Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: New methods are described for the synthesis of polymer/graphite nanocomposites using the
miniemulsion polymerization process. Natural graphite was functionalized by oxidation to
produce graphite oxide (GO) nanosheets. Poly(styrene-co-butyl acrylate) (poly(St-co-BA))
nanocomposite latices containing GO nanosheets were successfully synthesized using
miniemulsion as a one-step nano-incorporation technique. The approach followed included
expanding the GO nanosheets in situ during the miniemulsification step and then
polymerizing the monomers in the presence of these expanded nanosheets. Styrene (St) and
butyl acrylate (BA) were mixed with GO and then emulsified in the presence of a surfactant
and a hydrophobe to afford pre-miniemulsion latex particles. The stable pre-miniemulsions
were then polymerized to yield poly(St-co-BA)/GO nanocomposite latices. The
polymerization proceeded with relatively high monomer conversion and produced stable
nanocomposite latex particles. The nanocomposites exhibited mainly an intercalated
morphology, irrespective of the percentage of GO filler loading.
The synthesis of exfoliated polymer nanocomposites made with modified GO is described.
GO was modified with a surfmer (reactive surfactant), 2-acrylamido-2-methyl-1-propane
sulfonic acid (AMPS), which widened the gap between the GO nanosheets and facilitated
monomer intercalation between its nanogalleries. The AMPS-modified GO was used for the
synthesis of poly(St-co-BA)/GO nanocomposite latices using a similar miniemulsion
procedure. The obtained nanocomposites had exfoliated morphologies and the GO nanosheets
were largely exfoliated (about 2–5 nm thick) in the resultant films obtained from the
synthesized nanocomposite latices. The synthesized nanocomposites had enhanced thermal
and mechanical properties compared to pure polymer as a result of the presence of AMPSmodified
GO. Furthermore, the nanocomposites made with AMPS-modified GO had better
thermal and mechanical properties than the unmodified GO. The mechanical properties of the
nanocomposites depended on the AMPS-modified GO loading in the nanocomposites.
The synthesis of polystyrene/GO (PS-GO) nanocomposites using the reversible additionfragmentation
chain transfer (RAFT) mediated polymerization method is also described. The
GO was synthesized and immobilized with a RAFT agent to afford RAFT-functionalized GO
nanosheets. The RAFT-immobilized GO was used for the synthesis of PS nanocomposites in
a controlled manner using miniemulsion polymerization. The molar mass and dispersity of the
PS in the nanocomposites depended on the amount of RAFT-grafted GO in the system, in
accordance with the features of the RAFT-mediated polymerization. X-ray diffraction and transmission electron microscopy analyses revealed that the nanocomposites had exfoliated
morphology, even at relatively high GO content. The thermal stability and mechanical
properties of the PS-GO nanocomposites were better than those of the neat PS polymer.
Furthermore, the mechanical properties were dependent on the modified-GO content (i.e., the
amount of RAFT-grafted GO).
The hydrophobicity and barrier properties of the resulting films prepared from the synthesized
poly(St-co-BA)/GO nanocomposite latices to water and water vapor were also investigated.
The hydrophobicity of the synthesized nanocomposite films was determined using contact
angle measurements. The water permeability was determined by measuring the moisture
vapor transmission rate of the films. The GO in the nanocomposites was reduced to its
original form (i.e., graphite), and the barrier properties of the obtained nanocomposite films
were determined and compared to films containing the unmodified GO (as-prepared GO).
Results showed that reduction of GO had a significant impact on the water affinity of the
resultant films prepared from the synthesized nanocomposite latices. The presence of
reduced-GO (RGO) instead of unmodified GO in the miniemulsion formulation significantly
improved the hydrophobicity and barrier properties of the final films to water. However, the
barrier properties of the nanocomposites were unaffected by the amount of RGO in the
nanocomposites. / AFRIKAANSE OPSOMMING: Nuwe metodes is beskryf vir die sintese van polimeer/grafiet nanosamestellings deur gebruik
te maak van die miniemulsie polimerisasieproses. Natuurlike grafiet is gefunksionaliseer dmv
oksidasie om grafietoksied (GO) nanovelle te vorm. Polistireen-ko-butielakrilaat (poli[St-ko-
BA]) nanosamestellinglatekse wat GO nanovelle bevat is suksesvol gesintetiseer deur gebruik
te maak van miniemulsie polimerisasie as ‘n een-stap nano-insluitingstegniek. Die benadering
wat gevolg is het die uitbreiding van die GO nanovelle, in situ, gedurende die
miniemulsifiseringstap behels, gevolg deur die polimerisasie van die monomere in die
teenwoordigheid van hierdie uitgebreide nanovelle. Stireen (St) en butielakrilaat (BA) is met
GO gemeng en daarna emulgeer in die teenwoordigheid van ‘n seepmiddel (surfactant) en ‘n
hidrofoob om pre-miniemulsielateksdeeltjies te lewer. Die stabiele pre-miniemulsies is
gepolimeriseer om poli(St-ko-BA)/GO nanosamestellinglatekse te vorm. Die polimerisasie
het met redelike hoë monomeeromskakeling verloop en het stabiele
nanosamestellinglateksdeeltjies gelewer. Hierdie nanosamestellings het hoofsaaklik
geïnterkaleerde morfologie, onafhanklik van die persentasie GO vullers, getoon.
Die sintese van afgeskilferde polimeernanosamestellings berei met gewysigde GO is beskryf.
GO is gewysig met ‘n ‘surfmer’ (reaktiewe seepmiddel), 2-akrielamido-2-metiel-1-
propaansulfoonsuur (AMPS), wat die gapings tussen die GO nanovelle vergroot het en die
monomeer interkalering tusssen sy nanogange fasiliteer. Die AMPS-gewysigde GO is gebruik
vir die sintese van poli(St-ko-BA)/GO nanosamestellinglatekse deur gebruik te maak van ‘n
soortgelyke miniemulsie prosedure. Die nanosamestelling sό verkry het ‘n afgeskilferde
morfologie getoon en die GO nanovelle was grootendeels afgeskilfer (ongeveer 2–5 nm dik)
in die films wat berei is van die gesintetiseerde nanosamestellinglatekse. Laasgenoemde het
verhoogde termiese en meganiese eienskappe gehad in vergelyking met die suiwer polimeer,
as gevolg van die teenwoordigheid van die AMPS-gewysigde-GO. Die meganiese eienskappe
van die nanosamestellings hang af van persentasie AMPS-gewysigde GO vullers in die
nanosamestellings.
Die sintese van PSt/GO nanosamestellings dmv die omkeerbare-addisie-fragmentasieoordrag-
(OAFO-, Eng. RAFT-) bemiddelde polimerisasie metode is ook beskryf. Die GO is
berei en geïmmobiliseer met ‘n RAFT verbinding om GO nanovelle met RAFT
funksionaliteit te lewer. Die RAFT-geïmmobiliseerde GO is gebruik vir die sintese van PSt
nanosamestellings in ‘n gekontrolleerde manier mbv miniemulsie polimerisasie. Die molêre massa en dispersie van die PSt in die nanosamestellings hang af van die hoeveelheid RAFTgeënte
GO in die sisteem, in ooreenstmming met die kenmerke van RAFT-bemiddelde
polimerisasie. X-straaldiffraksie en transmissie-elektronmikroskopie analises het bewys dat
die nanosamestellings, selfs by relatiewe hoë GO inhoud, ‘n afgeskilferde morfologie gehad
het. Die termiese stabiliteit en meganiese eienskappe van die PSt-GO nanosamestellings was
beter as dié van die suiwer PSt polimeer. Verder was die meganiese eienskappe afhanklik van
die gewysigde-GO-inhoud (dws, die hoeveelheid RAFT-geënte-GO).
Die hidrofobisiteit en spereienskappe van die films berei vanaf die gesintetiseerde poli(St-ko-
BA)/GO nanosamestellinglatekse teenoor water en waterdamp is ook ondersoek. Die
hidrofobisiteit is ondersoek deur gebruik te maak van kontakhoekmeting. Die
waterdeurlaatbaarheid is bepaal deur die waterdampoordragtempo van die films te bepaal. Die
GO in die nanosamestellings is gereduseer tot sy eenvoudigste vorm (grafiet) en die
spereienskappe van die nanosamestellingfilms is bepaal en vergelyk met die films wat die
ongewysigde GO bevat het. Resultate het getoon dat reduksie van GO ‘n groot invloed gehad
het op die wateraffiniteit van die films wat berei is vanaf die gesintetiseerde
nanosamestellinglatekse. Die teenwoordigheid van die gereduseerde-GO (RGO) in plaas van
die onveranderde GO in die miniemulsie formulasie het die hidrofobisiteit en spereienskappe
van die finale films, teenoor water, baie verbeter. Die spereienskappe van die
nanosamestellings is egter nie beïnvloed deur die hoeveelheid RGO in die nanosamestellings
nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20119 |
| Date | 03 1900 |
| Creators | Etmimi, Hussein Mohamed |
| Contributors | Sanderson, Ronald D., Mallon, Peter E., Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Rights | Stellenbosch University |
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