Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / In papermaking, the addition of filler can be detrimental to the properties of the resulting
paper hence the use of additives that enhance paper properties are of paramount importance.
Syndiotacticity rich poly(vinyl alcohol) (PVA) microfibrils were prepared for use as filler
retention aids. They were prepared via in situ fibrillation during the saponification of high
molecular weight poly(vinyl pivalate). The resulting fibers had high thermal stability and
crystalline melting temperature. They were not fully soluble in water even at 100 oC. In order
to make them less water resistant the syndiotacticity of the PVA microfibrils was varied by
copolymerizing vinyl pivalate with vinyl acetate and saponifying the resultant copolymer. It
was observed that changes in syndiotacticity had a significant effect on the crystallinity,
morphology and thermal properties of the resultant PVA.
The surfaces of the fibers were modified by first crosslinking using glyoxal (a dialdehyde),
and then attaching cationic and anionic groups by grafting and by carboxymethylation.
Crosslinking prior to modification was beneficial in minimizing the solubility of the fibers in
the aqueous media in which they were modified. Heterogeneous modification techniques were
employed so that fiber properties could be preserved. Carboxymethylation was carried out
using the two step Williamson’s ether synthesis. The first step involves the formation of a
highly reactive alkoxide by the reaction of PVA with a strong base and the second its
etherification using a functional alkyl halide. Poly(methacryloyloxy ethyl trimethyl
ammonium chloride) and poly(acrylic acid) were grafted from the PVA microfibrils using the
KPS/Na2S2O3 redox initiation system. Grafting was confirmed by FTIR and NMR
spectroscopy.
Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were carried
out on both modified and unmodified PVA microfibrils. The results showed that crosslinking
resulted in an enhancement of the thermal properties of the microfibrils. A decline in the onset
temperature for thermal degradation and crystalline melting temperature were observed, and
were attributed to the modification of the PVA microfibrils.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2184 |
| Date | 03 1900 |
| Creators | Chirowodza, Helen |
| Contributors | Sanderson, R. D., 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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