Visualization of polypropylene crystallites formed from a stressed melt in extrusion. (28th September 2016)

• Record Type: Journal Article
• Authors: Tabatabaei, Alireza; Mark, Lun Howe; Park, Chul B.
• Is Part Of: Polymer. Volume 101(2016)
• Page Start: 48
• Page End: 58
• Publication Date: 2016-09-28
• Subjects: Flow-induced crystallization -- Extensional flow -- In-situ visualization -- Polypropylene; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2016.08.036
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: We performed in-situ optical visualization studies of a flowing melt in extrusion to investigate the crystallization behavior of polypropylene from a stressed melt at elevated temperatures. In the experiments, a tandem extrusion system equipped with a conical converging flow channel with a long tubular end was employed via direct visualization techniques. A secondary extruder and a converging channel were used to cool the polymer melts uniformly and to create extensional flow, respectively. We observed various crystallite morphologies depending upon the specific processing conditions, such as the temperature and the flow rate. The crystallites' sizes and quantities were quantified according to their light intensities. The in-situ observations of the flow showed that crystallization was more active in areas where the polymer melts were subjected to elongation. Moreover, a higher flow rate enhanced the crystallization kinetics by generating a larger molecular deformation, especially at lower temperatures. Graphical abstract: Highlights: The formation of polypropylene crystallites in extrusion was in-situ visualized. Effects of processing conditions on PP crystallization were visually investigated. The visualized crystallites were quantified based on their light intensities. Extensional flow induced crystallites even at a temperature higher than Tm . Higher flow rates enhanced crystallization especially at a lowered temperature.