Polymorphic Crystal Transition and Lamellae Structural Evolution of Poly(p-dioxanone) Induced by Annealing and Stretching

Semicrystalline polymers usually undergo multilevel microstructural evolutions under high-temperature annealing and stretching deformation; this is essential to tailor the physical properties of polymer products in industrial processing. Here, we choose poly(p-dioxanone) (PPDO), a typical biodegradable, biocompatible, and bioresorbable polymer, as a model semicrystalline polymer and investigated its polymorphic structural transition and crystalline lamellar evolution under high-temperature annealing and stretching. High-temperature annealing caused the α′-to-α phase transition of PPDO, accompanied by the improvement of crystallinity (Xc) and thickening of crystalline lamellae. Tensile strength and Young's modulus of PPDO increased but the breaking strain decreased as the annealing temperature increased. Stretch-induced phase transition of PPDO depended strongly on the initial structure and stretching temperature (Ts). The α-form PPDO transformed into its α′ counterpart during stretching at low Ts. This phase transition was irreversible and did not retain the α form with the release of stress. However, no phase transition took place for the α-form PPDO stretched at high Ts (≥40 °C). Original lamellae of α-form PPDO changed into the fibrillar lamellae during stretching via the melt-recrystallization mechanism.