ETD Collection

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Subject: search.filters.subject.Eucalyptus grandis

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    Synthesis and characterization of cellulose nanofibre for electrically conductive paper
    (2017) Ngobese, Sibonelo S.J.
    There is huge drive to identify sustainable, renewable, and environmentally friendly raw materials and right technologies to make or use them. These technologies should be applied in place of the conventional non-sustainable and nonenvironmentally friendly currently used materials. Nanotechnology involves the use of materials that have at least one side with dimension 10-9 m. There is considerable effort directed at the much abundant forest product such as cellulose which can be processed into cellulose nanofibrillated fibres (CNF) and cellulose nanocrystals (CNC). This study involved the synthesis and testing of an electrical conductive cellulose nanofibre made from microcrystalline eucalyptus grandis pulp. In this project, microcrystalline cellulose (MFC) from wood pulp was mechanically fibrillated using a Pilot Refiner to develop microfibrils. The microfibrilated pulp was oxidised with a mixture of 2,2,6,6-tetramethylpyradine-1-oxyl (TEMPO), sodium bromide (NaBr) and sodium hypochlorite (NaOCl) to produce CNF . The CNF was washed, sonicated and dried to produce translucent sheets. The oxidation process was able to achieve both CNF and CNC from wood pulp which was verified and characterized by Techpap, SEM, TEM, FTIR, Hounsfield Tensile Tester and Multimeter. The Techpap instrument indicated that the starting raw unfibrilated and mechanical fibrillated pulp fibre widths were 3.18 and 3.07 microns respectively. After oxidation process the FTIR Spectra produced an absorbance peak at approximately 1720 to 1740 cm-1 wavenumbers that is characteristic of the aldehyde carbonyl stretch which was not present on the unoxidised pulp. The average tensile strength of the paper strips were determined to be 4.51kN/m using the standard procedure of the experiment. From the TEM images it was observed that the CNF and CNC had dimensions ranging from 1.4nm to 594nm from pulp. The SEM images showed that on drying the CNF and CNC repolymerised into nanogel. The resistivity of the control CNF was in the infinity range. When the CNF was treated with the reduced Graphene Oxide (GO), the resistivity was determined to be 4400 Ω.m. This resistivity translates to an electrical conductivity of 2.27x10-4 Ω-1.m-1 for a length of a paper strip that was 5mm long. The conductivity of the CNF material was significantly improved and fell within the range of semi-conductive materials. The overall research showed that the synthesized cellulose nanofibre hold a semi-conductor behavior, which add value information in the explored research area.
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    Effects of site management on nutrition, sustainability and productivity in a Eucalyptus Grandis stand in South Africa
    (2008-08-11T11:34:57Z) Du Toit, Ben
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    Vegetation response to clearing of exotic invasive plants along the Sabie River, South Africa
    (2007-02-26T12:52:33Z) Garner, Richard David
    The Reconstruction and Development Programme’s Mpumalanga Working for Water Programme (WWP) has cleared exotic and commercial weed species from the riverine environment since 1994. This study serves as an assessment of the impact and modification caused as a result of invasion and the subsequent clearing of the exotic vegetation on flora in the riverine zone of the Sabie River Catchment. The experimental design compares the before and after clearing effects and includes altitude and invasion intensity variables. The investigations included: in situ soil seed banks, environmental modification, vegetation structure, species diversity and effectiveness of clearing. Clearing and invasion by exotic species altered soil chemical, physical and ground cover parameters. The extent of these modifications was dependent on the extent of invasion and clearing done within the community. Clearing of exotic species however, acted as an additional disturbance to that caused by invasion. Environmental modifications that occurred with clearing and invasion within the study were positively related to percentage soil organic matter, and ground cover (soil, litter, vegetation). Invasion by exotic species alters the vegetation structure, the extent of which was directly related to the invasion intensity. The main source of vegetation structure modification is attributed to tall growing exotic species such as Eucalyptus grandis and Solanum mauritianum. Both of these species dominated the indigenous vegetation, E. grandis by expanding the upper canopy and S. mauritianum by dominating the mid canopy. Clearing of invasive vegetation resulted in an additional disturbance proportional to the extent of invasion intensity. Invasion did not result in any large changes to the vegetation at low intensity but clearing at this intensity increased the disturbance and altered the vegetation structure. Soil seed banks were limited in the number of species and dominated by two exotic species. The soil seed bank of woody species related positively to the community species richness. The total soil seed bank density did not relate to invasion intensity or clearing thereof but propagules of individual species within the soil seed banks did. The seeds of the exotic species, Acacia mearnsii and S. mauritianum, illustrated burial as prerequisite for persistence in the soil seed bank. A. mearnsii and S. mauritianum seeds were found to have half-life’s of up to 25 years and 13 months respectively. The species richness and diversity varied only marginally because of invasion and clearing. Species alpha diversity increased with clearing due to weedy and pioneer species establishment. Beta diversity effectively highlights the species turnover with clearing and invasion. Success in eradication of exotic species had mixed results. Clearing of high invasion sites was effective but in lower invasion categories a number of exotic individuals were missed. Clearing effectiveness was good for certain species such as E. grandis and Pinus patula, but poor for others such as S. mauritianum. Coppicing is a significant issue for E. grandis and S. mauritianum. The persistence of individuals (coppicing & missed individuals) coupled with very large persistent seed banks has repercussions for the clearing programme, as it may prevent effective eradication. Initially the WWP has been successful in removing exotic vegetation, however there is a failure to address the regenerative properties of some exotic species. Unless a rigid schedule of follow up clearing treatments occurs, an even larger invasion problem could exist.