| Popis: |
Due to its ubiquitous presence in paints of all colours, titanium dioxide represents the primary pigment used in Organically Coated Steel (OCS) for construction applications. However the semi-conducting nature of TiO2 translates into a possibility of inducing photodegradation when exposed to Ultra Violet (UV) radiation such as that present in sunlight. Initial research concentrated on developing a test procedure of the photoactivity of these pigments within a PVC binder. Model coatings, using pigments of known performance, have been tested to evaluate the success of this rapid test technique and excellent correlation has been shown. Building on this, Chapter 4 details a unique cell that has been designed, constructed and tested resulting in a more versatile testing environment. This cell has been used to examine the photostability of 4 commercially available pigments while present within a standard emulsion paint binder. Chapters 5 and 6 detail work performed on Plasticised PVC paint films and the resultant effects this has on the kinetics of photodegradation as monitored via the evolution of CO2. Also incorporated into this design is the ability to identify and quantify volatile organic components that are evolved during the degradation process, thus providing information regarding the photodegradation mechanism occurring within the film. It has been found that in these model films, the addition of plasticiser increases the rate of photogenerated CO2 and also produces volatile components that can be directly related to the parent plasticiser molecule. There is some evidence to suggest that for certain plasticisers, a sacrificial protection mechanism is at work, resulting in increased CO2 evolution but decreased attack on the binder matrix. Finally in Chapter 7, a number of complimentary techniques are employed to assess the effect that TiO2 photocatalysed PVC degradation has on the underlying substrate material. The techniques include electrochemical impedance spectroscopy (EIS), electro-generated chemiluminescence (ECL) and 3-D scanning vibrating electrode technique (3-D SVET). Photodegradation leads to porosity development in coatings and eventual through coating penetrative defects lead to corrosion. |
