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TESTING | WEATHERING


Above: Application and customer performance needs dictate requirements for accelerated weathering testing for a given plastic compound


correlation and to validate accelerated tests - it is important to Test the Test.” Long-term sustainability and environmental


considerations for plastics may also affect acceler- ated weathering testing in the future. “There may be a need going forward to develop accelerated testing guidelines for some materials to ensure that they do break down upon exposure to weathering elements,” Francis says. “This is a paradigm shift basically from the complete history of weathering testing, where the goal has been to verify that products and materials could withstand outdoor conditions.”


Right: Accelerated weathering testing in a xenon arc tester at Avery Dennison


Understanding applications The application type and customer performance needs dictate the market requirements for acceler- ated weathering testing for a given plastic com- pound, according to Avery Dennison, a leading manufacturer of labelling and functional film materials for plastics with extensive experience of weathering assessment. “A material applied to a flat application, such as a sign or building, will have different physical property requirements than a material applied to a complex geometry, such as a vehicle for example. The purpose of both applica- tions might be the same, such as to provide a certain colour or appearance, but the means to achieve that property could be quite different based on the substrate type and design features that it is applied to,” says Mark Alesandro, R&D Product Durability Manager. In the case of the flat surface application, Alesan-


dro says a wider range of material options might be considered as it allows for greater variation in physical properties – thickness and stiffness. A three-dimensional application will require materials that have high elongation and conformability proper- ties. “Since the application determines the material options, it inherently factors into the cost and durabil- ity considerations as well. The challenge is often not


48 COMPOUNDING WORLD | December 2019 www.compoundingworld.com


in finding a material solution that meets the given market requirements, but rather finding one that is cost competitive and long lasting” he explains. “It is obvious that the market requirements will vary with different materials and different applica- tions, but it is also interesting to consider that these requirements often vary from customer to customer for the same material and application types. The reason for such variation is that each customer may define a material property failure differently,” he says. “For example, if a given plastic compound applied outdoors shows cracking after five years, it is likely that all customers would agree that the material failed at this point and therefore has five year durability. However, if the material remains physically intact and instead demonstrates colour fading or gloss loss with time, there is likely to be a much wider criterion used to define the failure point and material durability. Therefore, the same material used on equal applications can have different durability depending on the customer requirements and how they define failure.” Alesandro says the ongoing pursuit of correla-


tion to real world ageing remains the main factor driving the advancement of accelerated testing, with the most common question asked by custom- ers being how many hours of testing equal a year outdoors? “This question ultimately assumes that the accelerated testing is reproducing real life exposures, but in a much shorter time frame. From this, it is important to consider that there are numerous accelerated testing methods available from the Standards Committees. Additionally, many customers have their own internal accelerated testing methods. Each of these tests utilise different exposure cycles, varying temperature and humidity conditions, and different irradiance levels which represents the sunlight intensity,” he says. “In the same way that there are numerous


IMAGE: AVERY DENNISON


IMAGE: AVERY DENNISON


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