Mainz, University, Diss., 2005.

Mainz, Universiẗat, Diss., 2000.

This thesis explores the use of amine-functionalized silicone oils with various aliphatic and aromatic aldehydes as a novel method of crosslinking functional silicone materials via imines and the application of the resulting materials. These reactions overcome many of the drawbacks of traditional methods for crosslinking silicones and produces materials with novel properties that can enable their use in different applications. Furthermore, the differences in reactivity between the two types of aldehydes lead to two unique crosslinking motifs. Aromatic aldehydes produce conjugated Schiff-base crosslinks, while the crosslinking with aliphatic aldehydes undergoes various condensation reactions to give novel silicone materials. The use of small aliphatic aldehydes such as formaldehyde, glutaraldehyde, and glyoxal was found to rapidly crosslink aminopropylsilicones into elastomeric materials. The high reactivity of the aldehyde towards the amine-moieties also allows for robust crosslinking into elastomers that can occur even in the presence of water, a remarkable feature for silicones that are normally water insoluble. These properties allowed for the application of the material as an ink for 3-D printing, where the rapid crosslinking allowed for the study of a novel free-space droplet merging printing method. Silicone materials crosslinked with aromatic aldehydes produce conjugated Schiff-base bonds. These crosslinks can undergo dynamic exchange reactions in the presence of an amine catalyst to alter bonding in the material. These reactions gave the silicone chemoplastic and thermoplastic properties, allowing the material to be remoulded and reprocessed. Naturally-derived aromatic aldehydes can also be used as the crosslinker, allowing for a multi-faceted approach to increasing the sustainability of silicone materials by increasing their utility, making them reprocessable, thus extending their lifespan while using sustainable materials as a filler. / Thesis / Doctor of Science (PhD)

Silicones are useful in a variety of applications due to their diverse properties. The materials gain additional value when the basic constituents, oils and elastomers, are combined to create silicone gels. These materials possess excellent tunable properties such as moldability, tack, and adhesion, which are useful in certain circumstances. Only linear oils are currently used to make commercial silicone gels. While the materials initially possess desirable properties, over time the linear silicone oil can bleed out, and naturally, this is problematic for a variety of reasons. Among other things, the physical properties of the gel change and the oil that leaches out can be problematic. We test in this thesis the hypothesis that the use of branched silicone oils, as opposed to linear materials, in a gel could lead to lower levels of bleed (or slower release). There is currently very little research in the literature on the effect of adding branches to linear silicone polymers. This thesis explores the synthesis of branched structures (dendrons) synthesized using the Piers Rubinsztajn reaction. These compounds were subsequently grafted onto linear SiH bearing silicone polymers at different frequencies through a hydrosilylation reaction. The branched silicones were characterized by NMR and the viscosity of the various oils was measured; the latter property correlated with the frequency of branching. The viscosity increased in a linear fashion until a maximum viscosity was observed, at which point further branching led to a slight decrease in viscosity; this trend was observed with silicone backbones at three molecular weights. The branched silicone oils, capped with vinylpentamethyldisiloxane to remove remaining SiH sites, were then incorporated into gels. The Young’s modulus was measured and bleed measurements were collected twice over a ten-day period. Both measurements demonstrated that branching silicone polymers influenced the properties relative to linear silicone oils of comparable molecular weight. We discuss the possible origins of these differences. / Thesis / Master of Science (MSc)

No description available.

A busca por qualidade de vida apresenta diversas interpretações e se torna mais acirrada quando se é portador de alguma deficiência e/ou doença que cause alguma limitação. Para isso, as pessoas dispõem de próteses e órteses, produtos mundialmente difundidos, que abrangem as mais diversas áreas da saúde, como cardiologia, ortopedia, pneumologia, entre outras. Tratam-se de biomaterias, cuja utilização visa um reparo ou uma reconstrução. Com isso, os materiais para implantes, especificamente os stents, têm atraído grande interesse em vista das vantagens conferidas aos pacientes, principalmente, qualidade de vida. No entanto, os stents de silicone utilizados em vias aéreas ainda apresentam algumas deficiências e desvantagens a serem sanadas, como paredes espessas devido as baixas propriedades mecânicas, restringindo sua utilização, inclusive quanto ao tipo de broncoscopia utilizada. Sendo assim, o objetivo deste trabalho foi o estudo da adição de fibras ao elastômero de silicone, com intuito de conferir reforço ao mesmo, melhorando suas propriedades para uso em stents para vias aéreas. Para isso, foram utilizadas fibras de polietileno, poliamida e carbono. As fibras de carbono conferiram a melhor resposta às caracterizações mecânicas realizadas. Sendo assim, o silicone com adição de fibra de carbono foi submetido a estudos de biocompatibilidade, confecção de stents e testes in vivo. Foram feitas avaliações mecânicas e simulação por elementos finitos, onde foi verificada melhora nas propriedades devido a adição de fibras de carbono. Na avaliação in vivo realizada em ovelhas, o resultado foi equivalente ao stent tubular nacional da Medicone. Por fim, foi possível confeccionar stent de silicone reforçado com fibras de carbono para aplicação em vias aéreas, com redução da espessura da parede de 20% em relação ao único stent tubular nacional. / The search for quality of life has several interpretations, and becomes more fierce when one is carrying some deficiency and/or disease that causes some limitation. For this, people have orthesis and prothesis, products worldwide that cover the most diverse areas of health, such as: cardiology, orthopedics and pneumology, among others. These are biomaterials, the use of which is for repair or reconstruction. With this, implant materials, specifically stents, have attracted great interest in view of the advantages conferred to patients, mainly quality of life. However, silicone stents still present some deficiencies and disadvantages to clear up, such as thick walls due to low mechanical properties, restricting their use, including the type of bronchoscopy used. Therefore, the objective of this work was the study of the addition of fibers to silicone elastomer, in order to reinforce the same, improving its properties for use in airway stents. For this, polyethylene, polyamide and carbon fibers were used. The carbon fibers gave the best response to the mechanical characterizations performed. And so, the silicone with addition of carbon fiber has been subjected to studies of biocompatibility and stent manufacture. In the latter, mechanical evaluations were carried out, finite element simulation, where improvement in properties was verified due to the addition of carbon fiber. As was done in vivo evaluation in sheep whose result was equivalent to the national tubular stent of Medicone. Finally, it was possible to make a carbon fiber reinforced silicone stent for application in the airways, with a 20% wall thickness reduction in relation to the only national tubular stent.

This work is a contribution to the study of the curing of silicone prepolymers (hydroxyfunctional polydimethyl siloxanes) and the physical properties of the resulting networks. The kinetics of curing of one of the prepolymers has been studied with a simple new inexpensive piece of equipment i.e the Vibrating Needle Curemet~r (VNC). The order of reaction with respect to crosslinker and catalyst concentration has been determined to be unity and 0.24 respectively while an attempt has been made to determine the order of reaction with respect to silanol group concentration in the prepolymer. The effect of. crosslinker and catalyst concentration was observed to check the validity of the Lake and Thomas theory; namely that tear strength at a particular condition is proportional to the square root of the molecular weight between crosslinks. It has been found that varying crosslinker concentration is a better way to test this theory. Surprisingly the detailed physical properties such as tear and tensile of the supposedly different prepolymer networks showed little relationship to the molecular weight. The effect' of blending short and long chain polymers i.e bimodality, and that of the concentration of the crosslinker on the physical propert; es has been investigated. It became apparent that in addition to bimodality, the physical properties are dependent upon the amount of cross1inker used for curing This is a factor which has not previously been reported. It has also been shown that unfortunately, contrary to expectation bimodality has adverse effects on the physical properties of the highly filled networks. In the case of the tensile properties, the stress strain curves were analysed in light of tne phenomenological Mooney - Rivlin (MRL) and Martin, Roath and Stiehler (MRS) equations. Apart from successfully applying these theories to stress-strain curves, the structure factors of networks have been' obtained. These theories have been used in parallel to check and compare the results of one technique with the other. However, in the case of the filled HOPDMS networks it is evident that only the MRS equation can successfully describe the stress-strain data. The stress-strain data for the various HOPDMS filled networks have been compared with one another in terms of Young's modulus from their practical point of view.

Since soil and water were the most accessible building materials, humans used the mixture of soil and water to fabricate mud bricks or adobe. Iran, Syria, and Iraq have numerous mud brick buildings, and Arg-e Bam, located in Iran, was one of the most famous earthen monuments in the world; it was destroyed in a massive earthquake in 2003. In this research adobe samples were fabricated and different consolidants were applied to the samples. To determine the most effective consolidant, the tests were performed on the treated adobe. The soil for this research was supplied from Godfrey, a site near Kingston, Ontario, Canada. The soil was mixed with kaolin to achieve a similar grain size distribution to that of soil found in Bam. This research used four specific consolidant materials: a 5% (w/v) solution of Paraloid B-72 in toluene; a 50% (v/v) solution of methyl trimethoxy silane (MTMOS) in ethanol; a 50% (v/v) solution of ethyl silicate (TEOS) in ethanol; and Conservare H, which is the commercial brand of ethyl silicate. The research also studied the effects of Paraloid B-72 on surfaces previously treated with methyl trimethoxy silane and ethyl silicate. The chemicals were applied to the samples by brushing. After treatment, different physical properties were measured. The tests included study of density, porosity, water absorption, depth of penetration, abrasion resistance, hardness, compressive strength, bending strength and colour changes. Chemical analysis (X-ray diffraction) was used to study the chemical components of the soil and scanning electron microscopy showed changes to the treated surfaces after application of the chemicals. This research can be used as a guide in choosing the consolidants in adobe consolidation depending on the priorities defined in each building conservation project. Also, by applying all the same tests to samples made from the actual soil from Bam, this research can be used to evaluate how grain size distribution can affect the physical properties of the consolidated samples. By considering only the grain size of the soil used for adobe fabrication, the results from this research produced the following conclusion of consolidation of adobe from Bam; if the colour change is important, then the recommended consolidant is MTMOS or TEOS; if the colour change is not important, then the recommended consolidant is Paraloid B-72. The comparison among all the consolidants and their results, except results from failure strength, leads to the conclusion that the best consolidant is TEOS followed by a second coat of Paraloid B-72. / Thesis (Master, Art Conservation) -- Queen's University, 2008-09-26 12:01:30.22

Thesis (M.S.)--University of Michigan, Ann Arbor, 1966. / Typescript (photocopy). Includes bibliographical references (leave 55). Also issued in print.

Thesis (M.S.)--University of Michigan, Ann Arbor, 1966. / Typescript (photocopy). eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leave 55).