Quattrosoldi Silvia, Lotti Nadia, Soccio Michelina, Schick Christoph, Androsch René
Department of Civil, Chemical, Environmental and Materials Engineering, University of Bologna, Via Terracini 28, 40131, Bologna, Italy.
Interdisciplinary Center for Transfer-oriented Research in Natural Sciences (IWE TFN), Martin Luther University Halle-Wittenberg, 06099 Halle/Saale, Germany.
Polymers (Basel). 2020 May 11;12(5):1099. doi: 10.3390/polym12051099.
Tammann's two-stage crystal-nuclei-development method is applied for analysis of the thermal stability of homogenously formed crystal nuclei of poly(butylene isophthalate) (PBI) as well as their possible reorganization on transferring them to the growth temperature, using fast scanning chip calorimetry. Crystal nuclei were formed at 50 °C, that is, at a temperature only slightly higher than the glass transition temperature, and developed to crystals within a pre-defined time at the growth temperature of 85 °C. The number of nuclei, overcritical at the growth temperature, was detected as a function of the transfer-conditions (maximum temperature, heating rate) by evaluation of the developed crystal fraction. For different size-distributions of crystal nuclei, as controlled by the nucleation time, there is detected distinct reduction of the nuclei number on heating to maximum temperatures higher than about 90 to 110 °C, with the latter value holding for longer nucleation time. Longer nucleation allows for both increasing the absolute nuclei number and generation of an increased fraction of larger nuclei. Heating at 1000 K/s to 140-150 °C causes "melting" of even the most stable nuclei. While direct transfer of crystal nuclei from the nucleation temperature (50 °C) to the growth temperature (85 °C) reveals negligible effect of the transfer-heating rate, in-between heating to higher temperatures is connected with distinct nuclei-reorganization above 85 °C on heating slower than 1000-10.000 K/s. The performed study not only provides specific valuable information about the thermal characteristics of crystal nuclei of PBI but also highlights the importance of proper design of Tammann's nuclei development experiment for analysis of nuclei numbers. With the evaluation of critical rates of temperature-change for suppression of non-isothermal formation of both nuclei and crystals, the kinetics of crystallization of the slow crystallizing PBI is further quantified.
采用塔曼两阶段晶核形成法，利用快速扫描芯片量热法分析聚对苯二甲酸丁二醇酯（PBI）均匀形成的晶核的热稳定性，以及将它们转移到生长温度时可能发生的重组。晶核在50℃形成，即仅略高于玻璃化转变温度的温度下形成，并在85℃的生长温度下在预定时间内发育成晶体。通过评估发育的晶体分数，检测在生长温度下超临界的核数作为转移条件（最高温度、加热速率）的函数。对于由成核时间控制的不同尺寸分布的晶核，发现在加热到高于约90至110℃的最高温度时，核数明显减少，后一值适用于更长的成核时间。更长的成核时间既允许增加绝对核数，也允许产生更大比例的更大核。以1000K/s加热到140 - 150℃会导致即使是最稳定的核“熔化”。虽然将晶核从成核温度（50℃）直接转移到生长温度（85℃）显示转移加热速率的影响可忽略不计，但在加热到更高温度之间，当加热速度慢于1000 - 10000K/s时，在85℃以上会发生明显的核重组。所进行的研究不仅提供了关于PBI晶核热特性的特定有价值信息，还强调了为分析核数而正确设计塔曼核发育实验的重要性。通过评估抑制核和晶体非等温形成的临界温度变化速率，进一步量化了缓慢结晶的PBI的结晶动力学。
