Browsing by Subject "Degradation"

Now showing 1 - 4 of 4
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    Fully-renewable and degradable thermoplastic elastomers.
    (2009-01) Wanamaker, Carolyn Leigh
    The most common polymers derived from renewable feedstocks, poly(3-hydroxybutyrate), polyglycolide, and polylactide (PLA), have high stiffness and tensile strength, but are inherently brittle, thus limiting the potential for these polymers to replace elastic and ductile polymers derived from fossil fuels. The work described in this thesis was directed toward expanding the properties of renewable resource polymers through the investigation of completely-biorenewable thermoplastic elastomers. Polymenthide (PM), a soft biorenewable polymer derived from (-)-menthol, is immiscible with PLA and was utilized as the middle block in a PLA-containing ABA triblock copolymer. Tensile measurements demonstrated impressive elongations and elastomeric properties typical of thermoplastic elastomers, however, the materials were relatively weak. The tensile properties of the polymers were found to be highly dependent on the molecular weight and crystallinity of the polylactide blocks. Substituting the amorphous PLA with semi-crystalline PLLA or PDLA significantly improved the strength of the material. Blends of the enantiomeric triblock copolymers further increased the strength through stereocomplexation of the enantiomeric polylactide segments. These results led to the investigation of stereocomplexed micelles as nucleating agents for PLLA. Quantifiable improvements in the nucleation efficiency of PLLA were observed when blending PLLA with PDLA-containing triblock copolymers. Finally, potential applications of these all-biorenewable triblock copolymers were investigated through hydrolytic degradation and adhesion studies. During hydrolytic degradation, the triblock copolymers were able to maintain a significant amount of their mechanical properties for many weeks.
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    Parametric Evaluation of Water Treeing in EPR-Insulated Medium Voltage Cables using Finite Element Analysis
    (2021-05) O'Brien, Sean
    Medium voltage (MV) electric cables are used extensively in industrial settings, including nuclear power plants (NPPs). In NPPs, these cables provide supplementary power for safety systems to continue operating during emergency events. Despite efforts to maintain these cables, premature failure is known to occur, with the predominant causal factor being water tree-induced degradation of the cable’s insulation component. To better understand the effects of this degradation source, this thesis presents a parametric evaluation of various water tree and cable parameters using finite-element analysis (FEA). The parameters being evaluated for a MV cable insulated with ethylene propylene rubber (EPR) are water tree depth, composition, and geometry, as defined by aspect ratio (AR), and cable operating frequency and temperature. Evaluation is performed in five separate but interrelated areas pertaining to the measurement of degradation: global capacitance, global resistance, voltage and electric field distribution, localized specific energy absorption rate, and localized temperature rise. Results show that the rate of water tree-induced degradation is affected by each parameter. In general, rate of degradation was found to be directly related with water tree depth and AR, and cable temperature, but inversely related with cable operating frequency. Although values differed, these trends were largely maintained regardless of water tree composition. The results and findings of this parametric evaluation have provided an advanced understanding of water tree degradation in MV EPR-insulated cables. In addition, an argument for further use of FEA in conjunction with physical cable testing was presented, with the conclusion being that there exists a strong motivation to pair the two together.
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    Patulin degradation by yeast protein extract
    (2014-05) Folger, Brian Charles
    The mycotoxin patulin, produced by a number of fungi, most prominently Penicillium expansum, has proven problematic for the apple industry due to contamination of apple juice and apple cider. Presently, techniques to control patulin accumulation have proven increasingly ineffective due to the presence of antifungal resistant strains of mold, stability of patulin during thermal processing, and conflicting data on the efficacy of other treatments. However, fermented apple products such as hard ciders and apple cider vinegars are devoid of patulin. Fermentation with yeast resulted in complete degradation of patulin, possibly due to enzymatic degradation by yeast enzymes. Patulin has also been shown to be susceptible to adduct formation with free thiol containing molecules such as glutathione, which is naturally present in yeast cells. Limited studies have also looked at patulin adsorptivity onto the call walls of yeast. Degradation of patulin is, therefore, hypothesized to be caused by multiple mechanisms mainly caused by yeast proteins/enzymes.To assess the loss of patulin by protein extracted from yeast (Rhodosporidium kratochvilovae strain 62-121), patulin extraction methods were compared to determine the optimal method for patulin extraction from protein rich environments. The effect of boiling to halt any possible enzymatic degradation on total patulin loss was assessed by comparing patulin recovery to that of samples placed on ice after the assay. Yeast growth was optimized for the production of patulin-degrading protein extracts by surveying days of growth and subsequent storage at 4°C. Additionally, free thiol group reactivity with patulin was assessed upon incubation with protein extract, cysteine, and glutathione. Liquid chromatography and mass spectrometry (LC/MS) was used to detect patulin degradation products. Potential enzymatic activity was assessed by comparing the degradation activity of different protein extracts from yeast. Finally, patulin loss due to adsorption to inactivated yeast cell walls was determined. The use of acid and salt to precipitate the protein before patulin extraction resulted in the best patulin recovery from protein rich media, and an additional extraction following a modified AOAC method allowed for removal of excess salt without sacrificing patulin recovery. The use of boiling to denature the protein after the assay resulted in 10% higher patulin loss than when the samples were placed on ice, presumably due to adduct formation with thiol groups. Growing yeast for 6 days at room temperature was deemed adequate to obtain optimal patulin degradation; and subsequent incubation of the yeast at 4°C did not impair the patulin degradation activity. Yeast protein extracts were found to be inconsistent with respect to patulin degradation activity, nevertheless patulin degradation activity (up to 100% patulin) was observed in several batches. Patulin incubated with cysteine showed signs of free thiol blockage in both samples of protein extract and pure cysteine. Patulin incubated with glutathione was degraded at both pH 7 and 3.7, and one patulin-glutathione adduct (462 m/z) was identified via LC/MS. Lyophilized yeast cells demonstrated patulin adsorption capabilities after incubation at 30°C for 20 min. Observed results confirm that patulin can be degraded by the protein extract from yeast. The exact mechanism of patulin degradation by protein extracts remains unclear, yet it appears to be either enzymatic or chemical through thiol adduct formation. Our results indicated that the mechanism is a combination of the two. This research offers insight into possible patulin degradation mechanisms, and can give direction in applying this new method of patulin control in an industrial setting.
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    Phytoestrogen distribution and degradation in natural and engineered systems
    (2012-12) Fleischhacker, Nathan T.
    Phytoestrogens are plant-derived hormonally active compounds known to cause varied reproductive, immunosuppressive and behavioral effects in fish. Environmentally relevant concentrations of phytoestrogens have been identified in numerous industrial and wastewater effluents, but their presence in surface water has received little attention. Additionally, no work has been performed to assess the degradability of phytoestrogens in surface waters or to determine which microbial communities may be responsible for their degradation. Given the fundamental questions that exist regarding phytoestrogens in the environment, the objectives of this research were three-fold: 1) Determine the degradation capacity of genistein, a potent and common phytoestrogen species, in surface waters under a variety of environmental conditions, 2) Monitor the temporal and spatial fluctuations of 6 phytoestrogen species in wastewater-impacted and unimpacted surface waters, 3) Examine if genistein, like similarly structured steroidal estrogens, is capable of being degraded cometabolically by nitrifying organisms. Triplicate batch reactors with triplicate negative controls were used to investigate genistein degradation in both surface water and enriched nitrifying cultures. Grab samples were collected from impacted and unimpacted surface waters to identify temporal and spatial phytoestrogen patterns. Genistein degradation rates in surface water samples were found to vary significantly and depended on initial concentration, incubation temperature, season of water collection, and surface water source. Overall genistein degraded rapidly and variably, with the time to 50% degradation ranging from 15 to 70 hours. In reactors amended with 100 μg/L genistein, an enrichment period during which there was no or little degradation was followed by a period of rapid genistein degradation (zero-order), suggesting that genistein may be degraded intentionally as an energy source rather than incidentally via some cometabolic pathway. Experiments with nitrifying organisms indicated that genistein was not cometabolically degraded by nitrifying organisms, but it was degraded by organisms that were enriched under nitrifying conditions. Temporal and spatial studies detected several phytoestrogen species in surface waters at low nanogram per liter concentrations with no discernible temporal or spatial pattern. This research suggests that like genistein, phytoestrogens in general may be readily degraded in surface waters. It also suggests that phytoestrogens are not likely to cause widespread ecological harm, but caution should be taken as numerous compounds in this class exist and only a limited number of surface waters were sampled for phytoestrogen presence.