Progressing plastics circularity and its associated benefits can provide advantages to both practitioners and the broader environment. As technology continues to evolve and various industries increasingly embrace the principles of the circular economy, additive manufacturing cannot remain detached. The widespread utilization of additive manufacturing can be a valuable asset for reprocessing recycled plastics, for reuse as secondary life products. This study investigates the reuse of Low-density PolyEthylene (LDPE) in additive manufacturing via a robust, customized, low-cost pellet extruder 3D printing system. The system underwent evaluation through mechanical tests of 3D printing specimens and Finite Element Analyses (FEA). Four mixtures were created using different fractions of neat and recycled LDPE and tensile specimens were fabricated and tested under quasi-static tests, according to ASTM D638. The corresponding FE materials models were developed to create a numerical tool for the evaluation of LDPE 3D printed components. The tensile strength tests showed that specimens developed with 100% recycled LDPE performed 70.06% better in elastic modulus, 18.18% better in ultimate tensile strength (UTS), and 17.74% better in yield strength compared to specimens consisting of 60% recycled and 40% virgin LDPE, which exhibited the best mechanical properties among the tested mixtures. However, they exhibited a 14.34% reduction in elongation at break. The outcomes of this study established a sustainable and fully functional proof-of-concept of the developed 3D printing system to address the reduction, reuse and recycling of plastic waste under the Sustainable Plastic Strategy.