High-density polyethylene (HDPE) is regularly utilized for its structural properties, including in many outdoor applications. However, as with many polymers it is susceptible to environmental degradation which can alter its mechanical, physical, and chemical properties. The tensile behavior of HDPE is initially ductile, but after degradation it can rapidly turn brittle. Determining the conditions under which this change in properties occurs is necessary to better engineer HDPE blends and the systems in which it is employed. For this the effect of different exposure conditions (temperature, ultraviolet light, humidity) on its properties are explored using accelerated indoor tests, which are compared to HDPE exposed outdoors in a tropical climate (southern Florida, USA). Material properties were measured by tensile tests, scanning electron microscopy, x-ray diffraction, and Raman and Fourier-transform infrared spectroscopies. The rate of change in properties such as elongation at break, crystallinity, and oxidation index depend strongly on the exposure conditions. Over time the deformation and failure of tensile samples shows the most dramatic change, from ductile to brittle behavior. During tensile testing of HDPE in the ductile regime the degree of molecular orientation in the deformation region is high (Figure 1a). In the transition between ductile and brittle fracture a distinction between core and surface mechanical behavior is observed (Figure 1b), with the relatively more degraded surface undergoing brittle failure, and the core region experiencing ductile failure. In the brittle regime the core-surface distinction is smaller, and even disappears.<br/><br/>The transition from ductile to brittle failure can occur quickly, which has serious implications for the design of systems which use HDPE for its structural properties. Because of this is important to better understand under which conditions a change in material properties occurs.

Crystalline structure and fracture behavior of polyethylene after outdoor and accelerated indoor exposure

254th National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.