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Ageing of black filled rubber under deformation
von Asahiro Ahagon, Ph.D., Yoshiaki Kirino
Prolonged dynamic deformation of a rubber is found to significantly accelerate oxidative crosslinking due to mechanochemical oxidative crosslinking. The extent of acceleration is larger at lower temperatures and increases with increasing strain.
The activation energy of the rate of oxidative crosslinking decreases with increasing strain toward the highest value among the unit reactions of oxidative chain reaction cycle or the value of diffusion of oxygen, which is much smaller than that of static ageing. On the other hand, static deformation is also found to accelerate oxidative crosslinking but to considerably lesser extents.
Mechanochemical acceleration can be noticed only in the early stage of prolonged deformation. The degree of acceleration in prolonged deformation increased with increasing strain without change in the activation energy. The acceleration observed in prolonged static deformation is considered to arise from the increased area of exposure to the oxidising atmosphere. It appears that mechanochemical acceleration is merely spent to compensate the loss in crosslink density upon deformation in this case.