Rheo-Optical Studies on the Nature of Alpha and Beta Mechanical Dispersions of Polyethylene in Relation to the Deformation Mechanisms of Spherulitic Crystalline Texture

Abstract

The previous dynamic X-ray diffraction studies(1) of a row-nucleated HDPE revealed that the intralamellar crystal reorientation corresponding to the αl mechanical dispersion occurs in the following two preferential fashions. A mechanism of lamellar detwisting involving crystal rotation around the crystal b-axis is dominant in the machine direction of fabrication when applied stress is imposed perpendicularly to lamellar growth direction or lamellar axis, while the other mechanism of intralamellar shear involving crystal rotation around the crystal a-axis is prominant in the transverse direction when the applied stress is parallel to the lamellar axes. These two preferential crystal reorientation mechanisms are believed to serve as fundamental retardation processes in spherulitic polyethylene in which the former mechanism must be dominant in the equatorial zone while the latter mechanism must be accentuated in the polar zone of uniaxially deformed spherulite. The apparent crystal lattice compliance revealed a frequency dispersion at elevated temperatures which was believed to be a manifestation of the α2 mechanical dispersion. The primary objective of this study is to examine how the two fundamental mechanisms contribute to the αl process and whether or not the frequency dispersion of the apparent lattice compliance is associated with the α2 process. Furthermore, dynamic birefringence will be conducted to elucidate the nature of β Process. Four kinds of bulk-crystallized polyethylenes, i.e. two HDPEs (Sholex 6009 and MPE 200), one MDPE (KP 119), and one LDPE (G 201), which possess spherulitic crystal texture are used as test samples to account for the variances in the crystal reorientation retardation behavior in terms of the relative contribution of the two fundamental deformation processes.