1. The roles of TiO2 in the durability of exterior rigid PVC are:
(i) to absorb UV, limiting direct resindegradation;
(ii) to scatter light, thus masking discolouration from the absorption of visible light;
(iii) to catalyse photo-oxidation in the shallow, near surface region where UV is absorbed.
2. Chalking effects of TiO2 could accelerate the degradation of the PVC matrix by the photocatalysis chemistry, which can be suppressed by the silica encapsulation to achieve non-chalking or durable performance. Acid solubility can be used to differentiate
the chalking grade and non-chalking or durable grade TiO2.
3. Chalking by TiO2 is a disadvantage when gloss retention is important and also in coloured PVC when the increased light scattering limits opportunities for light absorption by the colorants, causing colour fade. Outdoor weathering supports the results from the accelerated weathering gloss loss rate for chalking grades.
4. Higher temperature, higher irradiance and dry climate resulted in the fastest gloss loss rate and higher colour change for rigid PVC among four outdoor exposure locations. ‘Dry’ climate and peak temperatures are key factors in the hot dry degradation of exterior PVC. Higher loading levels of durable TiO2 showed an advantage to retain gloss longer and minimise discolouration.
