Predictive ageing of elastomers: Oxidation driven modulus changes for polychloroprene
Résumé
The oxidative ageing in the range of 60 °C–140 °C of sulfur vulcanized polychloroprene has been studied by FTIR spectroscopy (double bond consumption), modulus changes and oxygen absorption measurements. Experiments were carried out on thin films and thick samples to investigate both homogeneous and inhomogeneous (diffusion controlled) oxidation with the goal of establishing the underlying correlation between oxidative degradation chemistry and mechanical property changes. A correlation between oxidatively driven degradation chemistry and modulus is possible using the established approaches of rubber elasticity where an effective crosslinking yield due to double bond reactions is of the order of 30% for this material (i.e. the loss of 3 double bonds results in one effective crosslink associated with material hardening). It is then possible to predict modulus changes induced by oxidation for vulcanized and unstabilized polychloroprene rubber. A kinetic model is introduced with two propagation reactions (hydrogen abstraction and radical addition to double bonds) and two stabilization processes involving sulfur containing moieties from the vulcanization process. The kinetic scheme was solved and the relevant rate constants determined. This model can adequately predict modulus changes in films and thick samples as a function of time and spatially resolved.
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