Repetitive recycling effects on mechanical characteristics of poly‐lactic acid and PLA/spent coffee grounds composite used for 3D printing filament

Abstract Due to its biodegradability, biocompatibility, and mechanical properties, poly‐lactic acid (PLA) is a leading biomaterial for numerous applications, especially for fused deposition modeling and fused filament fabrication. Nonetheless, the absence of a comprehensive recycling strategy may emerge as a significant source of plastic pollution in the future. Indeed, the polymer undergoes deterioration during melt recycling, resulting in a decrease in some mechanical properties that can compromise recyclability. To improve the properties of recycled PLA, the utilization of organic fillers coming from renewable materials can be considered as a sustainable solution. The objective of this work is then to evaluate the effect of recycling (reprocessing) on a virgin raw material as well as on biocomposites based on spent coffee grounds (incorporating 5% of spend coffee grounds in weight). The different types of filaments are extruded and re‐extruded and characterized under tensile, melt flow index, and hardness tests. The results show that the increase in the number of extrusions whether for virgin PLA or the composite contributes to the diameter fluctuation. Regarding the tensile properties, the rise in the frequency of recycling shows a weakness in the tensile strength and the elongation at break. On the other hand, Young's modulus values exhibit fluctuations. Concerning the addition of the spent coffee grounds filler, no major enhancement is observed in the tensile strength and the elongation at break, which is attributed to the poor adhesion between the matrix and the filler. The recycling process affects the hardness values of PLA, leading to an increase in these values, as well as those of the composite, which can be associated with the increased crystallinity caused by the recycling process and the SCG incorporation. Highlights Recycling and reusability strategy for poly‐lactic acid (PLA) and PLA/spent coffee grounds (SCG) filaments. Assessment of recycling effects on PLA and PLA/SCG. Mechanical characterization through tensile and hardness testing.