Upcycling is emerging as a crucial strategy for enhancing the value of polymers, driving the transition toward a circular material economy. In this study, we present a facile chemical method for converting high-density polyethylene (HDPE) waste into valuable long-chain dicarboxylic acids (LCDCAs) via a key enabling unsaturated double-bond formation step. That is, we propose introducing unsaturation points in HDPE using commercially available heterogeneous catalysts (e.g. Pt/Al₂O₃). The unsaturation level through CC double bond formation is around 10%, as confirmed by FTIR, Raman and X-ray photoelectron spectroscopy. A process of microwave-assisted oxidation is demonstrated to break down the dehydrogenated HDPE into a mixture of aliphatic diacids. This approach enhances the recyclability and value of HDPE by the transformation of polymer waste into bifunctional monomers for potentially novel polyester synthesis. This process offers a sustainable and value-added alternative to conventional recycling methods. While further optimizations are needed, initial estimates of the E-factor and sEF provide promising indicators of the potential environmental benefits of this upcycling approach.