Durability Elastomers
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Durability elastomers
General
In a durability test, one or more materials are exposed to practice-oriented conditions over a defined period of time. These conditions of artificial ageing can be very diverse and range from thermo-oxidative, thermal and thermal-medial stress to artificial weathering and a combination of these stresses with mechanical stress and/or alternating stress between the different types of stress. The reaction of the material(s) to the selected, realistic stress is to be recorded quantitatively in order to evaluate its durability. For this reason, test specimens or test pieces are usually taken at different times and tests are carried out. For polymer materials in general, a selection of direct and indirect methods is available for this purpose [1].
Indirect verification of durability
Indirect evidence of age-related material changes is usually provided by mechanical testing. The literature on elastomers very often describes the use of tensile tests and/or hardness tests to quantitatively measure ageing effects and thus indirectly prove ageing. Less frequently, for example, tear tests, investigations using dynamic mechanical analysis (DMA), special tests such as stress relaxation investigations or measurements of compression set are carried out. The use of fracture mechanics investigations should also be considered in the context of durability investigations due to their high structural sensitivity [2].
The evaluation of the characteristics of a surface, such as roughness or specific surface tension, in a before/after comparison can also be helpful in assessing durability and elucidating ageing mechanisms.
Direct verification methods for durability
Direct methods such as infrared spectroscopy (IR spectroscopy), nuclear magnetic resonance (NMR spectroscopy), X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), chemiluminescence, gel permeation chromatography (GPC) and Raman spectroscopy can be used to directly detect age-related changes such as (post-)cross-linking, chain scission, and the formation and degradation of functional groups.
In studies on the durability of elastomeric materials, IR spectroscopy is used to detect structural changes, e.g. in the form of age-related oxidation of chain segments with the formation of carbonyl or hydroxyl groups, for example, whereby limitations in applicability due to carbon black reinforcement often have to be accepted. A combination of thermogravimetric analysis (TGA) and FTIR spectroscopy, for which commercial devices are available, also allows temperature-resolved evaluation of decomposition and degradation processes. Investigations into swelling behaviour can also contribute to clarifying the change in cross-linking density due to ageing. |NMR spectroscopy can also be used to obtain information about the polymer network, i.e. ageing-related changes can be detected via the relaxation times to be determined.
Many studies documented in the literature on the ageing behaviour of elastomeric materials often deal only with either direct or indirect methods. The results have shown that a combination of the results of various direct and indirect methods and test procedures provides the most meaningful results in terms of elucidating age-related structural changes (see also: hybrid methods, examples).
See also
- Ageing
- Ageing elastomers
- Cross-linking elastomers
- Degree of cross-linking elastomers
- Hybrid methods, Examples
References
| [1] | Ehrenstein, G. W., Pongratz, S.: Beständigkeit von Kunststoffen, Carl Hanser, Munich Vienna (2007), ISBN 978-3-446-21851-2; see AMK-Library under G 31) |
| [2] | Reincke, K., Langer, B., Grellmann, W., Döhler. S., Heuert, U.: Alterung und Beständigkeitsuntersuchungen von Elastomerwerkstoffen. KGK Kautschuk Gummi Kunststoffe 67 (2014) 10, pp. 60–67 DOI: https://www.kgk-rubberpoint.de/wp-content/uploads/migrated/paid_content/artikel/3324.pdf |