CRYSTALLIZATION AND MELTING OF POLYMERS . 27. LAMELLAR STRUCTURE OF BETA-POLYPROPYLENE STUDIED BY SCANNING ELECTRON-MICROSCOPY

Hedrites are clusters of multilayer lamellar crystallites. A hedrite t hat is seen flat-on has hexagonal shape (hexagonit). A fan-like arrang ement of lamellae around a central axis perpendicular to the plane of the hexagonite was observed. On the surfaces of lamellae seen flat-on, hexagonal etch pits appear referring to screw dislocations. They are responsible for branching and proliferation of lamellae. Due to the br anches of lamellae, two formations develop symmetrically to the plane of the hexagonite, like a flower-cup. The lamellae are cup-shaped havi ng two-dimensional curvatures. In ovalites developed from a rod-like p recursor the majority of lamellae is seen edge-on. The top-view of lam ellae standing on the edge is C-shaped, i.e. they are curved. Hedrites may reach considerable sizes presumably due to a co-ordinated co-oper ative growth of lamellae. There is an unequivocal correlation between the character of birefringence and the morphological structure shown b y SEM of hexagonites, rods, ovalites and banded spherulites. It was sh own that the banded structure of beta-spherulites is produced due to a co-ordinated twisting of a bundle of the growing lamellae.