Vulcanization: Conventional and Dynamic

Abstract

Abstract Conventional vulcanization, has a history of over 150 years, during which there have been increasing needs for technology to permit more and more rapid processing before the vulcanization of a rubber article in its final shape. But, at the same time, one desired increased rates of crosslinking after the part was in its final shape, e.g., in a mold. These two objectives are opposed to one another. For fast processing, we would like to increase temperatures to reduce the resistance to flow; but we do not want vulcanization to occur before processing flow is complete. On the other hand, after a rubber article is in its final shape or form, we would like for vulcanization to occur as rapidly as possible. The reasons for these objectives, are to increase capital utilization and to reduce the cost of money. The use of the premature vulcanization inhibitor, CTP, can give improved processing safety without loss of vulcanization throughput. In the case of thermoplastic elastomers prepared by dynamic vulcanization, all of the vulcanization is done rapidly during mixing, before the rubber compound flows into its final shape, e.g., during rapid thermoplastic injection molding (in seconds, not minutes). The dynamic vulcanization process does add cost to the material; however, this is more than offset by the gains in capital utilization. I would be remiss if I did not mention some potential disadvantages associated with the thermoplastic elastomers. One of these is that, at temperatures above the temperatures of flow, there is a great reduction in the usefulness of the properties (the materials can melt). A related disadvantage is that resistance to permanent set at high temperatures may be inadequate. However, the elevated-temperature set resistance of thermoplastic elastomers prepared by dynamic vulcanization is generally better than that of those prepared by other means. Both kinds of vulcanization are important and may continue to be so for another 150, or so, years.