TY - JOUR A1 - Zaghdoudi, M. A1 - Kömmling, Anja A1 - Böhning, Martin A1 - Jaunich, Matthias T1 - Ageing of elastomers in air and in hydrogen environment - A comparative study N2 - EPDM, HNBR and FKM materials were exposed at 150 ◦C to air under atmospheric pressure and to hydrogen at 50 bar for different ageing times. All measurements after hydrogen exposure were conducted on samples in degassed condition to assess irreversible effects resulting from that exposure and to compare them to those after ageing in air. Density, hardness, tensile properties, compression set, and hydrogen permeability of all samples were analysed. In both ageing environments, HNBR exhibited the most significant changes of material properties. However, for both EPDM and HNBR, considerably less severe ageing effects were observed under hydrogen in comparison to ageing in air. On the other hand, FKM showed about the same low level of deterioration in both ageing environments but exhibited poor resistance against damage due to rapid gas decompression in hydrogen environment that can lead to seal failure. The obtained results may serve as a guidance toward a better understanding for design and utilisation of elastomeric materials in future hydrogen infrastructure components. KW - Rapid gas decompression KW - Condensed matter physics KW - Hydrogen KW - Sustainability and the environment KW - Rubber sealing KW - Renewable energy PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-597417 DO - https://doi.org/10.1016/j.ijhydene.2024.03.053 SN - 0360-3199 SN - 1879-3487 VL - 63 SP - 207 EP - 216 PB - Elsevier CY - Oxford AN - OPUS4-59741 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zaghdoudi, Maha A1 - Kömmling, Anja A1 - Jaunich, Matthias A1 - Wolff, Dietmar T1 - Erroneous or Arrhenius: A Degradation Rate-Based Model for EPDM during Homogeneous Ageing N2 - To improve the predictive capability of long-term stress relaxation of elastomers during thermo-oxidative ageing, a method to separate reversible and irreversible processes was adopted. The separation is performed through the analysis of compression set after tempering. On the Basis of this separation, a numerical model for long-term stress relaxation during homogeneous ageing is proposed. The model consists of an additive contribution of physical and chemical relaxation. Computer simulations of compression stress relaxation were performed for long ageing times and the results were validated with the Arrhenius treatment, the kinetic study and the time-temperature superposition technique based on experimental data. For chemical relaxation, two decay functions are introduced each with an activation energy and a degradative process. The first process with the lower activation energy dominates at lower ageing times, while the second one with the higher activation energy at longer ageing times. A degradation-rate based model for the evolution of each process and ist contribution to the total system during homogeneous ageing is proposed. The main advantage of the model is the possibility to quickly validate the interpolation at lower temperatures within the range of slower chemical processes without forcing a straight-line extrapolation. KW - Kinetic study KW - Arrhenius KW - TTS KW - Modeling KW - Chemical processes KW - Stress relaxation PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-512931 DO - https://doi.org/10.3390/polym12092152 SN - 2073-4360 VL - 12 IS - 9 SP - 1 EP - 21 AN - OPUS4-51293 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Vega Puga, E. A1 - Wachtendorf, Volker A1 - Kömmling, Anja A1 - Brendelberger, S. A1 - Jaunich, Matthias A1 - Sattler, C. T1 - Lifetime prediction and degradation assessment of FKM and FFKM O-rings under high temperature thermo-oxidative ageing N2 - To support the development of solar reactor technologies for hydrogen production, this study investigates the thermo-oxidative degradation mechanisms of fluorinated elastomers and predicts their lifetimes at high temperatures (200–300 ◦C) consistent with the application requirements. An accelerated ageing programme is conducted with FKM and FFKM O-rings and flat samples for up to 21 days. Optical microscopy is used to analyse the exposed seals’ morphological changes, while IR microscopy is utilised to investigate the underlying chemical degradation mechanisms of both elastomers. Findings suggest that FKM’s degradation arises from dehydrofluorination of the polymer, followed by chain scission and backbone cleavage as a result of the oxidation of newly formed C=C double bonds. FFKM’s degradation is primarily associated with chain scission, but there is also indication that post-curing processes may occur during material ageing. Furthermore, hardness, equilibrium compression set (CS), continuous compression stress relaxation (CSR) and leakage rate tests are used to evaluate changes in the mechanical properties and sealing performance of the elastomers. Equilibrium CS data is extrapolated using time-temperature shifts (TTS) and used to derive an end-of-life criterion of 75 % equilibrium CS, which correlates to leakage rates higher than a predetermined threshold. Service lifetime predictions of FKM and FFKM O-rings at several temperatures are performed and a seal operating temperature of 200 ◦C is suggested, which ensures reasonable O-ring replacement intervals of more than half a year in the solar reactor for both considered materials. KW - Fluoroelastomer KW - Perfluoroelastomer KW - Thermo-oxidative ageing KW - Lifetime prediction KW - Compression set PY - 2025 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-630112 DO - https://doi.org/10.1016/j.polymertesting.2025.108820 SN - 1873-2348 VL - 147 SP - 1 EP - 17 PB - Elsevier BV CY - Amsterdam AN - OPUS4-63011 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zaghdoudi, Maha A1 - Kömmling, Anja A1 - Jaunich, Matthias A1 - Wolff, Dietmar T1 - Understanding the recovery behaviour and the degradative processes of EPDM during ageing N2 - Recovery is an important measure for seal applications representing to which extent the elastomer regains its initial shape after deformation and release of an applied force. Compression set (CS) indicates the degree of recovery. Ethylene propylene diene rubber (EPDM) was aged at 75 ◦C, 100 ◦C, 125 ◦C and 150 ◦C for different ageing times up to five years and compression set measurements were performed at different times after disassembly and after additional tempering. Short- and long-term recovery up to one year after release for samples aged at 125 ◦C and 150 ◦C was also studied. To assess the curvature in the Arrhenius diagram that may occur due to non-sufficiently aged specimens, a degradation-rate based model was fitted to the CS data after tempering. For each ageing temperature, two decay fit functions were proposed, each with an activation energy and a corresponding degradative process. The influence of ageing on the leak-tightness after fast small partial release is investigated and estimated through the analysis of the shift factors from time temperature superposition (TTS) of CS measurements at different times after disassembly. Shift factors of CS measurement after 1 s and after additional tempering are in good agreement. KW - Compression set KW - Ageing KW - Recovery KW - Degradative processes KW - Leakage rate PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-573699 DO - https://doi.org/10.1016/j.polymertesting.2023.107987 SN - 0142-9418 VL - 121 SP - 107987 PB - Elsevier Ltd. AN - OPUS4-57369 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -