Morphological and structural evolution of tensile deformed high density polyethylene during melting: in situ synchrotron small-angle X-ray scattering study

Abstract

The morphological and structural evolution of quenched high density polyethylene specimens subjected to different strains during the heating process was explored via synchrotron small-angle X-ray scattering technique. On the basis of one-dimensional scattering intensity distribution profile analysis, a general scheme for the melting of polyethylene was proposed that surface melting occurs below the crystallisation temperature, followed by melting and recrystallisation and/or lamellar thickening process via sequential melting and stack melting at the ultimate stages of melting. It was shown that in the case of undeformed specimen, the crystallisation process has finished at the temperature of ∼90°C during quenching, while the crystallisation temperature is equivalent to 70°C for the highly oriented sample, which was attributed to the thermal effects in the necked region due to high strain rate. A qualitative argument that the isotropic material possesses a wide distribution of lamellar (or amorphous domain) thicknesses with respect to the highly oriented one can be made in terms of the temperature dependent one-dimensional correlation function. In addition, it could be evidenced that moderate deformation ratio does not affect the intrinsic property of existing stacks of lamellar crystals by a direct comparison of the evolution of structural parameters of their lamellar structure during heating.