Effects of Vulcanization Mode on the Mechanical Fatigue of Vulcanized Rubber

Changes in the Network Structure of Vulcanizates during Tensile Deformation

“…It was found that the shortest field sweep width was 7.5 mT, with a sweep time of approximately 20 sec, and that a minimum of two integrations was required, which meant that the time required for measurements at any given strain was about 40 sec. Considering the possible lifetime of the radicals, it would be impossible to ignore changes in radical concentration over this time [5]. However, the problem is unavoidable in field sweep measurements, and in the absence of a suitable remedy, the radical concentration was left uncorrected.…”

“…The network structure is in this case chiefly constituted by carbon-carbon bonds, carbon-sulphur bonds and sulphur-sulphur bonds. Given that the bond of lowest bond energy amongst these is the sulphur-sulphur bond and that the sulphur radicals do include a species with a g factor of 2.004, the absorption in Figure 4 is attributable to polyenyl and sulphur radicals [5]. The concentration of the radicals increased with increase in stretching deformation.…”

“…In contrast with the spectra shown in Figures 3 and 4, the absorption is made up of three components with g factors of 2.014, 2.004 and 1.978. Several species of radical with different values of g are evolved in sulphur crosslinked material, depending on the vulcanisation promoter used [5]. Although efforts are being made to identify the radical species by spectral resolution, no conclusion has yet been reached and the radicals still elude quantitative analysis.…”

“…The longevity of the radical species evolved by chemical bond scission is dictated by various factors. However, the radicals evolved in rubber at room temperature are generally short-lived [5], and the ESR measurements in the studies cited above were made with the specimen cooled to around -100°C directly after stretching at room temp erature to extend the radical lifetime. Although to some extent the radicals evolved are amenable to quantitative analysis in the frozen state, it is then impossible to quantify their behaviour immediately they are formed, especially the behaviour during stretching deformation.…”

Influence of Silica on Vulcanization by Sulphur/Cbs in Isoprene Rubber

“…As the ESR spectra recorded absorption for which the g-factor is 2.004, the radical species involved in absorption should be sulphur radicals [15]. The calculated radical concentration included a correction for the total amount of S and CBS per unit volume exclusive of filler.…”