Photoactivity test for TiO2 pigment photocatalysed polymer degradation

Titanium dioxide (TiO2) pigment photocatalysed degradation of organic coatings and structural polymeric materials can result in polymer photodegradation and chalking. Traditional accelerated testing techniques provide comparative data on pigment performance but can take many thousands of hours to complete. In this work a new testing procedure is described that enables a rapid assessment of TiO2 photoactivity to be made. The kinetics of CO2 production from solution cast unplasticised PVC (UPVC) films pigmented with 50% by weight TiO2 under UV-A illumination (365 nm) monitored by Fourier transform infrared spectroscopy in a closed loop flow system has been measured. A range of TiO2 samples with differing photoactivities ranging from unclassified materials (unsuitable for structural or coatings applications) through grade C (interior use), grade B (non-demanding external) and grade A (demanding external coatings and structural UPVC) have been tested. The rate of CO2 evolution from the irradiated films can be used as a photoactivity index to rank pigment photoactivity successfully within 6 h. In addition, the technique appears sensitive to differences in grade A pigment performance allowing rapid assessment of even the most photostable materials.