The degradation behaviour of filled elastomers is governed by the interplay between thermal ageing, oxygen availability, and mechanically induced structural rearrangements. In this work, we investigate how thermal ageing at 85°C under oxygen-limited conditions, combined with different mechanical preconditioning histories, alters the viscoelastic response of two carbon-black-filled natural rubber compounds with comparable nominal Shore A hardness. Ageing durations up to 64 days were applied, followed by three distinct preconditioning sequences: prior to ageing, after ageing, and both before and after ageing. Dynamic mechanical analysis across a wide temperature-frequency domain was used to construct master curves of the storage modulus, the loss modulus, and the loss factor at a reference temperature of 20°C. Changes in the storage modulus were quantified using a band-averaged percentage shift over the reduced-frequency range of 10-2 to 106 Hz. The results demonstrate that the sequence of mechanical preconditioning fundamentally alters the ageing-dependent viscoelastic response. Early ageing generally increased stiffness, indicating structural densification or changes in filler-matrix interactions, whereas prolonged ageing reduced this effect and, depending on the preconditioning path, produced a softer dynamic response. The influence of mechanical preconditioning after ageing was particularly pronounced, demonstrating that mechanically driven network rearrangements significantly modify the ageing-dependent degradation behaviour. Despite similar hardness, the two materials exhibited distinct ageing-mechanism signatures in their DMA responses. These findings highlight that mechanical preconditioning is not merely a testing step but a relevant degradation-history variable that must be considered when interpreting ageing-induced changes in filled elastomers.     «

The degradation behaviour of filled elastomers is governed by the interplay between thermal ageing, oxygen availability, and mechanically induced structural rearrangements. In this work, we investigate how thermal ageing at 85°C under oxygen-limited conditions, combined with different mechanical preconditioning histories, alters the viscoelastic response of two carbon-black-filled natural rubber compounds with comparable nominal Shore A hardness. Ageing durations up to 64 days were applied, foll...     »