High Temperature Elastomeric Compounds and Polymers

Abstract

Abstract While special purpose elastomers for high temperature applications have been available since the introduction of the polyacrylates and silicones in the early 1940's, the intensive development and study of such materials really began in the early 1950's. Prior to that period, the major effort in the field of synthetic elastomers was directed toward development of general purpose polymers, principally for such applications as military and civilian tires, wire and cable, and other large volume uses. The extensive synthetic rubber development program sponsored by the U. S. Government during and following World War II is a matter of common knowledge to every rubber technologist and is well covered by Whitby. However, less well known because of restrictions on distribution of reports and technical data are the history and accomplishments of programs sponsored or motivated primarily by the Department of Defense on development of special purpose elastomers for varied and critical high temperature applications. This review will emphasize current knowledge on these specialty elastomers and will attempt to summarize the general limitations of the more common commercially available elastomers when exposed to high temperature environments. for the reader interested in a comprehensive review of this latter subject, Firestone Tire and Rubber Company prepared an outstanding summary of available information prior to initiating an Air Force sponsored research program on high temperature rubber compounds in 1956. Arbitrary definition of what constitutes a high temperature elastomer will naturally provide for many areas of controversy. To the metallurgist, organic polymers in general are not considered high temperature materials, yet in certain applications, such as ablation materials for missile nose cones or rocket nozzles, these polymers will exceed the performance of the most advanced alloys, and are actually considered useful at temperatures above 4000° F. On the other hand, commercial polymer manufacturers publish volumes of data to show that their particular polymer will withstand prolonged aging periods at temperatures of 200–250° F and thereby claim high temperature performances. Obviously, when considering the entire field of elastomeric polymers, no fine line can be drawn between those which may be considered suitable for high temperature applications and those which should be excluded from such applications. Further complicating any generalizations regarding high temperature usefulness is the fact that the high temperature environment is rarely the only environment to be considered in any given application for elastomers. Effect of fuels, lubricants, hydraulic fluids, special chemicals, ozone, sunlight, nuclear radiations, and other adverse environments must usually be considered, singly or in combination, along with the heat effects. Finally, in any given application, consideration of a specific physical property, or combination of properties, is essential for satisfactory performance. These properties include, but are certainly not limited to, tensile strength, elongation, stress relaxation, compression modulus, hardness, abrasion, permeability, lubricity, resilience, tear, cut growth, adhesion, and many others which can have a major influence on the performance or service life of an elastomeric component. Control of these properties over a broad temperature range is the real challenge to today's rubber technologists, and the constant broadening of the temperature range, from extremely low (below −300° F) to extremely high (above 1000° F), will continue to be the basis for special purpose polymer and elastomer development in the years ahead.