Abstract
Thermoplastic polyolefin (TPO) roofing membranes have been used in the US low-slope roofing industry as single-ply membranes for over 15 years, and have seen widespread acceptance. TPO membranes have been defined by ASTM Standard D6878-08, “Standard Specification for Thermoplastic Polyolefin Based Sheet Roofing,” Annual Book of ASTM Standards, Vol. 04.04, ASTM International, West Conshohocken, PA, 2008, www.astm.org, which sets a minimum threshold for accelerated weathering performance. To be ASTM D6878 compliant, a TPO membrane shall not show any visual micro-cracking under 7X magnification after being exposed in a xenon arc light apparatus to a minimum irradiance of 10 080 kJ/m2 at 340 nm. While the ongoing development of TPO membranes uses D6878 as the basic standard, it is necessary for individual membrane manufacturers to develop an advanced understanding of TPO long-term weathering durability to further improve confidence in the expected service life. In this paper, a novel ultra accelerated outdoor weathering technique, atlas ultra accelerated weathering system (UAWS), is used to predict long-term weathering durability performance of TPO. The comparison and correlation of this novel technique with other artificial accelerated weathering methods, such as xenon arc light [ASTM G155-05a, “Standard Practice for Operating Xenon Arc Light Apparatus for Exposure of Non-Metallic Materials,” Annual Book of ASTM Standards, Vol.14.04, ASTM International, West Conshohocken, PA, 2005, www.astm.org] and fluorescent UV light [ASTM G154-06, “Standard Practice for Operating Fluorescent Light Apparatus for UV Exposure of Nonmetallic Materials,” Annual Book of ASTM Standards, Vol. 14.04, ASTM International, West Conshohocken, PA, 2006, www.astm.org] are shown and reviewed. The surface temperatures of TPO membranes exposed in the UAWS device as well as in the field are shown to further understand the heat impact on TPO durability. In addition, accelerated heat aging at temperatures up to 138 °C are shown to give very good correlation to other aging tests.
