Abstract
Elastomers are susceptible to chemical ageing, i.e., scission and cross-linking, at high temperatures. This thermally driven ageing process affects their mechanical properties and leads to limited operating time. Continuous and intermittent stress relaxation measurements were conducted on ethylene propylene diene rubber (EPDM) and hydrogenated nitrile butadiene rubber (HNBR) samples for different ageing times and an ageing temperature of 125 °C. The contributions of chain scission and cross-linking were analysed for both materials at different ageing states, elucidating the respective ageing mechanisms. Furthermore, compression set experiments were performed under various test conditions. Adopting the two-network model, compression set values were calculated and compared to the measured data. The additional effect of physical processes to scission and cross-linking during a long-term thermal exposure is quantified through the compression set analysis. The characteristic times relative to the degradation processes are also determined.
Highlights
Elastomers are widely used in industry and are often applied in sealing due to their ability to undergo high elastic deformation
The contributions of chain scission and cross-linking at different ageing states for EPDM and hydrogenated nitrile butadiene rubber (HNBR) are analysed and a new approach to separate physical and chemical processes that occur during stress relaxation is proposed through the analysis of compression set
Highly filled rubber compounds with about 80 phr of filler were used so that no ideal elastic recovery can be expected. It has been established on the basis of the experimental results that both chain scission and cross-linking occur during ageing of EPDM and HNBR
Summary
Elastomers are widely used in industry and are often applied in sealing due to their ability to undergo high elastic deformation. In operation, these materials are exposed to various thermo-mechanical and chemical factors, which affect their resilience and their sealing ability. An understanding of the long-term thermal and thermo-mechanical degradation of elastomeric components is of major interest to predict their lifetime in operating conditions. It is well known that these materials are in a non-equilibrium state below Tg and that any thermodynamic system brought out of equilibrium spontaneously evolves to re-establish its equilibrium state. Physical ageing is a reversible process associated with macromolecular rearrangement. This occurs when the chains in the perturbed state attempt to reach a new equilibrium configuration through the movement of entanglements and the relaxation of dangling ends [2,3]. A common measure of physical ageing relies on monitoring the recovery of a thermodynamic quantity such as volume or enthalpy [4]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
