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Doctoral Thesis
DOI
10.11606/T.76.2003.tde-09042008-093654
Document
Author
Full name
Elinton Luiz Leguenza
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2003
Supervisor
Committee
Giacometti, José Alberto (President)
Alfaro, Renê Armando Moreno
Berleze, Sérgio Luiz Meister
Bretas, Rosário Elida Suman
Ferreira, Guilherme Fontes Leal
Title in Portuguese
Comportamento dielétrico, viscoelástico e físico-químico do polietileno reticulado envelhecido sob condições aceleradas de múltiplo estresse
Keywords in Portuguese
Dielétrico
Envelhecimento
Espectroscopia e Polietileno
Abstract in Portuguese
Estudos do comportamento dielétrico, viscoelástico e fisico-químico, em função do tempo de envelhecimento, foram realizados no polietileno reticulado (XLPE). Neste trabalho, utilizaram-se amostras comerciais de cabos isolados, envelhecidas em condições definidas no laboratório e amostras envelhecidas em campo durante 25 anos. As amostras foram cortadas com aproximadamente 150 ?m de espessura, desde a camada mais externa até a camada mais interna do polietileno. A espectroscopia dielétrica foi realizada no intervalo de 10 ?Hz a 1 MHz e mostra a presença de picos de relaxação, obedecendo as formas assintóticas da função susceptibilidade de Dissado-Hill. Com o envelhecimento em laboratório a temperatura ambiente (RT) e campo, a região mais externa mostra processo de condução quase permanente, dominando com o envelhecimento. Por outro lado, com o envelhecimento em temperaturas superiores, observou-se um processo tipo perda plana ("flat-loss") de relaxação dipolar dominando em regiões mais internas. O comportamento viscoelástico foi investigado, através de análise dinâmico-mecânica, e indica que um envelhecimento de natureza eletroquímica gera diferentes processos como: quebra de cadeias, variações na cristalinidade e reticulação, com o envelhecimento. Além disso, estes resultados foram confrontados com outros resultados, obtidos através de técnicas adicionais, como: espectroscopia de infravermelho por transformada de Fourier, difratometria de raios-X, grau de reticulação, microscopias ópticas e de varredura eletrônica.
Title in English
Dielectric, Viscoelastic and physical-chemical behavior of cross-linked polyethylene aged under mult-stressing conditions
Keywords in English
Aging and polyethylene
Dielectric
Spectroscopy
Abstract in English
Dielectric, viscoelastic and physical-chemical studies have been performed in cross- Linked polyethylene (XLPE) as a function of the aging time. This work was carried out in insulation cables field aged for twenty five years and XLPE cables laboratory aged under multi-stressing conditions. The samples, field and laboratory aged, were peeled with approximately 150 ?m thickness, at the surface just below the outer layer just above the inner layer. The dielectric spectroscopy, carried out in the frequency range 1 ?Hz to 1 MHz, show the presence of relaxation peaks obeying the asymptotic foms of Dissado and Hill susceptibility functions. For the aged samples, obtained from the outer layer position, conduction near pemanent process with aging time was observed. On the other hand, at middle and inner layer positions, was observed a Flat-loss process, which becomes dominant with aging time. In addition, viscoelastic properties have also been investigated through dynamic mechanical analysis, suggesting that eletrochemical aging effects generates different processes involving: chains breakage, changes cristallinity and cross-linking with aging time. Furthermore, the previous results have been confronted with other results obtained with additional techniques such as: Fourier transform infrared spectroscopy, X-rays measurements, cross-link degree, optical and scanning electronic microscopies.
 
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ElintonLeguenza_D.pdf (6.77 Mbytes)
Publishing Date
2008-04-10
 
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