As an important class of biodegradable polymers, poly(glycolide-co-lactide) (P(GA-co-LA)) has attracted significant attention due to its excellent biocompatibility, controllable degradation behavior, and favorable mechanical properties. It demonstrates considerable research value and application potential, particularly in biomedical fields such as absorbable surgical sutures. However, the dynamic evolution mechanism of the aggregation structure of P(GA-co-LA) fibers during processing remains unclear, which hinders further improvement of product performance. To address this, the study prepares as-spun P(GA-co-LA) fibers with an LA content of 8 mol% via melt spinning, and systematically investigates the structural evolution during single-stage low-temperature stretching and multi-stage hot stretching using in-situ synchrotron radiation wide-angle X-ray diffraction (WAXD)/small-angle X-ray scattering (SAXS) techniques. The results indicate that during low-temperature stretching, the fibers undergo three stages: stretching of the amorphous regions, stress-induced crystallization, and stretching of the crystalline regions. The stress-induced crystallization stage promotes the formation of a large number of crystals, significantly increasing both crystallinity and orientation. During the high-temperature stretching stage, the coupled stress-temperature field drives further evolution of the crystalline structure: at 100 °C, fragmentation-recrystallization dominates, leading to the formation of fibrous crystals along with the generation of small-sized crystals; at 120–130 °C, molecular chain mobility reaches an optimal level, where lamellae perfection and the transformation into fibrous crystals occur synergistically, resulting in the highest crystallinity and crystallite size; at 140 °C, thermal relaxation and partial melting cause a decrease in crystallinity, and the structure is dominated by well-defined, thick lamellae.
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