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Conceptual modelling of microplastic fragmentation in the marine environment
Henri, J. T. 2025. Conceptual modelling of microplastic fragmentation in the marine environment. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/22027e8e-3a00-45b1-b9f1-d68cc7a0abf2
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2025
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| _version_ | 1867613784229543936 |
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| access_status_str | Open Access |
| author | Henri, Joshua Timothy |
| author2 | Akdogan, Guven |
| author_browse | Akdogan, Guven Henri, Joshua Timothy |
| author_facet | Akdogan, Guven Henri, Joshua Timothy |
| author_sort | Henri, Joshua Timothy |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Henri, J. T. 2025. Conceptual modelling of microplastic fragmentation in the marine environment. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/22027e8e-3a00-45b1-b9f1-d68cc7a0abf2 |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/132209 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:41:38.867Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/132209 Conceptual modelling of microplastic fragmentation in the marine environment Henri, Joshua Timothy Akdogan, Guven Dorfling, Christie Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Biodegradable plastics -- Environmental aspects Plastic marine debris -- Environmental aspects Marine pollution Fragmentation reactions UCTD Henri, J. T. 2025. Conceptual modelling of microplastic fragmentation in the marine environment. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/22027e8e-3a00-45b1-b9f1-d68cc7a0abf2 Thesis (MEng)--Stellenbosch University, 2025. ENGLISH ABSTRACT: Under the overarching context of the formation, fate, and transport of microplastic in the marine environment, the primary aim within the scope of this project was to develop a conceptual mathematical model describing plastic degradation within the marine ecosystem. The first objective of this study was to investigate the various degradation routes for plastic and the relationship between photo-oxidation and mechanical breakage. The second objective was to compare plastic degradation (due to photo-oxidation followed by mechanical breakage) rates in various environments such as urban areas, simulated by ceramic abrasion; beach environments, simulated by fine particulate sand abrasion; and ocean surf environments, simulated by wet sand abrasion in a rotating vessel. The third objective was to develop a conceptual mathematical model for the photo-oxidation mechanical degradation pathway. The fourth objective was to fit model parameters to experimental data through mathematical back-calculation techniques. The objectives of this study have been achieved by firstly studying plastic degradation mechanisms; secondly, designing a two-factor experiment to study the combined effect of photo-oxidative and mechanical abrasion upon plastic degradation characteristics; and thirdly, carrying out batch abrasion-fragmentation experiments to obtain microplastic breakage data to investigate the extent to which prior exposure of plastic particles to ultraviolet radiation affected its breakage characteristics. Fourthly, with experimental data generated, models were developed which fit the associated parameters and describe the breakage characteristics. To achieve the objectives stated, an ultraviolet radiation chamber was built with a capacity of 1000 g plastic and irradiation intensity of 1000 W/m2. Pretreatment of the plastic for abrasive fragmentation studies was carried out in the irradiation chamber, where accelerated photo-oxidative degradation mechanisms were induced for durations of 72 − 192 hr to understand breakage processes and rates of a plastic particle starting size class of 2800−4000 μm. A rotary abrasion vessel (D = 200 mm; L = 270 mm) was designed to be operated between 66 − 75 rpm on rollers driven by an electric motor. Thereafter, three different environmental attrition-fragmentation conditions were investigated in the rotary abrasion vessel with incrementing time intervals. Plastic mechanical fragmentation on pathways, rocks, and pebbles was approximated by investigating the breakage of particles when using ceramic milling media in the mill. Thereafter, finer fragmentation plastic experiences on the shoreline were simulated in the rotating vessel with sand as abrasion media. Finally, an abrasive environment in the surf was simulated in the rotating vessel causing the rupture of brittle plastic particles colliding with sand particles in the water and sand mixture. Analytical, average, and differential model solutions were developed for simulation conditions in the coastal environment. First-order differential equations were parameterised to model the breakage of the plastic and microplastic formation with respect to abrasion time. A key finding was the onset of plastic brittleness that occurred at an ultraviolet treatment time of approximately 70 hr, leading to mass loss in all the simulated environments. In the ceramic environment, with ultraviolet exposure times of 120 hr, it was found that polypropylene pellets in size class 2800−4000 μm loses 80 % of its mass to lower size classes within 32 min of abrasion, resulting in 74.4 % of particles reporting to the 2350−2800 μm size class and the balance to size class 0−2350 μm. Thus, mass loss from 2350−4000 μm size class is 5.6 %. Concatenation of sieve sizes into lower 0−1700 μm and upper 1700−4000 μm classes revealed a mass loss of 5.96 % within 32 min and 8.75 % in 136 min. Mathematical modelling yields selection function S = 0.1857ln(tnUV) + 0.1756. In comparison, similar plastic particles with a UV-T of 120 hr degraded with a 8.36 % mass loss after 72 hr of abrasion in the sand environment in repeatability tests. Analysis yields a selection function S = 0.0023ln(tnUV) + 0.0026. While in the sand and water environment, plastic loses 14 % of its mass after 120 hr of ultraviolet treatment and 120 hr of abrasion in a sand and water abrasion environment under the irradiative-abrasive conditions simulated. Analysis yields a selection function S=0.001ln(tnUV)+0.0015. AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar. Masters 2025-05-30T05:19:11Z 2025-05-30T05:19:11Z 2025-03 Thesis https://scholar.sun.ac.za/handle/10019.1/132209 en Stellenbosch University 164 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Biodegradable plastics -- Environmental aspects Plastic marine debris -- Environmental aspects Marine pollution Fragmentation reactions UCTD Henri, Joshua Timothy Conceptual modelling of microplastic fragmentation in the marine environment |
| title | Conceptual modelling of microplastic fragmentation in the marine environment |
| title_full | Conceptual modelling of microplastic fragmentation in the marine environment |
| title_fullStr | Conceptual modelling of microplastic fragmentation in the marine environment |
| title_full_unstemmed | Conceptual modelling of microplastic fragmentation in the marine environment |
| title_short | Conceptual modelling of microplastic fragmentation in the marine environment |
| title_sort | conceptual modelling of microplastic fragmentation in the marine environment |
| topic | Biodegradable plastics -- Environmental aspects Plastic marine debris -- Environmental aspects Marine pollution Fragmentation reactions UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/132209 |
| work_keys_str_mv | AT henrijoshuatimothy conceptualmodellingofmicroplasticfragmentationinthemarineenvironment |