The crystallinity affects the most of the properties of the products made of semi‐crystalline engineering polymers, such as poly (butylene terephthalate) (PBT) optical fiber loose buffer tubes. Precise control of crystallinity of PBT can be crucial for the quality of an optical fiber cable. Proper determination of crystallinity index from differential scanning calorimetry (DSC) measurements can be challenging for PBT as various processes occur between devitrification and melting that influence the initial crystallinity. Discrepancy between industrial and laboratory conditions leads to difficulties in transfer of laboratory‐scale procedures to technological processes. In this article, simple and time effective, small‐scale laboratory procedure based on Melt Flow Indexer was proposed for the preparation of samples with varying crystallinity indices to simulate industrial products of PBT extrusion, namely loose buffer tubes for optical fibers. Moreover, the conventional “linear” DSC method of characterization of PBT crystallinity index was revised with wide‐angle X‐ray scattering as the reference. Analysis showed the complexity of the thermal processes occurring in PBT melt‐extruded samples between Tg and Tm that strongly influenced the value of crystallinity index of PBT measured by DSC. These processes were identified and new semi‐empirical method of their extraction from the thermograms was proposed. Cold melting of the crystalline phase was found to have dominant contribution in the “pre‐melting” region that is between approx. 130°C and the onset of the fundamental melting peak, with only minor interrupting low‐intensity exothermic event. The contribution of this “pre‐melting” endotherm was more significant for the samples cooled at lower rates.

中文翻译：

---

差示扫描量热法观察质量挤出产品中聚对苯二甲酸丁二醇酯的结晶度

结晶度会影响由半结晶工程聚合物制成的产品的大多数性能，例如聚对苯二甲酸丁二醇酯（PBT）光纤松散缓冲管。精确控制PBT的结晶度对于光纤电缆的质量至关重要。从差示扫描量热法（DSC）测量中正确确定结晶度指数对于PBT可能具有挑战性，因为在失透和熔化之间会发生各种影响初始结晶度的过程。工业条件和实验室条件之间的差异导致将实验室规模的程序转移到技术过程中遇到困难。在本文中，简单而又省时，提出了一种基于熔体流动指数仪的小型实验室程序，用于制备具有不同结晶度指数的样品，以模拟PBT挤出的工业产品，即用于光纤的松散缓冲管。此外，以广角X射线散射为参考，对表征PBT结晶度指标的常规“线性” DSC方法进行了修订。分析表明，PBT熔融挤出样品中发生的热过程的复杂性介于Tg和Tm对DSC测定的PBT结晶度指标值有很大影响。确定了这些过程，并提出了从热谱图中提取它们的新的半经验方法。发现结晶相的冷熔在“预熔”区域（约介于）之间具有主要作用。130°C和基本熔化峰的开始，只有少量中断低强度放热事件。对于以较低速率冷却的样品，这种“预熔化”吸热的作用更为明显。