Interlamellar shear in anisotropic polyethylene sheets

The mechanical anistropy of the α -relaxation process in oriented high-density polyethylene and of the β -relaxation process in oriented low-density polyethylene is analyzed in terms of an inter-lamellar shear relaxation mechanism. On the basis of a few general assumptions regarding the nature of the shearing deformation of the disordered regions between the lamellar planes, quantitative expressions are obtained for the anisotropy which agree well with the experimental results. These expressions relate the changes in compliance, and relative energy losses (tan δ) in certain directions in the plane of the oriented sheet samples, to the angular distribution of lamellar plane orientation.