Investigating the physicochemical property changes of plastic packaging material exposed to UV radiation
| dc.contributor.advisor | Akdogan, G. | en_ZA |
| dc.contributor.advisor | Dorfling, Christie | en_ZA |
| dc.contributor.advisor | Chimphango, Annie F. A. | en_ZA |
| dc.contributor.author | Conradie, Willem Johannes | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. | en_ZA |
| dc.date.accessioned | 2020-11-25T10:37:12Z | |
| dc.date.accessioned | 2021-01-31T19:40:50Z | |
| dc.date.available | 2020-11-25T10:37:12Z | |
| dc.date.available | 2021-01-31T19:40:50Z | |
| dc.date.issued | 2020-12 | |
| dc.description | Thesis (MEng)--Stellenbosch University, 2020. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: Global plastic production is increasing, and as a consequence more waste is generated and released into the environment. Oceanic weathering f actors such as ultraviolet (UV) radiation, temperature, and salinity result in the degradation of these plastics and subsequent f ormation of microplastics (MPs). These MPs in-turn pose a specific threat to ecosystems and their respective inhabitants.This study aimed to evaluate UV induced degradation of conventional packaging material made of polypropylene (PP) homopolymer and amorphous poly(ethylene terephthalate). Plastic sheets were prepared into four different shapes: small circles (6 mm dia.), large circles (12 mm d ia .), small rectangles (8x4 mm), and large rectangles (40x10 mm). Sequential degradation was considered with samples initially degraded solely by UV radiation in air. The experiments were conducted in a UV chamber that offered two levels of irradiance exposure: 65 W/m2 and 130 W/m2. After the initial degradation in air, samples were further exposed to either constant temperatures (25°C or 60°C) or cyclic UV conditions (65 W/m2 or 130 W/m2) while immersed in different aqueous solutions (demineralised water or seawater). Each experimental run commenced for six weeks, and samples were drawn and analysed fortnightly. The physicochemical properties monitored over time were mass, crystallinity, microhardness, and chemical functional groups (carbonyl and hydroxyl). These properties were measured via standard analytical techniques such as precision balance, differential scanning calorimetry (DSC), Vickers microhardness tester, and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy.Results from the initial experiments indicated that UV irradiance proportionally instigated changes in plastic properties. Increased mass loss accompanied by considerable increases in carbonyl index was observed for the PPs. Shape did not significantly affect mass loss or functional group developments. Clear polypropylene (CPP) reflected the most severe degradation, resulting in the most considerable mass loss, increase in crystallinity, an d highest carbonyl content. Overall PPs degraded more than PET; differences were mainly attributed to alternative compositions, with PP having high frequencies of tertiary carbon atoms whilst PET contained stabilising aromatic rings increasing its stability towards photo-oxidative degradation. The peak wavelength sensitivity of PP also almost exactly corresponded to the peak wavelength intensity of the UV lamps used in this investigation. Furthermore, it was suspected that black polypropylene (BPP) contained a UV absorbing additive (carbon black) responsible for shielding its interior from radiation by terminating free radical reactions and converting energy to heat. Results f rom experiments performed with plastic samples immersed in aqueous solutions w ere more irregular. It was concluded that degradation occurred substantially f aster in air than in seawater. The most significant property changes in crystallinity, microhardness, and chemical functionalities were observed for material without any previous degradation history. Samples with previous histories showed more resistance to crystallinity changes. This was attributed to prior exposure weakening the material, presenting crosslinking and structural defects which inhibited polymer chains from realigning into crystalline structures. Carbonyl groups reduced f or material with previous degradation histories. This was due to the following occurrences: (i) changes in surface energy with polymer chains rearranging leaving carbonyl products concealed below the observed surface and (ii) the degraded surface layer eroding, or hydrophilic products dissolvinginto the surrounding solution medium leaving a fresh unexposed layer of plastic being analysed. Solution medium did not have a significant effect on the property changes of untreated material. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Raadpleeg teks vir opsomming | en_ZA |
| dc.format.extent | 128 pages | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/109240 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject | Polypropylene | en_ZA |
| dc.subject | Environmental degradation | en_ZA |
| dc.subject | UV radiation | en_ZA |
| dc.subject | Marine environment pollution | en_ZA |
| dc.subject | Microplastics | en_ZA |
| dc.subject | UCTD | en_ZA |
| dc.title | Investigating the physicochemical property changes of plastic packaging material exposed to UV radiation | en_ZA |
| dc.type | Thesis | en_ZA |