Abstract
During their useful life, polymers are subject to degradation processes due to exposure to specific environmental conditions over long times. These processes generally lead to changes, almost always irreversible, of properties and performances of polymers, changes which would be useful to be able to predict in advance. To meet this need, numerous investigations have been focused on the possibility to predict the long-term performance of polymers, if exposed to specific environments, by the so called “accelerated aging” tests. In such procedures, the long-term behavior of polymeric materials is typically predicted by subjecting them to cycles of radiations, temperatures, vapor condensation, and other external agents, at levels well above those found in true conditions in order to accelerate the degradation of polymers: this can produce effects that substantially deviate from those observable under natural exposure. Even following the standard codes, different environmental parameters are often used in the diverse studies, making it difficult to compare different investigations. The correlation of results from accelerated procedures with data collected after natural exposure is still a debated matter. Furthermore, since the environmental conditions are a function of the season and the geographical position, and are also characteristic of the type of exposure area, the environmental parameters to be used in accelerated aging tests should also consider these variables. These and other issues concerning accelerated aging tests applied to polymers are analyzed in the present work. However, bearing in mind the limitations of these practices, they can find useful applications for rating the durability of polymeric materials.
Highlights
Synthetic and natural polymers, as any other material, experience some type and level of degradation during their service-life, resulting in an alteration of their properties, affecting their performance and shortening their useful life-cycle [1,2,3,4,5,6,7]
The long term behavior of a polymeric material is influenced by its chemical nature, the process conditions used to manufacture and/or to apply it, on the load regime to which it is subjected and, mostly, on the kind and level of environmental exposure in which the material operates, i.e., by its service conditions
In which polymeric materials perform a certain task, are characterized by distinctive service conditions, as for examples: automotive components, typically made in thermoplastic polymers, are exposed to medium/high temperatures, water/humidity, radiations, fuels, chemicals; elastomeric polymers composing tires are exposed to oxygen and medium temperatures, water/humidity, fuel, chemicals, mechanical stresses; thermosetting matrices to manufacture fiber reinforced polymers (FRP) applied in aeronautical fields are subjected to radiations and exposure to thermal cycles, water/humidity, ice, fuel, chemicals, mechanical stresses
Summary
As any other material, experience some type and level of degradation during their service-life, resulting in an alteration of their (mechanical, thermal, optical, functional, other) properties, affecting their performance and shortening their useful life-cycle [1,2,3,4,5,6,7]. These procedures are intended to provide previsions on the durability of a polymeric material, i.e., they would predict its long-term properties and characteristics, amplifying at selected levels one or more environmental parameters characterizing the true exposure. In this way, employing proper environmental chambers or specific devices, these procedures try to simulate in a very short time the effects on the polymer of the same parameters due and proposals of new routes to explore in order to improve the research in this field are, presented
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