Practical Application of Xenon Arc Weathering: Q&A with Jeff Marek
What are the basic elements that contribute to weathering?
The three main factors affecting the durability of products exposed to the outdoor environment include solar radiation, temperature and moisture. Obviously, harsher weather environments including intense sunlight, heat, humidity or large swings in temperatures can provide a more difficult test for products to meet customer durability expectations. Many industry weathering specifications include additional requirements to meet the needs of these harsh environment states / countries.
Which industries require weathering most often?
The easy way to look at the effects of weathering by industry is simply to look at products that are exposed to external environments. The most common industries include:
- Automotive
- Paints and coatings
- Building / construction products
- Vinyl films
- Lawn and garden products
- Rubber and plastic products or components
What are the benefits of accelerated laboratory testing vs. outdoor / natural weathering?
As with any type of testing, laboratory testing will provide more repeatability and reproducibility of testing results. In addition, by accelerating the testing in a laboratory, product manufacturers can gather performance data much quicker allowing them to make design decisions and launch their new products more efficiently.
In many cases, outdoor / natural weathering is also desired in order to get a balanced look at performance data and to correlate to the laboratory testing. Some testing standards also require outdoor / natural weathering in addition to laboratory weathering.
Plastic materials introduced into global markets that they were not designed or tested for can potentially result in product failures. Sometimes a product will have a unique sensitivity to the local environment that was not predicted and tested for.
What exposure does a Xenon Arc lamp provide (compared with UV only)?
Natural sunlight is made up of three primary wavelength ranges: Ultraviolet, Visible and Infrared. The shorter the wavelength range, the more intense the photon energy; thus more effect on the material that it is in contact with. That being said, UV (the most powerful range of radiation) makes up less than 7% of total radiation.
A Xenon Arc lamp, when filtered properly, most closely simulates both UV and visible wavelength ranges making it an excellent option for testing exposure to natural solar radiation. In order to more closely simulate natural exposure, a few more considerations must be reviewed:
Orientation of the product or sample in service. Horizontal exposures can have a different effect than vertical exposures.
The geography where the product will be used (latitude, proximity to the ocean / water, altitude, etc.)
Typical operating temperatures.
What are the potential effects of weathering on materials?
On Rubber / Polymer products, there are a variety of effects that can occur due to weathering. Several of the most common include:
- Chalking and surface degradation – UV exposure can cause the surface layer molecules eroding away exposing the underlying layers of fillers and pigment particles. These particles can become a powdery (often white) substance on the surface.
- Color shift, yellowing, or fading – After prolonged exposure, materials can exhibit changes in color or yellowing that negatively affect the surface appearance. For products that require aesthetic consistency over time such as coatings, films or product surfaces in the automotive industry (for example), understanding these properties provide manufacturers with data to develop the most appropriate product warranties.
- Cracking – Effects of both solar radiation and moisture can cause expansion and contraction of a polymeric material which can lead to stress and ultimately surface fracture. In addition to Xenon arc weathering, ozone (created by solar radiation reacting with oxygen or air pollution) can create free radicals that break the bonds of chemical bonds in the rubber / polymeric material, leading to cracks.
- Gloss loss – Much like yellowing and color fading, solar radiation and elevated temperatures can cause the material surface to lose gloss.
What types of testing are used to evaluate materials post weathering?
After weathering, it is critical to understand how the material has changed in appearance and performance. There are a wide variety of post weathering tests that can be conducted to best determine how a given polymeric material will react. Some of the most common tests are:
- Changes in color – Colorimeters use several filters to mimic the appearance of color by the human eye. It can measure the difference in color pre and post weathering.
- Changes in gloss – By measuring the reflectance of light from the surface of the material in question, gloss meters can provide the variance in gloss.
- Material properties – Retention of physical properties such as tensile, tear, impact, hardness, or melt flow index can be tested to understand the full effects of weathering on a given material. Benchmarking several, similar materials can provide researchers with a range of options that could be used based on physical property requirements in the product.