EuroWire May 2023

Technical Article

Lightfastness and weather resistance: key steps for avoiding the degradation of polymers and the discolouration of cables By Manel Miret, product developer, Delta Tecnic

This must be distinguished when looking for solutions, since pigments that offer good resistance to light may not work properly in different temperature ranges or levels of solar radiation. The behaviour of pigments outdoors can be measured with a test that accelerates the exposure state of plastics under different conditions of sunlight, temperature and humidity, and with the compound used to produce the cable. It must be taken into account that the behaviour of pigments may differ according to outdoor exposure. There are pigments with a polyethylene solution that have good resistance to weathering, but the same pigments and concentrations do not fare as well in the solar test, which uses a halogen-free flame-retardant (HFFR) compound. For this reason, it is highly recommended to check the behaviour of the pigments in the most commonly used polymers and compounds in the cable industry, to check what type of behaviour can be expected from the colour of the cables in outdoor applications. This facilitates the selection of the pigments and, therefore, the prediction of the non-discolouration of the outdoor cable. Therefore, installations made for energy or wireless networks require cables whose design can withstand photodegradation. Industries that operate with medium voltage cables, photovoltaic cables for solar panels, electrical cables for buildings or fibre optic cables seek to avoid this cumulative and irreversible process. To understand it better, it is necessary to know that ultraviolet radiation (UV) causes a photo-oxidative degradation that leads to the degradation of the polymer used in the cable design. The solar spectrum ultraviolet light reacts with the polymeric chain causing its rupture, generating free radicals, which start a chain reaction that leads to the degradation of the visual appearance of the cable, its brightness and its surface, as well as its mechanical properties, all of which limit its useful life. To assess polymer degradation, mechanical property studies are performed before and after exposure. As a general rule, a limit is set on the tensile properties at break and elongation at break, not allowing a drop of more than 25 per cent. How to prevent photodegradation in cable polymers There are three strategies to reduce the photodegradation of polymers when used outdoors.

How can we prevent outdoor conditions from degrading cables? Many companies ask this question when they see how their cables fall victim to discolouration, and polymers lose their mechanical properties in both power and fibre optic cables, which should have a useful outdoor life. Cables that are outdoors suffer the consequences of exposure to outdoor conditions, such as exposure to light, changes in temperature and humidity, that directly affect their useful life. These effects are basically applicable to two concepts: resistance to light (exposure to light) and weathering, which in addition to light encompasses factors such as wide temperature ranges, from very low temperatures in winter to high temperatures in summer, and humidity.

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May 2023