement de 1cm d’aorte sous rénale de rat. Ces implants, ont été utilisées comme modèle d’entrainement basse fidélité à la microchirurgie, avec de meilleurs résultats sur l’acquisition de la technique d’anastomose microchirurgicale, que les tubes en silicone antérieurement utilisé, lors de l’enseignement chez 71 étudiants. Un nouveau moyen d’imagerie pour l’exploration vasculaire par angiographie par résonance magnétique, en temps de vol sans injection chez l’animal, et la première application chez l’homme sont rapportés. Apres avoir présenté notre methode de fabrication par reticulation physique (Lyophilisation Congelation) et chimique (STMP) Cdu PVA, directement sous forme de tubes, nous avons confirmé l’hypothèse que les micro implants à base de PVA associé à la gélatine à hauteur de 1%, a permis d’améliorer la perméabilité par rapport au PVA seul, ou à tout autre ratio de gélatine ; et ce grâce à une endothélisation in situ constatées histologiquement. Les performances biomécaniques de l’implant ont aussi étaient évaluées. Au delà de 2 mois la perméabilité chute de 75% à 50%. Le vieillissement du matériel par son enraidissement, et le relargage de la gélatine pourrait expliquer cette diminution des performances au cours du temps. / Non communiqué

<p> An experimental study of the steric stabilizing ability of a water soluble polyvinyl alcohol (PVA) polymer is presented.</p> <p> The free film thickness of a lamella formed between a drop of n-butylchloride and bulk n-butylchloride stabilized by PVA was measured by the Hodgson and Woods technique in order to evaluate the stabilizing ability of the polymer. A maximum in the stability was observed as the concentration of the polymer was increased. This maximum trend can be explained by the HVO theory.</p> / Thesis / Master of Engineering (MEngr)

Metal-organic framework (MOF) materials are a novel set of porous crystalline materials that have generated great scientific interest within the past two decades due to their attractive properties such as high porosity, surface areas and tunable pore structure. These properties have made them emerge as potential candidates suitable for a broad range of applications such as gas separations and storage, catalysis and drug delivery. Despite their fascinating properties, MOFs are often unsuitable for most industrial applications due to their instability when exposed to mechanical stress. The challenge therefore is to convert the MOFs to high strength materials capable of withstanding such stress while still maintaining their exciting properties. This thesis thus focuses on investigating the effects of different binders on a zirconium based metal-organic-framework, UiO-66, in an attempt to enhance the mechanical strength of the adsorbent samples. Three different binders, kaolinite, polyvinyl alcohol and tartaric acid, are mixed with the parent MOF material in different weight percents, pressed into solid disc pellets at different pressures and calcined at different temperatures. Properties such as changes in structure, density, porosity, surface area, radial crush strength, and the adsorption capacity with CO2 are measured and evaluated. Results gathered from this work reveal that polyvinyl alcohol is the most promising of the three binders due to the increase in the strength of pellets and the slight decrease in CO2 adsorption it offers. Recommendations for future research work aimed at driving these materials towards reaching their maximum application potentials are proposed.

A co-polymer made from Polyvinyl Alcohol and Polyacrylic Acid (PVA-PAA) has been synthesized to form new robotic actuation systems which use the contractile and variable compliance properties of this material. The stimulation of these fibres is studied (particularly chemical activation using acetone and water), as are the factors which influence the response, especially those relating to its performance as an artificial muscle. Mathematical models and simulations of the dynamics of the polymeric strips have been developed, permitting a thorough analysis of the performance determining parameters. Using these models a control strategy has been designed and implemented, with experimental results being obtained for a gripper powered by a flexor/extensor pair formed using these polymeric actuators. An investigation of a second property of the polymer, its variable compliance is alsoincluded. Use of this feature has lead to the design, construction and testing of a multi degree-of-freedom dextrous hand, which despite having only a single actuator, can exercise independent control over each joint.

No description available.

Thesis (M.Eng.). / Written for the Dept. of Biomedical Engineering. Title from title page of PDF (viewed 2008/07/29). Includes bibliographical references.

Orientador: Alcides Lopes Leão / Banca: Elisabete Frollini / Banca: Pedro de Magalhães Padilha / Resumo: O momento atual de maior preocupação ambiental global, a crescente escassez dos recursos fósseis, bem como as novas regulagens ambientais força a busca por materiais que sejam renováveis e compatíveis com o ambiente. Novos materiais estão sendo desenvolvidos a partir de várias fontes naturais e, entre eles a celulose é o mais abundante dos polímeros naturais e um dos mais utilizados. Logo, o objetivo desta dissertação de mestrado foi obter nanofibras de celulose tendo como fonte a fibra vegetal de curauá. Os processos utilizados foram químicos e mecânicos, baseados nos processos de polpação e branqueamento, a fim de isolar a celulose, seguido de processos mecânicos para atingir a escala nanométrica. As nanofibras de celulose propiciam vantagens como melhoria nas propriedades mecânicas e de barreira, além de manter a transparência de polímeros em geral. A fim de comprovar a capacidade de reforço em matrizes poliméricas, as nanofibras de celulose obtidas foram incorporadas nas mesmas. No entanto, para evitar a tendência de aglomeração das nanofibras, principalmente quando retiradas do meio aquoso, o álcool polivinílico (pva) foi escolhido como a matriz polimérica a ser testada, devido à sua compatibilidade com nanofibras de celulose, por ambos serem de natureza hidrofílica, o que aumenta a compatibilidade interfacial de fases entre a nanocelulose e a matriz escolhida. Após a incorporação das nanofibras na matriz polimérica ocorreram significativas melhoras nas propriedades mecânicas da matriz. Ao incorporar 4% de nanofibras da celulose de curauá obteve-se um ganho de 36% e 67% para a tração e para o módulo de young, respectivamente. Com 5% de nanofibras, o aumento nas propriedades foram ainda mais significativos em torno de 44% para a tração máxima e 448% para o módulo de young / Abstract: Nowadays is a era of greatest environmental concern, with growing scarcity of fossil resources, as well as new environmental regulations obligating the search for materials that are renewable and environmentally friendly. New materials are being developed from various natural sources, and among them, cellulose is the most abundant natural polymers and the one most used. Therefore, the purpose of this thesis was to obtain cellulose nanofibers fibers from curaua plant. The procedures used were based on chemical and mechanical treatment. Pulping and bleaching, in this sequence were done in order to isolate the cellulose, followed by mechanical processes to achieve the nanometer scale. The cellulose nanofibers provide advantages such as improvement of mechanical properties and barrier, besides maintaining transparency of polymers in general. To prove the capacity of reinforcement in polymer matrices, the cellulose nanofibers obtained were incorporated into them. However, to avoid the tendency of nanofibers agglomeration when removed from water, the polyvinyl alcohol (PVA) was chosen as the polymer matrix to be tested, for the reasons that both are hydrophilic in nature and compatible to cellulose nanofibers, which increases the interface between the matrix and the nanocelulose chosen. After the incorporation of nanofibers in the polymer matrix, a significant improvement were observed in its mechanical properties by incorporating 4% of cellulose nanofiber curauá which provided a gain of 36% and 67% for tension and Young's modulus, respectively. With 5% of nanofibers, the increase in properties was even more significant at around 44% for maximum tension and 448% for Young's modulus / Mestre

Made available in DSpace on 2014-06-11T19:24:41Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-09-03Bitstream added on 2014-06-13T18:52:26Z : No. of bitstreams: 1 souza_sf_me_botfca.pdf: 1653750 bytes, checksum: 3aa87de3ba9ede42d6a64a6e7aef2e61 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O momento atual de maior preocupação ambiental global, a crescente escassez dos recursos fósseis, bem como as novas regulagens ambientais força a busca por materiais que sejam renováveis e compatíveis com o ambiente. Novos materiais estão sendo desenvolvidos a partir de várias fontes naturais e, entre eles a celulose é o mais abundante dos polímeros naturais e um dos mais utilizados. Logo, o objetivo desta dissertação de mestrado foi obter nanofibras de celulose tendo como fonte a fibra vegetal de curauá. Os processos utilizados foram químicos e mecânicos, baseados nos processos de polpação e branqueamento, a fim de isolar a celulose, seguido de processos mecânicos para atingir a escala nanométrica. As nanofibras de celulose propiciam vantagens como melhoria nas propriedades mecânicas e de barreira, além de manter a transparência de polímeros em geral. A fim de comprovar a capacidade de reforço em matrizes poliméricas, as nanofibras de celulose obtidas foram incorporadas nas mesmas. No entanto, para evitar a tendência de aglomeração das nanofibras, principalmente quando retiradas do meio aquoso, o álcool polivinílico (pva) foi escolhido como a matriz polimérica a ser testada, devido à sua compatibilidade com nanofibras de celulose, por ambos serem de natureza hidrofílica, o que aumenta a compatibilidade interfacial de fases entre a nanocelulose e a matriz escolhida. Após a incorporação das nanofibras na matriz polimérica ocorreram significativas melhoras nas propriedades mecânicas da matriz. Ao incorporar 4% de nanofibras da celulose de curauá obteve-se um ganho de 36% e 67% para a tração e para o módulo de young, respectivamente. Com 5% de nanofibras, o aumento nas propriedades foram ainda mais significativos em torno de 44% para a tração máxima e 448% para o módulo de young / Nowadays is a era of greatest environmental concern, with growing scarcity of fossil resources, as well as new environmental regulations obligating the search for materials that are renewable and environmentally friendly. New materials are being developed from various natural sources, and among them, cellulose is the most abundant natural polymers and the one most used. Therefore, the purpose of this thesis was to obtain cellulose nanofibers fibers from curaua plant. The procedures used were based on chemical and mechanical treatment. Pulping and bleaching, in this sequence were done in order to isolate the cellulose, followed by mechanical processes to achieve the nanometer scale. The cellulose nanofibers provide advantages such as improvement of mechanical properties and barrier, besides maintaining transparency of polymers in general. To prove the capacity of reinforcement in polymer matrices, the cellulose nanofibers obtained were incorporated into them. However, to avoid the tendency of nanofibers agglomeration when removed from water, the polyvinyl alcohol (PVA) was chosen as the polymer matrix to be tested, for the reasons that both are hydrophilic in nature and compatible to cellulose nanofibers, which increases the interface between the matrix and the nanocelulose chosen. After the incorporation of nanofibers in the polymer matrix, a significant improvement were observed in its mechanical properties by incorporating 4% of cellulose nanofiber curauá which provided a gain of 36% and 67% for tension and Young's modulus, respectively. With 5% of nanofibers, the increase in properties was even more significant at around 44% for maximum tension and 448% for Young's modulus

This diploma thesis studies short fiber reinforced composites for dental applications. Barium particulate filler, nanosilica and short glass and polyvinylalcohol fibers were added to the matrix consisting of four dimethacrylate types of monomers. The effect on material properties was observed. For characterization of different types of composite materials following methods were used: thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), three point bending test for notched and un-notched samples and scanning electron microscopy (SEM). Viscoelastic properties, modulus of elasticity and strength, critical values of stress intensity factor and strain energy release rate and polymerization shrinkage of composite materials were determined. It is possible to improve these properties of composite materials by adding short fibres to particulate reinforced composite. To make this modification more efficient, it is necessary to change surface treatment of fibres and preparation method of short fiber reinforced composites. Viscosity of material has raised after adding short fibers and processing of these types of dental material in dental laboratory is considered difficult to provide.