Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: In papermaking, fillers and additives are used to enhance paper properties. In this study spherical
modified poly(vinyl alcohol) (PVA) particles were prepared for use as fillers. In order to determine
the mechanism of adhesion of additives to cellulose (paper) fibres, these particles were modified to
have surface functionality, with cationic and anionic surface charges, similar to charged
polyelectrolyte additives.
Typically, retention aids used to improve the fibre–fibre and fibre–filler bonding are able to
conform to the surface of the fibres and fillers. Oppositely charged components show strong affinity
for each other, e.g. cationic polyelectrolyte groups adhere to anionic surface charges on the fibres.
The spherical PVA particles were prepared by the saponification of spherical poly(vinyl
pivalate) (PVPi) precursor particles. These PVPi particles, prepared via suspension polymerisation,
were cross-linked with a divinyl ether comonomer. The vinyl pivalate (VPi) suspension
polymerisation was successfully carried out and afforded relatively uniformly distributed PVPi
particles, with diameters of 0.5–10 mm.
The cross-linked PVPi particles were then saponified in tetrahydrofuran (THF) as swelling
solvent, to afford PVA with various degrees of saponification (DS). The spherical shape was lost and
fibrous material was obtained when uncross-linked PVPi particles were saponified. Cross-linking the
spherical PVPi particles (PVA precursor) proved innovative, and essential in maintaining the spherical
form during saponification to PVA/PVPi. By varying the saponification time periods, various DS
were obtained, as characterised by solid state NMR spectroscopy.
Surface modification of the PVA/PVPi particles was carried out with cationic and anionic
groups via the Williamson ether synthesis. Ionic modification of these rigid spherical PVA/PVPi
particles was carried out in order to study their adherence to cellulose fibres, compared to the
adherence of similarly modified starches with cellulose fibres. Fluorescent labelling of the different
modified particles was carried out using two complimentary coloured fluorescent markers.
Fluorescence imaging and scanning electron microscopy (SEM) enabled the observation of particle–
fibre and particle–particle interaction. Results indicated that the negative groups are sparse on the
cellulose fibres, and therefore particles with low functionality but which are able change shape and
conform and adhere to the surface of the cellulose fibres are required for effective adhesion.
These modified spherical PVA/PVPi particles are unique as they mirror the chemistry of
functionalised starch and cellulose particles, yet maintain their shape and have a fixed size,
measurable by SEM and transmission electron microscopy (TEM). Field-flow fractionation was also
used to characterise and measure these relatively large cross-linked and fixed diameter particles. / AFRIKAANSE OPSOMMING: In papierproduksie word vulstowwe en bymiddels gebruik om die eienskappe van papier te verbeter.
In hierdie studie is sferiese poli(vinielalkohol) (PVA) partikels berei vir gebruik as vulstowwe. Om
ten einde die meganisme van die bymiddelklewing aan die sellulose vesels (papier) te bepaal, is die
oppervlakke van hierdie partikels gewysig met kationiese of anioniese groepe, om 'n oppervlak
soortgelyk aan dié van funksionele poliëlektrolietbymiddels te verskaf.
Die retensiemiddels wat gebruik word om die vesel–vesel en vesel–vulstof binding te verbeter
is tipies in staat om te konformeer aan die oppervlak van die vesels en vulstowwe. Teenoorgesteldgelaaide
komponente toon 'n sterk affiniteit vir mekaar, bv. kationiese poliëlektrolietgroepe is
vasklewend aan die anioniesgelaaide oppervlakke van die vesel.
Die sferiese PVA partikels is berei deur die verseping van sferiese poli(vinielpivalaat) (PVPi)
partikels. Hierdie voorloper PVPi partikels, berei deur suspensiepolimerisasie, is gekruisbind met 'n
divinieleter ko-monomeer. Die vinielpivalaat (VPi) suspensiepolimerisasie is suksesvol uitgevoer en
relatief eenvormig verspreide sferiese PVPi partikels is berei, met deursnitte tussen 0.5–10 mm.
Die gekruisbinde PVPi partikels is daarna gesaponifiseer in tetrahidrofuraan (THF) as
oplosmiddel, om PVA met verskillende grade van verseping (DS) te berei. Die sferiese vorm raak
verlore en veselagtige materiaal is verkry wanneer PVPi partikels met geen kruisbinding verseep is.
Kruisbinding van die sferiese PVPi partikels (PVA voorloper) is voordelig en noodsaaklik om die
sferiese vorm tydens die verseping tot PVA/PVPi te behou. Deur die tydsduur van verseping te
verander, is verskeie grade van verseping verkry en bevestig deur vaste toestand KMR spektroskopie.
Oppervlakwysiging van die PVA/PVPi partikels, om kationiese en anioniese groepe aan te heg,
is uitgevoer via die Williamson etersintese. Ioniese wysiging van hierdie stram, sferiese PVA/PVPi
partikels is uitgevoer om ten einde hul klewing met sellulose vesels te bestudeer en te vergelyk met die
klewing van soortgelyk gewysigde stysels. Fluoressensie merking van die verskillende gewysigde
partikels is uitgevoer met behulp van twee komplimentêre gekleurde fluoressensie merkers.
Fluoressensie beeldvorming en SEM verskaf die waarneming van partikel–vesel en partikel–partikel
interaksie. Die resultate dui daarop dat die negatiewe groepe van die sellulose vesels skaars is, en
daarom is partikels met ‘n lae funksionaliteit, maar wat in staat is om van vorm te verander, aan te pas
en te konformeer aan die oppervlak van die sellulose vesels, nodig vir effektiewe adhesie.
Hierdie gewysigde sferiese PVA/PVPi partikels is uniek aangesien hulle die chemie van
gewysigde stysel en sellulose partikels naboots, maar steeds hul vorm behou met 'n vaste grootte;
meetbaar deur SEM en TEM. Veld-vloei-fraksionering is ook gebruik vir die karakterisering van
hierdie relatief groot, stram, gekruisbinde partikels met bepaalde deursneë.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5475 |
| Date | 12 1900 |
| Creators | D Aguiar, Donna-Leigh |
| Contributors | Sanderson, Ronald D., Pasch, Harald, 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 |
| Rights | University of Stellenbosch |
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