Surface modified cross-linked poly(vinyl alcohol)/poly(vinyl pivalate) suspension particles

D Aguiar, Donna-Leigh (2010-12)

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010.

Thesis

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.

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