No description available.

No description available.

This thesis comprises an investigation into the reaction of halogenated xenobiotics and anaesthetic agents, with hepatic microsomal stearate desaturase. The levels of stearate desaturase in the hepatic microsomes were routinely elevated by re-feeding the experimental animals a high carbohydrate diet. The interaction of the xenobiotics with stearate desaturase was assessed by monitoring their effects on the redox steady state of hepatic microsomal cytochrome b₅, in the presence and absence of cyanide.

No description available.

No description available.

Thesis (PhD.(Chemical Engineering)--University of Pretoria, 2005. / Includes bibliographical references.

The proton magnetic resonance absorption of the C-form of stearic acid has been studied, over the temperature range 77°K to 3^2.5°K. The broadline spectra are decomposed into a wide and narrow component for solid and liquid regions in the lattice respectively. The appearance of the narrow component on the usual broadline spectrum at temperatures greater than room temperature is interpreted to be caused, by large liquid regions in the lattice. The number and size of these defects increase with increase in temperature and. with the incorporation of various types of defects in the solid lattice The spin-lattice relaxation times, T₁, were measured by adiabatic rapid, passage. The results indicate that the principal zeeman energy-thermal bath coupling occurs through methyl group reorientations. An activation energy of 2.2 kcalories/mole for methyl group rotation about the C₃ axis in solid stearic acid and a rotation frequency of 4 x 10⁵ sec⁻¹ at 77°K were determined from the T₁ data. / Science, Faculty of / Chemistry, Department of / Graduate

Please read the abstract in the section 00front of this document / Dissertation (MSc (Agric))--University of Pretoria, 2005. / Food Science / unrestricted

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High density polyethylene (HDPE) is a widely used plastic but it is also a combustible material. One way of reducing flammability is to add fillers, such as magnesium hydroxide (Mg(OH)2). However, this has a deleterious effect on the mechanical properties of composites. It has been found that one possible method of restoring mechanical properties is to modifY the filler particles with coating agents, such as stearic acid. In the present work, this idea was taken a stage further with the use of various metal stearates (e.g. magnesium stearate, calcium stearate, and zinc stearate) for modifying filler. The fillers examined were magnesium hydroxide and calcium carbonate. A filler loading of 40% w/w was used in all samples. Samples were moulded into a variety of shapes for mechanical testing. Such tests included, tensile, flexural, and impact testing. To obtain deeper understanding of the effect of the coating agents on the fillers, a variety of fundamental tests were carried out. These included Diffuse Reflectance FTIR (DRIFT), Thermal Analysis using a DSC cell, Xray Diffraction (XRD), contact angle measurement. Unfilled HDPE, uncoated filled-HDPE, and coated filled-HDPE were compared using uncoated filled-HDPE as a base line. Uncoated filled-HDPE is more brittle than unfilled HPDE. Surface modification of filler improves the toughness properties. Comparing coated filled-compounds, stearic acid and zinc stearate caused a small improvement, magnesium stearate improved the properties significantly with calcium carbonate while calcium stearate gave the best results for coating magnesium hydroxide. One monolayer coating gave the best compound properties compared to other degrees of coating. Although, tensile/flexural strength was not greatly affected elongation at yield, extension at maximum load, and impact properties increased significantly. DSC was used to observe the disappearance and conversion of coating agents as coating proceeded. X-ray diffraction showed the effect of injection moulding on the orientation of the filler and polymer. During coating of the filler particles, XRD and DSC were used to follow incorporation of stearate particles to produce the monolayer coverage. Surface free energy results showed that surface modification of filler resulted in the reduction of hydrophilicity of filler leading to tougher composites compared with uncoated filled-compounds.