State Key Laboratory of Chemical Engineering, College of Biological and Chemical Engineering , Zhejiang University , 38 Zheda Road , Hangzhou 310027 , China.
J Phys Chem B. 2019 May 2;123(17):3822-3831. doi: 10.1021/acs.jpcb.8b12111. Epub 2019 Apr 22.
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.
半结晶聚合物通常在高温退火和拉伸变形下经历多层次的微观结构演变；这对于在工业加工中调整聚合物产品的物理性能至关重要。在这里，我们选择聚对二氧环己酮（PPDO），一种典型的可生物降解、生物相容和可生物吸收的聚合物，作为模型半结晶聚合物，研究了其在高温退火和拉伸下的多晶型结构转变和结晶层片演变。高温退火导致 PPDO 的 α'-到-α 相转变，同时结晶度（X）提高，结晶层片增厚。随着退火温度的升高，PPDO 的拉伸强度和杨氏模量增加，但断裂应变减小。PPDO 的拉伸诱导相转变强烈依赖于初始结构和拉伸温度（T）。在低 T 下拉伸时，α 形式的 PPDO 转变为其 α'对应物。这种相转变是不可逆的，在释放应力时不会保留α形式。然而，对于在高 T（≥40°C）下拉伸的α形式的 PPDO，没有发生相转变。α 形式的 PPDO 的原始层片通过熔融再结晶机制在拉伸过程中转变为纤维状层片。
