<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors></contributors><titles><title><style face="normal" font="default" size="100%">The viscoelastic properties of cork</style></title><secondary-title><style face="normal" font="default" size="100%">Journal of materials science</style></secondary-title></titles><dates><year><style  face="normal" font="default" size="100%">2002</style></year></dates><volume><style face="normal" font="default" size="100%">37</style></volume><pages><style face="normal" font="default" size="100%">257-263</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The viscoelastic properties of cork (from Quercus suber) have been investigated in the temperature range −40 to 120 ◦ C using the technique of Dynamic Mechanical Analysis (DMA). The results were compared with dielectric data previously reported. A relaxation was detected with a maximum in tan δ at ca 20 ◦ C (f = 1 Hz) and with a mean activation energy of 140 kJ ·mol−1 . A decrease in the intensity of the relaxation and an increase of the storage modulus is observed when cork is previously subjected to an annealing process above 60 ◦ C. This result is in agreement with previously reported dielectric data. Thermogravimetric experiments seem to conﬁrm that such effect could be caused by the desorption of water molecules. Specimens oriented along the prismatic direction presented higher storage modulus than the ones oriented along the transverse prismatic direction. The rheological properties of cork also showed a dependence upon the mechanical mode used during measurements: for example, the stiffness is the highest for the tensile mode and the lowest for the compression mode.</style></abstract></record><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors></contributors><titles><title><style face="normal" font="default" size="100%">The molecular relaxation mechanisms in cork as studied by thermally stimulated discharge currents</style></title><secondary-title><style face="normal" font="default" size="100%">Journal of Materials Science</style></secondary-title></titles><dates><year><style  face="normal" font="default" size="100%">1995</style></year></dates><volume><style face="normal" font="default" size="100%">30</style></volume><pages><style face="normal" font="default" size="100%">2035-2041</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">The dielectric relaxation mechanisms present in cork have been investigated in the temperature range -100 to 100~ using the technique of thermally stimulated discharge currents. A relaxation mechanism was detected which showed a compensation behaviour as observed for the a-relaxation (or glass transition relaxation) of synthetic polymers and which lead us to attribute to cork a glass transition-like temperature of 18~ 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.</style></abstract></record></records></xml>