Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item MORPHOLOGY OF CELLULOSE AND CELLULOSE BLEND THIN FILMS(2017) Lu, Rui; Briber, Robert M.; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cellulose is the most abundant, renewable, biocompatible and biodegradable natural polymer. Cellulose exhibits excellent chemical and mechanical stability, which makes it useful for applications such as construction, filtration, bio-scaffolding and packaging. It is useful to study amorphous cellulose as most reactions happen in the non-crystalline regions first and at the edge of crystalline regions. In this study, amorphous thin films of cotton linter cellulose with various thicknesses were spincoated on silicon wafers from cellulose solutions in dimethyl sulfoxide / ionic liquid mixtures. Optical microscopy and atomic force microscopy indicated that the morphology of as-cast films was sensitive to the film preparation conditions. A sample preparation protocol with low humidity system was developed to achieve featureless smooth films over multiple length scales from nanometers to tens of microns. X-ray reflectivity, X-ray diffraction, Fourier transform infrared spectroscopy and high resolution sum-frequency generation vibrational spectroscopy were utilized to confirm that there were no crystalline regions in the films. One- and three- layer models were used to analyze the X-ray reflectivity data to obtain information about roughness, density and interfacial roughness as a function of film thickness from 10-100nm. Stability tests of the thin films were conducted under harsh conditions including hot water, acid and alkali solutions. The stability of thin films of cellulose blended with the synthetic polymer, polyacrylonitrile, was also investigated. The blend thin films improved the etching resistance to alkali solutions and retained the stability in hot water and acid solutions compared to the pure cellulose films.Item Processing of Cellulose for the Advancement of Biofuels(2011) Watson, Brian James; Lloyd, Isabel; Hutcheson, Steven; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The enzymatic degradation of cellulose polymers is currently a rate-limiting step in the bioconversion of biomass to biofuels. Cellulose polymers self assemble to form crystalline structures stabilized by a complex network of intermolecular interactions such as hydrogen bonding. The network of interactions in crystalline cellulose (cellulose nanostructure) poses an energy barrier that limits enzymatic degradation as apparent from the activity of Cel5H. To improve the degradability of cellulose the intermolecular interactions must be disrupted. The interactions of the cellulose nanostructure prevent solubilization by water and most other common solvents, but some organic solvents aid degradation of cellulose suggesting they influence cellulose nanostructure. The objective of this work is to understand the influence of solvents on cellulose nanostructure with the goal of improving the degradability of cellulose nanostructure using solvents. To understand solvent interaction with cellulose, phosphoric acid was used to first solubilize cellulose (PAS cellulose) followed by adding an organic liquid or water to wash the phosphate from the system. The Flory Huggins theory was used to predict wash liquids that could favorably interact with cellulose. A favorable wash liquid was predicted to prevent the reformation of crystalline domains to yield a disrupted cellulose nanostructure, which should be more degradable. Low molecular weight alcohols and glycols were calculated to be favorable wash liquids. Washing PAS cellulose with the predicted favorable liquids yielded semi-transparent gel-like materials compared to the opaque white precipitate formed when water or unfavorable solvents were used in the wash. Fractal analysis of small angle neutron scattering (SANS) of these apparent gels indicated cellulose polymers likely have the properties of clustered rods. This partial disruption increased degradability relative to the water washed PAS cellulose. The apparent rod-like cellulose nanostructures suggested the presence of intra and interpolymer hydrogen bonding. Characterization of the hydrogen bonding network by Fourier transform infrared resonance (FTIR) indicated the gel-like material formed by ethanol washes was the result of heterogeneous interpolymer hydrogen bond cross-links. The interactions leading to gel-like materials were evaluated using Hansen solubility parameters, which predicted mixtures of ethanol and water may be most effective for disrupting cellulose nanostructure. Fractal analysis by SANS indicated 40 % ethanol/water was most effective. Similar results were obtained when 40 % ethanol was used to disrupt the cellulose nanostructure in municipal office waste (MOW). Ethanol washes increased the degradability of MOW by at least 30 % relative to conventional water washing. This is significant because increased degradability of MOW could further the development of cellulosic biofuels by reducing the amount of enzyme required to digest the material.