Nitrification, the process whereby ammonical-nitrogen (NH i+4 - N) is changed into nitrate- nitrogen (NO3-N), is one of the more important biochemical processes associated with agriculture. Nitrate appears to be the form of N that most crops can most readily utilize.

MS, Pharmaceutical Affairs, Faculty of Health Sciences, University of the Witwatersrand / PEO (Polyethylene Oxide) is one of the most important biodegradable polymers used in pharmaceutical formulations, mainly because of its non-toxicity, high water-solubility and swellability, insensitivity to the pH of the biological medium and flexibility during dosage form production (Kim, 1995; Picker-Freyer, 2006; Kiss et al., 2008). The lack of studies attempting to achieve controlled drug delivery of hydrophilic drugs has provided us with motivation to use a drug of this nature but we have combined it with a PEO-electrolyte combination in order to control drug delivery. This study was aimed at modifying the physicochemical and physicomechanical properties of PEO in order to influence the hydrodynamic diffusion of its three-dimensional network. Hence, through such alteration, it was envisaged that if drug is loaded into its PEO matrix, its solubility and dissolution can be regulated in order to achieve zero-order influx of dissolution medium. The interaction between PEO and electrolytes may allow for precipitation of ions on the polymer backbone. This would lead to the attraction of water molecules to the ions. As a result, this would cause dehydration of the polymer matrix, hence minimising its mobility and relaxation. In this study, 36 PEO-electrolyte combinations were prepared by combining a high molecular weight PEO with different statistically planned combinations of electrolytes. The 36 formulations were microscopically analyzed and subjected to textural analysis. The salted-out PEO-electrolyte combinations were then further selected and analyzed. Assessment of the molecular structural transition and thermal compatibility analysis indicated minimal interaction between the electrolytes and PEO indicating that the polymer-electrolyte combination was stable enough to be employed as a medium for controlled drug release. The polymer-electrolyte combination was combined with a model drug, diphenhydramine HCl to form a tablet matrix and then subjected to dissolution. In vitro drug release varied depending on the different electrolytes and their combinations. The type of polymer, molecular weight of the polymer, concentration of the polymer, different electrolyte combinations and solubility of the drug played a significant role in controlling drug release. After optimization of the fracture force, resilience and work performed values, results have established that equal concentrations of Na2CO3 and K2HPO4 are desirable for achieving controlled release of drug from the salted-out PEO combination in a zero-order manner. Furthermore, Na2CO3 and K2HPO4 had a significant influence on controlling the release of drug from the salted-out PEO combination due to crosslinking between PEO and the electrolytes ultimately leading to zero-order release kinetics. The salting-out of PEO notably modified the physicochemical and micromechanical properties of basic PEO, which demonstrably enhanced the ability of the sample to achieve controlled drug release. The formulation strategy employed in this study where in our sample drug, diphenhydramine HCl was combined with a PEO-electrolyte combination has shown promising results in regulating drug release.

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Esta tesis estudia el impacto que tienen los COV presentes en los plásticos reciclados para la economía circular. Actualmente, la industria del reciclaje actual no puede cubrir la creciente demanda de plásticos reciclados de alta calidad en los últimos años. Hasta ahora, el reciclaje mecánico es la solución más utilizada a nivel mundial, y su eficacia y fiabilidad han sido demostradas para el tratamiento del residuo plástico post-industrial. Sin embargo, el mismo reciclaje mecánico aplicado a los residuos plásticos post-consumo da lugar a un material reciclado de menor calidad que solamente es apto para aplicaciones de bajo valor añadido, como son las tuberías de riego o cubos de basura. Por ello, esta tesis evalúa la influencia que tienen las sustancias orgánicas que aparecen en los plásticos reciclados post-consumo dentro el sector del plástico. / Investigación cofinanciada por el Vicerrectorado de Investigación y Transferencia de Conocimiento para el fomento de la I+D+i de la Universidad de Alicante y Cadel Deinking, S.L.

<p> The objective of this work was to investigate the potential of poly(vinyl pyrrolidone) (PVP) as a protein resistant biomaterial. Two types of PVP surface were studied: (1) plasma polymerized N-vinyl pyrrolidone monomer on polyethylene (PE), and (2) grafted PVP surfaces formed by reaction of the activated polymer with plasma polymerized allyl amine on PE. Surfaces were also prepared by grafting polyethylene oxide (PEO), a known protein repellent, to plasma polymerized allyl amine and for comparison to PVP. The surfaces were characterized chemically by water contact angle and X-ray photoelectron spectroscopy (XPS). Protein interactions were studied using radiolabeled fibrinogen in PBS buffer. </p> <p> Plasma polymerized N-vinyl pyrrolidone surfaces were prepared in a microwave plasma reactor. Reactions were carried out both at room temperature and at 50°C (increased vapour pressure) in an attempt to increase the extent of plasma polymer deposition. The resulting surfaces showed structures chemically different from conventional linear PVP. XPS analysis suggested the presence of a variety of functional groups, including amines, amides, hydroxyls, carbonyls and urethanes. Mechanisms for the reactions occurring could not be ascertained but it appeared that the monomer was extensively fragmented in the plasma. Although these surfaces were hydrophilic (contact angles of 20 to 30°), they did not resist fibrinogen adsorption: in fact they showed adsorption levels approximately 10% greater than unmodified polyethylene. </p> <p> Methods for direct grafting of polyvinyl pyrrolidone and polyethylene oxide to plasma polymerized allyl amine (PPAA) surfaces were designed on the assumption that the PPAA surfaces would be rich in amino groups for reaction with appropriate polymer chain ends. Although there was 8-12% of nitrogen on the surfaces, the C1 s high resolution showed that amide and urethane functionalities are also present in addition to amines. The hydroxyl end groups of preformed PEO and PVP chains were activated by reaction with either 1-[3- (dimethylamino) propyl], 3-ethylcarbodiimide and N-hydroxy succinimide (EDC/NHS), and N-N-disuccinimidyl carbonate (DSC). NMR spectra of the products of these reactions showed that for PEO, the yields were moderate, and for PVP, the yields were low. Surfaces grafted using polymers activated with EDC/NHS were more hydrophilic than surfaces grafted with DSC-activated polymers. XPS data did not provide clear evidence that significant polymer grafting had occurred in any of the systems. It was concluded that changes in the allyl amine plasma polymer in different environments following plasma polymerization may affect the efficiency of grafting subsequently. XPS data suggested that the allyl amine plasma surfaces undergo oxidation over time in air. Also the films may be partly removed from the polyethylene surface when placed in buffer as suggested by XPS and contact angle data. Various parameters were examined in an attempt to improve the allyl amine plasma polymerization process for greater stability of the film. Increasing the treatment time from 1 0 to 30 minutes gave surfaces that showed a slower change in contact angle when stored in air. </p> <p> Despite the lack of strong chemical evidence of extensive polymer grafting, all of the grafted surfaces were found to be significantly protein repellent, with reductions of 10 to 36 % compared to unmodified polyethylene. The PEO surfaces were more repellent than the PVP, although the differences were not significant. Surfaces grafted using polymers activated with EDC/NHS were more protein repellent than those grafted with DSC-activated polymers. Protein adsorption was not affected by PVP molecular weight in the range 2,500 to 10,000. Since there is considerable overlap of the molecular weight distributions (MWD) of these two polymers, it is speculated that the MWDs of the grafted polymers may be more similar than those of the polymers themselves, possibly due to "selection" of similar, presumably optimal molecular weights. </p> <p> Discussion of the possible reasons for the better protein resistance of PEO compared to PVP is given in terms of chain structure in relation to the steric exclusion and water barrier theories of protein repulsion. </p> / Thesis / Master of Applied Science (MASc)

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