Enzymatic devulcanization of waste rubber product /
Enzymatic devulcanization is one of the newest techniques to prepare waste rubber products for recycling. The process deems more efficient and less expensive compared to various other devulcanization methods. The technique basically used enzyme secreted from bacteria to break the sulfur bonds in the...
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
Gombak, Selangor :
Kulliyyah of Engineering, International Islamic University Malaysia,
2011
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| Subjects: | |
| Online Access: | Click here to view 1st 24 pages of the thesis. Members can view fulltext at the specified PCs in the library. |
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| Summary: | Enzymatic devulcanization is one of the newest techniques to prepare waste rubber products for recycling. The process deems more efficient and less expensive compared to various other devulcanization methods. The technique basically used enzyme secreted from bacteria to break the sulfur bonds in the vulcanized rubber structure, rendering it more acceptable to be recycled. In this study, tetrathionate hydrolase releasing Thiobacillus ferrooxidans bacterial strain was used. The study aims at looking into the optimization of the process conditions for bacterial growth which leads to the best devulcanization process. Designs of experiments and the analyses of results were conducted by using STATISTICA® computer software where factorial experimental designs were applied in three different phases. In determining the optimal physical conditions and the medium composition for minimum doubling time of the bacterial growth, six independent variables were tested. This was followed by the determination of the optimal cultivation medium compositions to maximize the protein secretion and accumulation, where three independent variables were evaluated. Finally in order to determine the optimal conditions for devulcanization of rubber waste, two independent variables were examined. Analyses of the final phase include physical observation by Field Scanning Electron Microscope (FESEM), followed by the mechanical testing of the newly revulcanized rubber. For the first phase of the experiment, five-level six-factor central composite design was used to evaluate the effects of medium components and physical conditions on the growth of Thiobacillus ferrooxidans. The optimized conditions to promote the best growth of bacteria were by incubating the bacteria at 25ºC, with the initial pH buffer of 4 and at an agitation speed of 125 rpm, with salt concentration as follows; in (g/l) of KH2PO4 = 4g, (NH4)2SO4 = 4g, and MgSO4.7H2O = 0.3g. The second phase experiment was conducted to investigate the effects of medium compositions together with optimized physical condition towards the production of protein. Results show that in order to achieve the highest protein production, the optimized salt concentration in this fivelevel three factor central composite design are as follows; in (g/l) of KH2PO4 = 4g, (NH4)2SO4 = 4g, and MgSO4.7H2O = 0.1g. For the third phase experiment which was conducted with central composite design with two factors and three-level of parameters, result showed that the optimum conditions for rubber degradation to achieve the highest tensile strength when revulcanized was by cultivating the bacteria at the above optimized parameters and shaking it at an agitation speed of 250 rpm for a period of 24 hours with 7g/100ml pulp density. The FESEM analyses show a differential surface change in the rubber incubated in the optimized conditions where cavities were uniformly visible throughout the surface. On revulcanization of treated rubber, the highest strength reading obtained was 8.21 MPa, an increase of 32.42% from the untreated rubber. This study shows that with thorough observations and studies of the characteristics of rubber, the quality of the recycled rubber via enzymatic devulcanization can be improved and the objective to recycle higher percentage of waste rubber can be achieved. |
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| Item Description: | Abstracts in English and Arabic. "A dissertation submitted in fulfilment of the requirement for the degree of Master of Science (Biotechnlogy Engineering)."--On t.p. |
| Physical Description: | xvi, 148 leaves : ill. ; 30cm. |
| Bibliography: | Includes bibliographical references (leaves 124-135). |