Surface Melting in Melt-Crystallized Linear Polyethylene

Abstract

Morphological changes during the premelting of linear polyethylene were investigated by small-angle X-ray scattering using correlation-function analysis. The thickness of the amorphous regions, ⟨da⟩, showed a reversible change with temperature, which indicates presence of a local equilibrium state. During heating, the average thickness of lamellae ⟨dc⟩ decreases first for temperatures below the initial crystallization temperature (Tc). The simultaneous decrease in ⟨dc⟩ and increase in ⟨da⟩ provide evidence for a surface melting of the lamellae. Above Tc an irreversible thickness growth of the crystalline lamellae (increase of ⟨dc⟩) is observed. It does not affect the thickness of the amorphous regions, which remains unchanged.