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 ( X) 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 ( T). The α-form PPDO transformed into its α' counterpart during stretching at low T. 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 T (≥40 °C). Original lamellae of α-form PPDO changed into the fibrillar lamellae during stretching via the melt-recrystallization mechanism.