Thesis (PhD)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The crystallization of polyolefins is an important parameter in determining the properties of
such materials. The crystallization phenomenon generally depends on the molecular
symmetry (tacticity) and molecular weight of the material. In this study, a series of
polypropylenes was prepared using heterogeneous MgCl2-supported Ziegler catalysts with
two different external donors, diphenyldimethoxysilane (DPDMS) and methyl-phenyldimethoxysilane
(MPDMS), and two different homogeneous metallocene catalysts, racethylene-
bis(indenyl) zirconium dichloride, Et(Ind)2ZrCl2 (EI), and rac-ethylene-bis(4,5,6,7-
tetrahydro-1-indenyl) zirconium dichloride, Et(H4Ind)2ZrCl2 (EI(4H)). Molecular hydrogen
was used as terminating agent.
In order to establish a correlation between the molecular weight and the crystallization of
these polymers, fractionation of the materials according to crystallizability was performed by
means of temperature rising elution fractionation (TREF). This affords the opportunity of
blending materials of different molecular weights but similar symmetry.
These materials were characterized using various analytical techniques: differential scanning
calorimetry (DSC), wide-angle X-ray diffraction (WAXD), 13C nuclear magnetic resonance
spectroscopy (13C-NMR), high temperature gel permeation chromatography (HT-GPC) and
Fourier-transform infrared spectroscopy (FT-IR).
DSC was used to study the bulk crystallization of different polypropylene blends, most of
which showed only one melting peak. The latter is usually associated with a high degree of
cocrystallization. Turbidity analysis of the different polypropylene polymers, obtained using
solution crystallization analysis by laser light scattering (SCALLS), provided good
crystallization information – similar to that provided by crystallization analysis fractionation
(CRYSTAF) and TREF. It was also possible to differentiate between polypropylenes with
similar chemical structure but different tacticity and molecular weight. SCALLS results also
showed that the blends of different isotactic polypropylene polymers were miscible and
cocrystallization had occurred, whereas, the blends of syndiotactic polypropylene and
different isotactic polypropylenes were not miscible and some interaction between phases had
occurred.
Optical microcopy (OM) and scanning electronic microscopy (SEM) were used to study the
morphological properties of different isotactic polypropylenes. Results revealed a welldefined
and large spherulitic morphology of mixed a1 (disordered) and a2 (ordered) crystal
form structures. OM and SEM images also clearly showed an effect of molecular weight and
tacticity on the crystal structure of the different polypropylene samples.
Finally, various homopolymers and blends were studied to investigate the effect of molecular
weight on the mechanical properties of these materials. This was done using microhardness
testing and dynamic mechanical analysis. / AFRIKAANSE OPSOMMING: Die kristallisasie van poliolefiene is ‘n belangrike faktor wat die eienskappe van hierdie tipe
materiale bepaal. In die algemeen hang kristallisasie af van die molekulêre simmetrie (taktisiteit)
en molekulêre massa van die materiaal. ‘n Reeks polipropilene is berei deur gebruik te maak van
heterogene MgCl2-ondersteunde Ziegler-kataliste met twee verskillende elektron donors,
difenieldimetoksisilaan (DPDMS) en metielfenieldimetoksisilaan (MPDMS), en twee
verskillende homogene metalloseenkataliste, rac-etileen-bis(indeniel) sirkoniumdichloried,
Et(Ind)2ZrCl2 (EI), en rac-etileen-bis(4,5,6,7-tetrahidro-1-indeniel) sirkoniumdichloried,
Et(H4Ind)2ZrCl2 (EI(4H)). Molekulêre waterstof is gebruik as termineringssagent.
Ten einde ‘n verband te bepaal tussen die molekulêre massa en kristallisasie van hierdie
polimere is hulle gefraksioneer op die basis van hulle kristallisseerbaarheid deur gebruik te maak
van temperatuurstyging-elueringsfraksionering (TREF). Deur hierdie tegniek verkry ons
materiale van verskillende molekulêre massa maar met dieselfde taktisiteit wat ons kan vermeng.
Verskeie tegnieke is gebruik om hierdie materiale te karakteriseer: differensiële
skandeerkalorometrie (DSC), wyehoek X-straal diffraksie (WAXS), 13C-kernmagnetiese
resonansspektroskopie (13C-KMR), hoë-temperatuur gelpermeasiechromotagrafie (HT-GPC) en
Fourier-transform-infrarooispektroskopie (FT-IR).
DSC is gebruik om die vaste-toestand kristallisasie van verskeie vermengde polipropilene te
bestudeer., en net een smeltpunt is in meeste gevalle waargeneem. Laasgenoemde word
gewoonlik verbind met ‘n hoë mate van kokristallisasie. Oplossingkristallisasie analise, dmv
laserligverstrooiing (SCALLS), is gebruik om die turbiditeit van die verskillende polipropileen
kopolimeervermengings te bepaal. Goeie inligting aangaande die kristallisasie in oplossing –
soortgelyk aan dié wat dmv die kristallisasie-analise-fraksioneringstegniek (CRYSTAF) en
TREF bepaal is, is verkry. Dit was ook moontlik om te onderskei tussen polipropilene met
soortgelyke chemiese strukture maar verskillende taktisiteit en molekulêre massas. SCALLS data
het ook getoon dat die vermengings van verskeie isotaktiese polipropileen polimere versoenbaar
was en dat kokristallisasie plaasgevind het, terwyl vermengings van sindiotaktiese polipropileen
en verskeie isotaktiese polipropilene nie versoenbaar was nie en dat ‘n mate van fase-skeiding
plaasgevind het.
Optiese mikroskopie (OM) en skandeer-elektronmikroskopie (SEM) is gebruik om die
morfologiese eienskappe van verskillende isotaktiese polipropilene te bepaal. Goed gedefineerde
en groot sferulitiese morfologie van gemengde a1 (onordelike struktuur) en a2 (ordelike
struktuur) kristal-strukture is waargeneem.
OM en SEM beelde het ook gewys dat molekulêre massa en taktisiteit ‘n effek het op die
kristalstruktuur van die verskillende polipropileenmonsters.
Laastens is die meganiese eienskappe van ‘n verskeidenheid homopolimere en vermengde
materiale bestudeer, deur gebruik te maak van mikro-hardheid metings en dinamiesmeganiese
analise (DMA).
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6649 |
| Date | 03 1900 |
| Creators | Amer, Ismael |
| Contributors | Van Reenen, A. J., University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
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