Molecular Mobility in the Amorphous Phase Determines the Critical Strain of Fibrillation in the Tensile Stretching of Polyethylene
Molecular Mobility in the Amorphous Phase Determines the Critical Strain of Fibrillation in the Tensile Stretching of Polyethylene
复制标题
非晶相中的分子迁移率决定了聚乙烯拉伸拉伸中原纤化的临界应变
DOI：
10.1007/s10118-020-2362-5
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发表时间：
2019-11-27
影响因子：
4.3
通讯作者：
Jiang, Zhi-Yong
中科院分区：
文献类型：
--
作者：
Li, Rui;Yang, Guo-Xing;Jiang, Zhi-Yong
利用扫描同步小角x射线散射（SAXS）技术研究了不同温度退火后双峰高密度聚乙烯拉伸变形的微观组织发展与应变的关系。在拉伸变形时，两种不同的变形机制依次激活：在小变形时，晶块的层间滑动主导了变形行为，而在临界应变时，应力诱导的晶块碎裂和再结晶过程发生，产生新的晶体，分子链优先沿拉伸方向取向。发现双峰样品中与层状到纤维状转变相关的临界应变为0.9，明显大于单峰高密度聚乙烯（0.4）。这一观察结果主要是由于双峰样品具有更大的非晶相迁移率，从而降低了纠缠非晶网络的模量。h - nmr2弛豫时间进一步证明了非晶相的迁移率是临界应变的决定因素。这些发现有助于我们对管道用双峰聚乙烯优异的抗慢裂纹扩展性能的理解。
The microstructural development of bimodal high density polyethylene subjected to tensile deformation was investigated as a function of strain after annealing at different temperatures by means of a scanning synchrotron small angle X-ray scattering (SAXS) technique. Two different deformation mechanisms were activated in sequence upon tensile deformation: intralamellar slipping of crystalline blocks dominates the deformation behavior at small deformations whereas a stress-induced crystalline block fragmentation and recrystallization process occurs at a critical strain yielding new crystallites with the molecular chains preferentially oriented along the drawing direction. The critical strain associated with the lamellar-to-fibrillar transition was found to beca.0.9 in bimodal sample, which is significantly larger than that observed for unimodal high-density polyethylene (0.4). This observation is primarily due to the fact that the bimodal sample possesses a greater mobility of the amorphous phase and thereby a reduced modulus of the entangled amorphous network. The conclusion of the mobility of the amorphous phase as a determining factor for the critical strain was further proven by the1H-NMRT2relaxation time. All these findings contribute to our understanding of the excellent slow crack growth resistance of bimodal polyethylene for pipe application.