A Study of Polymers. III. Technique of Mechanical Tests of Vulcanizates of Rubber and Plastics

Abstract

Abstract 1. From the point of view of mechanical properties, the special attributes of highly polymeric substances, including rubber vulcanizates, are clearly defined by their reversible highly elastic deformation as a function of time. The time required for attaining this deformation within a given interval of time varies practically from zero to infinity. 2. Disregard of the temperature and time relation of deformation of highly polymeric substances leads to erroneous conclusions regarding their industrial working properties, and is the cause of the unsatisfactory results obtained by conventional methods of investigation. 3. The effect of increased degree of vulcanization on the mechanical properties of rubber is manifest in a decrease in complete elastic deformation and shift of the temperature-apparent modulus (inverse to the deformation in a given time) curve toward higher temperatures. 4. Conventional ideas of the plastic (irreversible) and elastic deformation of solid materials, when applied to highly polymeric substances without concern for the laws governing their deformation, lead to erroneous conclusions regarding the existence of specific properties of individual substances, e.g., ebonite and synthetic resins, and mistaken hypotheses regarding structural changes during their deformation. In the present communication, this is illustrated by studies of various investigators. 5. Conventional methods of studying thermal stability and brittleness, as well as other methods of testing, of highly polymeric substances frequently do not make it possible to evaluate the actual technical utility of materials within intervals of temperature encountered in service and they should be critically reëxamined with regard to the relations between deformation and reversibility, time and temperature.