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Created page with "{{Language_sel|LANG=ger|ARTIKEL=Alterung}} {{PSM_Infobox}} Ageing __FORCETOC__ ==Definition== Ageing is understood to be the totality of all chemical and physical processes irreversibly occurring in a material over the course of time. Ageing takes place under natural environmental conditions. In special cases, however, ageing may have special characteristics, such as elevated temperatures,..."

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{{Language_sel|LANG=ger|ARTIKEL=Alterung}}
{{PSM_Infobox}}
Ageing
__FORCETOC__

==Definition==

Ageing is understood to be the totality of all chemical and physical processes irreversibly occurring in a [[Material & Werkstoff|material]] over the course of time. Ageing takes place under natural environmental conditions. In special cases, however, ageing may have special characteristics, such as elevated temperatures, chemical attack, and mechanical [[Stress|stress]]. For testing purposes, increased influence to a factor may be desirable to achieve time acceleration (see also: [[Stepped Isothermal Method, Macro Indentation Method|stepped isothermal method, macro indentation method]]). However, this time-lapse does not normally allow direct extrapolation to long-term behaviour. It is possible, however, to evaluate relatively simple processes, such as creep behaviour or thermal ageing. However, since in most cases the natural ageing conditions do not act individually and cannot be shortened in time, the statement for long-term application based on short-term tests is always problematic.

==Internal and external ageing==

In general, a distinction is made between internal and external ageing. Internal ageing is due to thermodynamically unstable states of the polymeric material, e.g. the breakdown of [[Tensile Test Residual Stresses Orientations|residual stresses]], [[Crystallinity|post-crystallization]], phase separation in multi-component systems, plasticizer migration or swelling. External ageing, such as [[Environmental Stress Cracking Resistance|stress cracking]], fatigue cracks, thermo-oxidative degradation, [[Water Absorption|swelling]] or similar phenomena, is caused by physical or chemical effects of the environment on the [[Polymer|polymer]] material. The distinction between chemical and physical ageing processes is not always unambiguous, since there are usually complex effects.

==Influence of ageing on the material value level==

If ageing is understood to mean only the time-dependent, irreversible processes, then it should correctly also be understood to mean an improvement in the service value of the material, if, for example, post-condensation, [[Cristallinity|post-crystallization]] or radiation crosslinking leads to an improvement in certain desired properties. 
For example, for a medially stressed (washing solution, 95 °C) particle-filled (e.g. talc) polypropylene ([[Plastics – Symbols and Abbreviated Terms|abbreviation]]: PP), depending on the ageing time (up to 2,000 h), the [[Elastic Modulus|modulus of elasticity]] ''E''t can decrease significantly, the [[Tensile Strength|tensile strength]] ''σ''M can increase slightly, the nominal [[Tensile Strength|tensile strain]] at break ''ε''tB and the technically more significant nominal strain at tensile strength εtM show no changes, and the [[Notched Impact Test|Charpy impact strength of notched specimens]] ''a''cN can increase noticeably. These structure-dependent property changes of the mechanical values as a function of the ageing time can also be quite different in other examples. For this reason, a multi-parameter property evaluation is particularly important in the formulation optimization of complex polymer material systems, e.g. [[Polymer Blend|polymer blends]]. 
Stabilizers have even been developed against a number of particularly critical environmental influences, which delay the undesirable changes in material and service properties during processing or use. As a result, the [[Plastic Component|plastic component]] retains its required properties during the service life. The most important stabilizers are processing stabilizers, heat and light stabilizers, UV absorbers, antioxidants and hydrolysis protection agents.

==See also==

* [[Ageing Elastomers|Ageing elastomers]]
* [[Durability Elastomers|Durability elastomers]]
* [[Stepped Isothermal Method, Macro Indentation Method|Stepped isothermal method, Macro indentation method]]
* [[Stepped Isothermal Method, Tensile Stress|Stepped isothermal method, Tensile stress]]

'''References'''
*[[Ehrenstein, Gottfried W.|Ehrenstein, G. W.]]: Polymerwerkstoffe. Struktur und mechanisches Verhalten. Grundlage für das technische Konstruieren mit Kunststoffen. Carl Hanser, Munich Vienna (1978) p. 173 (ISBN 3-446-12478-0; see [[AMK-Büchersammlung|AMK-Library]] under G 28)
*Lechner, M. D., Gehrke, K., Nordmeier, E. M.: Makromolekulare Chemie – Ein Lehrbuch für Chemiker, Physiker, Materialwissenschaftler. Birkhäuser, Basel Boston Berlin (2010) 4. revised and expanded edition, pp. 488 ff, (ISBN 978-3-7643-8890-4; see [[AMK-Büchersammlung|AMK-Library]] under N 11)
*[[Grellmann, Wolfgang|Grellmann, W.]], Schoßig, M., [[Reincke, Katrin|Reincke, K.]], [https://de.wikipedia.org/wiki/J%C3%B6rg_Kirbs Kirbs, J.]: Bewertung der Alterungsbeständigkeit von Folien durch künstiche Bewitterung. In: [https://www.researchgate.net/profile/Wolfgang-Grellmann Grellmann, W.] (Eds.): Neue Entwicklungen in der Werkstoffprüfung – Herausforderung an die Kennwertermittlung. Tagung "Werkstoffprüfung 2011", 1. und 2. Dezember 2011, Berlin, Proceedings pp. 173–178 (ISBN 978-3-9814516-1-0; see [[AMK-Büchersammlung|AMK-Library]] under A 13)
*Langer, B., Schoßig, M., Reincke, K., [https://de.wikipedia.org/wiki/Wolfgang_Grellmann Grellmann, W.]: Charakterisierung des Alterungsverhaltens von Polymerwerkstoffen. In: Borsutzki, M. and Moginger, G. (Eds.): Fortschritte in der Werkstoffprüfung für Forschung und Praxis. Tagung Werkstoffprüfung 2012, 06. – 07. Dezember 2012, Bad Neuenahr, Proceedings pp. 145–152 (ISBN 978-3-514-00794-9; see [[AMK-Büchersammlung|AMK-Library]] under M 24) [https://www.polymerservice-merseburg.de/fileadmin/inhalte/psm/veroeffentlichungen/Charakterisierung_des_Alterungsverhaltens_von_Polymerwerkstoffen_WP2012.pdf Download as pdf]

[[category:Ageing]]

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