Modern automobiles are painted with basecoat, technology which is either metallic, solid colour or pearlescent. This requires protection from chemicals, scratching, weathering and UV light by applying a protective top coat (clearcoat) over the basecoat. For the clearcoat to cure into a hard protective shell it undergoes an irreversible crosslinking process. This usually takes place over the first four to five hours, depending on the formulation and weather conditions. The speed of crosslinking can be enhanced by temperature. Pot life is important as it can affect the overall quality of the painted surface. If crosslinking occurs too quickly, before the clearcoat is applied onto the surface, the clearcoat cannot be used to produce a good quality finish. The “expired” mixture is thus discarded. If used, the quality of the finished product cannot be guaranteed to last, and the paintwork may have to be redone. This often means removing the underlying paint and primer as well with the clearcoat film. Besides the time lost, the discarded clearcoat mixture often lands in the landfill, polluting ground water and the environment. It is thus important from the point of view of both the environment preservation and waste management, that as much clearcoat as possible is used without being wasted. It was proven in an earlier study (BSc Hon Formulation Science Treatise, 2011) that adding eugenol to a clearcoat mixture after crosslinking had started could reduce its viscosity, which is an indicator of crosslinking progress. Crosslinking subsequently resumed at a lower rate than in traditional blends. If stored away from oxygen and high temperatures, this blend could maintain optimum viscosity indefinitely. In this follow up study an optimum formulation was developed using D - optimal experimental design. It sought to extend the pot life to avoid waste to spray painters while saving the environment from pollution. The formulation that gave the desired viscosity after five hours of pot life was adopted. It was hypothesised that the optimum formulated clearcoat mixture would have a longer pot life than its traditional counterparts, and that it would perform just as well as the traditional clearcoat mixtures. To study the rate of crosslinking (disappearance of functional groups and appearance of the urethane bond), FTIR spectrometry was performed on a mixture produced from the optimized formula in comparison to that of a traditional mixture (the control). The rate of disappearance of functional groups was found to be lower in the eugenol mixture than in the control mixture. After six hours, eugenol was added into the control mixture, and this seemed to reduce the viscosity with the re-emergence of functional groups in the mixture. After 24 hours of crosslinking, an FTIR scan was done on the solid sample and this revealed that the eugenol mixture had crosslinked fully, with no detectable functional groups in the sample.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nmmu/vital:20707 |
| Date | January 2016 |
| Creators | Bukula, Nwabisa Asanda |
| Publisher | Nelson Mandela Metropolitan University, Faculty of Science |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Masters, MTech |
| Format | 120 leaves, pdf |
| Rights | Nelson Mandela Metropolitan University |
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