Sulfur crosslinking was discovered by Charles Goodyear and Thomas Hancock more than 150 years ago and led to the development of a new material science application—rubber.
Since the first discovery of ways of vulcanizing rubber for improved dimensional stability, mechanical properties and chemical resistance, sulfur continued to be analyzed to elucidate its role in the crosslinking process.
Although the discovery of sulfur crosslinking was in itself a game changer, it was determined that vulcanization was too slow for commercial purposes and, as such, methods to expedite the crosslinking reaction were studied. Zinc oxide in combination with stearic acid were discovered as the best ways for improved sulfur reactivity in the vulcanization process. Zinc ions combine with stearic acid and cyclic tetrasulfide (acting as a sulfur accelerator) to form an active complex which catalyzes the vulcanization process.
Because the mechanism of reaction is complex, analyzing the structure at the nano level could yield an insight into the process. This paper is focusing on transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX) for an in-depth analysis of the process, with an emphasis on ZnO crystallography/surface chemistry and its influence on sulfur crosslink process.