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WEATHERING | TESTING


Understanding the effects of the elements is crucial to finding the appropriate plastics compound for the right application. Accelerated weathering tools can assist in that. Mark Holmes finds out more


Getting to grips with the weather


Laboratory-based accelerated weathering is an essential tool for the plastics industry in developing new applications, discerning material suitability and shortening time to market. However, weather- ing is a complex process driven by a combination of variables and understanding that, and other factors that can impact on the long term stability of a polymer compound in the field, is critical in making an accurate and reliable assessment. One company with a long track record in


material durability testing equipment and services for plastics is Q-Lab Corporation. “Weathering is a combination of sunlight, heat and water, which cause some degradation or breakdown of a plastic,” says Andy Francis, Weathering and Corrosion Marketing Projects Manager at Q-Lab. “The combination of two of the elements, such as sunlight and heat, can be defined as lightfastness, but weathering requires all three.” Most of the sunlight spectrum - 55% - is visible light and another 38% is comprised of infrared light, which manifests itself as radiant heat. Ultravio-


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let (UV) light accounts for only 5-7% of the spec- trum, but for plastics and polymers it is responsible for virtually all polymer degradation – colour change, fading and loss of gloss, for example. However, Francis says the situation is different for an indoor product as materials behind window glass are subject to a different spectrum and some of the dangerous short wavelength UV light can be filtered out. “Heat by itself does not cause weathering;


however, heat in combination with sunlight can accelerate a lot of photo-oxidation effects. There can be dimensional change, as materials typically tend to expand when they get hotter and contract when they get cooler. This can cause thermal stress and cracking. Heat can also cause evaporation of water that has been absorbed into a plastic and has to get out when heated, which can cause blistering, delamination and other defects,” Francis says. “Thermal cycling can also age a material quite


quickly. In addition, the effect of heat is influenced by colour, with darker colours having higher


December 2017 | COMPOUNDING WORLD 57


Main image: Weathering is a complex process driven by a variety of different environmental factors, making simulation a challenge


PHOTO: SHUTTERSTOCK


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