Study on Melting and Recrystallization of Poly(butylene succinate) Lamellar Crystals via Step Heating Differential Scanning Calorimetry
Study on Melting and Recrystallization of Poly(butylene succinate) Lamellar Crystals via Step Heating Differential Scanning Calorimetry
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分步加热差示扫描量热法研究聚丁二酸丁二醇酯层状晶体的熔融和重结晶
DOI：
10.1007/s10118-017-1986-6
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发表时间：
2017-12-01
影响因子：
4.3
通讯作者：
Xu, Jun
中科院分区：
文献类型：
--
作者：
Lv, Zhi-yu;Zhang, Michael C.;Xu, Jun
差示扫描量热法（DSC）已广泛应用于研究材料的结晶和熔融。然而，对于聚合物层状晶体，在加热过程中的熔融热谱通常表现出一个宽的吸热峰，甚至多个吸热，这可能是由于通过重结晶过程的亚稳性的变化。有时，由于再结晶峰与熔融吸热峰重叠，无法观察到再结晶峰。在这项工作中，我们采用了一个步骤加热程序组成的连续加热和温度保持阶段，以测量等温结晶的聚（丁二酸丁二醇酯）（PBS）晶体的亚稳性。利用该方法可以得到不同温度范围内晶体的熔化分数，定量检测合金的熔化-再结晶行为。熔融-重结晶行为取决于聚合物链结构和结晶温度。例如，PBS嵌段共聚物几乎不显示重结晶行为，而PBS低聚物和高分子量PBS均聚物显示显著的熔融-重结晶现象。高分子量PBS等温结晶在低温范围内显示出多重熔融重结晶，而那些等温结晶在高温下不表现出可观察到的重结晶行为。此外，通过熔化动力学方程拟合了熔化吸热曲线。原始等温结晶的层状晶体表现出与在最高温度范围内熔化的再结晶层状晶体完全不同的熔化动力学，这归因于不同程度的稳定化。最后，对熔融再结晶的机理进行了简要的讨论。我们认为，当预制片晶的熔化和较厚片晶的再结晶具有相似的自由能垒时，可以观察到明显的熔化再结晶现象。
Differential scanning calorimetry (DSC) has been widely applied to study crystallization and melting of materials. However, for polymeric lamellar crystals, the melting thermogram during heating process usually exhibits a broad endothermic peak or even multiple endotherms, which may result from changes of metastability via recrystallization process. Sometimes, the recrystallization exotherm cannot be observed due to its overlapping with the melting endotherm. In this work, we employed a step heating procedure consisting of successive heating and temperature holding stages to measure the metastability of isothermally crystallized poly(butylene succinate) (PBS) crystals. With this approach we could gain the fraction of crystals melted at different temperature ranges and quantitatively detect the melting-recrystallization behavior. The melting-recrystallization behavior depends on the polymer chain structure and the crystallization temperature. For instance, PBS block copolymer hardly shows recrystallization behavior while PBS oligomer and high molecular weight PBS homopolymer demonstrate remarkable melting-recrystallization phenomenon. High molecular weight PBS isothermally crystallized in the low temperature range shows multiple melting-recrystallization while those isothermally crystallized at elevated temperatures do not exhibit observable recrystallization behavior. Furthermore, the melting endotherms were fitted via the melting kinetics equations. The original isothermally crystallized lamellae demonstrate quite different melting kinetics from the recrystallized lamellar crystals that melt at the highest temperature range, which is attributed to the different degrees of stabilization. Finally, the mechanism of melting-recrystallization is briefly discussed. We propose that apparent melt-recrystallization phenomenon be observed when melting of preformed lamellar crystals and recrystallization of thicker lamellae have similar free energy barrier.