Morphological changes, molecular chain orientation, and Viscoelastic properties related with mosaic block structure of bulk-crystallized polyethylene

Publisher Website
Google Scholar
Abstract
The deformation mechanism of bulk-crystallized high-density polyethylene, upon stretching at various temperatures from 15 to 100°C in uniaxial and biaxial directions, has been extensively studied using detachment replicas of free surfaces onto which a thin metal film of Pt-Pd was vapor-deposited perpendicularly prior to stretching. The morphological changes related to the β-, the α1-, and the α2-relaxations have been observed for samples drawn in the corresponding temperature ranges. That is, various irreversible deformation behaviors, such as interlamellar slip, decomposition into small crystalline blocks with lateral sizes of 150 to 300 Å, and disruption into large crystalline blocks with lateral sizes of 1500 to 3000 Å, have been observed upon drawing in the temperature ranges of the β-, the α1-, and the α2-relaxation mechanisms. These deformations are mainly associated with micro-Brownian motion of loosely folded chains on the lamellar surface, with the deformation of the intermosaic block region within the limits of linear response, and with the translational or twisting molecular chain motion in the crystalline region, respectively. It has been confirmed, from external-internal strain relationships obtained from the magnitudes of the deformed and undeformed regions on the electron micrographs, that upon drawing in the temperature range of the α1-process, microcrazes or microcracks may be preferentially initiated from the mosaic block boundary without any deformation in the mosaic block core. Upon drawing in the temperature range of the α2-mechanism, shear deformation of the crystalline lamellae may occur in addition to their decomposition into large crystalline blocks with lateral sizes of 1500 to 3000 Å. In addition, the molecular chain orientation in the preferentially deformed region, upon drawing in the temperature range of the α1 relaxation process, has been investigated by resolution of the integral diffracted X-ray intensity into the intensity resulting from the deformed and the undeformed regions, respectively. This resolution was accomplished on the basis of the volume fractions of these regions, which were evaluated from the magnitude of the fold fraction obtained from IR absorption measurements.

This publication has 16 references indexed in Scilit: