Deformation Mechanism of Polyethylene Spherulite at Elevated Temperatures Near the Crystal Disordering Temperature

Abstract

In the previous paper, the deformation mechanism of polyethylene spherulite based on the affine deformation was proposed. Individual crystal lamellae were taken as the orientation units within the spherulite, and were allowed to rotate around the a- and b-axes of the crystal by the rotation degree f^m and fⁿ, respectively, where m and n were parameters of the ease of the crystal rotations, and f was the functions of deformation ratio of the spherulite and orientation angle of the orientation unit.
In this paper, the orientation behavior of polyethylene crystallites during the stretch of polyethylenes in bulk at several temperatures ranging from room temperature up to the crystal disordering temperature has been measured by X-ray diffraction technique, and evaluated in terms of the change of orientation factor of the three crystallographic axes.
Generally, the degree of orientation of crystal a- and c-axes decreases with the increase of the stretching temperature, especially beyond the crystal disordering temperature where the thermal expansion coefficient of a-axis changes abruptly, while that of crystal b-axis does not change sosystematically as a- and c-axes do. This phenomena will be discussed in details in terms of the parameters, m and n of the spherulite deformation mechanism by taking into account the possible deformation mechanisms of the crystal lamellae.