Annealing of PET/PETG specimens made with material extrusion

This work investigated the influence of deposition orientation and post-process salt annealing on the thermal and mechanical performance of Polyethylene terephthalate (PET) and glycol-modified PET parts produced by Material Extrusion. The aim was to appraise the mechanical performance of salt-annealed specimens, evaluating the correct temperature window and its interaction with the build orientation. Dog-bone and flexural specimens were realized with the XY and XZ orientations, respectively, in accordance with ISO 527 and ISO 178. The parts were then placed in a bed of dried sodium chloride powder after fabrication and annealed for 120 min at 100-190 °C. Differential Scanning Calorimetry confirmed that the feedstocks were amorphous, with glass transition temperatures, and that no crystallization peaks were observed within the processing window. Infrared spectroscopy revealed temperature-dependent band shifts and salt-induced surface effects. A mild 100 °C anneal maximized the properties of both materials, whereas higher temperatures led to degradation relative to room-temperature baselines (reductions exceeding 20%). Orientation effects were also significant, with XZ specimens exhibiting lower properties than XY. Salt embedding improved thermal homogeneity but roughened and opacified surfaces, particularly in PET.