Browsing by Subject "Lignin"

Now showing 1 - 4 of 4
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    Isolation of Lignin-converting Microbes Contributing Towards Recalcitrant Carbon Degradation in Boreal Forest System
    (2022-08) Singh, Nandini
    Plant biomass, composed of cellulose, hemicellulose and lignin, are being explored as renewable carbon feedstock that could replace a significant amount of petroleum-derived chemicals and other products. Lignin, a component of wood, is the second most abundant natural organic polymer after cellulose. It provides strength and rigidity to plants and is highly recalcitrant to degradation due to its complex, three-dimensional structure. The valorization of lignin is essential for viable and sustainable uses of lignocellulosic biomass for the production of renewable fuels and chemicals. In order to achieve this, microbial degradation is extensively researched as microorganisms have evolved different enzymatic and/or non-enzymatic strategies to utilize biomass (Janusz et al., 2017). In boreal forest ecosystem, brown rot fungi are dominant players for decomposing and recycling carbon sources sequestered in tree biomass, but the carbohydrate-selective nutritional mode of these fungi does not allow them to consume all the forms of carbon in wood, with the undecayed lignin residues creating a recalcitrant carbon pool in the forest ecosystem. In this research, we investigated up to 200 functional microbes, including fungi and bacteria, involved in the breakdown of lignin components in this distinctive brown rot niche. Preliminary screening of the microbes was performed using indicator dyes, resulting in eight fungi and fourteen bacteria which were then screened to be further characterized. These isolates were identified using DNA extraction, PCR and sequencing and were further evaluated for their ability to degrade and metabolize lignin and aromatic lignin monomers. We anticipate understanding the lignin-degrading characteristics of microbes occurring naturally and its role in industrial lignin conversion or bioremediation of related recalcitrant aromatic hydrocarbons.
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    An organic geochemical record of inland migration in a coastal marsh, Chesapeake Bay, Maryland, USA
    (2017-05) Van Allen, Rachel
    Organic matter accumulation in marsh soils affects marsh survival under rapid sea level rise (SLR). This work describes the changing organic geochemistry of a salt marsh located in Blackwater National Wildlife Refuge on the eastern shore of Chesapeake Bay that is transgressing inland with SLR. Marsh soils and vegetation were sampled along an elevation gradient from the intertidal zone to the adjacent forest. Stable carbon isotope analysis of bulk organic matter suggests a broad transition towards C4-dominated marsh vegetation over time. Vegetative source of the organic matter shifts along a marsh-upland mixing line from herbaceous angiosperm-sourced lignin in the low marsh to a woody gymnosperm signature at the upper border of the marsh. Stable isotope and lignin chemistry results illustrate that landward encroachment of marsh grasses results in deposition of herbaceous tissues that exhibit relatively little decay. This presents a possible mechanism for organic matter stabilization as marshes migrate inland.
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    Thermo-Mechanical Characteristics of Polyethylene/Tobacco Lignin Blends
    (2019-12) Mahmood, Samsul Arfin
    With the expected exponential growth prospects of additive manufacturing, petroleum-based plastic products and applications are also expected to increase. Since last two decades, plastic pollution has become a concerning fact. About 25 million tons of plastics find their way into the environment annually. Traditional plastics are not biodegradable and hence they end up in landfills which is detrimental for the environment. Hence, there exists a need for renewable alternatives to traditional petroleum-derived plastics. Lignin, an abundant plant-derived feedstock, has been a perfect candidate for renewable materials. The work in this thesis focuses on investigating the effects of mixing lignin extracted from tobacco with high-density polyethylene (HDPE) in varying concentrations. This work is performed in three stages. The first stage is the making blends of HDPE-lignin at varying concentrations (5, 10, 15 & 30 wt.%). Later all the materials were melt mixed using a single screw extruder. In the later stage for mechanical testing purposes, tensile specimens were processed via injection molding. During this process effect of lignin in injection molding parameters were investigated. In the second stage, mechanical, physical and thermal tests were conducted to analyze the effects of blending on the performance of the resulting products. Tensile tests were performed to evaluate the ultimate tensile strength (UTS), Young’s modulus and elongation at break for each blend composition. To evaluate the physical properties, hardness and density of the blends were measured. The miscibility of the blends was studied using optical microscopy. TGA tests were performed to study the thermal stability of blend materials. In the third stage, maleic anhydride grafted polyethylene was used to compatibilize blend materials. Compatibilized HDPE-Lignin blend materials were later subjected to mechanical and physical tests to analyze and compare the effect of compatibilizer.
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    Through lignin biodegradation to lignin-based plastics
    (2015-01) Wang, Yun-Yan
    The consequences of strong noncovalent intermolecular interactions between oligomeric and/or polymeric lignin components are encountered during enzyme-catalyzed lignin degradation and in the properties of lignin-based plastics. A new chapter in the 30-year quest for functional lignin-depolymerizing enzymes has been opened. The lignin-degrading capacity of the flavin-dependent monooxygenase, salicylate hydroxylase acting as a putative lignin depolymerase, has been characterized using a water-soluble native softwood lignin substrate under mildly acidic aqueous conditions. When macromolecular lignins undergo lignin-depolymerase catalyzed degradation, the cleaved components tend to associate with one another, or with nearby associated lignin complexes, through processes mediated by the enzyme acting in a non-catalytic capacity. As a result, the radius of gyration (Rg) falls rapidly to approximately constant values, while the weight-average molecular weight (Mw) of the substrate rises more slowly to an extent dependent on enzyme concentration. Xylanase, when employed in an auxiliary capacity, is able to facilitate dissociation of the foregoing complexes through its interactions with the lignin depolymerase. The flavin-dependent lignin depolymerase must be reduced before reaction with oxygen can occur to form the hydroperoxy intermediate that hydroxylates the lignin substrate prior to cleavage. In the absence of the cofactor, NADH, the necessary reducing power can be provided (albeit more slowly) by the lignin substrate itself. Under such conditions, a simultaneous decrease in Rg and Mw is initially observed during the enzymatic process through which the lignin is cleaved.The partially degraded product-lignins arising from lignin depolymerase activity can be readily converted into polymeric materials with mechanical properties that supersede those of polystyrene. Methylation and blending of ball-milled softwood lignins with miscible low-Tg polymers, or simple low-molecular-weight compounds, readily produce plastics with 80-100% lignin contents that exhibit >60 MPa tensile strengths and >10% elongations at break. X-ray powder diffraction analyses reveal that these materials are largely composed of associated lignin complexes. During casting, continuity between the macromolecular species is established through conformational changes in the peripheral components of the associated complexes that make up the plastics. Such a working hypothesis is supported by atomic force microscopy of surfaces created by ultramicrotomy of these new lignin-based polymeric materials.