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Biowaste to 3D printed biocomposites.The enhancement of the mechanical and thermal characteristics of 3D printed polylactic acid (PLA) composites reinforced by coir fiber powder (CFP) has been investigated by varying the weight percentage (wt%) of the reinforcement and annealing process. CFP/PLA composite filaments with CFP compositions of 0.1, 0.3, and 0.5?wt% were fabricated. These filaments were used to print CFP/PLA test specimens. The specimens were annealed at 90°C for 120?min in a hot air oven followed by cooling at room temperature. Mechanical, morphological, crystalline, and thermal characterizations were conducted on these specimens. The tensile and flexural strength of neat PLA were observed as 49.7 and 82.4?MPa which decreased by 6.4% and 8.13% respectively for printed composite specimens with 0.5?wt% CFP as reinforcement material. On the other hand, the annealed CFP/PLA composite specimen, with 0.1?wt% CFP as a reinforcement material, demonstrated higher tensile and flexural strength. Specifically, it exhibited a maximum tensile strength of 56.4?MPa and a maximum flexural strength of 92.9?MPa, which are 13.5% and 12.7% higher, respectively, than neat PLA. These strengths are 15.5% and 16.7% higher, respectively, than those of the unannealed CFP/PLA composite specimen with the same wt% of CFP reinforcement. The annealing process increased the crystallinity of composites by enhancing the crystallinity index (63%) and crystalline size (6.7?nm). The high thermal stability of composites (with a glass transition temperature of 256°C) makes them suitable for applications in food and medical packaging.HighlightsEnhancement of thermo?mechanical characteristics of 3D printed bio?composites.Annealing process improved mechanical features of 3D printed bio?composites.Annealed composite with 0.1?wt% as reinforcement demonstrated better properties.SEM and XRD studies confirmed failure mechanisms and crystalline structure.Thermal and mechanical assets favor its utilization in food wrapping applications.