TESTING | WEATHERING
Right: Mark Alessandro in the Avery Dennison accelerated weathering and durability laboratory
technique does not generate any visible light and can deliver condensation but cannot control relative humidity. It is also much easier to use and less expensive than a Xenon arc tester.” Independent laboratories, such as UK-based Impact Solutions, offer accelerated weathering and lightfastness testing services. Acceleration in one of its units is typically about eight times, according to Jo Snow-Tyler, New Business Develop- ment Manager. With around 8,000 hours in a year, she says that exposure in one of the company’s chambers for 1,000 hours will equate to a year’s worth of real-time testing in just six weeks. How- ever, she says this is the current maximum; efforts to increase this would not replicate results correctly in the natural environment.
Weathering expertise A company making extensive use of accelerated weathering and durability testing is Avery Denni- son. “Weathering resistance is a function of the components used to develop a plastic compound,” says Mark Alessandro, R&D Product Durability Manager at Avery Dennison. “For a given material, the durability can vary by years depending on the stabiliser, plasticiser and pigment selection,” he says. “Therefore, it is essential to keep pace with
emerging technologies from additive suppliers to maintain state-of-the-art product developments with optimal weathering resistance. The level of understanding of weathering resistance is only as good as the tools and methods used to evaluate it. Along with product performance, testing technol- ogy continues to evolve as well. Newer testing standards, such as ASTM D7869, have emerged throughout the industry in pursuit of increased correlation between the laboratory and real-life benchmark conditions, such as the environment in south Florida,” Alessandro says. “There are positives and negatives to consider
with UV stabilisation packages. The positives are fairly obvious in terms of extending product
durability by increased resistance to sunlight exposure. However, there are many UV stabiliser technologies available, and with these various options comes differing levels of UV absorption. The absorption amount and spectral range of absorption will likely play a key role in the level of weathering resistance that can be realised for a given material. As these properties increase, so too might the cost of the UV stabiliser,” he says. “Another common challenge with UV stabilisers
is colour,” Alessandro says. “For example, many of these stabilisers could add a significant yellowish tint to the material, which may set a limitation on the desired loading level or even the type of stabiliser that can be pursued. A third considera- tion with UV stabilisers is the process for incorpo- rating them into the material formulation. The first step in UV stabiliser selection should be to check for adequate dispersion. This can be a challenge with several stabiliser products and may limit the options for a given material.”
Developments in stabiliser technologies are also
providing specific problems for testing the weather resistance of these compounds. “As the durability of materials increase, so too does the time required to assess it,” says Alessandro. “The limiting factor
Figure 1: Comparison of xenon arc and fluorescent UV testing equipment Fluorescent UV
Xenon arc
UVA-340 – best simulation of short wavelength UV light UVB-313 might be too severe
No visible light Stable spectrum
No relative humidity control necessary Condensation or water spray Relatively inexpensive and simple Source: Q-Lab
62 COMPOUNDING WORLD | December 2017 Full spectrum (UV-Vis-IR) Best simulation of long wavelength UV and visible light Spectrum changes
Relative humidity control Water spray
More expensive and complex
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PHOTO: AVERY DENNISON
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