Weatherability | materials testing
Assessing the weatherability of plastics compounds
Understanding how to best protect a plastic part from the effects of weathering needs to include an analysis of several important factors. It should take account of the polymer type, colour and additives. An estimation of what the actual exposure will be is also critical – for example, it could be desert-like conditions, humid or rainy weather, or sunlight coming through window- glass. It is also vital to be aware of how the customer defi nes quality – for example, is it colour, gloss and/or the retention of physical properties? Added to this complexity are various methods of
accelerated testing, including outdoor testing and laboratory testing in a fl uorescent-UV or xenon-arc test chamber, which are used to predict how a material will perform under long-term weathering. Suppliers of equipment and materials agree that accelerated laboratory weathering tests are excellent tools for comparing formulations, but they are not quantitative predictors of actual service life. However, long-term research into improving the predictive accuracy of accelerated test methods is leading to increased confi dence and reliability in this area. Weathering test methods typically use conditions specifi c to an application, such as artifi cial turf, wood-plastic composite decking, vinyl siding, or automotive coatings. Standards for one application, however, may be borrowed for other areas. For example,
www.compoundingworld.com New standards, equipment and
testing procedures are improving the reliability of accelerated weather testing. Jennifer Markarian reports
a new ASTM standard for the accelerated weathering of automotive coatings (ASTM D7869-13) is seen as relevant for the plastics industry even though it was written for automotive coatings. Tad Finnegan, plastic additives technical manager at BASF, which helped develop the standard, explains: “Previous automotive weathering specifi cations soon spread beyond the transportation industry and coatings industry to become ‘general’ standards for weathering materials, including plastics”.
New ASTM accelerated test Published last year, ASTM D7869-13, Standard practice for xenon arc exposure test with enhanced light and water exposure for transportation coatings, is designed to replace SAE J1960 and SAE J2527. These have been used since the 1980s, but are now seen as defi cient in providing meaningful correlation to fi eld results. D7869, which is seen as a breakthrough in test
development, meets the industry goal of better replicating real-world exposure. As an added benefi t, the new protocol reduces testing time by 40% over SAE
June 2014 | COMPOUNDING WORLD 35
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