Degradation of carboxylated styrene butadiene rubber based water born paints. Part 1: Effect of talc filler and titania pigment on UV stability

The photo-oxidation of cast self-supporting films of a carboxylated styrene butadiene random copolymer (c-SBR) containing talc and TR92 (coated rutile) (both separately and together) has been investigated using ATR-FTIR, toluene swelling measurements and DSC (for Tg determination). An imaging chemiluminescence (ICL) method was also used to depth profile the oxidation. Both the wavelength of the UV source and the presence of filler and pigment were found to affect the major degradation products and the propensity for surface crosslinking. At relatively low levels (<50 phr) talc showed an optimum UV stabilising effect at the irradiated surface (as measured by ATR-FTIR determination of carboxylic acid carbonyl index), though, due to iron impurities in the talc, higher loadings impaired the stabilisation performance. However, due to a physical barrier effect (verified using ICL), Tg measurements indicated a progressive increase in overall stabilisation with increasing talc loading. As expected, TR92 significantly retarded surface photo-oxidation and was manifested as slow growth of the carbonyl absorption bands. Carboxylic acid was by far the major component of the latter bands throughout the entire exposure period. Even at advanced stages of oxidation, αβ-unsaturated carbonyl species were the major surface photo-oxidation products in samples containing talc. Interestingly talc also led to significant surface crosslinking whilst the TR92 did not.