No description available.

No description available.

Increased understanding of plasma-polymer interactions is required to further the technological use of such processes, and elucidates heterogeneous physico-chemical reactions which occur under bombardment by complex combinations of energetic species. This thesis presents a systematic investigation into the effect of exposing organic and inorganic polymeric surfaces to controlled non-isothermal plasmas. Concurrently, a novel process is presented by which metal oxide gas barrier coatings are synthesized on polymer substrates by non- isothermal plasma treatment. Organic polymers exhibiting a range of structures were modified using non-isothermal plasmas at atmospheric and low pressure. The extent of atmospheric discharge oxygenation, measured by X-ray photoelectron spectroscopy (XPS), correlated with the polymers' ozonolysis rate constants. Surface physical disruption, studied using atomic force microscopy (AFM), after atmospheric discharge treatment was more pronounced than after low pressure plasma treatment. During low pressure oxygen plasma treatment, polymers containing phenyl groups were oxygenated to an extent which varied with the strength of π-π* valence band excitation in XPS C(1s) spectra of the untreated polymers, suggesting a dominance of reaction of plasma atomic oxygen at polymer radical sites excited by plasma vacuum ultraviolet radiation. The size of globules, observed by AFM, on the plasma modified surfaces correlated with the extent of surface chemical modification, inkeeping with a mechanism of chemically driven agglomeration of plasma oxidized low molecular weight polymer material. Oxygen plasma was more effective than water plasma in chemically modifying the surface of films of zirconium-normal-butoxide spin coated on polyester substrates, and the resulting optimized treatment produced a significant reduction in gas permeation of the substrate. XPS studies showed that oxygen plasma treatment of a polyphenylsilsesquioxane film on polyester film created a SiO(_2) layer less than 8 nm thin, which reduced O(_2) and Ar permeation of the coated film by 37.5 % and 31.6% respectively.

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This thesis is concerned with the study by solid-state NMR of the polymers formed by acid anhydride/hydroxyl cross-linking systems. The polymers studied in this thesis are based on a copolymer containing either itaconic or maleic anhydride which cross-Jinks with a polyester tipped with triethanolamine. The mobility of the polyester chains in the cross-linked films is probed by solid-state NMR, and the kinetics of the cure between acid anhydride/hydroxyi systems is discussed. The degradation of the cross-Jinked films is studied by (^13)C solid-state NMR. The films are shown to undergo hydrolysis when subjected to their exposure environment. The theory behind transient nuclear Overhauser effects in the solid state is discussed, and comparisons are made between the theoretical simulations and the experimented data for the cross—linked films. Lastly, a solid-state heteronuclear NOESY experiment is presented for a (^13)C(_2)-enriched acid anhydride/hydroxyl cross-linked film.

Edible coatings controlling preservative migration from surface to food bulk could inhibit surface microbial growth which is often the main cause of spoilage for many food products. In this project we focused our attention upon methylcellulose, hydroxypropyl methylcellulose, and chitosan as the structural component for such edible films. These films were generally transparent and effective at thicknesses in the order of 20 to 100 μm. We expect them to have little impact on the sensory properties of a food. Permeability cell measurements were used to evaluate the effect of coating composition. Further film characterization included film thickness and electron microscopy studies. To gain an understanding of the permeation process, the permeability tests were done at 5, 24, 32, and 40°C. Among these polysaccharide films, methylcellulose was the most promising diffusion barrier with a permeability constant of 3.4 and 1.4xl0⁻⁸ (mg/sec cm²)(cm)/(mg/ml) at 24 and 5°C, respectively. These barrier properties were enhanced by the incorporation of lipids into the film formulation. The permeability of sorbates in methylcellulose and hydroxypropyl methylcellulose emulsified with lauric, palmitic, stearic and arachidic acid was found to depend upon the polysaccharide, the fatty acid chain length, and the number of fatty acid double bonds. Potassium sorbate permeation increased in the following order lauric>palmitic>stearic>arachidic acid. The effect of the double bond type, i.e. cis vs. trans was also determined. The permeability rate of potassium sorbate increased in the order of oleic>elaidic>stearic acid. The effect of temperature on potassium sorbate permeability was analyzed using an Arrhenius activation energy model for the permeation process. Permeability determinations at four different temperatures showed excellent agreement with this model and suggest that the permeation process is diffusion controlled. Electron microscopy studies showed the absence of pores, channels or other defects which might be introduced during casting, drying, handling or permeability determination. This observation is consistent with our hypothesis that potassium sorbate permeation is diffusion controlled. Furthermore, our experimental data suggest that the diffusion is controlled by the properties of the solvent embedded in the film. Further studies are required to confirm this hypothesis. The effect of casting technique was examined by coating a pure polysaccharide film with a fatty acid mixture or bees wax and by laminating a fatty acid mixture or hydrogenated palm oil between two layers of pure polysaccharide films. Unfortunately, most of these films cracked easily and could not be tested in our permeability cell. On the other hand, hydroxypropyl methylcellulose films coated with bees wax showed exceedingly low potassium sorbate permeability values. These modifications of the polysaccharide film properties reduced the potassium permeability down to 10⁻⁹ to 10⁻¹¹ (mg/sec cm²)(cm)/(mg/ml) depending upon temperature, film composition and film casting technique. A simplified procedure previously published was used to evaluate surface microbial stability enhancement. With this information a food processor can select the appropriate film, application procedure and film thickness to achieve the desired shelf life under ambient or refrigerated storage conditions. / Graduation date: 1988

The use of edible coatings in combination with antimicrobial agents enhances the microbial stability of foods. In this study we evaluated the potassium sorbate and sorbic acid permeability of an edible methylcellulose (MC) - palmitic acid (PA) film with a MC:PA ratio of 3:1. Permeability cell measurements were used to evaluate the effect of pH and water activity (a [subscript w]) on the film permeation rate by sorbic acid and potassium sorbate. For films with a thickness of 55-66 pm, potassium sorbate permeability increased from 2.3x10⁻¹⁰ to 2.0x10⁻⁸ (mg/sec cm²)/(cm)/(mg/mL) as a [subscript w] increased from 0.65 to 0.80. Films were not stable at a [subscript w] levels above 0.80. The permeability of the film to sorbic acid decreased from 3.3x10⁻⁸ to 9.1x10⁻¹⁰ (mg/sec cm²) (cm)/(mg/mL) when pH in the permeability cell was increased from 3 to 7. This permeability decrease with pH could balance the loss of effectiveness of sorbates due to the lowering of the percentage of undissociated molecules at high pH. Another characterization of the MC-PA film was the evaluation of the effect of relative humidity (RH) on its oxygen transmission rate (OTR). In general, the film was highly permeable to oxygen (OTR values at 24°C, 660 to 1400 mL O₂ (STP)/m² 24h atm, average film thickness of 55 μm). Therefore, there is no risk to develop anaerobic conditions on food surfaces coated with the MC-PA film. There was no relative humidity effect on OTR in the 0-60% RH range; whereas, the OTR doubled when the RH was increased from 60 to 80%. These results agree well with the moisture uptake of the MC-PA film. Its moisture sorption isotherm shows a large moisture content increase at RH levels larger than 60%. The application of methylcellulose-based films as moisture permeability barriers in simulated sundae ice cream cones showed that a MC-PA film practically stopped moisture transfer from the ice cream to the sugar cone. Sugar cone crispness was retained for a period longer than three months when stored coated at -10°F and +10°F. The crispness of commercial sundae ice cream cones is retained for periods much less than three months. / Graduation date: 1990

Thesis (M.S.)--Rochester Institute of Technology, 1991. / Includes bibliographical references (leaves 132-134).

Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Science, 2008. / "December, 2008." Title from electronic dissertation title page (viewed 12/28/2008) Advisor, Roderic P. Quirk; Committee members, Scott Collins, Ali Dhinojwala, Li Jia, Mark D. Soucek; Department Chair, Ali Dhinojwala; Dean of the College, Stephen Z. D. Cheng; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Thesis (M.Sc.(Agric.)(Food Science))-University of Pretoria, 2004. / Includes bibliographical references. Available on the Internet via the World Wide Web.