The effect of controlled rheology on the evolution of chemical composition distribution of commercial Heterophasic Ethylene Propylene Copolymers (HEPCs)
Date
2020-03
Authors
Journal Title
Journal ISSN
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Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: The vis-breaking of heterophasic ethylene-propylene copolymers (HEPCs) is an important
industrial process. While the changes in molar mass properties are easy to track using hightemperature
size exclusion chromatography (HT-SEC) before and after vis-breaking, changes
in the chemical composition are much more challenging due to the complex chemical
composition resulting from different ethylene contents and ethylene block lengths. The present
work tracks the microstructural changes of three samples with 0 – 10.8 mol.% ethylene content
before and after vis-breaking with the aid of molar mass and chemical composition sensitive
chromatographic techniques. Bulk sample analyses indicated that the rubber phase, which is
ethylene rich was essential in aiding peroxide mobility during vis-breaking as indicated by the
narrower dispersities and lower peak molar masses with increasing ethylene content.
Preparative temperature rising elution fractionation (p-TREF) and solvent gradient elution
fractionation (SGEF) were used to fractionate the non vis-broken and vis-broken HEPC bulk
samples into several fractions for further analyses. Upon vis-breaking, the SGEF fractions with
high molar mass were observed to diminish after vis-breaking. Furthermore, the increase in
ethylene content was observed to reduce the impact of the peroxide on the fraction quantities
before and after vis-breaking implying that vis-breaking affects more the polyolefin chains with
more PP segments and less those with more ethylene co-monomer. However, SGEF may not
be suitable for the fractionation of mixtures of homopolymer and copolymers due to the
different solubilities in the solvent/non-solvent mixtures. Furthermore, in-situ solid state NMR
experiments revealed the greater sensitivity of copolymers containing short ethylene sequences
to peroxide degradation. Long chain ethylene sequences were found to be resistant to radical
degradation.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Description
Thesis (PhD)--Stellenbosch University, 2020.
Keywords
Rheology, UCTD, Ethylene, Polyolefins, Molecular composition