Structural changes on hot‐rolling of polyethylene. I. Crystallite orientation and lamellar deformation

The crystallite orientation and lamellar deformation produced by hot‐rolling in polyethylene have been investigated. In the lightly rolled stage, the [110]* axis of polyethylene crystals orientates in the plane perpendicular to the rolling direction and the c axis becomes aligned with the rolling direction. In the heavily rolled stage the a, b, and c axes coincide with the macroscopic directions in the sample. These orientational changes are interpreted in terms of a slip mechanism. Small‐angle x‐ray scattering (SAXS) investigations of hot‐rolled polyethylene show the following. (1) There are two kinds of lamellar structures; one in which inclined lamellae give a four‐point diagram in the SAXS photograph and another in which lamellar normals are oriented around the rolling direction even at the lightly rolled stage. The latter structure is attributed to the mechanism of unfolding and recrystallization. (2) The chain‐fold length in the original structure remains unchanged in the lamellae up to a roll ratio of four although the apparent long period decreases. This is explained by inclination of polymer chains in the lamellae. Further rolling aligns the polymer chains with the rolling direction and the fold length decreases.