The fractionation and characterisation of propylene-ethylene random copolymers
Date
2005-12
Authors
Harding, Gareth
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
This study involves the fractionation and characterisation of three propyleneethylene
random copolymers. The fractionation technique used in the study was
temperature rising elution fractionation (TREF). The TREF fractions were
subsequently analysed offline by crystallisation analysis fractionation (CRYSTAF),
differential scanning calorimetry (DSC), 13C NMR, high-temperature gel-permeation
chromatography (HT-GPC), and wide-angle x-ray diffraction (WAXD). The effect of
the ethylene comonomer on the crystallisability of the propylene was investigated,
along with the effect of the comonomer on the type of crystal phase formed during the
crystallisation. The results show that the comonomer inhibits the crystallisation of the
copolymer and that as the ethylene content increases, the crystallisation and melting
points decrease. It was also shown that the higher the ethylene content, the more of
the γ-phase crystal type is formed. The distribution of the comonomer throughout the
copolymers was also investigated. The results show that there is an uneven
distribution of the comonomer with most of the comonomer accumulating in the
amorphous areas, and very little actually being incorporated in the crystalline regions.
It was also observed that the fractions eluting at the highest temperatures had
considerably higher polydispersities and lower molecular weights than the fractions
eluting just before them. The highest temperature fractions also have lower melting
and crystallisation temperatures than the preceding fractions. This has been attributed
to a nucleation effect by the sand support used during the TREF fractionation.
Description
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005.
Keywords
Polypropylene, Polyethylene, Polymers separation, Polymers analysis, Dissertations -- Polymer science, Theses -- Polymer science