materials testing | Weatherability
new test method required the development of a new calibration method to ensure that a minimum amount of moisture consistently reached the samples. Mini- mum water delivery and verification using this calibra- tion method should be considered for all global weathering standards.” The new method also requires use of a light source
with a precise spectral match to meet a tighter definition of daylight. The Atlas Right Light filter and Q-Lab’s Daylight F filter meet this new definition. The method requires repositioning of the samples, which previously had been only recommended, and calls for more realistic temperature cycling. Temperature is one of the crucial variables in testing
Q-Lab’s outdoor weather testing facility in Florida
J2527, based on the rate of UV deposited, claims Oscar Cordo, standards manager at Ametek-Atlas Material Testing Technology. The ASTM standard is the culmination of 10 years of
Q-Lab’s Q-Sun Xe-3 was used in creating the new ASTM standard
research, notes Jeffrey Quill, director of technical applications at Q-Lab. One of the most significant results of this initial research was a realization of the importance of the effect of moisture on the surface of coatings when trying to replicate exposure in a humid environment such as Florida, which is considered a benchmark environment. Researchers looked carefully at the outdoor environment and tried to replicate it in the lab. For example, researchers found that water spray and high humidity during a test chamber’s dark cycle, followed by a dry light-cycle, best replicated the moisture absorption and drying found outdoors in Florida.
The ASTM standard test
incorporates the findings of these correlation studies. “This test, for the first time, accurately replicates several key forms of degradation (such as gloss loss, colour change, delamination and photo-oxidation) because the research thoroughly evaluated the importance of all three key weathering vari- ables, namely light, heat and moisture. In the past, researchers thought the light spectrum was the main issue relating to correlation, but we found that accurate re-creation of outdoor moisture is another key component,” explains Quill. “The
36 COMPOUNDING WORLD | June 2014
weathering, in both laboratory and outdoor tests. In the next article in this magazine, the effects of temperature and spectral distribution in outdoor testing of vinyl using Fresnel concentrators are discussed by Henry Hardcastle of Atlas. “Temperature of the material will affect rates of
chemical changes and, ultimately, the actual physical or appearance changes as a result of weathering,” explains Matt McGreer, product manager at Atlas. “Knowing the surface temperature of a specimen during exposure can allow for a better understanding of degradation rate and service-life prediction.” Atlas offers the S3T (Specific Specimen Surface Temperature) system, which provides real-time temperatures of each sample during exposure. An appendix to the ASTM D7869 method delineates
the steps taken to develop the method and provides justification for each test segment. “This text provides a benchmark for future standards development and a template for future research of similar methods for other industries,” notes Cordo. “More importantly, as the background research done to develop this cycle was unprec- edented, it now serves as the de facto standard justifying the work required to develop adequate test methodology. The work demon- strates that good scientific methodology and an understand- ing of both material sensitivities and details of the natural environ- ment can be used to develop better artificial test cycles. Ultimately, the intent is to provide faster test results and fewer field failures, both of which will reduce costs in the long run.” “Weathering is not an exact,
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