The molecular relaxation mechanisms in cork as studied by thermally stimulated discharge currents
- 67 Downloads
The dielectric relaxation mechanisms present in cork have been investigated in the temperature range -100 to 100 °C using the technique of thermally stimulated discharge currents. A relaxation mechanism was detected which showed a compensation behaviour as observed for the α-relaxation (or glass transition relaxation) of synthetic polymers and which lead us to attribute to cork a glass transition-like temperature of 18 °C. One lower temperature mechanism was also observed, with low activation enthalpy and entropy, which is presumably originated by local motions (internal rotations) of polar molecular groups. An upper Tg relaxation of higher intensity was also detected which was attributed to large-scale non-cooperative motions of polymeric segments.
KeywordsEntropy Enthalpy Glass Transition Internal Rotation Synthetic Polymer
Unable to display preview. Download preview PDF.
- 1.J. V. NATIVIDADE, “Subericultura” (Ministério da Economia, Direcção dos Serviços Florestais e Agrícolas, Lisboa, 1950).Google Scholar
- 4.H. PEREIRA, M. E. ROSA and M. A. FORTES, Int. Assoc. Wood Anat. Bull. 8(3) (1987) 213.Google Scholar
- 9.I. M. VEIGA, A. C. FERNANDES, B. S. ALMEIDA and A. J. GROSZEK, J. Mater. Sci. Lett. 12 (1993) 1206.Google Scholar
- 14.L. J. GIBSON and M. F. ASHBY, “Cellular Solids. Structure and Properties” (Pergamon Press, Oxford, 1988).Google Scholar
- 16.J. F. MANO, J. J. MOURA RAMOS, A. C. FERNANDES and G. WILLIAMS, Polymer 35 (1994) 5171.Google Scholar
- 17.J. F. MANO, N. T. CORREIA, J. J. MOURA RAMOS, A. C. FERNANDES, J. Polym. Sci. Polym. Phys. Ed., in press.Google Scholar
- 22.R. F. BOYER, in “Computational Modelling of Polymers”, edited by J. BICERANO (Marcel Dekker, New York, 1992) pp. 1–52.Google Scholar
- 24.N. T. CORREIA, J. F. MANO and J. J. MOURA RAMOS, manuscript in preparation.Google Scholar