Masters Degrees (Chemical Engineering)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6658

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Evaluation of paper substrates for microfluidic application in medical diagnostic kits.
(2018) Moodley, Revesa Sadasivan.; Land, Kevin.; Sithole, Bishop Bruce.; Van Zyl, Werner Ewald.; Andrew, Jerome Edward.
Recent studies in the biomedical field have shown the use of paper in microfluidic analytical devices. However, no studies have been undertaken to ascertain what type(s) of paper substrates are ideal for such microfluidic applications. Hence, this study was conducted to determine the feasibility of using different paper substrates for implementation in microfluidic analytical devices, specifically in the South African context, compared to currently used materials such as glass and silicone. In addition, fibres in paper substrates were substituted with nanofibrillated cellulose (NFC) fibres to ascertain the impact of NFC on the microfluidics of the paper substrates. The wicking rate of the substrates was the focus of the study, with high -resolution field emission gun-scanning electron microscopy and contact angle tests being used to support the results obtained. Solid wax printing was also conducted to determine whether the paper substrates were suited to fabrication for microfluidic applications. High-resolution morphological studies of the paper substrates showed that pore sizes of the pulp fibres were in the order sulphite> bleached kraft > unbleached kraft > Whatman No. 1 Chromatography Filter Paper > Whatman 3MM Chromatography Filter Paper > thermo-mechanical > recycled. It was concluded that the larger pore size of fibres correlated with faster wicking rates of the relevant paper substrates. The substitution of pulp fibres with NFC led to reduced pore size of the fibres thus leading to reduced wicking rates due to the presence of the small NFC particles. Contact angle is directly linked to the hydrophobicity of the substrate and is indicative of the resistance to absorption of a liquid. The results revealed that all the paper substrates were hydrophilic. However, the hydrophilicity of two of the substrates (sheets substituted with 100% NFC unbleached kraft pulp and 100% NFC recycled pulp) were higher than those of the other substrates indicating that, although these substrates were still hydrophilic in nature, their absorption of aqueous liquid would take longer periods of time. The results showed that Whatman glass microfiber GF/D filter paper was the fastest wicking substrate, using both dye and blood simulant as wicking liquids. Similarly, paper substrates made with recycled fibres exhibited the slowest wicking rates when using both wicking liquids. These results can be used when determining which of the substrates to use for paper-based microfluidic device (μPAD) application, whereby the desired detection time would be the factor used to establish which of the substrates to use. Comparison of vertical and horizontal tests showed varying results. In theory, the horizontal wicking test should result in a faster wicking rate than the vertical test, taking hydrostatic pressure into consideration. The majority of the substrates showed that the horizontal wicking rate was faster when using the dye solution, whereas vertical wicking was faster when using the blood simulant. Discrepancies between the results obtained from the dye and blood simulant experiments could be attributed to the additional viscosity drag when using the higher viscosity liquid (blood simulant), as well as possible capillarity differences of the samples. The results were used in conjunction with the morphological studies, whereby the pore size was correlated with the wicking rate. The solid wax printing test revealed that, in general, the substrates were not well suited to the fabrication method. The results showed that the wax was not able to penetrate through the depth of the sheet, hence allowing for the possibility of leakage of liquid from the channels. Two of the substrates (Whatman No. 1 Chromatography filter paper and paper made from sulphite pulp fibres containing 20% nanofibrillated cellulose) exhibited 100% wax penetration and could be considered for μPAD application. However, for paper substrates that do not meet requirements for μPAD applications, their pulp fibres could be chemically modified to induce hydrophobicity thus altering the microfluidic characteristics of the paper substrates.
Fractionation and valorisation of bark extractives from Eucalyptus species.
(2018) Masetlwa, Jethro.; Sithole, Bishop Bruce.; Andrew, Jerome Edward.
The notion of zero-waste in industrial production processes of widely used materials has gained momentum, as industries aim to gain revenue from waste materials which were previously considered as waste. Tree bark from wood obtained from sustainably managed plantations used in the production of timber and pulp industries is an underutilised waste that is mainly used for energy production in mills or left on plantations after debarking. Eucalyptus tree species are commonly used as raw-material in the pulp and paper industry throughout the world. In this thesis, the potential beneficiation of bark from South African planted Eucalyptus tree species (Eucalyptus grandis, Eucalyptus dunnii, Eucalyptus smithii and Eucalyptus nitens) as a source of valuable materials is investigated. Secondary metabolites such as phenolic components, terpenes, steroids and alkaloids can extracted from Eucalyptus bark. In this study, accelerated solvent extraction was investigated for extraction of components in the bark and the components were characterised by a variety of analytical techniques. The investigation was undertaken by optimising the extraction process using the following parameters, temperature (80 to 160℃), number of static extraction cycles (1-3 cycles), solvent type (80% v/v of ethanol or 50% acetone v/v), Eucalyptus species, and particle size (850-500 μm, 500-375 μm and <375 μm). The extraction process was optimised and response surface methodology (RSM) was used to model experimental data for statistical analysis of the Box-Beheknen design of the extraction process. A quadratic model was fitted, and optimum extraction parameters were a temperature of 117℃ with greater than 2 number of static extraction cycles, and bark particles greater than 355 μm. The two target objectives were total phenolic content and total extractive content when using ethanol as the extraction solvent. The amount of phenolic components in the bark extracts was determined by the Folin–Ciocalteu method which using gallic acid as a calibration standard and detection on a UV-vis spectrophotometer. Amongst the four Eucalyptus bark species studied, Eucalyptus dunnii contained the highest amount of phenolic components (5.52g/100g GAE) In addition to using the Folin–Ciocalteu method, the chemical compositions of acetone and ethanol extracts of the bark samples were determined using Pyrolysis-Gas Chromography/Mass Spectrometry. The analysis showed that condensed tannins, with a building block of catechol units, were the most abundant phenolic components present in the bark extracts. Other components that were detected in high amounts were terpenes and terpenoids, and smaller amounts of monoterpenes and sesquiterpenes. Steroid components were also detected, with 𝛽-sitosterol being the most predominant one. The extractive-free bark samples, remaining after removal of solvent extracts, was analysed using high pressure liquid chromatography to determine their chemical content of cellulose, hemicellulose and lignin.
Impact of hexenuronic acid on the physical and chemical properties of eucalyptus clonal pulps during ECF bleaching .
(2007) Andrew, Jerome Edward.
The work described in this dissertation was aimed at obtaining an understanding of

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Browsing Masters Degrees (Chemical Engineering) by Author "Andrew, Jerome Edward."