On lamellar organization in certain polyethylene spherulites

Abstract

The lamellar structure of certain polyethylene spherulites grown very slowly at low supercoolings (regime I crystallization) has been exposed by using new techniques. A highly regular texture is found whose main element is ridged sheets of alternating {201} facets, ca. 1 pm wide, growing outwards with b as spherulitic radius. The first-formed sheets enclose columns of melt leading to the lateral segregation of slower crystallizing species and eventually to mimicry of a fibrous habit with a breadth and cross section controlled by the facet width. Although the morphology is similar to that expected according to the theory of Keith & Padden (1963), the facet width is ca. 10~5 of their characteristic length Apparently additional factors need to be invoked to explain spherulitic crystallization under conditions of extremely slow growth. {201} facets agree with earlier predictions but it is considered that folds cannot lie exclusively in {200} planes. The sectored morphology with its regular geometry indicates that folds have a preferred shape and that fold surfaces are ordered to an extent. The degree of ordering decreases for lower crystallization temperatures and for longer molecules.