HIGH-TEMPERATURE VULCANIZATION OF ELASTOMERS

Vulcanization is a process which decreases the plastic properties of rubber while maintaining or improving the elastic properties. The term vulcanization has been applied in the past mainly to the reaction of rubber with sulfur, but now is generally used for the process which results in changes in properties, by sulfur or some other agent. This paper is concerned with the vulcanizations taking plce between 160 degree C and 220 degree C. The range in practice extends up to about 250 degree C in fluid beds and salt baths. Practical vulcanization processes apply heat to the outside of the article being cured and rely on the conduction of heat to the inside. Since no drastic change can be made in the thermal conductivity of practical rubber compounds by compounding modifications, higher temperature is a common method of achieving faster vulcanization. Higher curing temperatures are used in the newer curing or molding processes such as injection molding, the liquid curing medium (LCM) process, and microwave curing. The discussion covers the following topics - (1) technical properties and vulcanizate structure; (2) polymer-filler interaction and high temperature vulcanization, (3) compounding requirements for high-temperature vulcanization; (4) kinetics at higher vulcanization temperature.