The Theory of Permanent Set at Elevated Temperatures in Natural and Synthetic Rubber Vulcanizates

Abstract

Abstract Certain materials, including natural and synthetic rubbers, after being deformed for finite periods of time and then released, do not return completely to their original dimensions. This phenomenon is called “permanent set”. There are many different types of measurements, made under a great variety of conditions, all of which are described as measurements of permanent set. The molecular causes of permanent set are not the same under all of these conditions. For this reason we shall restrict ourselves in the present article to a discussion of the permanent set taking place in thin rubber samples which are maintained at constant extension at elevated temperatures. We shall show that the permanent set which occurs under these conditions is due to chemical changes which affect the structure of the rubber network, and that a quantitative molecular description of permanent set can be accomplished by the use of concepts already developed concerning the nature of these deteriorative chemical processes.