Browsing by Author "Nel, Delene"

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    Degradation of plastics in the marine environment with reference to temperature and environmental factors
    (Stellenbosch : Stellenbosch University, 2020-12) Nel, Delene; Akdogan, G.; Dorfling, Christie; Chimphango, Annie F. A.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH ABSTRACT: Plastic waste is an increasing problem, especially in the marine environment, where it has detrimental effects on the ecosystem . For a better comprehension of the environmental implications and eventual fate of plastic waste, research on the degradation is required. This project aimed to fill some of the knowledge gaps by completing a laboratory investigation on temperature associated plastic history, which refers to the degradation induced via temperature on plastics waste during their journey to the ocean, and the effect this has on the degradation behaviour of the plastic in the marine environment. Influences of various environments and plastic properties were also considered. Tests at various temperatures were conducted to investigate the effect of temperature associated with plastic history. The tests were conducted at the following temperatures: 25 ̊C, 100 ̊C and a weekly cycle of 25 ̊C – 60 ̊C. In these tests, three plastics, namely, black polypropylene, clear polypropylene, and clear PET, were investigated in various sizes and shapes. For example, there were large and small, circle and rectangles shapes. The temperature, size, type of plastic and colour additive was found to have important effects on the degradation rate. In the second set of tests to investigate what transpires under marine environmental conditions, samples collected after completion of the constant 25 ̊C and 100 ̊C initial tests were subjected to the following respective treatments: constant temperatures of 25 ̊C or 60 ̊C or 12-hour cycles of 65 W/m2 or 130 W/m2UV radiance – submerged in either seawater or demineralised water, respectively. The UV radiance appeared to be predominantly responsible for greater and/or accelerated degradation compared to naturally expected temperatures, especially for clear polypropylene that exhibited physically visible embrittlement under 130 W/m2 UV radiance. Nonetheless, prolonged exposure is recommended for investigating the 65 W/m2 and 25 ̊C. For both the initial and secondary tests the colour additive is suspected of hindering mechanical property degradation. The 100 ̊C initial treatment is, however, suspected of passivating the colour additive; since after the 100 ̊C treatment, the colour additive did not hinder degradation effectively. The investigation into the effect of environment indicated that under controlled conditions with identical temperatures the addition of water resulted in degradation rate increases. This suggests that the real-life phenomenon of lower degradation in the marine environment than on land could be due to water regulating the temperature. It was furthermore observed that salinity has an accelerating effect on the degradation of polypropylene. PET tended to react similarly to the salinity but the data were not conclusive enough to affirm this theory.