Effect of Annealing on Tensile Strength of 3D Printed PLA with Material Extrusion

Polylactic acid (PLA) is a commonly used material in 3D printing processes. In the Material Extrusion (MEX) technique, the final 3D printed parts have lower mechanical properties. The objective of this study was to investigate the tensile strength of 3D-printed PLA specimens that had undergone annealing. The variables considered were the annealing temperature and the annealing time, with three temperature levels: 70℃, 90℃, and 110℃, and two annealing times: 60 and 90 minutes. The cooling rate is set at 10C per hour and cools in the furnace for 24 hours. The results showed annealing significantly affected the tensile strength, with annealed parts demonstrating a notable increase in tensile strength compared to non-annealed parts. Comparing the tensile strength values of pieces that did not undergo annealing, annealed pieces exhibited higher tensile strength. The elasticity modulus tends to decrease, and the workpiece size shrinks slightly in all directions. In the results of the annealing experiment on the ankle foot orthosis (AFO) for pediatric patients with foot drops, it was found that the ankle foot orthosis specimen that had been annealed shrank in all directions with relatively little change. When annealed workpieces are applied, there is no need to compensate for the workpiece size. The highest tensile strength was achieved when annealing was carried out at a temperature of 110C for a duration of 90 minutes. The annealed specimen showed an average 42% increase in tensile strength when compared with the printed. The higher the temperature of this glass transition, the higher the calorific value, which will affect the arrangement of the chain and the crystallinity of the plastic and lead to changes in its physical properties. Moreover, the study findings indicate that the optimizing tensile strength of thermoplastic materials can be considerably increased by choosing the ideal process parameters and post-processing conditions.