Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The distribution of different free chemical functional groups on wood and pulp
fibres was determined by means of atomic force microscopy (AFM) with
chemically modified tips. Because these functional groups show a higher
affinity to similar groups on the substrate surface during scanning, AFM
images were recorded using an additional digital pulsed-force mode (DPFM)
controller. This allowed the distribution of the chemical components to be
imaged and to a degree, also to be quantified. The investigated tip coatings
showed different sensitivities towards the major chemical components present
in wood fibres. These components were determined on spin-coated films as
well as wood fibres. It was possible to make a clear distinction between
cellulose and lignin in both cases. This technique could therefore be used to
differentiate between cellulose and lignin present on pulp fibre surfaces and to
confirm the successful removal of lignin by pulping.
The chemical composition of wood fibres and fibre surfaces of several acacia
and eucalyptus species, and hybrids originating from various growth sites in
South Africa, are compared. The objective was to determine the differences in
chemical surface composition due to genetics or site. The motivation for this
was to eventually facilitate a tailor-made supply of wood for pulping which
results in an optimal blend of fibres that can be pulped together with similar
yields. This, however, first requires a sound knowledge of the fibre properties.
The surface functionality on the single fibre level is a key property because it
determines how good inter-fibre bonding will be when paper is formed, which
in turn depends to a large degree on the amount of free hydroxyl groups that
are available and therefore on the cellulose content on the fibre surface.
The cellulose and lignin contents on the fibre surface were determined with
chemical force microscopy (CFM), a variation of AFM. CFM involves the use
of chemically modified tip using selected functional groups. Since, the general
bulk composition of the fibre and the surface composition differ, both
parameters were determined. Significant differences in the cellulose and lignin
content on fibre surfaces were found, with regard to genotype and site, respectively. In some, but not all, cases the surface composition of wood
fibres followed the bulk composition and differences were generally more
pronounced. Differences due to genotype were significant, especially with
regards to the surface lignin content - but variation due to site was also
distinctly recognisable.
This variation in surface functionality could be the reason why some pulpwood
blends result in a lower pulp yield and different quality. / AFRIKAANSE OPSOMMING: Die verspreiding van verskillende vrye chemiese funksionele groepe op hout
en pulpvesels is bepaal deur middel van atoomkragmikroskopie (AFM), met
chemies-gemodifiseerde punte (tips). Omdat hierdie funksionele groepe 'n
hoër verwantskap tot soortgelyke groepe op die substraat se oppervlak
gedurende skandering toon, kan AFM-beelde wat met 'n addisionele
digitalepulskragmodusbeheerstel bepaal word dit moontlik maak om die
verspreiding van die chemiese komponente uit te beeld en tot op ‘n sekere
vlak te kwantifiseer. Die ondersoekte punt-oppervlakmiddels het verskillende
sensitiwiteite teenoor die hoof chemiese komponente in die houtvesels en
spin-bestrykte films getoon. 'n Duidelike onderskeid kon in beide gevalle
tussen sellulose en lignien gemaak word. Hierdie tegniek kon dus gebruik
word om te onderskei tussen sellulose en lignien wat op die
pulpveseloppervlak teenwoordig was en om die suksesvolle verwydering van
lignien gedurende die pulpproses (pulping) te bevestig.
In hierdie studie is die chemiese samestelling van houtvesels en die
veseloppervlaktes van verskeie akasia en eucalyptus spesies, asook dié van
gekruisde spesies wat van verskeie werfliggings in Suid-Afrika afkomstig is,
vergelyk. Die doel was om te toets vir verskille in chemiese
oppervlaksamestellings, wat veroorsaak kan word deur genetika of werf
verskille, met die uiteindelike mikpunt om ‘n spesiaal-gemaakte voorraad van
hout vir pulping te fasiliteer, wat kan lei tot 'n optimale mengsel van vesels wat
saam gepulp kan word met soortgelyke opbrengs. Dit vereis natuurlik 'n goeie
kennis van die veseleienskappe. Die oppervlakfunksionering van enkel vesels
is ‘n kritiese eienskap omdat dit bepaal hoe goed interveselverbindings sal
wees wanneer papier gevorm word. Dit hang tot ‘n groot mate af van die
hoeveelheid vry hydroksielgroepe wat beskikbaar is en dus ook van die
sellulose inhoud op die veseloppervlak.
Die sellulose- en lignieninhoud op die veseloppervlak is bepaal met chemiese
kragmikroskopie – 'n variasie van atoomkragmikroskopie. Omdat die
algemene grootmaat samestelling van die vesel en die oppervlaksamestelling mag verskil, is altwee parameters bepaal. Beduidende verskille in die
sellulose- en lignieninhoud, met betrekking tot genotipe en werfligging, op
veseloppervlaktes is gevind. In sommige, maar nie alle, gevalle het die
oppervlaksamestelling van houtvesels ooreengestem met die
grootmaatsamestelling, en verskille was oor die algemeen meer beduidend.
Verskille as gevolg van genotipe was beduidend, veral met betrekking tot die
oppervlak lignieninhoud, maar variasie as gevolg van werfligging was ook
duidelik herkenbaar.
Hierdie variasie in oppervlakfunksionering kan die rede wees hoekom
sommige pulp–hout mengsels lei tot 'n laer pulpopbrengs en verskille in
kwaliteit.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5287 |
| Date | 12 1900 |
| Creators | Klash, Abdalah |
| Contributors | Meincken, M., 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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