High-density polyethylene reinforced with carbon dots for improved processing cycles and recyclability traceability

Abstract

The sustainable utilization of polymers depends on efficient recycling and the ability to retain their critical physical properties for further processing. In this study, high-density polyethylene (HDPE) nanocomposite properties were enhanced by the integration of carbon dots (CDs), in terms of processability and optical traceability during recycling. HDPE composites with varying CDs loadings were prepared to assess their effects on optical and mechanical properties over three consecutive recycling cycles. The composite containing 0.5 wt% CDs demonstrated a 17% increase in tensile strength after recycling, with a maximum strain of 11%, significantly outperforming the neat HDPE while preserving its crystalline structure. Additionally, incorporating 0.1 wt% CDs reduced the wear rate by up to 98%, highlighting a substantial improvement in durability. Improved processability of the recycled material was confirmed by producing 3D-printed specimens at each CDs concentration. Notably, composites containing 0.1 wt% CDs exhibited excellent printability even after three recycling cycles. CDs have also been utilized as luminescence tracers. This study revealed that the quenching of the blue phosphorescence associated to the carbonyl groups of the polymer backbone was highly dependent on the CDs content. Importantly, nanocomposites with 0.1 wt% CDs exhibited progressive luminescence changes corresponding to the number of recycling cycles, enabling quick and reliable traceability and sorting using standard mobile phone cameras. These findings are highly promising, paving the way for rapid, automated, and scalable HDPE recycling. This innovation offers significant potential for advancing the circular economy of HDPE and enhancing the sustainability of polymer materials.