About a year ago, Stockwell Elastomerics started a test on a variety of materials on the roof of the main office building in Philadelphia, PA. (View the blog post about the start of that test.) The experiment tested 37 samples of rubber polymers, including SBR (styrene-butadiene rubber), neoprene (polychloroprene), EPDM (ethylene propylene di-monomer), ECH (epichlorohydrin), PORON® microcellular urethane foam, silicone sponge, silicone foam, solid silicone and fluorosilicone. The wide-ranging climate of the area means that these materials saw temperatures ranging from 5°F to 100°F, precipitation totaling 65.3 inches (including snow), and winds as high as 60 mph (source: NOAA).
As predicted last year, the silicone-based materials were mostly unaffected by this year-long exposure, experiencing little change in size or thickness, no cracking, and minor discoloration that was primarily the result of dirt building up on the samples. This is in part due to the chemical structure of silicone elastomers. An inorganic backbone increases resistance to other chemicals, so silicone-based materials do not degrade the way seemingly similar materials do. In addition, the high bond strength between silicone and oxygen at an atomic level makes silicone elastomers highly resistant to both heat and UV exposure.
Other polymers did not fare as well, however, including Poron and blended sponge. While Poron and other urethane foams are excellent gasket materials for indoor environments, prolonged exposure to the elements, particularly UV rays, causes severe cracking and embrittlement.
Low-density urethane foams fared even worse, including disintegration over time, as the pictured Pyrell samples demonstrate.
The neoprene and blended sponges that were in the year-long test show a similar level of damage, as the samples were lost or destroyed during the experiment’s run. Sunlight and high temperatures likely dried the samples, which then eroded until a gust of wind probably ripped them from their anchors on the test board.
Non-silicone solid rubber materials experienced overall slight shrinkage. Silicone-based conductive materials lost some of their conducting ability, undergoing significant increases in surface resistivity. Conversely, a conductive neoprene material gained much conductivity due to the loss of a resistive surface coating.
It is often easy when designing a gasket to focus only on the unique mechanical, chemical, or electrical needs of an application. However, these weather tests illustrate that outdoor and UV exposure should play a critical role in gasket material selection, and for some materials weather exposure can be a deciding factor. While many materials have specialized properties that best suit the distinct challenges of a specific design, it remains important to ensure that weather exposure will not cause material degradation.
Stockwell Elastomerics’ Applications Engineers bring extensive knowledge and experience on gasket materials and often provide engineering technical tips to customers that include considerations about exposure to weather, sun and temperature extremes. Contact Stockwell Elastomerics for further assistance.