Combined Effect of MWCNT Reinforcement and Thermal Annealing on the Mechanical Performance and Interlayer Bonding of FDM ‐Printed PETG Composites

Fused deposition modeling (FDM)‐printed polymer components often exhibit weak interlayer adhesion due to the layer‐by‐layer deposition process, resulting in anisotropic mechanical properties. The incorporation of nanofillers, such as multiwalled carbon nanotubes (MWCNTs), can further influence interlayer diffusion, making the interfacial bonding behavior more complex. In this study, the combined effect of MWCNT reinforcement and thermal annealing on the mechanical performance and interlayer bonding behavior of polyethylene terephthalate glycol (PETG) was investigated. PETG filaments reinforced with 0.5, 1, and 2 wt.% MWCNTs were used to fabricate tensile, flexural, and lap shear specimens using the FDM process. The printed specimens were annealed at 80°C, 100°C, and 120°C for durations of 60, 120, 240, and 480 min, and their postprocessing effects were investigated. Mechanical characterization revealed that the MWCNT reinforcement improved the tensile and flexural strengths up to an optimal loading of 1 wt.%. Thermal annealing improved the mechanical performance and interlayer bonding of both PETG and PETG/MWCNTs composites, with optimal properties obtained at 120°C for 480 min. Lap shear testing demonstrated that annealing enhanced the interlayer bonding, shown by the failure transition from interlaminar debonding to adherend tensile failure. Microscopy and scanning electron microscopy (SEM) observations confirmed the reduction in interlayer voids and better interfacial continuity following annealing. The results showed that the combined use of MWCNTs reinforcement and optimized annealing conditions effectively enhances the interlayer bonding and mechanical properties of FDM‐printed PETG composite specimens.