J. Varga et al., CRYSTALLIZATION AND MELTING OF POLYMERS . 27. LAMELLAR STRUCTURE OF BETA-POLYPROPYLENE STUDIED BY SCANNING ELECTRON-MICROSCOPY, Magyar kemiai folyoirat, 103(8), 1997, pp. 359-364
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.