Structural evolution of poly(glycolide-co-lactide) under stress-temperature coupled fields based on in-situ WAXD/SAXS

Abstract

As one of the most promising biodegradable polymeric materials, P(GA-co-LA) has become a hot research topic due to its excellent biocompatibility, tunable degradation properties and good mechanical performance. In this study, the synchrotron in-situ WAXD/SAXS techniques were employed to systematically investigate the evolution of the aggregated state structure of highly crystalline P(GA-co-LA) with an LA content of 8 mol% during hot-stretching at temperatures ranging from 50 °C to 150 °C. The research results indicate that the initial eutectic structure of P(GA-co-LA) significantly influences its stretching-induced structural evolution, exhibiting distinct temperature-dependent structural evolution characteristics: under low-temperature (50–70 °C) stretching conditions, crystal slip and fragmentation dominate, leading to a significant reduction in crystallite size; whereas under high-temperature (120–150 °C) conditions, enhanced molecular chain mobility promotes the formation of stress-induced highly oriented crystals. Notably, unlike the homopolymer PGA, P(GA-co-LA) does not exhibit significant cavitation during stretching at 70–150 °C, which is mainly attributed to the disruptive effect of LA units on the homogeneity of the amorphous regions. Moreover, under high-temperature stretching conditions, the free energy for the exclusion of LA units from the lattice decreases, and the increase in the unit cell parameter b is significantly reduced, indicating that the highly oriented crystalline structure effectively inhibits the reincorporation of LA units.