Fatigue Resistance of Polybutadienes and Effect of Microstructure
Rubber failure upon application of stress is delayed by: i) viscoelastic energy dissipation and ii) crystallization upon strain of the base polymer. A peculiar rubber failure, namely fatigue failure, is also affected by the same factors. The presence of carbon black or other reinforcing agents does not diminish the contribution of the base polymer on fatigue resistance.
A base polymer particularly interesting as a model for fatigue resistance tests is represented by polybutadiene. Polybutadiene microstructure can be changed at will by making use of existing catalyst systems. In particular, the high vinyl structures are able to show high viscoelastic dissipation and therefore to delay fatigue failure by the mechanism indicated under i). The high cis structures of polybutadiene are capable of crystallizing upon strain and therefore are able to delay fatigue failure by the mechanism indicated under ii).
In this work it is shown that the mechanism ii) is more effective than i) in improving fatigue resistance of polybutadiene. Also a small decrease of chain defects (in particular 1,2 units) in the vicinity of 100% cis content is able to show a substantial improvement in fatigue resistance, both in reinforced and in pure gum polybutadienes.
KeywordsFatigue Life Fatigue Resistance Base Polymer Elongation Ratio Improve Fatigue Resistance
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