Browsing by Subject "plastic"

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    Characterizing mVenus adsorption to photodegraded polyethylene using circular dichroism and fluorescence spectroscopy
    (2022-08) Amaris, Althea
    Due to their versatility and relative cost-effectiveness, plastics as a material have gained increasing popularity and are heavily utilized by almost every major industry in the modern day. Their exponential rate of production coupled with a lack of proper disposal methods, however, have resulted in the global environmental issue of plastic pollution. Upon entering the ecosystem, plastic surfaces can act as a foundation for the formation of microbial communities known as biofilms. An initial key step to biofilm growth is the attachment of bacterial surface proteins onto the polymer. In this study, we examine structural changes of a “hard” model protein in the presence of environmentally relevant plastics. Using the intrinsic probes of the mVenus protein, a model yellow fluorescent protein (YFP), we study its structural response to variably photo-aged polyethylene (PE) through circular dichroism (CD) and tryptophan (W)/YFP-fluorescence spectroscopy. Upon binding to aged PE, mVenus undergoes mild secondary structure rearrangement. Interestingly, a forbidden transition in W-fluorescence is observed, evolving from the interaction between the sole tryptophan in mVenus and the increasingly hydrophilic surface of PE as the polymer is progressively photo-oxidized. The beta barrel and beta sheet structure of mVenus retains the overall stability of the protein, whereas the local structure and turn regions accommodate the protein-polymer interactions based on polymer surface chemistry. We can therefore start to predict that proteins bind variably during the initial docking of cells as the secondary structure behaves distinctly based on the age of the film to which it attaches. The dependence of protein docking on the extent of PE-irradiation reveals that film age, polymer type, and structural stability can either accelerate or inhibit biofilm growth.
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    On the Intrinsic Kinetics of Polyethylene Pyrolysis
    (2023-05) Mastalski, Isaac
    Global plastic use has grown exponentially over the past several decades, and this has led to a concomitant increase in plastic waste. Because current plastics, and polyolefins such as polyethylene in particular, have become a necessity for modern life, it is unlikely that more sustainable, alternative plastics can displace them anytime soon, so one of the best ways to mitigate plastic waste is to develop more sustainable, alternative recycling methods. Pyrolysis, or thermal degradation under an inert atmosphere, shows great promise in this regard, since it is capable of chemically recycling plastics back to their constituent monomers or to value-added chemicals. However, knowledge of the mechanisms and reaction kinetics underlying polyethylene pyrolysis remains extremely lacking, hindering development of large-scale plastic recycling capabilities. Therefore, the primary objective of this thesis was to investigate those kinetics and shed new light on the reasons behind the vast discrepancies reported in the literature. Fundamental understanding of polyethylene pyrolysis has previously been limited due to an inability to obtain intrinsic reaction kinetics; instead, the literature presently reports only apparent kinetics, which are a combination of intrinsic kinetics and a variety of other transport and system design limitations. In this thesis, an extensive summary of these limitations in other works is presented, and a new system, known as the Pulse-Heated Analysis of Solid Reactions, or PHASR, system was developed to overcome these limitations. The PHASR system is uniquely capable of operating under “isothermal, reaction-controlled” conditions, at which intrinsic kinetics can reliably be measured. The PHASR system was validated extensively to ensure operation in this desired regime, and detailed descriptions of the reactor setup and experimental methodologies are presented. Alongside this system, a second, Visual PHASR system was developed as well, to enable visualization of polyethylene pyrolysis reaction phenomena for the first time, via integrated high-speed photographic equipment. The method of PHASR was then used to study the intrinsic kinetics of polyethylene pyrolysis. Conversion of low-density polyethylene to pyrolysis products was measured over a range of reaction temperatures (550 to 650 °C) and reaction durations (20 ms to 2.0 s), and three distinct product lumps were characterized via integrated gas chromatography and a microgram-resolution balance. Lumped intrinsic reaction kinetics were calculated using these product fractions. The results were further validated by applying a generalized Rice-Herzfeld radical reaction model to the polyethylene pyrolysis system; good agreement was found between this first principles approach and the PHASR experimental data. Additionally, extensive characterization was performed on the residues left behind in PHASR post-pyrolysis, and this helped elucidate new insights into the different reaction timescale regimes that are present during polyethylene pyrolysis.