Structural Determinants of the Entropic Recovery Force in Poly(Ethylene Terephthalate) Filaments

ABSTRACT This study highlights the critical role of entropic force, closely linked to chain conformation and molecular orientation, in the shape recovery performance of poly(ethylene terephthalate) (PET) filaments. The correlation between structural parameters and recovery behavior was investigated using differential scanning calorimetry (DSC), birefringence, x‐ray diffraction (XRD), and dynamic mechanical thermal analysis (DMTA). Results show that increasing the draw ratio up to an optimal point enhances crystallinity and molecular orientation, improving recovery efficiency. Moreover, analysis of activation energy during the recovery process showed that entropy changes play a significant role in reducing activation energy and further enhancing recovery. Thermal conditioning above the glass transition temperature amplified this effect. Specifically, the high‐temperature treated sample with a 1.8 draw ratio showed the best performance, with about 30% higher recovery within the first 5 min compared to room‐temperature conditioned samples. After multiple cycles, recovery speed and total recovery increased, with recovery from the fifth cycle reaching up to 34% higher than the first cycle in highly oriented samples, whereas samples with lower orientation failed to achieve full recovery.