Effect of Few‐Layer Graphene ( <scp>FLG</scp> ) and Relative Photodegradation Depth on the Ductile to Fragile Transition of High‐Density Polyethylene

ABSTRACT Photo‐stabilization is essential for thermoplastics in outdoor applications, as it extends service life by protecting polymer chains from UV‐induced degradation. Graphene has emerged as a multifunctional stabilizer with capabilities including UV screening, barrier effects, and radical scavenging. However, its influence on the depth profile of photodegradation under UV exposure is not fully understood. This work investigates the effect of few‐layer graphene (FLG) on the photodegradation of high‐density polyethylene (HDPE). Neat HDPE and composites with 0.5 wt% FLG were prepared in two thicknesses (3 and 2 mm) and exposed to UV radiation for varying durations. Elongation at break was measured as a function of exposure time and correlated to the degradation depth, determined by chemi‐crystallization using Raman microscopy. In neat HDPE, embrittlement occurred when the degraded layer reached ~10% of the thickness, after 10 and 7 days for 3‐ and 2‐mm samples, respectively, preceding the appearance of surface cracks. In contrast, HDPE with 0.5 wt% FLG retained 50% of its initial elongation at break, characterizing a ductile failure, even after 45 days despite surface cracks. Additionally, embrittlement was only observed when the relative degradation depth reached 12.5%, exceeding the 10% threshold observed for the neat HDPE. The persistence of ductility is attributed to the photo‐stabilizing effect of FLG and the detachment of the degraded surface from the ductile core, leading to a material with enhanced UV resistance for outdoor packaging and coating applications.