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No description available.

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Electrodepositable paints are used in the auto industry to provide the majority of the protection against corrosion to mild steel car body shells. They are generally epoxy/blocked isocyanate resins systems which are applied by action of an electropotential between the car and an anode. Upon heating to 175°C the blocked isocyanate deblocks, and crosslinking occurs predominantly via the formation of urethane and urea linkages. The aim of the project was to gain a better understanding of the factors which may affect the adhesion of the electrocoat resin polymer to a steel surface, to investigate possible replacements for the tin catalyst currently used, and to develop a quantitative mechanical test for paint adhesion. This was achieved by employing various analytical techniques including Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and mechanical testing.

Abstract This dissertation describes a study of the treatment of wastewater using the flocculation process. Wastewater samples from Barloworld Plascon paints were used for the research. Environmental pressure has necessitated the introduction of a new generation of low-solvent paints. The behaviour of these in coagulation and flocculation treatment processes has not been investigated previously. The optimum flocculent dosage for these paints was investigated. It was found that for paint wastewater to be flocculated, the effect of the dispersants needs to be counteracted, which destabilizes the colloidal suspension, enabling flocculation and settling to occur. Results showed a correlation between the solid content of wastewater and flocculent dosage. Changes in redox potential have been found to be associated with good flocculation. In this work, redox potential was evaluated as an indicator for destabilisation of the dispersants. It was shown that redox potential can be used as an indicator of good flocculation at low dispersant concentrations. Owing to the importance of the hydrolysis reactions of Al3+ in flocculation, which are affected by pH, the pH range in which good flocculation occurs was determined. Results show that optimal flocculation occurred between pH 4 and 5. A strong relationship between flocculent dosage and particle nucleation and growth was observed. Results also showed that mixing improves flocculation kinetics.

The objective of this work was the investigation of the polymeric interactions in tablet coating films in relation with effective film formulations. The polymeric interactions were studied by means of torsional braid analysis. For this purpose an existing torsional braid analyser was improved and successfully interfaced to a microprocessor for data acquisition and reduction. Discussion on the contribution of the substrate to the thermomechanical spectra of the TBA as well as factors associated with the optimisation of the technique are presented. The dynamic mechanical behaviour of EC, HPMC, HPMCP-HP50, HPMCP-HP55, HPC and CAP film formers was studied with particular attention to structure- Tg relationship. The plasticisation of two of the most common film formers, namely EC and HPMC, with a series of polyethylene glycols was investigated. It was shown that PEGs efficiently plasticise HPMC, whereas they exhibited limited interactions with EC. The relation of the plasticising efficiency to the size and concentration of the PEGs with respect to the optimisation of the tablet coating formulation is also discussed. The thermomechanical behaviour of blends of EC with water-/pH-dependent film formers was also studied with TBA, in conjunction with the requirements for controlled release coatings. All polyblends exhibited phase separation and the required domain morphology, which was shown capable of retaining small amounts of water-/pH-dependent components even after prolonged leaching. Moreover, the modification of the thermomechanical performance of 80/20 w/w EC/HPMC blends plasticised with PEG200 and PEG400 was investigated. These studies indicated diffusion of the plasticisers into both phases. Finally, the effects of blend composition and interactions in terms of efficient sustained release coatings are identified and discussed.

No description available.