No description available.

No description available.

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)

No description available.

No description available.

The most practical treatment for reducing the noise of present diesel engines is to replace the thin-section, noise-radiating components with constrained damping layers, where a viscoelastic layer is sandwiched between two elastic layers to give the composite panel high damping characteristics. The damping ability of such panels is highly dependent on dynamic shear properties of viscoelastic materials as well as on the selection of elastic materials. The damping shear properties of viscoelastic materials are highly dependent on frequency and temperature. Experimental data on the damping properties of viscoelastic materials are, so far, limited to a small low frequency range. The forced vibration non-resonant technique is adopted in the present investigation. Atest rig has been designed, built and developed to measure the dynamic shear properties of some visoelastic materials over a wide range of temperature (40 to 1000C). These properties are also measured over a wide range of frequency (50-1500 Hz), covering part of the audio frequency range, in which the severity of engine noise occurs. Polysulphide rubber and ethylene propylene rubber have been tested. Their dynamic shear properties have been obtained, tabulated and plotted as functions of frequency and temperature. The effect of strain amplitude has been investigated and discussed. A new approach for an easy, fast and direct measurement of the loss shear modulus has been proposed. It has been found that both viscoelastic materials possess considerable damping, especially over the frequency range of 900-1500 Hz. The effect of strain amplitude was found negligible. The optimum design and damping ability of three layer composite panels have been investigated. The effects of elastic and viscoelastic material on the damping of these panels has been examined. Magnesium has been found to be a superior elastic material of those investigated. Aluminium is the next most suitable elastic material, with steel as the least suitable elastic material. Polysulphide rubber and ethylene propylene rubber have been found suitable for use in composite damping panels, but their relative attractiveness is strongly dependent on frequency and temperature.

Thesis (MAppSc)--University of South Australia, 1995

Thesis (MAppSc)--University of South Australia, 1997

Thesis (MAppSc)--University of South Australia, 1997

Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: James M. Dickson. Includes bibliographical references (leaves 393-400). Also available online.