Photo-stabilization mechanisms of High-Density Polyethylene (HDPE) by a commercial few-layer graphene

This work studied few-layer graphene (FLG) dominant action mechanisms as a photo-stabilizer. High-density polyethylene (HDPE) containing 0-0.5 wt% FLG were exposed to UVA radiation in a QUV chamber, according to ASTM G154 for different exposure times, ranging from 0 to 672 h. The chemical, rheological, and mechanical properties were tracked using attenuated total reflection-Fourier transform infrared (ATR-FTIR), rheological measurements, and tensile tests. The experimental results showed that the addition of only 0.25 wt% FLG fully stabilized 1- to 3-mm thick HDPE for an exposure time of 672 h. Electron paramagnetic resonance (EPR) test was performed on the UV-exposed mixture of hydrogen peroxide (H2O2) and the FLG aqueous suspensions (0, 0.2, 1, and 5 mg/mL), to study the FLG performance and mechanisms as a photo-stabilizer. The results showed that FLG effectively decreased the characteristic EPR signal intensity due to both UV absorption/reflection and free radical scavenging. Fifty-seven percent of the reduction was found to be due to UV absorption/ reflection and 43% due to free radical scavenging. It is demonstrated that UV absorption/reflection and free radical scavenging are the dominant ones among the three FLG photo-stabilizing mechanisms (UV absorption/reflection, free radical scavenging, and physical barrier to oxygen).