Effects of UV-Thermal Exposure Sequence on the Compressive Performance of FDM-Printed Polymers

Ultraviolet (UV) radiation and elevated temperatures can alter the compressive performance of fused deposition modeled (FDM) polymers, but the combined effects, and especially the order of exposure, have not been systematically investigated under compressive loading. This study quantifies the sequence-dependent effects of UV-A exposure and thermal exposure on the compressive behavior of Nylon-CF, PLA, and TPU. Using response surface methodology, UV duration (8−16 h), thermal exposure temperature (80°C–140°C), and thermal exposure time (1–5 h) were varied, with treatment sequence as a categorical factor. Thermal exposure followed by UV exposure gave the most favorable Nylon-CF response, delivering up to 27% higher compressive strength, whereas UV exposure followed by thermal exposure generally reduced peak strength and promoted higher deformation. PLA showed modest strength gains below 5%, but selected UV-first schedules preserved or increased stiffness. TPU showed the opposite trend, with both sequences degrading compressive performance, particularly when UV exposure preceded thermal exposure, thereby identifying conditions that should be avoided. Scanning electron microscopy provided mesostructural evidence of sequence-driven changes, including reduced porosity and improved interlayer fusion in Nylon-CF and void coalescence in severely treated PLA. These findings establish treatment sequence as a key design parameter for FDM polymers.