Graduation date: 1994

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No description available.

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Encapsulation is a wide spread industrial technique. The use of biopolymers to form capsules has an obvious advantage for food, biomedical or personal care applications, as they can be made of food grade and biodegradable materials. Polyelectrolyte complexes (PEC) have been widely used to form capsules by the multilayer technique, usually coating a solid core with a layer by layer deposition technique involving various steps of deposition of polyelectrolyte of opposite charge. In this thesis we focused on capsules made with a one step technique where a liquid drop containing a concentrated solution of the polycation is dropped into a dilute solution of the polyanionic solution. Chitosan was the natural polycation used, due to its interesting properties such as biodegradability, biocompatibility or muco-adhesion, and because it is one of the rare cationic polysaccharides which is safe to be used in food applications. The simple one step technique used to form these capsules brings an advantage in terms of manufacturing. The drop deformation due to the impact of droplets at the surface of a liquid bath was studied and the conditions for these droplets to detach from the surface and disperse into the solution were examined. It was found that a balance between the kinetic energy and the absorbed viscous energy of the drop during impact is necessary for the formation of capsules by this technique. Initial work was performed on capsules made with chitosan and polyanionic biopolymers such as alginate or pectins. However, these biopolymers are usually provided with a polydispersed molecular weight distribution and impurities. Polyacrylic acid was thus chosen to study the effect of molecular weight, charge density, and pH on the microstructure, mechanical, swelling and release behaviour of these capsules. The microstructure of the capsules was observed by cryo-scanning electron microscopy, and the effect of molecular weight charge density of the polyelectrolytes on the shell thickness were shown and related to the mechanical and release properties of the capsules. It was shown that the molecular weight has an important role as it determines the thickness of the shell. The charge density of the polyelectrolytes, which can be controlled by the pH and ionic strength of the solution, dictates the density of the shell. The study of the release properties of these capsules showed that they could be completely impermeable to molecules with a molecular weight higher than 2000 g/mol, and surprisingly, the capsules could withstand a wide range of pH extending beyond the pH where electrostatic interactions occur, as they only dissolved at extreme pHs of 2 and 12. Chitosan was also used to make swellable hydrogels microparticles, by cross-linking with glutaraldehyde. The swelling behaviour in gastro-intestinal environment was studied in vitro and in vivo using Magnetic Resonance Imaging techniques.

Chitosan-based copolymers (CH-GL1:6, CH-GL1:1, CH-GL1:0.5, and CH-GL1:0.25) were prepared at variable weight ratios of chitosan (CH) to glutaraldehyde (GL). Physiochemical properties of cross-linked copolymers were characterized using FTIR (Fourier Transform Infrared) spectroscopy, PXRD (Powder X-ray Diffraction), CHN analysis, and thermogravimetric analysis (TGA). The swelling behaviour of the polymers along with chitosan was investigated. The sorption properties of copolymers with arsenate oxoanions were investigated at various pH using 10 mM phosphate buffer systems and also in aqueous solution without buffer. The Sips sorption model describes the best fit parameters for adsorption. The relative monolayer sorption capacities Qm (mg/g) of the adsorbents are given in parentheses in the following order: CH-GL1:1(14.4) > CH-GL1:0.5(12.0) > CH-GL1:0.25(10.3) > CH-GL1:6(2.24). In general, the sorption capacities are listed in descending order as follow: un-buffered > buffered (pH 5.0) > buffered (pH 8.5). The removal efficiencies for 20 mg of polymers over a variable concentration range ( 1-200 mg/L) of arsenate in aqueous solution without buffer are as follow: CH-GL-1:1(20-95%), CH-GL1:0.5(14-97%), CH-GL1:0.25(10-98%), CH-GL1:6(2.0-56%), and CH (0.007-3.9%). The sorption properties of the adsorbents were also determined in bicarbonate buffer to evaluate the competitive effect of phosphate buffer on adsorption of arsenate oxoanions. X-ray absorption spectroscopy (XAS) of chitosan and CH-GL1:1 was performed after adsorption at different pH conditions using two buffer systems to evaluate the chemical environment around the arsenate species. In addition, sorptive properties of phenolic adsorbate (i.e. PNP) were estimated with CH-GL copolymers at various pH conditions. The estimated sorptive capacities (Qm; mmol/g) for PNP are in the range 0.07-0.21(mmol/g) while removal efficiencies for PNP are greater at lower pH conditions.

No description available.

Chitin is a natural polymer which is extracted from a number of biological sources. This polymer is deacetylated to form the related polymer chitosan. The design and preparation of chitosan derivatives has been investigated to tailor the physical and chemical properties towards specific applications. To this end, this thesis describes the synthesis and characterisation of a number of chitosan derivatives. The prepared polymers contained either naphthalimide groups, thiol groups, poly(methyl methacrylate) side chains or poly(oligoethylene glycol methyl ether methacrylate) side chains. Chitin was successfully extracted and purified from squid pens by literature methods to give polymers with DD values from 12 to 23%. The Kurita method was used to obtain chitosan samples with a range of DD values from 75 to 91%. The prepared polymers were characterised by microanalysis, IR, �H NMR and solid-state ��C NMR spectroscopy. The MW distributions of the chitosan samples were determined by GPC in 0.3 M AcOH/0.2 M AcONa(aq) solution with dextran standards. The N-(naphthalimide)-chitosan derivatives were fluorescent materials and were typically prepared from the reaction of 4-bromonaphthalic anhydride with chitosan. This reaction was thoroughly investigated to find the optimal reaction conditions. The bromo groups were subsequently displaced by one of four nucleophiles: dimethylamine, piperidine, methoxide or vinylferrocene. The polymers were characterised by microanalysis, GPC, IR, �H NMR, UV-vis and fluorescence spectroscopy. The excitation and emission wavelengths and Stokes shifts were dependent on the substituent present in the naphthalimide group. Chitin and chitosan were sequentially reacted with tosyl chloride, potassium thioacetate and sodium methoxide to form the thiolated derivatives. The success of the tosylation reaction was dependent on the synthetic route used and the DD of the polysaccharide. The thiolated chitin polymers were well defined although the samples were completely insoluble. The thiolated chitosan polymers were also characterised and were highly swollen in acetic acid solution. These thiolated polysaccharides were used as macroinitiators for the free-radical polymerisation of MMA. The products obtained from the reaction of 6-mercaptochitin in DMSO with MMA were typically prepared with low yields and low amounts of grafting. The products prepared from 6-mercaptochitosan under the same conditions contained larger amounts of the synthetic polymers although the products were highly variable. MMA was subsequently polymerised with 6-mercaptochitosan in acetic acid buffer to form highly grafted copolymers. Chitosan was reacted with the monomer OEGMA by ATRP to form chitosan-graft-poly(OEGMA) copolymers. Two synthetic routes were investigated. The "grafting-from" route involved. the formation of a chitosan macroinitiator and polymerisation of OEGMA with this polymer. The polymers contained a large amount of grafted side chains as estimated from the �H NMR spectra. However, the purification was not satisfactory as determined by the presence of two peaks in the GPC traces. The "grafting-to", route involved the formation of poly(OEGMA) by ATRP with activated initiators and subsequent attachment to chitosan. The prepared copolymers showed large differences in their appearance with even very low amounts of grafting. The purification of the polymers prepared by this method was successful with no detectable homopolymer as determined by GPC analysis.

Chitin is a natural polymer which is extracted from a number of biological sources. This polymer is deacetylated to form the related polymer chitosan. The design and preparation of chitosan derivatives has been investigated to tailor the physical and chemical properties towards specific applications. To this end, this thesis describes the synthesis and characterisation of a number of chitosan derivatives. The prepared polymers contained either naphthalimide groups, thiol groups, poly(methyl methacrylate) side chains or poly(oligoethylene glycol methyl ether methacrylate) side chains. Chitin was successfully extracted and purified from squid pens by literature methods to give polymers with DD values from 12 to 23%. The Kurita method was used to obtain chitosan samples with a range of DD values from 75 to 91%. The prepared polymers were characterised by microanalysis, IR, �H NMR and solid-state ��C NMR spectroscopy. The MW distributions of the chitosan samples were determined by GPC in 0.3 M AcOH/0.2 M AcONa(aq) solution with dextran standards. The N-(naphthalimide)-chitosan derivatives were fluorescent materials and were typically prepared from the reaction of 4-bromonaphthalic anhydride with chitosan. This reaction was thoroughly investigated to find the optimal reaction conditions. The bromo groups were subsequently displaced by one of four nucleophiles: dimethylamine, piperidine, methoxide or vinylferrocene. The polymers were characterised by microanalysis, GPC, IR, �H NMR, UV-vis and fluorescence spectroscopy. The excitation and emission wavelengths and Stokes shifts were dependent on the substituent present in the naphthalimide group. Chitin and chitosan were sequentially reacted with tosyl chloride, potassium thioacetate and sodium methoxide to form the thiolated derivatives. The success of the tosylation reaction was dependent on the synthetic route used and the DD of the polysaccharide. The thiolated chitin polymers were well defined although the samples were completely insoluble. The thiolated chitosan polymers were also characterised and were highly swollen in acetic acid solution. These thiolated polysaccharides were used as macroinitiators for the free-radical polymerisation of MMA. The products obtained from the reaction of 6-mercaptochitin in DMSO with MMA were typically prepared with low yields and low amounts of grafting. The products prepared from 6-mercaptochitosan under the same conditions contained larger amounts of the synthetic polymers although the products were highly variable. MMA was subsequently polymerised with 6-mercaptochitosan in acetic acid buffer to form highly grafted copolymers. Chitosan was reacted with the monomer OEGMA by ATRP to form chitosan-graft-poly(OEGMA) copolymers. Two synthetic routes were investigated. The "grafting-from" route involved. the formation of a chitosan macroinitiator and polymerisation of OEGMA with this polymer. The polymers contained a large amount of grafted side chains as estimated from the �H NMR spectra. However, the purification was not satisfactory as determined by the presence of two peaks in the GPC traces. The "grafting-to", route involved the formation of poly(OEGMA) by ATRP with activated initiators and subsequent attachment to chitosan. The prepared copolymers showed large differences in their appearance with even very low amounts of grafting. The purification of the polymers prepared by this method was successful with no detectable homopolymer as determined by GPC analysis.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Oct. 31, 2008). PDF text: x, 336 p. : ill. (chiefly col.) ; 6 Mb. UMI publication number: AAT 3309211. Includes bibliographical references. Also available in microfilm and microfiche formats.