Thesis (PhD (Chemistry and Polymer Science))--Stellenbosch University, 2008. / Polysaccharides were modified with selected polymers via the grafting technique. Both
anionic and cationic polysaccharides were prepared. Random and crosslinked graft
copolymers were also prepared. The percentage grafting was determined by gravimetric
analysis and results were confirmed by cross-polarization magic angle spinning carbon-13
nuclear magnetic resonance microscopy (CP/MAS 13C NMR). These modified biodegradable
polymers were then used to flocculate precipitated calcium carbonate (PCC). The effects of
pH, percentage grafting, crosslinker concentration and polysaccharide concentration on PCC
flocculation were evaluated. Furthermore, the effects of anionic and cationic starch, either
added to PCC sequentially or simultaneously, on PCC flocculation were also investigated.
Generally, anionically modified starch showed excellent flocculation properties, which are
desirable for the end application of PCC retention.
The effect of polyacrylic acid (PAA) and polyacrylamide (PAM) modified cellulose fibers on
calcium carbonate crystal nucleation and growth modification was investigated. When the
heterogeneous crystallization of CaCO3 was carried out in the presence of modified cellulose
fibers the CaCO3 crystals were found to be residing on the surface of the fibers. The
morphologies of the crystallized CaCO3, polymorph and fiber surface coverage were different
for cellulose materials grafted with polymers of different functionalities, meaning that there is
interaction between the crystal growth modifier and the growing nuclei.
The effect of the modified starch on the crystallization of calcium carbonate gave useful
insight into designing CaCO3 filler morphologies. It was found that the filler size,
morphology and surface properties of fillers can be tailor-made by choosing suitable CaCO3
crystallization conditions as well as a suitable crystal growth modifier. The crystallized
CaCO3 had a negatively charged surface. Results of fluorescence studies showed that the
PAA modified starch (polymeric additive used) resided on the surface of the crystals. Thus
the presence of the polysaccharide on the surface of a filler could be advantageous for
strengthening fiber–filler bonding in paper applications.
Anionic starch materials were also used to prepare anionic-starch-coated starch particles. Both
the anionic starch and anionic-starch-coated starch particles were evaluated for PCC retention
and other properties of hand sheets. When anionic-starch-coated starch particles were used
there was generally an improvement in the PCC retention, while the other paper properties
remained desirable. The success achieved with the use of anionic-starch-coated starch
particles now opens the way for the further preparation and testing of various modified starch
particles, for optimization of filler retention.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1396 |
| Date | 12 1900 |
| Creators | Matahwa, Howard |
| Contributors | Sanderson, R. D., Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | Stellenbosch University |
Page generated in 0.0018 seconds