Effect of Few-Layer Graphene (Flg) and Relative Photo-Degradation Depth on the Ductile to Fragile Transition of High-Density Polyethylene

Abstract

In this study, the effect of adding a few-layer graphene (FLG) on the photo-degradation depth of high-density polyethylene (HDPE) was investigated. For that, samples of neat HDPE and composites containing 0.5 wt% FLG with two different thicknesses, i.e., 3 and 2 mm, were exposed to ultraviolet (UV) radiation for several durations. The elongation at break was evaluated as a function of UV exposure time and correlated to the photo-degradation depth at which chemi-crystallization occurs using Raman microscopy.  The results showed that embrittlement occurs when the relative photo-degradation depth reaches around 10% in neat HDPE, which takes place at early exposure times, i.e., 10 and 7 days, for 3- and 2-mm thick samples, respectively. This embrittlement preceded the appearance of surface cracks on both samples. Conversely, the samples containing 0.5 wt% FLG maintained a ductile failure behavior even at longer exposure times of up to 45 days. In spite of the presence of surface cracks, this ductile behavior was observed even at a relative photo-degradation depth of 12.5%.  The persistence of ductile behavior was attributed to the photo-stabilizing effect of FLG, as well as to the tendency of the degraded layer to detach from the composite’s ductile core.

Keywords: Photo-Degradation, Embrittlement, graphene