| Summary: | Thesis (PhD)--Stellenbosch University, 2013. === ENGLISH ABSTRACT: Heterophasic copolymers (also known as HECO polymers) or often referred to only as impact
copolymers or block copolymers comprise a polymer matrix with a dispersed rubbery
copolymer phase. The polymer under investigation in this study consists of a polypropylene
homopolymer matrix and ethylene-propylene copolymers (EPCs). Due to its diverse range of
applications and unique properties, polypropylene is the choice of polymer for a vast array of
applications. This has led to the development of an entire class of polypropylene materials
known as visbroken or controlled rheology polypropylene. By adding a suitable peroxide to the
polymer in the presence of heat, radicals are formed which will attack the polymer chains in a
random fashion. The resultant polymers generally have a higher melt flow rate (MFR), a
narrower molecular weight distribution than the parent polymer, and good impact-stiffness
balance.
The main focus of this investigation was to determine if there exist any differences in the
molecular structure and physical properties of controlled rheology HECO polymers and if
differences do exist, how they influence the physical characteristics of the polymer. Eight HECO
polymers with equal ethylene contents were visbroken to varying degrees by making use of two
different types of organic peroxide. The effects of the amount of visbreaking on the molecular
characteristics and physical properties were subsequently studied by making use various types
of fractionation techniques, including preparative temperature rising elution fractionation (PTREF)
and crystallisation analysis fractionation (CRYSTAF). Subsequent offline analysis was
then done on the fractionated samples that included nuclear magnetic resonance spectroscopy
(NMR), differential scanning calorimetry (DSC), high temperature size exclusion
chromatography (HT-SEC), Fourier transform infrared spectroscopy (FTIR) and deposition of
the SEC fractions via the LC Transform Interface (SEC-FTIR) as well as high temperature high
performance liquid chromatography (HT-HPLC), a novel technique for the characterization of
olefins according to their chemical composition. === AFRIKAANSE OPSOMMING: Heterofase kopolimere, ook bekend as HECO polimere, of dikwels na verwys net as impak
kopolimere of blok kopolimere bestaan uit 'n polimeer matriks met 'n verspreide rubberagtige
kopolimeer fase. Die polimeer wat in hierdie studie ondersoek was het bestaan uit 'n
polipropileen homopolimeer matriks en etileen-propileen kopolimere (EPCs). As gevolg van sy
veelseidigheid van toepassings en unieke eienskappe is polipropileen die keuse van polimeer
vir 'n wye verskeidenheid van toepassings. Hierdie veelseidigheid het gelei tot die ontwikkeling
van 'n hele klas van polipropileen materiaal bekend as gevisbreekte of beheerde reologie
polipropileen. Deur die byvoeging van 'n geskikte peroksied tot die polimeer in die
teenwoordigheid van hitte, word radikale gevorm wat die polimeerkettings in 'n ewekansige
wyse sal aanval. Die gevolglike polimere in die algemeen het 'n hoë smelt vloeitempo (MFR), 'n
smaller molekulêre gewig verspreiding as die moeder polimeer, en 'n goeie impak/styfheid
balans.
Agt HEKO polimere met gelyke etileen inhoude was gevisbreek in wisselende hoeveelhede deur
gebruik te maak van twee verskillende tipes organiese peroksiedes. Die gevolge van die
hoeveelheid van visbreeking op die molekulêre eienskappe en fisiese eienskappe was
vervolgens gebestudeer deur gebruik te maak van verskillende fraksionasie tegnieke, insluitend
preparatiewe TREF (P-TREF) en CRYSTAF. Daaropvolgende analiese is gedoen op die
gefraktioneerde monsters en sluit in kernmagnetiese resonansie spektroskopie (KMR),
differensiële skandeer kalorimetrie (DSC), 'n hoë temperatuur grootte uitsluitings
chromatografie (HT-SEC), Fourier transform infrarooi spektroskopie (FTIR) met deponeering
van die SEC fraksies via die LC transform koppelvlak (SEC-FTIR) sowel as 'n hoë temperatuur
hoë werkverrigting vloeistof chromatografie (HT-HPLC), 'n nuwe tegniek vir die karakterisering
van olefiene volgens hul chemiese samestelling.
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