Sunlight incidence, temperature cycles and humidity cause weathering: an irreversible chemical process that causes discolouration of the cable colour and loss of the mechanical properties of the polymers.
Delta Tecnic recommends the use of Masterbatch incorporating additives to prevent degradation of the polymers exposed to the sun and an appropriate selection of pigments to minimise long term discolouration of the cables.
The environment has a negative influence on the service life of cables. The incidence of sunlight, temperature cycles and humidity cause weathering: an irreversible chemical process that causes discolouration and the loss of the mechanical properties of polymers. DeltaTecnic, a leading technology company in industrial colour chemistry, proposes a series of solutions to prevent these effects on cables exposed to outdoor conditions.
The cable market offers several designs and applications for outdoor cable use. We see this in medium voltage cables, photovoltaic cables for solar panels, power cables for buildings, the increasingly sought-after overhead fiber optic cables or those required for electric car chargers. Clearly, the new trends present a set of challenges for the cable industry.
Photodegradation reduces life expectancy of cables
Photodegradation is a photochemical process produced by sunlight that is cumulative, meaning that it worsens over time, and irreversible. The degradation of the polymer by ultraviolet (UV) radiation influences the physical properties and thus its life expectancy.
Thus, UV radiation causes a photooxidative degradation that results in the breakage of the polymer chains, producing free radicals, which initiate a chain reaction of polymer chain breakage, leading to the deterioration of their mechanical properties. Consequently, there is a degradation of the visual appearance, gloss, and surface, as well as a loss of the mechanical properties of the cable, which limits its useful life in optimal conditions.
It should be remembered that when a plastic is exposed to solar and climatic conditions, there are two independent phenomena: polymeric degradation and photodegradation of the chromophore groups present in the pigments, which is responsible for the final colour of the cable.
How to preserve the properties of an outdoor cable
There are three ways to mitigate polymeric photodegradation:
- Use additives called UV filters that have the ability to absorb the ultraviolet light that causes degradation. Thus, when sunlight meets these additives, they react and prevent it from reaching the polymer, as if it were a sunshade.
- Through HALS (Hindered Amine Light Stabilizer), this family of additives reacts to free radicals, blocks them, and prevents the initiation of polymer chain breakage. When UV light strikes and the free radical is generated, HALS acts to stop the polymer degradation process.
- With black pigment (carbon black). The high absorption capacity of carbon black of UV radiation of light acts as a trap for this energy, preventing it from reacting with the polymer. The most effective grades are those of smaller particle size, as they have a larger surface area to trap solar radiation.
What about the colour? There is no additive that protects the colour of the cable as there is for the polymer. The solution in this case is to formulate the colour using pigments prepared to withstand outdoor conditions. In other words, it is necessary to choose the right pigment or combination of pigments that are lightfast from the start. The in-depth study of the behaviour of pigments in the different types of polymers used in the cable industry (PVC, HFFR, TPU, XLPE, EPDM, etc.) under outdoor conditions is key to ensure the colour stability of the cable during its lifetime outdoors.
How to predict the behaviour of an outdoor cable
Delta Tecnic, in line with its commitment to innovation and new technological solutions, measures the behaviour of pigments outdoors in its laboratory. The company carries out a test that accelerates the state of exposure of plastics to different sunlight conditions. This is called the Sun Test and is carried out with an instrument that emits visible sunlight and cycles through changes in temperature, humidity, and dryness.
Thanks to Sun Test’s laboratory trials with the different compounds used in the cable industry and with a multitude of pigments, it has gained the in-depth knowledge necessary to define the optimum formulations to meet the most demanding requirements of cable regulations, at the lowest possible cost.
Weathering’ and ‘lightfastness’.
Ultimately, there are effective ways of knowing what kind of behaviour to expect from outdoor cables, which facilitates pigment selection and thus the prediction of the life expectancy of the plastic. This facilitates decision making and contributes to the installation of solid cable capable of withstanding weathering and lightfastness conditions.
In addition to the historical concept of lightfastness, which considers the incidence of light, there is also the concept of weathering, which, apart from light, takes into account factors such as temperature and humidity. In fact, pigments that have a good lightfastness behaviour may not work properly in different temperature ranges, solar radiation and are also affected by the polymer used in the definition of the cable. Both terms combine to create a problem faced by designers of outdoor cables, but fortunately there is a solution.