In situ synchrotron small angle X-ray scattering investigation of structural formation of polyethylene upon micro-injection molding
In situ synchrotron small angle X-ray scattering investigation of structural formation of polyethylene upon micro-injection molding
复制标题
微注射成型聚乙烯结构形成的原位同步加速器小角X射线散射研究
DOI：
10.1016/j.polymer.2021.123390
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发表时间：
2021-01-12
期刊：
影响因子：
4.6
通讯作者：
Men, Yongfeng
中科院分区：
文献类型：
--
作者：
Liao, Tao;Zhao, Xintong;Men, Yongfeng
为了模拟实际微成型过程中固有的极端加工条件，设计了一种定制的微注射成型装置，在填充腔中安装一对金刚石窗。该装置与同步辐射相结合，可以在制造过程中实时研究多尺度结构的发展，从而可以评估一系列聚合物材料的流动诱导结晶特性。本文采用同步加速器小角x射线原位散射技术，研究了高密度聚乙烯在纳米尺度下的结构演变。根据所得数据，广泛分析了串片的结构参数（包括长周期、晶片和非晶相的平均厚度）和串的形成（如串的旋转半径、长度和错位）。发现烤肉串晶体的生长表现出两步行为：在成型开始时，薄晶的熔化随后发生再结晶过程，而在后期阶段，退火诱导的片层完善被激活。尽管最初鱼的长度和半径减小，但后来鱼结构的长度和取向偏差总体上有所增加，这可归因于部分定向链在现有鱼的纵向表面上的结晶。该装置与同步辐射的独特结合所获得的结果可以为实际聚合物微注射成型过程中结构形成的预测和最终产品形态的调节提供有效的手段。
A customized micro-injection molding apparatus with a pair of diamond windows in the filling cavity was specifically designed to simulate the extreme processing conditions inherent in the practical micro-molding process. This setup combined with synchrotron radiation allows real-time investigation of multi-scale structural development during the manufacturing process, which enables evaluation of flow-induced crystallization features for a range of polymeric materials. In this study, the structural evolution of high density polyethylene at the nanoscale was investigated by in situ synchrotron small angle X-ray scattering technique under injection molding. The respective structural parameters of kebab lamellae (including the long period, and the average thickness of crystalline lamellae and amorphous phase) and shish formation (such as the radius of gyration, length, and misorientation of the shish) were extensively analyzed from the resulting data. The growth of kebab crystals was found to exhibit a two-step behavior: melting of thin crystallites followed by a recrystallization process occur at the onset of molding whereas an annealing-induced perfectioning of the lamellae is activated at a later stage. In spite of the initial decrease of the shish length and radius, there is an overall increase in the length and misorientation of the shish structure at later times, which can be attributed to a crystallization of partially oriented chains onto the longitudinal surface of the existing shish. The results acquired by the unique combination of this apparatus and synchrotron radiation can provide an effective means to predict the structural formation and modulate the morphology of final products in practical micro-injection molding process of polymers.