Upcycling waste plastics into <scp>3D</scp> printing filaments for a circular and sustainable future

Abstract Growing environmental concerns over plastic waste have spurred the development of sustainable recycling methods. One promising solution involves transforming post‐consumer plastics into filaments for additive manufacturing. Waste poly(lactic acid) (PLA) from injection‐molded and 3D‐printed products was successfully upcycled through catalyst‐free aminolysis, yielding N ‐lactoylethanolamine and its methacrylated derivative dimethacrylate ester with high purity. The resulting dimethacrylate ester–4‐acryloylmorpholine photocurable resins demonstrated superior performance, including higher T g (up to 173 °C), enhanced tensile strength, and improved thermal stability compared to commercial resins. This study establishes an efficient, sustainable chemical recycling pathway that converts PLA waste into advanced, high‐performance materials suitable for precision 3D printing applications. For the conversion of post‐consumer high‐density polyethylene (HDPE) milk bottles into high‐performance 3D‐printing filaments reinforced with 0–60 wt% glass fiber (GF), waste HDPE was cleaned, shredded, and co‐extruded with industrial GFs, followed by re‐shredding to improve dispersion and achieve a consistent filament diameter of 1.5–1.6 mm. Mechanical properties were significantly enhanced, with tensile strength increasing from 27.94 MPa for pure HDPE to a 95% enhancement at 45 wt% GF, and flexural strength rising by 145% at 30 wt%. Fiber agglomeration above 45 wt% reduced overall performance. Studied were the mechanical and anisotropic properties of 3D‐printed PLA and acrylonitrile–butadiene–styrene, highlighting the effects of layer orientation and deposition patterns. Tensile testing was conducted following ASTM D638 standards to evaluate material performance. Five print orientations (0°, 30°, 45°, 60°, and 90°) were evaluated, with six samples tested per orientation, totaling 30 samples per experimental run. A preliminary ‘proof of concept’ trial was first carried out using PLA material. The integration of plastic recycling with additive manufacturing not only contributes to a circular economy but also opens new avenues for low‐cost and customizable production across various industries. © 2026 Society of Chemical Industry.