The properties of rubbers are subject to change as a result of ageing, ultimately to the point where the material is no longer capable of fulfilling its function. In many applications, the longevity of rubber components is of critical importance. During its lifetime a rubber may be subjected to a variety of exposure conditions leading to different types of degradation. After a brief introduction to the main environmental and mechanical factors affecting performance, the authors of this Rapra Review Report focus on the thermo-oxidative ageing of rubber. As the lifetime for some products is measured in decades, reliance has to be placed on accelerated tests to provide estimates of resistance to ageing, and this review considers the methods of, and the published results from, both natural and accelerated tests. The use of the Arrhenius equation and the William Landel Ferry equation to obtain lifetime predictions is reviewed and their limitations highlighted.

A major section of the report is devoted to exposure and test techniques with discussion of the methods of physical and chemical analysis. These include physical tests involving the measurement of properties such as the tensile stress/strain characteristics, hardness, stress relaxation and compression set. Alternatively, chemical analysis may be utilised: thermogravimetric analysis, spectroscopic methods, pyrolysis techniques and gel permeation chromatography. In the final section, published data resulting from long-term natural ageing studies and from short-term and accelerated testing is reviewed.

Roger Brown is Manager of Technical Projects at Rapra Technology, and is the author or co-author of over 60 technical papers and the author or editor of five books. Martin Forrest is Principal Consultant Analyst, and has been involved in the analysis of a wide variety of polymers using a range of analytical techniques. Gerald Soulagnet is an Assistant Test Engineer, and has been involved in both mechanical and chemical analysis of polymers.

This review is accompanied by an indexed section containing several hundred references and abstracts selected from the Polymer Library. These provide the reader with a valuable reference source for further information relating to the ageing of rubber.