Comparisons of Sulfur, Selenium, and Tellurium Cure Systems in Natural Rubber
The original discovery of vulcanization centered on the use of sulfur, an element which can react with double bonds of polyisoprene and other kinds of unsaturated polymers to create molecular crosslinks. However, two other elements in the same column of the periodic table are selenium and tellurium, and as might be expected, both of them can also produce crosslinks in these polymers. There is relatively little use of the pure elements or their derivatives in accelerators and curatives due to their expense, but it has been claimed that their use provides more stable crosslinks, and thus provides some improved properties in the final vulcanizate.
However, little data can be found to definitively confirm this, and it was decided to run a designed experiment to carefully compare various ways of using all three elemental materials and their variations in curatives and accelerators to determine what contrasts might actually exist in final properties due to the creation of non-sulfur crosslinks.
The design type chosen was a Hyper-Graeco-Latin Square in which combinations of all three elements and four types of sulfur based curatives/accelerators plus two types of selenium and two types of tellurium based curatives/accelerators were employed in various combinations. Standard processing tests, basic physical properties, compression set and aging tests were all applied to generate data for comparison.