Weather testing of polymers
It covers plastic materials (polymers, fillers and various additives) or intermediates that are the transformers that use their thermoplastic property for the manufacture of objects by processes such as extrusion, injection molding, etc.
Under the influence of external stresses that generate primary radicals attacking chemical bonds (especially the most abundant ones, between carbon and hydrogen), reactions occur with atmospheric oxygen.
The simulation of photothermal ageing is generally done by exposing samples in centers approved for their geographical location (Arizona, Florida, South of France) and their ability to know precisely the exposure conditions (duration and intensity of sunshine, temperature, humidity level, etc.).
Most instruments allow control of light intensity, temperature of the surrounding environment, humidity level and water sprinklers can be programmed to simulate the effect of rain.
The use of xenon lamps is based on a similarity with the solar spectrum but that the principles of photochemistry (in particular the existence of vibrational relaxations of excited states) do not exclude the use of other light sources to simulate or accelerate photothermal ageing.
As early as 1978, the principles mentioned above led to the design of specific units by the Laboratory of Molecular and Macromolecular Photochemistry, now integrated into the Institute of Chemistry of Clermont-Ferrand (https://iccf.uca.fr).
Today, a dozen French and European standards refer to these enclosures (agricultural films, cables) and about twenty companies have included SEPAP tests in their specifications for their subcontractors.
From the photochemical point of view, multi-photonic effects are for example to be feared, just as the oxygen starvation may occur very quickly and strongly disrupt the degradation mechanisms.
The ultra-accelerated approach developed in the SEPAP MHE unit makes it possible to solve in particular the problem of very long-term stability required for certain applications (cable-stayed bridges, photovoltaic panels, wind turbines, ...) or the need to be able to homologate a new material very quickly (automotive industry, ...).
Too frequent water sprinkling can also lead to premature extraction of low molecular weight stabilizers and wrongly disqualify polymeric materials.
Studies to predict the behavior of polymeric materials subjected to different environmental constraints (sunlight, heat with or without moisture) or failure analyses of polymer parts can be carried out in collaboration with the R&D departments of manufacturers.
The Centre National d'Evaluation de Photoprotection is now associated with about sixty companies and annually carries out more than 450 studies covering all areas of application of polymers including works of art.
