In situ synchrotron small angle X-ray scattering investigation of structural formation of polyethylene upon micro-injection molding. (12th February 2021)

• Record Type: Journal Article
• Authors: Liao, Tao; Zhao, Xintong; Yang, Xiao; Coates, Phil; Whiteside, Ben; Barker, David; Thompson, Glen; Lai, Yuqing; Jiang, Zhiyong; Men, Yongfeng
• Is Part Of: Polymer. Volume 215(2021)
• Publication Date: 2021-02-12
• Subjects: Micro-injection molding apparatus -- Small angle X-ray scattering -- Polyethylene -- Shish-kebab structure; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2021.123390
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: 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. Graphical abstract: Image 1 Highlights: A customized micro-injection molding apparatus was specifically designed for in situ synchrotron X-ray scattering. The growth of kebab lamellae was found to exhibit a two-step behavior upon injection molding of polyethylene. A crystallization of partially oriented chains onto the longitudinal surface of the existing shish occurred at the later stages of crystallization.