Adesivos sensíveis à pressão (PSA do inglês - Pressure Sensitive Adhesives) são produtos que aderem a superfícies imediatamente após a aplicação de pequenas pressões. Têm grandes vantagens sobre outros tipos de adesivos, principalmente por necessitarem apenas de uma aplicação inicial de pressão para apresentar o efeito permanente de adesão. Neste trabalho foram avaliadas três composições distintas de PSA, sendo uma delas considerada como referência, e duas condições diferentes de processamento, com o objetivo principal de obter um adesivo com alta resistência ao cisalhamento e boa aderência. Todas as amostras foram produzidas em laboratório utilizando um moinho de dois rolos e um misturador do tipo sigma. Essas composições foram baseadas em borrachas com insaturações, que permitem a formação de ligações cruzadas, tornando o adesivo mais resistente. As alterações impostas na composição (adição de óxido metálico e resinato) e a mudança na condição de processamento (nível de reação para formação de ligações cruzadas) levaram a diferentes propriedades dos adesivos obtidos; como valores de adesão, grau de ligação cruzada, resistência a cisalhamento e peso molecular. Os resultados encontrados neste trabalho mostram que a adição de 5pcr de óxido de zinco aumenta em até 64% a resistência ao cisalhamento em relação à amostra de referência, enquanto que 5 pcr de resinato de zinco causa um incremento de aproximadamente 21%. Também foi possível observar que o alto nível de reação (60 minutos) confere uma quantidade de ligações cruzadas pelo menos duas vezes maior que a obtido para o baixo nível de reação (30 minutos) / Pressure Sensitive Adhesives (PSA) are materials which bond to adherent surfaces at room temperature immediately as low pressure is applied. This kind of material has a number of advantages of adhesives bonding, especially because they need low pressure to effect permanent adhesion to an adherent. In this work three different PSA formulations were tested under two process condition. The final product obtained can be used over flexible web, as poly (vinyl chloride) tapes. Samples were prepared trough a two-roll mill and sigma mixer in a laboratory production scale. The composition was based on rubber material that has double molecular chain, which allows cross-linking, making the adhesive more resistant. Small changing on formulation (adding5phrofmetallic oxide or zinc resinate) and process condition (reaction level) took to different results as cross-link degree, adhesion properties, shear resistance and molecular weight. The results showed that adding small amount of metallic oxide can increase up to 64% of shear resistance and adding zinc resinate compound can increase about 21%. And also is possible to conclude that high reaction level (60 minutes) takes to at least double cross-linking degree compared with low reaction level (30 minutes)

The effect of antiplasticization on barrier properties of poly(ethylene terephthalate) (PET) has been investigated through transport measurements and some supplementary characterization techniques including dynamic mechanical measurements and solid state 13C cross polarization/magic angle spinning (CP/MAS) NMR. Our oxygen and carbon dioxide transport results were well described by a combination of the free volume based interpretation and interaction energy estimation. Transport characterization and DSC techniques verified that there exists a third element, a de-densified amorphous fraction in crystallized PET. Both oxygen and carbon dioxide permeabilities at 1 atm at 35ºC in PET with different crystallinities were well described by the Nielsen model due to the presence of an adjustable parameter, Ar, even though it is based on a two phase model. The comparison of the barrier improvement factor (BIF) values for samples annealed at 100ºC demonstrated that a combination of antiplasticization and crystallization allows for very efficient chain packing, which significantly improves the barrier properties of PET. A thorough molecular level study using dynamic mechanical analysis supported the synergistic effect of antiplasticization and crystallization on the molecular motion in PET. Lastly, a vapor/gas permeation system with a new concept of a flexible humidity and methanol vapor partial pressure clamp was designed and constructed. Even though its permeation results are not available at this point, its operational feasibility was well verified by pre-calculations and physical explanations. This system may be used for future studies to evaluate barrier properties of PET or modified PET samples.

A series of particulate reinforced natural rubber composites are prepared using both model (glass sphere) and commercial (carbon black and precipitated silica) reinforcing filler materials having a range of surface activities. Small strain reinforcement and viscoelastic behaviour of the model (glass sphere-filled) microcomposites are found to be well described by hydrodynamics and temperature-insensitive stiffening mechanisms such as strain amplification and elastomer occlusion. This means that the energy applied to the model materials during small strain deformations is entirely stored and dissipated within the elastomer phase. For carbon black-filled natural rubbers such mechanisms are no longer found to completely describe the levels of reinforcement and viscoelastic behaviour. This is the case particularly for high surface area carbon blacks of small aggregate size. For carbon blacks, additional mechanisms of reinforcement are identified and associated with the formation of a filler network and with effects at the polymer-filler interface. For all the compounds considered in this study, no direct experimental evidence is found for the formation of significant volumes of interphase polymer exhibiting retarded chain dynamics near the filler surface. The observation of a secondary dissipation process in rubbery region small strain dynamic mechanical and creep measurements of carbon black-natural rubber compounds where the polymer filler interaction is particularly poor (where the carbon black surface is graphitised) indicates that there may be a significant slippage of polymer chain segments at the filler-elastomer interface. There is some limited evidence from small strain creep testing to indicate that this process also occurs in commercial carbon black-filled compounds but to a much reduced extent. To the best of the author's knowledge this is the first time that such processes have been observed in carbon black filled elastomers.

This study aims to understand the behaviour of a novel elastomer where hollow microspheres are used as a particulate filler. The behaviour of elastomers filled with rigid particles, is fairly well understood, where the stiffness increases as the amount of filler material is increased, alternatively, foamed elastomers which are usually produced with either closed cells or open cells, have been shown to become softer as the volume of the voids are increased. When traditional foam materials are compressed they exhibit non-linear behaviour in three distinct phases, the cell walls firstly bend, then they buckle and this is followed by densification. To understand the overall physical behaviour of the material, tensile tests of the elastomer material were conducted using unfilled materials and filled with a range of the hollow sphere filler volume fractions. Compression tests were also conducted on small cylinders, again using unfilled and filled rubbers with a range of filler volume fractions. The physical tests showed that increasing the filler volume fraction increased the reinforcing effect at low strains with an associated increase in stiffness, but the material then became increasingly less stiff at higher strains. To understand the behaviour of the bulk material, the mechanical behaviour of single hollow spheres under strain were investigated, both as a standalone material and then also embedded in an elastomer. To examine the mechanical behaviour of a single hollow plastic sphere a single microsphere was compressed using nano-indentation, the tests were then replicated at a larger scale using model table tennis balls. FEA software was used to model the behaviour of both types of hollow sphere, as well as a wide range of other spheres to better understand their buckling behaviour, to help predict the behaviour of microspheres with different ratios of wall thickness to diameters. To examine the behaviour of hollow spheres in a rubber matrix, simple cylindrical unit cells were made with a single hollow plastic sphere embedded within them. These model cylinders were produced with a translucent elastomer containing a single table tennis ball. Their behaviour in compression and in tension and that of a single hollow plastic sphere embedded in an elastomer was also modelled using FEA software, the effects of debonding and buckling were determined for small and large strains and were used to examine the more complex behaviour of the filled composite. A comparison between the measured behaviour and the various models indicates that the bulk behaviour of the microsphere filled elastomers is primarily determined by a progressive dewetting process of the rubber away from the microsphere in tension and by buckling phenomena of the hollow spheres in compression.

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Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Richard P. Wool, Dept. of Chemical Engineering. Includes bibliographical references.

Thesis (Ph. D.)--Lehigh University, 2002. / Includes bibliographical references and vita.

Thesis (Ph. D.)--School of Textile and Fiber Engineering, Georgia Institute of Technology, 2004. Directed by Haskell Beckham. / Vita. Includes bibliographical references (leaves A1-A2).

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 225-228). Available also in a digital version from Dissertation Abstracts.

No description available.