Morphological and crystalline studies of isotactic polypropylene plastically deformed and evaluated by small-angle X-ray scattering, scanning electron microscopy and X-ray diffraction

Abstract

Morphological and structural properties of isotactic polypropylene (i-PP) submitted to uniaxial plane strain deformation at ambient temperature with compression pressures of 3, 10 and 20 MPa, were investigated using wide angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Two kinds of samples were studied, namely: sample A: Mw = 117,400 g/mol Mn = 17,300, Mw/Mn = 6.8 and sample B: Mw = 271,000 g/mol Mn = 43,700 Mw/Mn = 6.2, both with isotactic content = 95%. Crystalline α- and β-phases are clearly identified by WAXD. The lamellar long period, as well as, the crystalline and amorphous lamellar thickness for the non-deformed samples measured by SAXS indicates the presence of a more symmetric spherulitic structure for sample A, while the sample B displays anisotropic scattering. The WAXD study of the apparent relative crystallinity and the orientation of crystallites, revealed that plastic deformation of i-PP by plane-strain compression, leads to preferred orientation of main axis of crystallites at relatively early stage of the deformation process induced a monocrystal texture and an excellent molecular alignment along the FD, in both samples. The SEM evaluation shows that a gradual change occurs in the spherulitic structure and seems to transform gradually and disappear almost for the 37% deformations. The sample with highest deformation shows thin shear bands oriented along the FD-view which originate an appearance of a layered structure. Concomitantly the crystalline lamellae were detected by TEM technique.