(Excerpted from the article “Speeding the route to material insight” in December 2021 Compounding World Magazine.)
North American ﬁrm EYE Applied Optix, which is a division of Iwasaki Electric’s EYE Lighting International subsidiary, offers an alternative lamp technology that is said to further accelerate weather testing of plastics. The Super UV (SUV-W161) test chamber uses Iwasaki’s metal halide light source, which is said to achieve a higher UV irradiance than both ﬂuorescent UV and xenon lamps.
The Super UV technology uses ﬁlters to prevent heating by far visible and infrared light and to remove the short UV wavelength not present in natural sunlight. Results have been shown to correlate to accelerated testing with a xenon lamp and to outdoor data, says Doug Vermillion, Director of EYE Applied Optix. Chambers using the technology can decrease the amount of time needed for screening tests when compared to conventional xenon or ﬂuorescent UV, he adds.
In a recent project, a building products manufacturer wanted to test the long-term UV resistance of a transparent ﬁlm intended for outdoor use. The manufacturer was concerned about mechanical performance of the ﬁlm as well as its colour and gloss retention. Vermillion says the ﬁrst step in the project was to evaluate a well-understood subject material in the Super UV chamber.
“We do have benchmark test methods for a variety of materials, but differences in test subject material formulations and properties will likely require several iterations to fully understand the interaction between high irradiance, and other control variables such as temperature and time,” explains Vermillion. “It is important to fully understand your product failure modes from natural weathering and their root causes.”
While the initial benchmark experiment reproduced the failure mode (colour change) correctly, the researchers ran several further experiments to determine the optimal Super UV test conditions to best match the degradation observed in static outdoor weathering including surface cracking. It was known that water exposure can contribute to the cracking, so the time of wetness was increased in the second experiment by reducing the temperature and increasing the relative humidity during the dew cycle, says Vermillion.
In outdoor exposure, colour change and surface cracking occur simultaneously; in the ﬁnal two test iterations, the researchers aimed to ﬁne-tune the temperature settings to synchronise the failure modes. This was achieved by ﬁrst adjusting the temperature during the dew cycle to increase the rate of reactions occurring during the dark phase and after that by evaluating the effect of temperature during UV irradiance of the sample.
“The customer has found that the Super UV results correlate to xenon and outdoor weathering, and conﬁrmed that highly accelerated weathering tests can be used effectively for product qualiﬁcation. Some upfront work is required to validate correlation with natural weathering, but this is true when using any type of laboratory weathering equipment,” says Vermillion.
(Excerpted with permission from Compounding World. See the entire article and edition here.)