Imaging and quantifying the different crystalline structures of polypropylene with the atomic force microscope
Date
2006-03
Authors
Klash, Abdalah
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
Isotactic polypropylene (iPP) exists in four different crystalline phases: α-, β-, γ- and
the mesomorphic (smectic) form. The α-phase is probably the most predominant form
of iPP with a monoclinic unit cell, whereas the unit cell of the γ-phase is
orthorhombic. The aim of this study was to examine the ability of AFM to identify
the α and γ crystalline forms of polypropylene and polypropylene copolymers that
were not especially treated.
Spherulites imaged on propylene-ethylene random copolymer surfaces had diameters
ranging from 10-30μm and predominantly radial lamellae. The cross-hatching
phenomenon of isotactic polypropylene was observed for samples containing both the
α- and γ-phase. Two types of γ-phase spherulites were observed, namely a featherlike
form for samples with a high content of the γ-phase and a bundle-like form with
varying sizes, which is typical for the mixed structure of both α- and γ-forms. In some
images of polypropylene-ethylene copolymer sample lozenge-shaped structures could
be observed between the γ-spherulites, which might be single polyethylene crystals.
Both the α- and γ-phase of iPP were successfully imaged and identified with AFM
without prior treatment of the surface. The degree of crystallinity obtained from AFM
images was calculated as a percentage of the surface area exhibiting regular
structures. The results compared well to X-ray results.
Description
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006.
Keywords
Polypropylene, Polyolefins, Dissertations -- Polymer science, Theses -- Polymer science