Rh. Olley et Dc. Bassett, ON SURFACE-MORPHOLOGY AND DRAWING OF POLYPROPYLENE FILMS, Journal of macromolecular science. Physics, B33(2), 1994, pp. 209-227
Two nominally equivalent grades of polypropylene designed for similar
applications were extruded into sheets, with one surface chilled rapid
ly, giving a smooth texture; and the other being rougher, with a struc
ture of spherulites separated by crevices formed by retraction of the
last traces of molten polymer. Differences in the two grades gave rise
to differences in spherulitic morphology, in terms of both spatial di
stribution of spherulites among die lines and the proportions of alpha
- and beta-spherulites. The sheets were subjected to three kinds of de
formation: unrestricted monoaxial, restricted monoaxial (plane strain)
, and biaxial. The effects of surface variations persisted right throu
gh the drawing process. The morphology of the rough surface in particu
lar was observed (a) to dominate the process of deformation, especiall
y necking as it initiated at surface crevices between spherulites; and
(b) to affect the optical quality of the final product, most signific
antly in the structure and number of haze rings. Legacies of beta-sphe
rulites in fully drawn films can be observed at all levels, from the u
naided eye down to lamellar structures observed in the transmission el
ectron microscope.