Technical products are exposed to a variety of environmental influences throughout their entire service life. These can influence the function and/or appearance of a component and thus reduce its service life. Artificial ageing in climatic tests simulates the long-term behaviour under severe external conditions and thus qualifies a product for given environmental conditions. The aim of environmental simulation is to discover weak points in products quickly and effectively and to avoid complaints. Environmental influences are all forms of physical, chemical or other effects on the object under investigation.
Plastics are subject to ageing, which is often due to the effects of temperature. Stresses in the plastic can, for example, lead to component deformation (warpage) under the influence of heat and thus to problems in the accuracy of fit within an assembly. Different coefficients of thermal expansion (e.g. metal and plastic) can cause cracks or material detachment, especially with frequently changing temperatures of a temperature cycling test. A change in mechanical strength or material embrittlement is also frequently observed. It therefore makes sense to combine the storage tests with a check of the product properties such as strength, hardness, adhesive strength (cross-cut test) before and after the climatic test.
The temperatures and duration of a climatic test are adapted to the conditions of use of the product and its life expectancy. Temperatures of -35 °C to +85 °C are frequently found in the automotive sector, for example. However, depending on the area of application, significantly lower or higher temperatures are also possible.
Especially polar plastics with functional groups such as polyamides, polyesters or polyurethanes show hydrolysis ageing. In this process, the functional group of these polymers is split under the influence of water. The resulting cleavage of the molecular chains changes, among other things, the mechanical and thermal properties of these plastics. The temperature to which the plastics are exposed during hydrolysis ageing also has a strong influence. In this respect, the simple moisture storage of plastics provides only limited information with regard to hydrolysis resistance. For further statements, therefore, condensation water constant climate tests and hot water tests are also carried out in order to be able to test the influence of water and temperature on the plastic and to derive a property profile from this.
Plastics can also age under the influence of light (especially UV radiation). Colour pigments can bleach out as a result of a light fastness test and thus lead to a change in colour or yellowing. Therefore, after each lightfastness test, an assessment of colour and gloss is carried out. More serious than optical changes are possible structural changes in the plastic itself, which can, for example, negatively alter the mechanical properties of the material. Splitting of molecular chains or post-cross-linking, for example, can cause the material to become brittle. Exposure tests are sometimes also carried out in conjunction with temperature and/or humidity.
This is generally understood to be the influence of radiation, temperature and humidity/water. In artificial weathering in the laboratory, these parameters are regulated in a controlled way.