Effect of Annealing on the Mechanical Properties of Carbon Fiber-Reinforced PLA

Additive manufacturing of polylactic acid reinforced with carbon fiber, specifically via fused deposition modeling, offers significant advantages for fabricating complex geometries; however, inherent extrusion defects often restrict its use in high-performance mechanical components. While post-printing annealing treatments promote polymer crystallization and interlayer cohesion, the highly non-linear effects of this process on PLA composites remain underexplored. This study investigates the specific effects of annealing temperature and exposure time on parametrically optimized 3D-printed polylactic acid reinforced with short carbon fiber. An orthogonal experimental design evaluates temperatures ranging from 55 °C to 95 °C and times between 4 and 12 h. The mechanical behavior was mapped utilizing Analysis of Variance and Response Surface Methodology, supported by Differential Scanning Calorimetry and dimensional analysis. The results revealed that annealing temperature is the governing factor, whereas exposure time has a marginal impact. An optimal window emerged between 75 °C and 85 °C. Relative to the as-printed baseline, optimal factors improved Ultimate Tensile Strength by 13.74%, ductility by 24.78%, bed surface hardness by 5.58% and Young’s modulus by 39%, driven by substantial matrix crystallinity increments (29.4%) verified via DSC. In contrast, top surface hardness was negatively affected by the heat treatment. Furthermore, temperatures exceeding 85 °C triggered severe dimensional distortions. Ultimately, this research provides experimentally validated statistical models for the reliable design of PLA-SCF components.