ABSTRACT
Like already mentioned oxidation is a dominant factor of ageing in a lot of applications where the material is exposed to an oxygen-containing environment (Hoffman et al. 2011, Assink et al. 2005, Celina et al. 2006a, Johlitz 2012). Furthermore an important parameter affecting the oxidation of polymers is the temperature, which has significant influence on the processes taking place and defines, which dominates more or less (Ehrenstein & Pongratz 2007, Celina 2013). The combination of both effects, ie. the presence of oxygen and heat input, are known as thermoxidative ageing and cause extensive changes in the chemical structure. Elevated temperature accelerates the process (Domininghaus & Elsner 2012). The consequences of the oxygen consumption for polymers differ from case to case and depend on the configuration of the material used and its manufacturing technique as well as on other factors like the operation
1 INTRODUCTION
Due to the increasing importance of polymer material in a wide field of technical application it is essential to gain more knowledge about the changing properties during lifetime of such components. Especially elastomeric devices are sensitive to environmental influences because of their preferred range of application as, for example, coating material to protect surfaces of other materials or as bearings. For this reason these polymers have to ensure stability against degradation during the entire time of operation. A major point when talking about the ageing of elastomers is the influence of oxygen, which is omnipresent in a lot of common applications. Generally it must be distinguished between physical and chemical ageing, whereby the former is a reversible process. Chemical ageing in contrast is irreversible and can influence the material properties in such a way that damaging occurs (Johlitz 2012). Tobolsky et al. (Tobolsky 1967) indicate the effect of oxygen in the ambient environment of natural rubber by testing the stress relaxation in air and for comparison under the exclusion of oxygen in pure nitrogen. They found oxidative degradation to dominate the process of chemical ageing.
