This study investigates the effects of annealing on the mechanical and thermal properties of PLA and PLA/Wood composites processed via FDM. PLA/Wood, a composite containing 20 wt% recycled pine wood particles, was annealed at 50°C and 100°C to enhance structural reliability and mechanical performance. Specimens were printed in 0°/90° and −45°/45° orientations and subjected to tensile, four-point bending, and Charpy impact tests. Annealing at 50°C enhanced tensile strength by 62.3% in the 0°/90° orientation (from 17.83 MPa to 28.95 MPa) and 66.6% in the −45°/45° orientation (from 16.55 MPa to 27.58 MPa). Flexural modulus also improved, reaching 2.78 GPa (0°/90°) and 3.12 GPa (−45°/45°), compared to untreated samples (2.38 GPa and 2.83 GPa, respectively). Impact resistance of PLA/Wood at 50°C increased to 48.86 kJ/m2 (0°/90°) and 54.38 kJ/m2 (−45°/45°), while annealing at 100°C led to lower mechanical performance, reducing impact resistance to 38.78 kJ/m2 (0°/90°) and 46.00 kJ/m2 (−45°/45°). Pure PLA exhibited the highest impact resistance, reaching 70.71 kJ/m2 (0°/90°) and 81.12 kJ/m2 (−45°/45°), and superior hardness (82.1 Shore D in 0°/90° and 80 in −45°/45°) compared to untreated PLA/Wood (77.5 and 75.5, respectively). Microscopic analyses confirmed that annealing at 50°C reduced voids to 11.48% (0°/90°) and 11.42% (−45°/45°), while at 100°C void content further decreased to 9.77% and 9.35%, respectively. These findings underscore the potential of controlled annealing to optimize PLA/Wood composites for structural applications, emphasizing the critical role of thermal processing parameters.
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