R.S. Lankone, G. Sarti, M. Zammarano, C. Cardelli, L-P Sung
National Institute of Standards and Technology,
Keywords: weathering, siding, PVC, release, degradation
Summary:Home exterior materials are the outermost barrier between occupants of a home and the surrounding environment. In the United States, one of the more popular home exteriors is polyvinyl chloride (PVC) siding. Vinyl siding is conventionally about one millimeter thick and embossed with a pattern that resembles the grain of wood. Commonly, a variety of particulate additives from the nano to micron scale are incorporated into the thin embossed layer and the PVC bulk to confer desirable properties such as increased impact resistance, improved UV stabilization, and/or enhanced appearance. While home siding is engineered to specified performance standards, the polymer matrix is inherently susceptible to weathering during its use – particularly UV-driven photodegradation – that can result in siding failure. Largely unknown is both the extent to which nano to micron scale particulate additives regulate the kinetics of overall material aging and the degree to which such additives will release into the environment during polymer matrix degradation. These knowledge gaps regarding environmental exposure of vinyl siding and the fate of their particulate additives were investigated through evaluation of performance, degradation, and nanomaterial release after artificial weathering. Artificial weathering studies were realized with both the NIST SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) and a QUV Weatherometer to age commercially available vinyl siding. Vinyl siding samples were characterized spectroscopically and morphologically to track the rate of polymer degradation and monitor the emergence and exposure of embedded particulate additives that resulted from each exposure strategy. A key component of this study was the examination of how the differing patterns of UV and moisture exposure produced in NIST SPHERE and QUV Weatherometer impacted the kinetics of vinyl degradation and particulate additive exposure. Formulations of PVC with specified concentrations of select particulate additives were prepared and artificially aged as well. These samples were evaluated to determine the extent to which the presence and concentration of specific additives regulated the degradation and impact performance of PVC during aging. Collectively, these investigations characterized the degradation behavior of this ubiquitous siding material as well as evaluated the extent to which UV driven aging of exterior materials resulted in nanomaterial release and exposure to humans and the environment.