From filler–polymer interfacial rearrangements to silica enrichment: Microstructural origins of mechanical degradation in hydrothermally aged HTV silicone rubber

This study presents the evolution of standard mechanical properties of a silica-filled silicone rubber subjected to cyclic ageing conditions, including vacuum phases at 80 °C and high-pressure steam phases at 134 °C. The observed changes in mechanical properties are associated with molecular and macromolecular-scale transformations reported in a previous study. Over the course of ageing, Shore A hardness increased in correlation with rising silica content. The observed loss of elastic recovery, indicated by the compression set, was linked to alterations in network topology, particularly due to complex rearrangements at the polymer–filler interfaces. Monotonic tensile tests at both low and high strain levels revealed the respective impacts of increasing silica content and polymer network hydrolysis. Additionally, the changes in the Mullins effect was associated with microstructural changes. The tensile behavior was modeled using a hyperelastic approach incorporating a hydrodynamic amplification factor, which supported a phenomenological understanding of the ageing effects on both monotonic tensile responses and the Mullins effect.