The nature of the lamellar overgrowth in polyethylene shish-kebab fibres as revealed by small-angle X-ray scattering and electron microscopy

The melting, dissolution and crystallization behaviour of the lamellar overgrowth in polyethylene shish-kebab fibres have been studied by small-angle X-ray scattering and electron microscopy. SAXS experiments in which fibres were heatedin situ demonstrated the irreversible reorganization of the lamellar overgrowth already at 60° C. Reorganization continued in an inhomogeneous manner until the fibre lost its porosity around 140° C. The morphology that developed upon cooling depended on the crystallization temperature as well as on the maximum temperature attained before crystallization. Transmission electron microscopy observations showed the influence of molecular weight on aggregation. The SAXS patterns obtained duringin situ dissolution experiments disclosed that the lamellae dissolved in dodecane above 115° C. Recrystallization of the lamellae on to the backbones was almost complete within 10 min at 110° C. These high temperatures, as compared with single-crystal behaviour, indicate that the cilia nucleated with exceptionally high stem lengths on to the backbones. SAXS of fibres elongated to a maximum ratio of 1.5 at 90° C demonstrated the role of the lamellar overgrowth as a matrix between the elementary fibrils. The shish-kebab morphology could be restored after elongation by selective dissolution of the lamellae and recrystallization.