Production and 3D printing optimization of PLA/spent Turkish coffee grounds biocomposites: Investigation of mechanical performance

Spent Turkish coffee grounds (STCG) were investigated as a locally available bio-based filler for polylactic acid (PLA) filaments intended for fused deposition modeling (FDM). After drying, grinding, alkaline treatment, and sieving through a 325-mesh sieve with a nominal aperture of 45 µm, STCG was incorporated into PLA at 1, 3, and 5 wt.%. Filament processability, 3D printability, FTIR characteristics, SEM morphology, and the mechanical response of 3D-printed specimens were evaluated. FTIR spectra retained the principal PLA absorption bands without distinct new peaks after STCG incorporation. Temperature-tower tests identified a practical processing window of 200–215°C, with 210°C selected for subsequent printing. At this temperature, 3DBenchy specimens containing up to 3 wt.% STCG showed comparatively stable formation, whereas the 5 wt.% formulation exhibited partial first-layer detachment and base distortion. The 1 wt.% STCG formulation exhibited the highest mean mechanical response: tensile strength increased from 52.1 to 55.2 MPa (+5.95%), flexural strength from 83.0 to 88.8 MPa (+6.99%), flexural modulus from 3480 to 3857 MPa (+10.83%), and Charpy-mode impact strength from 9.67 to 16.23 kJ/m 2 (+67.84%) relative to PLA. Tensile toughness also increased from 1.068 MJ/m 3 to 1.148 MJ/m 3 . Higher STCG loadings were accompanied by lower tensile and flexural responses and greater morphological heterogeneity, including localized voids, filler-rich regions, and discontinuous fracture features. Shore D hardness remained essentially unchanged up to 3 wt.% and decreased at 5 wt.%. In addition, the coffee bean-shaped planter was designed in SolidWorks and 3D printed using 1 wt.% STCG formulation, demonstrating the practical printability of the composite filament. These findings support the use of locally sourced STCG as a filler for PLA filaments in sustainable FDM applications.