Enhancing the creep resistance of 3D-printed polylactic acid at varied operating temperatures by heat treatment: An experimental and numerical analysis

Abstract

Creep deformation significantly affects polymer design, especially for polylactic acid (PLA), which is prone to deformation at high temperatures. This study investigates the impact of heat treatment as a post-processing technique on the short-term creep behavior of 3D-printed PLA, emphasizing the role of increased crystallinity in improving creep resistance. PLA samples were analyzed in untreated (UT) and heat-treated (HT) states at temperatures of 75 °C and 90 °C for varying curing durations, with differential scanning calorimetry employed to measure crystallinity levels. Creep tests conducted in tensile mode at room temperature (27 °C) revealed that the PLA sample heat-treated at 90 °C for 2 h (HT90(2h)) exhibited the highest resistance to creep deformation. Further evaluations at elevated temperatures (37 °C and 47 °C) indicated that HT90(2h) had a reduced creep rate than UT, with effectiveness enhanced by a factor of 1.85 at 47 °C. Increased crystallinity inhibits chain mobility in crystalline lamella, improving stiffness and creep resistance. A nonlinear viscoelastic Burgers model was utilized to predict the creep response under varying thermal and mechanical loads, with the model parameters dependent on crystallinity, stress, and temperature. The multi-curve optimization technique in MATLAB was used to analyze loading and unloading behavior at different stresses and temperatures. The linear viscoelastic Burgers model could trace the creep data at 27 °C, while the nonlinear version captured the creep response with increasing stress at elevated temperatures. Thus, heat treatment enhances PLA's creep resistance, improving its suitability for high-temperature, long-term mechanical applications.