- Title
- Analysis of the effectiveness of Tulbaghia Violacea extracts as devulcanizing agents for synthetic CIS-1,4-polyisoprene vulcanizates
- Creator
- Gxakuma, Lutho
- Subject
- Plant extracts
- Subject
- Plant products -- South Africa Medicinal plants -- South Africa Plants -- Analysis
- Date Issued
- 2020
- Date
- 2020
- Type
- Thesis
- Type
- Masters
- Type
- MSc
- Identifier
- http://hdl.handle.net/10948/49093
- Identifier
- vital:41600
- Description
- Tulbaghia violacea is an indigenous plant commonly known as wild garlic, wilde knoffel in Afrikaans, isihaqa in Zulu or itswele lomlambo in Xhosa. Its leaves and bulbs are widely used as herbal remedies for various ailments and its medicinal uses include fever and colds, asthma, tuberculosis and stomach problems. Like all other members of the Alliacea family, Tulbaghia violacea produces a distinctive garlic-like odour when its leaves or rhizomes are damaged, resulting in the release of cysteine-derived sulphur compounds which include the oil-soluble organo-sulphur compounds and water-soluble cysteine derivatives. Chemically synthesized sulphur containing compounds have been reported to be effective devulcanizing agents and many industries prefer to perform devulcanization using them. Most commonly applied devulcanizing agents include disulphides, thiophenols and their zinc salts, and mercaptans which are mixed with the rubber scrap powder under specific reaction conditions. In this study, instead of performing devulcanization by using industrial synthesized sulphur containing compounds, the effectiveness of the extracts of organo-sulphur containing compounds from Tulbaghia violacea are evaluated as potential devulcanizing agents for synthetic cis-1,4-polyisoprene vulcanizates. This is a new, cheap and greener practice of rubber devulcanization. Diallyl disulphide, which is one of the organo-sulphur containing compounds present in Tulbaghia violacea, is the devulcanizing agent of interest to this study. The organo-sulphur containing compounds were extracted from the bulbs, roots and leaves of the plant using the soxhlet and ultrasonic bath extraction method. The solvent system used in the soxhlet extraction method was 2% of 2-propanol in n-hexane whereas in ultrasonic bath extraction method the solvent system used was 100% ethanol. An essential oil extract was obtained from the plant organs. The yield of the essential oil extracts obtained using the soxhlet extraction method was higher compared to the yield of the essential oil extracts obtained using the ultrasonic bath extraction method. According to the Fourier-Transform Infrared spectroscopy, the organo-sulphur containing compounds were present in the essential oil extracts of the plant. The essential oil extracts that were extracted using the soxhlet extraction method were chosen for further analysis. It was found out that the allyl sulphide and diallyl disulphide have the same retention time from the High Performance Liquid Chromatography (using a normal phase column). The Differential Scanning Calorimeter indicated that the allyl sulphide was not present in the essential oil extracts whereas the diallyl disulphide was present in the essential oil extract of the roots and leaves. The High Performance Liquid Chromatography was used to quantify the presence of the diallyl disulphide in the essential oil extract of roots and leaves. The quantity of diallyl disulphide was 23% in the dry mass of the essential oil extract of roots. In the essential oil extract of leaves the diallyl disulphide was very low concentrated and the High Performance Liquid Chromatography was less sensitive to detect it. According to the Thermogravimetric Analyser, it was found that the essential oil extracts begin to degrade at 120 °C and experience a multistage degradation. The softening temperature of the essential oil extracts was 60 °C from the Simultaneous Differential Scanning Calorimeter-Thermogravimetric Analyser. Conventional vulcanization of synthetic cis-1,4-polyisoprene was prepared with the vulcanization ingredients of zinc oxide, sulphur, stearic acid and N-tert-butyl-2-benzothiazole sulphenamide. The vulcanized synthetic cis-1,4-polyisoprene produced, under the heating temperature of 160 °C, was mixed with the essential oil extracts using the internal mixer at 60 °C and the two-roll mill. The overall torque, tan delta and the total crosslink density were the properties of interest of synthetic cis-1,4-polyisoprene vulcanizate in this study. The devulcanization temperature for the treated synthetic cis-1,4-polyisoprene vulcanizate with the essential oil extracts was optimized using the Dynamic Moving Die Rheometer and Dynamic Rubber Process Analyser. The amount of essential oil extracts at which they are effective devulcanizing agents for synthetic cis-1,4-polyisoprene vulcanizate was also optimized. During optimization a change on the latter mentioned properties of synthetic cis-1,4-polyisoprene vulcanizate was observed, indicating that the essential oil extracts have an effect as potential devulcanizing agents. The essential oil extracts increased the tan delta and reduced the overall torque, and total crosslink density of synthetic cis-1,4-polyisoprene vulcanizate as expected from devulcanizing agents. 200 °C was a preferable devulcanization temperature whereas essential oil extracts were effective as devulcanizing agent at 1.4%. However, the essential oil extracts influenced the overall torque and tan delta of synthetic cis-1,4-polyisoprene vulcanizate during the mixing process in the internal mixer at 60 °C, which was before heating at 200 °C. The essential oil extracts had a higher influence on the overall torque of synthetic cis-1,4-polyisoprene vulcanizate under heating at 200 °C whereas at 60 °C, during the mixing process, they had a higher influence on the tan delta of synthetic cis-1,4-polyisoprene vulcanizate. The essential oil extract of leaves had a higher influence on the overall torque whereas the essential oil extract of bulbs had a higher influence on the tan delta of synthetic cis-1,4-polyisoprene vulcanizate at 200 °C. The essential oil extract of roots shown a greater influence on the overall torque and tan delta of synthetic cis-1,4-polyisoprene vulcanizate at 60 °C during the mixing process. The effect of the essential oil extracts on the reversing heat capacity of synthetic cis-1,4-polyisoprene vulcanizate was also investigated using the Modulated Differential Scanning Calorimetry method. The essential oil extract of bulbs and roots influenced the reversing heat capacity of synthetic cis-1,4-polyisoprene vulcanizate by reducing it whereas the essential oil extract of leaves caused a temperature shift of the reversing heat capacity curve from the Modulated Differential Scanning Calorimeter thermogram of synthetic cis-1,4-polyisoprene vulcanizate. Therefore, the results indicated that the essential oil extracts of Tulbaghia violacea have an effect as an alternative potential devulcanizing agents for conventional vulcanized synthetic cis-1,4-polyisoprene whether the diallyl disulphide compound is present or not in them.
- Format
- xxii,118 leaves
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
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NMU School of BioMolecular and Chemical Sciences
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