Supercooling-controlled heterogeneous and homogenous crystal nucleation of polyamide 11 and its effect onto the crystal/mesophase polymorphism
Supercooling-controlled heterogeneous and homogenous crystal nucleation of polyamide 11 and its effect onto the crystal/mesophase polymorphism
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DOI：
10.1016/j.polymer.2016.10.050
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发表时间：
2016-12
期刊：
影响因子：
4.6
通讯作者：
A. Rhoades;Nichole Wonderling;C. Schick;R. Androsch
中科院分区：
文献类型：
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作者：
A. Rhoades;Nichole Wonderling;C. Schick;R. Androsch
用快速扫描切片量热仪(FSC)分析了尼龙11(PA 11)在60~170℃的较宽温度范围内的熔融结晶动力学。结晶速率与温度呈双峰关系，这与熔体低过冷时非均相成核向高过冷时均相成核转变有关，交叉发生在115℃左右。结果表明，交叉温度取决于所研究的特定尼龙11牌号，即可能作为非均相成核剂的存在。支持晶化速率随温度变化最小与形核机制改变有关的观点。在等温结晶实验结束后，立即将FSC样品快速冷却到常温，用X射线衍射仪分析其相结构。这些数据表明，δ‘-中间相的形成主要发生在快速均匀成核的温度范围内，在该温度范围内，由于成核密度高、成核位距小，阻碍了晶体的生长。在较高的晶化温度下，晶核密度较低，并观察到δ/α晶体的生长与晶化温度有关。无论等温结晶温度如何，都没有检测到明显的三相结构。
Fast scanning chip calorimetry (FSC) was used for analysis of the kinetics of melt-crystallization of polyamide 11 (PA 11) in a wide range of temperatures between 60 and 170 °C. The crystallization rate exhibits a bimodal temperature-dependence which is associated with a transition from heterogeneous crystal nucleation at low supercooling of the melt to homogeneous crystal nucleation at high supercooling, with the cross-over occurring at around 115 °C. It is shown that the cross-over temperature depends on the particular PA 11 grade investigated, that is, on the presence of additives which may act as heterogeneous nucleators, supporting the notion that the minimum in the temperature-dependence of the crystallization rate is related to a change of the nucleation mechanism. Immediately after the isothermal crystallization experiment, the FSC samples were rapidly cooled to ambient temperature, for analysis of the phase structure using X-ray diffraction. The data suggest that formation of the δ’-mesophase mainly occurs in the temperature range of fast homogeneous nucleation in which crystal growth due to the high nuclei density and small distance between the nucleation sites is hindered. At higher crystallization temperatures the nuclei density is much lower, and growth of δ/α-crystals with a perfection depending on the crystallization temperature is observed. Regardless of the isothermal crystallization temperature, a distinct three-phase structure is not detected.