Embrittlement in oxidative aging

SBR also differs from NR in its aging behaviour. Whereas oxidation causes chain scission of the NR molecule and a softening of the rubber in bulk, SBR molecules tend to cross-link, this leading eventually to hardening and embrittlement. 

Relating Kinetic Models to Embrittlement in Polymer Oxidative Aging... 

When the peroxyl population was quickly destroyed by 2-methyl -2-nitrosopropane treatment, post-y oxidation still occurred (Figure 7). In addition, film which had been pre-oxidized by xenon-arc photo-initiated oxidation showed an identical, slow, thermal oxidation during storage, as well as a rapid embrittlement in the accelerated aging at 60°C (Figure 6). The photo-oxidation of PP is well... 

The method described in DIN 53383 [164], Part 2 for measuring thermal-oxidative aging in polyethylene is based on the experience that far reaching embrittlement of polyethylene has taken place at a CO number of two. 

Aging Properties. The main features of ethylene—acryhc elastomers are heat (177°C) and oil resistance. At elevated temperatures, ethylene—acryhc elastomers age by an oxidative cross-linking mechanism, resulting in eventual embrittlement, rather than reversion. A general heat... 

While Barrow solved the main problem, there are other modes of degradation which must be considered. As an organic material, cellulose and paper can be easily oxidized. Very small amounts of the transition metals, compounds of iron, copper, and cobalt, under humid conditions can accelerate oxidation and embrittlement of paper. This type of degradation, as is shown later, does not show up in the dry-oven accelerated aging which Barrow used. Thus his alkaline papers, if they contained the oxidation catalysts, may not always have been permanent. 

Aging of an irradiated sample does not improve the mechanical properties they continue to deteriorate with time as seen in Figure 9. Post-embrittlement is caused by post-oxidation as a result of residual radicals and is discussed later (3). However, the oxidative reaction initiated by the irradiation cycle does not cease with irradiation but continues for long periods of time. 

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