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Ultraviolet photo-chemical degradation of polyethylene terephthalate for use as an alternative recycling method
Title
Ultraviolet photo-chemical degradation of polyethylene terephthalate for use as an alternative recycling method
Creator
Smith, Andrew Thomas
Date
2020
Description
Consumer plastics are a deeply integrated part of the modern world. Their inherent properties which make them cheap, durable, moldable, and...
Show moreConsumer plastics are a deeply integrated part of the modern world. Their inherent properties which make them cheap, durable, moldable, and versatile have caused plastics to be used in many consumer products available for market. However, these same properties have made them a detriment to local and global environments. plastic has begun accumulating in the world’s waterways and oceans, leading to severe ecological consequences. Polyethylene terephthalate (PET) is one of the most pervasive consumer plastic, and a large contributor to the amount of waste. Because of its prevalence in the market, PET has been the focus of research into its recycling and reuse. However, all methods face issues of profitability due to operation and equipment costs, preventing widespread recycling of plastic waste. This leaves the door open to explore other processes of plastic recycling.In this study, ultraviolet photo-chemical degradation of PET was explored as an alternate route to plastic recycling. Ultraviolet irradiation has long been known to depolymerize PET plastic products, but has not been studied in order to enhance these effects. This method has the potential to reduce operation and equipment costs associated with traditional chemical recycling methods by carrying out depolymerization in the solid state. By harnessing this process, PET could be used to degrade material down to a state usable in in other, higher value products. An irradiation chamber was built as a preliminary prototype. This chamber used light of a specific ultraviolet wavelength determined from the absorbance spectrum of PET samples. This allowed the irradiation to be safer, while still maintaining absorption.Ultraviolet degradation of PET was first examined using infrared, contact angle, and fluorescence analysis, and birefringence observation to analyze the chemical and surface effects of irradiation. The results were used to understand the complex mechanisms behind the photo-chemical degradation process. Results were then discussed alongside similar experiments performed in the literature for a deeper understanding of the underlying mechanism.The molecular weight of exposed bottle samples was evaluated using both viscosity and dynamic light scattering methods. This information is key, as it is the main metric that determines the success of the process. In addition, the ultraviolet absorbance of the sample was analyzed along with the principles of Beer’s law. This yielded quantitative analysis on the effect of thickness of the sample, the degradation rate, and the quantum yield of the process.Finally, building upon the information gathered in the study, two key process modifications are made. Thinner samples are first produced, and receive irradiation on both surfaces. The degradation of the modified process was compared to that of previous results on the basis of molecular weight reduction, reaction rate and quantum yield. Using these results, conclusions were drawn about using ultraviolet photo-chemical degradation as a recycling process.
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