Cavitation and Other Deformation Instabilities in Plastic Deformation of Semicrystalline Polyethylene Modified with Paraffin Wax.

Abstract

The deformation behavior and instabilities occurring during the drawing of high-density polyethylene (HDPE) were investigated using wide- and small-angle X-ray scattering (WAXS and SAXS) and scanning electron microscopy (SEM) in plain HDPE and paraffin wax- and/or chloroform-modified samples. In contrast to neat HDPE, the modified materials demonstrated strongly suppressed cavitation. However, regardless of cavitation, the tensile deformation of all samples was found to be governed by crystallographic mechanisms active in the crystalline lamellae, supported by shear in the amorphous layers, i.e., the same mechanisms as those operating in other deformation modes. In addition to cavitation, which seems to be a tension-specific phenomenon that does not have a major effect on the deformation sequence, two other important deformation instabilities were observed: microbuckling followed by development of lamellar kinks, at true strain of e = 0.3-0.4, and slip localization instability leading to lamellar fragmentation at e > 0.6. These instabilities were found to be common and very important steps in the deformation sequence, greatly influencing the deformation behavior and occurring in similar strain ranges in both compression and tension, regardless of cavitation. In contrast, cavitation is not able to substitute or significantly modify the main deformation mechanisms, and, furthermore, it does not compete with the main instabilities associated with crystalline lamellae, especially microbuckling; therefore, it may be considered a tension-specific side effect that is not essential for plastic deformation behavior, although it can still significantly affect the final properties and appearance of the drawn material.