Consideration of roles of commercial TiO2 pigments in aromatic polyurethane coating via the photodegradation of dimethyl toluene-2,4-dicarbamate in non-aqueous solution

Abstract

Dimethyl toluene-2,4-dicarbamate (2,4-TDC) was selected as a model compound for aromatic polyurethane to investigate the photo-chemical behavior of commercial TiO 2 pigments in non-aqueous solution. The UV-Visible spectrometry analysis results showed that the UV-shielding ability of the rutile TiO 2 pigment was better than that of the anatase TiO 2 pigment. Photodegradation experiments suggested that the photodegradation of 2,4-TDC was retarded by rutile TiO 2 pigment, while accelerated by anatase TiO 2 pigment. With the help of the degradation intermediates during the photodegradation process and calculated data, such as point charges and bond length, the preliminary photodegradation mechanism of 2,4-TDC was also briefly elucidated, including the addition of hydroxyl radicals and the cleavage of the carbamate side chain. Additionally, the photodegradation of 2,4-TDC was used to evaluate the photoreactivity of TiO 2 pigments, this is proved to an efficient approach with potential application in industry.

Consideration of Photoactivity of TiO2 Pigments via the Photodegration of Methyl Orange under UV Irradiation

“…The above-mentioned results suggest that the photoactivity of the commercial TiO 2 pigments can be rapidly evaluated and decrease in the order P1 > P2 > P3. These experimental results were consistent with our previously reported findings [ 43 ].…”

Degradation and stabilization of polyurethane elastomers

“…It is noteworthy that after inorganic oxides absorb UV energy, they can also exert oxidising power and produce reactive free radicals such as perhydroxyl radicals (HO2 • ), an oxygen radical anion (O2 •− ) and hydroxyl radicals (HO • ). [276,288,291,292,[303][304][305][306][307][308][309][310][311]. These radicals will attack neighboring polymer chains to abstract hydrogen atoms, forming carbon-centred radicals.…”

“…evident at a particle size of less than 100 nm [288,309,310,312]. Anatase TiO2 nanoparticles are known to have a strong photocatalytic effect [276,288,[303][304][305][306][307][308][309][310]. In contrast, rutile TiO2…”

“…nanoparticles have high UV opacity and low photoactivity [288,308] and are an effective stabilizer for retarding the photooxidation of PUs [282].…”

“…For resistance to weathering, TiO2 or ZnO particles may need to be heavily coated (up to 10% w/w) with alumina, silica, zirconia, ceria, or phosphates of other metals[276,281,308,312]. Among the different techniques used to modify nanoparticles, silane treatment methods offers definite advantages such as simplicity, low cost and low processing temperatures[260,299,300,313].…”