When it comes to weathering testing, a commonly asked question is when to use Fluorescent-UV device and when better a xenon-arc instrument. The following explanations may be useful to answer that question.
Degradation by Weather Stress
All polymers undergo irreversible physical and chemical changes caused by ultraviolet radiation UV-B and UV-A, eventually visible light, heat, and moisture. With oxygen present, UV radiation initiates photo oxidation. Temperature drives the degradation. Water causes physical and chemical stress. Colors react to visible light.
The property changes caused by the effects of weather(ing) can be:
• Yellowing, especially for transparent or white materials
• Color change
• Cracking
• Gloss loss
• Embrittlement
Major Differences Between Xenon and Fluorescent-UV
Filtered xenon-arc and fluorescent-UV (Fl-UV) devices follow two completely different approaches. Both types differ considerable in how and in which wavelength range they simulate the sun’s spectral irradiance. Another key difference is water delivery to the specimens.
FL-UV lamps – as the name says - are limited to UV radiation in the range 295-350 nm. Water is usually delivered through condensation. Therefore, FL-UV testing is mostly confined to the rapid screening of paint and resin formulations against basic weathering stability. Furthermore, it is commonly applied to test wood coatings and clear coats for the same reason. Since FL-UV is lacking long wavelength UV-A and visible light, it is not recommended to test dyed or pigmented coating systems or study light/UV stabilizers.
Xenon-arc weathering devices simulate and control all three primary weather factors: full solar spectrum, irradiance level, temperature, and moisture. Their optical filters provide full-spectrum solar radiation conditions in the UV, VIS, and IR range 295-2500 nm. Together with water spray, and wide temperature and RH control ranges, xenon devices can replicate a variety of different outdoor and indoor conditions in a realistic way.
Xenon-arc weathering is known as being more reliable for effectiveness studies of light/UV stabilizers, and testing color and appearance changes of products. For critical and premium applications, such as the weathering of transportation coatings, OEM’s in particular prefer xenon-arc devices. They want to be on the safe side when it comes to approvals of the best materials, coming in a variety of colors, polymer types, and resin technologies used in their vehicles.
More Information
A
technical guide and a
recorded online seminar provide more detailed information on differentiating the two testing technologies and getting the most out of your weathering and UV-durability testing.
In addition, the Atlas website provides numerous
video tutorials,
recorded online seminars,
technical documents, and a
training schedule, all helping you to make the right testing decisions.