On the morphology of melt-crystallized polyethylene - I. Lamellar profiles

Abstract

The morphology of melt-crystallized polyethylene has been surveyed, and it has been revealed that all specimens are highly lamellar. Classifi­cation of the textures is possible in terms of the lamellar profiles in b-projection, i. e. down the radii of spherulites. For polyethylene crystal­lized as the orthorhombic phase only three types of lamellar profile have been observed for readily accessible growth conditions. There are ridged sheets of alternating {201} facets, planar {201} sheets and S-shaped sheets which are, to a first approximation, derivable from {201} platelets by shear of the lateral regions displacing {100} parallel to c. It is possible, moreover, to distinguish between the first-forming or dominant lamellae which lay down the framework of the texture and the later-forming or subsidiary lamellae which fill the framework. Dominant lamellae may have ridged, planar or S-shaped profiles but subsidiary lamellae appear only ridged or planar. Ridged dominant sheets form under régime I conditions as a consequence of distinct facets on the growth front. The association of ridges and growth facets indicates regularity in folding. S-shaped sheets are usually dominant in régime II growth. They appear to have been deformed from planar {201} sheets by forces associated with the forma­tion of banded spherulites.