Abstract
The multiple functions of titanium dioxide (TiO2) in exterior PVC durability are reviewed. TiO2 absorbs UV light to protect the polymer from direct UV degradation, and provides light scattering for visible light for opacity and to mask the discoloration of PVC. In addition, TiO2 photocatalytically degrades the PVC surface which is detrimental to gloss retention and causes colour fade. The chalking effect of TiO2 to PVC surface degradation was further analysed and the acid solubility test was introduced to differentiate the chalking grades and durable grades. A two year outdoor weathering study of rigid PVC at representative exposure sites included exposures in the USA, France and Belgium. The gloss loss and colour change due to weathering and UV exposure was discussed with the influence of different exposure climates, stabiliser types, TiO2 loading and chalking effects.
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