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

[摘要] ENGLISH ABSTRACT: In papermaking, fillers and additives are used to enhance paper properties. In this study sphericalmodified poly(vinyl alcohol) (PVA) particles were prepared for use as fillers. In order to determinethe mechanism of adhesion of additives to cellulose (paper) fibres, these particles were modified tohave surface functionality, with cationic and anionic surface charges, similar to chargedpolyelectrolyte additives.Typically, retention aids used to improve the fibre–fibre and fibre–filler bonding are able toconform to the surface of the fibres and fillers. Oppositely charged components show strong affinityfor 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(vinylpivalate) (PVPi) precursor particles. These PVPi particles, prepared via suspension polymerisation,were cross-linked with a divinyl ether comonomer. The vinyl pivalate (VPi) suspensionpolymerisation was successfully carried out and afforded relatively uniformly distributed PVPiparticles, with diameters of 0.5–10 mm.The cross-linked PVPi particles were then saponified in tetrahydrofuran (THF) as swellingsolvent, to afford PVA with various degrees of saponification (DS). The spherical shape was lost andfibrous material was obtained when uncross-linked PVPi particles were saponified. Cross-linking thespherical PVPi particles (PVA precursor) proved innovative, and essential in maintaining the sphericalform during saponification to PVA/PVPi. By varying the saponification time periods, various DSwere obtained, as characterised by solid state NMR spectroscopy.Surface modification of the PVA/PVPi particles was carried out with cationic and anionicgroups via the Williamson ether synthesis. Ionic modification of these rigid spherical PVA/PVPiparticles was carried out in order to study their adherence to cellulose fibres, compared to theadherence of similarly modified starches with cellulose fibres. Fluorescent labelling of the differentmodified 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 thecellulose fibres, and therefore particles with low functionality but which are able change shape andconform 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 offunctionalised 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 alsoused to characterise and measure these relatively large cross-linked and fixed diameter particles.

[发布机构] Stellenbosch University