Theses and Dissertations
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DissertationChemical upcycling of waste plastics via non-thermal plasma and advanced pyrolysis( 2024-12)Escalating waste plastic disposal and increasing CO2 emissions together have caused great environmental problems. So far, various chemical recycling technologies have been explored to convert plastics into platform and commodity chemicals. Polyolefins account for nearly two-thirds of global plastic production dominating single-use plastic waste streams. However, both their mechanical and chemical recycling are challenging compared to other common plastics due to low-quality products and costly multistep conversion processes. Chemical upcycling via conventional thermochemistry in the short-term while developing more energy-efficient and unconventional techniques for the long-term, such as non-equilibrium plasma, offers the most promise to convert polyolefin waste into valuable chemicals and fuels. Till now, non-thermal plasma, an upcoming technology, was considered a suitable technology only for biomass conversion under a chemically reactive atmosphere produced by plasma at mild conditions. This dissertation expands the scope of plasma-based conversion technologies to the conversion of waste plastics and greenhouse CO2 to produce valuable platform and commodity chemicals. This dissertation also explored pathways to improve and better understand the current conventional thermochemical technologies, such as thermal pyrolysis and catalytic pyrolysis, to produce high-value platform chemicals and monomers. The first study pioneers an electrified approach to upcycle waste plastics into carbon-negative commodity chemicals using greenhouse gas CO2 as the oxidant and additional carbon source. Herein, we report a selective and energy-efficient co-conversion of waste polyolefins and CO2 for oleochemicals and syngas CO using a single-step low-temperature plasma approach. We obtained up to 97.6 wt% of fatty alcohols from polyolefins within minutes under ambient pressure. It showed that CO2 plasma is efficient in oxidatively depolymerizing plastics under mild conditions at high reaction rates, while plastics can serve as carbon sinks to improve CO2 conversion. Furthermore, mixing CO2 with a small amount of O2 resulted in a facile approach to control plasma reactions and tailor product selectivity toward fatty alcohols. This catalyst- and solvent-free process requires electricity only, providing a promising waste upcycling route to enable carbon-negative chemicals. In the second study, a new molten-phase unsaturation strategy was studied to enhance the chemical upcycling of waste plastics by fast pyrolysis. Fast pyrolysis is a robust deconstruction technology for chemically upcycling waste plastics. However, highly viscous molten polyolefins and large amounts of waxy hydrocarbons can negatively impact the reactor operation. The products with broad molecular weight distributions can also affect the processibility of pyrolysis products during downstream separation and upgrading. We found that coupling a molten-phase thermal preheating and subsequent fast pyrolysis is a facile approach to improve polyolefin pyrolysis and catalytic upgrading compared to direct pyrolysis of polyolefins. It shows that the molten phase thermal treatment increased unsaturated carbon-carbon bonds in the treated polyolefins. During subsequent pyrolysis, the preheated polyolefins significantly reduced wax range hydrocarbons in the condensable products without increasing gas formation. The wax yield from pyrolysis of high-density polyethylene preheated to 295 ℃ and low-density polyethylene preheated to 275 ℃ was 20.5% and 26.5%, respectively, compared to 38.6% and 46% produced from pyrolyzing untreated polyolefins. When catalytically pyrolyzed using a zeolite catalyst, the preheated polyolefins produced more olefins during ex-situ catalytic pyrolysis and more aromatic hydrocarbons during in-situ catalytic pyrolysis. During ex-situ catalytic pyrolysis, ethylene yield increased to 23.3% and 24.7% for the preheated HDPE and LDPE compared to 16.7% and 9.3% for untreated HDPE and LDPE, respectively. Chemical upcycling offers a promising method to convert polyolefin waste into valuable chemicals and fuels, and understanding the influence of additives is crucial for optimizing this process. The third study in this dissertation investigated the pyrolysis behavior of polyolefins in the presence of various common polymer additives, including antioxidants, stabilizers, pigments, fillers, and slip agents. The additives studied include hindered phenol and phosphite antioxidants, hindered amine light stabilizers (HALS), titanium dioxide (TiO2) pigment, carbon black pigment, and fillers such as calcium carbonate (CaCO3), kaolin, talc, and barium sulfate (BaSO4). Thermogravimetric analysis (TGA) and pyrolysis-gas chromatography-mass spectrometry-flame ionization detector (Py-GC/MS-FID) were employed to analyze the thermal stability and pyrolysis products of HDPE samples co-extruded with these additives. The results indicate that antioxidants and stabilizers delayed pyrolysis initiation, while fillers and slip agents significantly affect the yield and composition of pyrolysis products. Specifically, kaolin and zinc stearate increased char formation and gas yields. The effect of these additives on in-situ and ex-situ catalytic pyrolysis of polyolefins was also studied, and the product analyses shine the light on the reaction chemistry in the presence of additives. This research enhances understanding of additive effects in pyrolysis, supporting the development of efficient recycling technologies for heterogeneous plastic wastes in a circular economy.
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DissertationAn investigation of branched-chain amino acid interactions in nursery pigs and lactating sows( 2024-12)Amino acids (AA) are fundamental nutrients that form the building blocks of tissues, milk proteins, enzymes, and various signaling molecules essential for supporting growth, reproduction, and lactation. Dietary protein is a costly component in swine diets; thus, a precise understanding of AA requirements is critical for enhancing production efficiency. With the increased use of feed-grade AA to reduce dietary crude protein, optimizing AA balance is essential to prevent deficiencies or imbalances that may impair performance. Among these, the branched-chain amino acids (BCAA) leucine, isoleucine, and valine play vital roles in protein synthesis and metabolism. However, their shared catabolic pathway creates a potential for antagonistic interactions, where an excess of one BCAA can accelerate the catabolism of the others, decreasing their availability and increasing their dietary requirements. This issue is especially relevant in diets containing corn co-products, which typically contain high levels of Leu relative to Ile and Val. There is sufficient evidence to suggest that interactions among Leu, Ile, and Val influence growth rates and feed intake in nursery pigs; however, these relationships remain incompletely defined, making it challenging to identify an ideal BCAA balance for diet formulation. For lactating sows, the data is equivocal, with variation in reported BCAA requirements suggesting that interactions between BCAA may impact lactation outcomes. However, more investigation is needed to determine these effects conclusively. Understanding the practical implications of BCAA interactions in swine nutrition is crucial for developing dietary strategies to promote efficient growth in nursery pigs and enhance lactation performance in sows. Therefore, the overall objective of this dissertation was to assess BCAA interactions in nursery pigs to determine optimal levels for growth and feed efficiency and to evaluate BCAA effects in lactating sows to explore their role in nutrient requirements and productivity. To accomplish these objectives, a series of experiments were conducted and are reported in three research chapters (Chapters 2, 3, and 4). Research presented in Chapter 2 utilized a central composite design (CCD) to simultaneously evaluate how Leu, Ile, and Val interact to influence growth performance in 10- to 20 kg nursery pigs. The results indicated that concurrently increasing dietary Leu and Ile reduces growth rate and feed efficiency, which is likely a consequence of increased BCAA catabolism limiting Val availability for growth. Furthermore, it was shown that increasing dietary Val can offset the adverse effects of excess Leu on feed intake, suggesting that optimizing Val levels is critical in practical diet formulation. However, given the mixed curvature of the response surfaces, a single optimal BCAA combination was not identified within practical dietary levels, underscoring the importance of considering both ingredient cost and specific production goals when formulating nursery pig diets. This study supports the use of CCD in evaluating complex nutrient interactions and provides a foundation for refining dietary BCAA balance to maximize production efficiency in nursery pigs. Building on the relationships identified in Chapter 2, the research reported in Chapter 3 examined whether similar BCAA interactions affect lactating sow performance. Across all metrics evaluated, there was no evidence to suggest that the various BCAA levels impacted lactating sow or piglet performance; however, high feed intake in this study resulted in potentially excessive intakes of all BCAA, which may have mitigated the potential negative consequences of BCAA interactions. Furthermore, increasing soybean meal (SBM) inclusion reduced sow lactation feed intake, independently of dietary BCAA balance, indicating other factors beyond BCAA, such as trypsin inhibitors, contributed to reduced sow feed intake with high SBM inclusion (Chapter 4). Collectively, the results of Chapters 3 and 4 do not support that BCAA interactions are altering sow lactation performance within practical dietary BCAA ranges. Overall, this research emphasizes the value of optimized BCAA ratios in nursery pig diets and suggests further exploration of AA metabolism in lactating sows to refine dietary AA requirements. These findings provide actionable insights for swine diet formulation, supporting production efficiency and sustainable practices.
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DissertationAddressing process variation in aerosol jet printing and accelerating conformal electronics manufacturing( 2024-12)Aerosol jet printing (AJP) is an additive manufacturing technique used for printing electronics. Capable of printing features on the order of 10-100 μm, AJP excels at patterning on surfaces with 3D topography, such as 3D structures and microelectronics packages, due to its large nozzle-to-surface offset of 1-5 mm. Of particular benefit in R&D applications, AJP is a digital technique capable of printing a wide variety of materials on nearly any substrate, making prototyping convenient. Printed materials often include common conductors, polymeric dielectrics, ceramics, and carbon-based materials, though an ink’s viscosity must be between approximately 1-500 cP. The use of AJP thereby presents a compelling opportunity to manufacture 3D circuits, allowing engineers in aerospace, automotive, medical, and consumer sectors to pursue size or weight reduction explore new types of connected devices. However, AJP has been slow to penetrate into production environments due to problems with process variability and drift. Manufacturing tolerances expected with incumbent electronics fabrication technologies are difficult to hit and quality control tools are lacking. Additionally, while AJP is well-suited for conformal electronics manufacturing, existing hardware and software capabilities are inadequate for AJP to reach its full potential. This work covers recent advances in a process monitoring technique employing light scattering measurements enabling closed-loop operation and data-rich quality control measures. Light scattering measurements have been shown successful over timescales spanning milliseconds to hours, enabling both closed-loop control and in-situ qualification for individual prints. Furthermore, fundamental work related to conformal electronics manufacturing employing an aerosol jet printer mounted on a 6-axis robot arm will support printing on meter-scale structures and multi-layer, conformal circuit manufacturing.
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DissertationThe effect of the cost of caregiving on financial security: Who takes care of caregivers?( 2024-12)Population aging is accelerating worldwide. Comparing different countries is essential, as it allows for contrasting experiences and mutual learning. Ensuring financial security is a key aim of social policies for older adults. Guided by life course theory and bioecological model, this dissertation examines how informal caregiving affects individuals' financial security in later life. It comprises three projects. The first project investigates how mid-life caregiving experiences impact women's financial security in later life using data from the Survey of Health Aging and Retirement in Europe (2004 and 2014). Findings indicate that intensive mid-life caregiving significantly increases the likelihood of economic deprivation in later life. Additionally, caregiving experiences interact with negative life events, further deteriorating women’s economic security. The study highlights the need for continued or increased public spending on long-term care and healthcare to protect female caregivers from economic hardship in old age. Using the same data, the second project explores the impact of caregiving on individuals’ savings using multi-level analysis. Contrary to conventional beliefs, caregiving is not negatively correlated with savings. Moreover, results indicate the effect of family support on savings varies by gender: sons providing short-term care with at least one sister have greater savings, while daughters with at least one brother engaged in long-term care have lower savings. Welfare regimes also impact savings differently based on caregiving duration. Long-term caregivers experience more change in savings over time in defamilialism welfare regime, whereas short- term caregivers have more savings in unsupported familialism regime. The third project evaluates the effectiveness of a financial educational program for family caregivers in Iowa. Quantitative findings show a significant increase in participants' financial knowledge, confidence, and behaviors as a result of completing the program. Qualitative analysis highlights three main factors contributing to participants' satisfaction: the content of the course, its design, and the quality of the instructors. This study emphasizes the significance of customized financial education in empowering caregivers and highlights the crucial role of satisfaction in driving positive outcomes. Findings from these interconnected projects indicate that older adults’ financial security is shaped by multiple levels of factors, including micro-level family resource, meso-level community resources, and macro-level cultural and policy contexts across different countries. Moreover, the results suggest that caregiving experiences interact with other life-changing events, putting informal caregivers at a higher risk of financial insecurity in later life. This underscores the need for policies and programs that address the unique financial challenges faced by caregivers, taking into account the broader social and economic environments in which they live.
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DissertationOptimizing oral fluid-based surveillance for an evolving swine industry( 2024-12)Beginning in the early 1900s and continuing today, pork producers have transitioned toward housing pigs indoors in order to better shelter the animals and optimize productivity [1,2]. Nevertheless, the disease pressures in these ever-larger populations and the costs associated with clinical and subclinical infections is significant, e.g., the economic impact of PRRSV was estimated at $664 million annually in the US [3]. To respond to the health challenges posed by infectious agents, surveillance methods have been developed to detect and follow their spread. In particular, aggregate samples, e.g., oral fluids, have become increasingly popular among producers and veterinarians because they are easily collected and facilitate routine surveillance of farms [4]. Oral fluids are amenable to the detection of a wide variety of viral and bacterial pathogens of swine, including some of the most economically impactful, e.g., African swine fever virus, classical swine fever virus, foot-and-mouth disease virus, Porcine circovirus type 2, Porcine Reproductive and Respiratory Syndrome virus, pseudorabies virus, swine influenza virus, and others [5]. Despite the acceptance of oral fluid diagnostics by pork producers and veterinarians, sensu stricto, pig behaviors associated with oral fluid sample collection are not well documented. With the goal of optimizing oral fluid sampling across the industry, we first set out to understand the current swine industry and, in particular, the range of pens sizes used in production systems. To that end, Chapter 3 describes two surveys conducted in swine producers and veterinarians in which it was found that the average pen size for grow-to-finish farms was 75 to 82 pigs. Due to this information, subsequent field studies were conducted across a range of pen sizes. Thus, Chapter 5 describes pig participation in oral fluid sampling in terms of the effect of previous experience with rope sampling ("training"), variable number of ropes suspended in the pen, and increasing sampling time in pens of different sizes. Notably, this research focused on pig behavior and not on diagnostic target detection; albeit higher pig participation in oral fluid collection would likely lead to a higher probability of population-based detection. The results showed that training, providing additional ropes, and extended sampling time each increased pig participation across pen sizes. Likewise in this research, we addressed a fundamental question of oral fluid sampling in pigs. That is, it is well documented that diagnostic targets present in oral fluids may represent systemic infection or replication in buccal tissues. However, in swine and other animals, it is widely postulated that diagnostic targets in oral fluid samples may also reflect their presence in the environment. This is because normal swine behavior includes rooting, biting, smelling, and tasting the environment [6]. Diagnostic targets encountered in the environment during this exploratory process may be retained in the oral cavity, deposited in the oral fluid sample, and detected by testing [7]. However, despite the wide acceptable of this point of view, scientific data was lacking. Scientific documentation of the process of collecting environmental targets and depositing them in an oral fluid sample is best done using a non-infectious and non-toxic tracer. In Chapter 2, we reviewed non-infectious traces (rhodamine B, tetracyclines, and iophenoxic acid) in free-ranging pig populations and their wide use evaluating the delivery of oral vaccines and/or bioactive compounds. However, tracers used in free-ranging pigs are not suitable for farm-raised pigs because of the residuals that remain in meat intended for human consumption. In Chapter 4, we describe the use of a non-infectious and safe tracer (red food coloring) which we subsequently used to document the transfer of a target both directly from pigs and indirectly from their environment into pen-based oral fluid samples. The results showed detectable levels of red food coloring in oral fluid samples from 78 of 89 pens (87.6%), including 43 of 47 (91.5%) pens in which pigs were directly exposed to the tracer and 35 of 42 (83.3%) pens in which the tracer was placed in the environment. Thus, oral fluid samples contain both pig-derived and environmental targets. Overall, this reach has contributed measurably to our understanding and use of oral fluid sampling in the field.