Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The properties of polymer nanocomposites depend greatly on the
chemistry of the polymer matrices, the nature of the nanofillers, and the way in
which they are prepared. Understanding the synthesis–structure–property
relationship of nanocomposites is vital for the development of advanced
polymer nanocomposites with enhanced mechanical strength, stiffness and
toughness for structural engineering applications. To this end, the primary aim
of this study was to determine the impact that the preparation methods have
on the properties of PP/filler nanocomposites, with specific focus on the in situ
polymerization of propylene via the methylaluminoxane (MAO) activated
metallocene catalyst technique.
Two different fillers (Silica and Calcium carbonate) were used as
support for the metallocene catalysts. Different supporting methodologies for
the synthesis of the supported catalyst were examined. A C2 symmetric
metallocene catalyst ansa dimethylsilylbis(2-methyl benzoindenyl) zirconium
dichloride (MBI) was used in this study. The catalyst systems were then
evaluated for propylene polymerization.
The early observation shows that a direct adsorption of the metallocene
onto the filler has a diminishing effect on the catalyst productivity and the
fillers had to be treated with MAO in order to avoid catalyst deactivation by the
filler surface. Due to the low productivity of the supported active species, the
presence of soluble catalyst active species, besides the supported active
species is required in the synthesis of PP nanocomposites via in situ
polymerizations.
The syntheses of PP nanocomposites were carried out via in situ
polymerization in which different quantities of MAO treated fillers were reacted
with pre-activated catalyst solution. The effect of the addition of MAO-filler on
the polymerization kinetics and consequently on PP matrix microstructure was
investigated. Changes in the in situ polymerization kinetics, compared to
kinetics of homogeneous polymerization, were observed. Therefore, the microstructure of the polymer matrix was also influenced by the presence of
nanofillers in the polymerization media.
The influence of the different synthesis methods on the performance of
the nanocomposites was investigated using melt-mixed PP/filler
nanocomposites obtained using PP homopolymer. The dispersed phase
morphologies of the different nanocomposites were investigated by
transmission electron microscopy (TEM). Results show that PP
nanocomposites with improved filler dispersion were achieved by in situ
polymerization compared to melt-mixed nanocomposites.
The influence of the synthesis method on the crystallization behaviour
of PP nanocomposites was also investigated. It was found that, for the in situ
prepared nanocomposites the tacticity of the PP matrix plays the major role in
determining the degree of crystallinity. Results also show that when
nanocomposites with comparable PP matrices are compared, the overall
crystallization rate of the in situ polymerized nanocomposites is higher than
that of the melt mixed nanocomposites.
The mechanical properties of in situ polymerized PP and melt mixed
PP nanocomposite were also investigated and compared. Due to improved
nanoparticle dispersion in the PP matrix, in situ polymerized nanocomposites
show enhanced mechanical properties, especially tensile and impact
properties, compared to pure PP and melt mixed prepared nanocomposites
when a PP matrix of equivalent microstructure was used.
Finally, the melt compounding method was further investigated using
different fillers and commercial PP as a matrix. The effect of filler type, size
and applied surface coating on the flow and mechanical properties of PP
nanocomposites was studied. The aim of this part of this study is to obtain a
good trade-off between the processability and the mechanical properties and
to gain insight into the cause of the emergence of different properties for
nanocomposites prepared by melt compounding. / AFRIKAANSE OPSOMMING: Die eienskappe van polimeer nanokomposiete hang grotendeels af van
die chemie van die polimeer matriks, die wese van die nano-vullers, en die
manier waarop hierdie materiale berei word. Om die sintese-struktuureienskap
verwantskap te verstaan is noodsaaklik vir die ontwikkeling van
gevorderde nanokomposiete met beter meganiese eienskappe, styfheid en
taaiheid vir strukturele ingenieurstoepassings Die primêre doelstelling van
hierdie studie was dus om die impak van voorbereidingsmetodes op die
eienskappe van PP/vuller nanokomposiete te bestudeer, met spesifieke fokus
op die in-situ polimerisasie van propileen met metiel alumoksaan-geativeerde
metalloseen kataliste.
Twee verskillende vullers (silika en kalsium karbonaat) is gebruik as
ondersteuning vir die metalloseen kataliste. Verskillende metodiek is gebruik
om die ondersteunde kataliste te berei. ‘n C2 simmetriese metalloseen katalis
ansa-dimetielsiliel(2-metiel bensoindeniel) sirkonium dichloride (MBI) is in die
studie gebruik. Die katalissisteme is daarna evalueer vir propileen
polimerisasie.
Daar is oorspronklik vasgestel dat direkte adsorpsie van die
metalloseen op die vuller ‘n negatiewe effek op die katalis aktiwiteit gehad het,
en dat die vuller oppervlak eers met MAO behandel moes word om
deaktivering van die katalis deur die vuller-oppervlak te vermy. As gevolg van
die lae aktiwiteit van die ondersteunde aktiwe katalisspesies, is die
teenwoordigheid van opgeloste aktiewe katalis nodig vir die voorbereiding van
PP nanokomposiete via in situ polimerisasie-reaksies.
Die sintese van PP nanokomposiete is uitgevoer deur in –situ
polimersiasie waartydens verskillende hoeveelhede MAO-behandelde vullers
gereageer is met vooraf-geaktiveerde katalis oplossings. Die effek van die
byvoeging van MAO-vuller op die polimerisasie-kinetika en gevolglik op die
PP matriks mikrostruktuur is ondersoek. Dit is gevind dat die mikrostruktuur
van die polimeer-matriks beinvloed word deur die teenwoordigheid van
nanovullers in die polimerisasie-medium. Die invloed van verskillende bereidingsmetodes op die eienskappe van
die nanokomposiete is ondersoek deur smelt-vermengde PP/vuller
nanokomposiete te maak. Die dispersie-fase morfologie van verskillende
nanokomposiete is ondersoek deur transmissie elektron mikroskopie (TEM).
Resultate wys dat PP nanokomposiete met verbeterde vuller-dispersie berkry
is deur in situ polimerisasie in vergelyking met die smelt-vermengde materiale.
Die effek van die sintese-metode op die kristallisasie van die PP
nanokomposiete is ook ondersoek. Daar is gevind dat, vir die in situ bereide
nanokomposiete, die taktisiteit van die PP matriks die grootste rol speel in die
bepaling van die persentasie kristalliniteit. Resultate het ook gewys dat,
wanneer nanokomposiete met soortgelyke PP matrikse vergelyk word met die
in situ nanokomposiete, die laasgenoemde se tempo van kristallisasie hoer is
as vir die smelt-vermengde nanokomposiete.
Die meganiese eienskappe van die in situ bereide en smelt-vermengde
PP nanokomposiete is ook ondersoek en vergelyk. As gevolg van verbeterde
nano-partikel dispersie in die PP matriks, het die in situ bereide
nanokomposiete beter meganiese eienskappe openbaar, in vergelyking met
die smelt-vermenge nanokomposiete, veral trek- en slagsterkte. .
Laastens is die smelt-vermengings metode verder ondersoek deur
gebruik te maak van verskillende vullers en kommersiële PP as matriks. Die
effek van die tipe vuller, die grootte en die oppervlakbedekking van die
vullerpartikels op die vloei en meganiese eienskappe van die PP
nanokomposiete is ondersoek. Die doel van hierdie studie was om ‘n balans
te kry tussen prosesseerbaarheid en meganiese eienskappe en om insig te
verkry oor die verskille in eienskappe wat openbaar word wanneer smeltvermengde
nanokomposiete bereie word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5310 |
| Date | 12 1900 |
| Creators | Soltan, Omar |
| 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 | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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