Photooxidation of cellulose treated with amino compounds

The effect of short wavelength UV radiation on celluloses treated with different amino compounds was studied. Samples of cotton cellulose were treated in aqueous solutions of different pH with polyethylenimine (PEI), hexamethylenetetramine (HMTA) and ethylenediamine (EDA), and irradiated in air with a low pressure mercury vapour lamp for different times. The photoyellowing was measured using standard colorimetry and the degradation processes and products were characterized using diffuse reflectance (FTIR and UV-visible) spectroscopy. The degradation processes were compared with those observed in the same materials during thermal treatments. Celluloses treated with EDA and PEI show an intense photoyellowing which depends on the pH of the treating solution. Colour changes in these materials correlate well with the appearance of imine groups and the disappearance of amino groups, determined by FTIR measurements. However, HMTA-treated cellulose, which suffers an intense thermal yellowing, shows only insignificant photoyellowing. These results were explained considering that the photoyellowing is due to the coloured Schiff bases produced in the condensation between amino and carbonyl groups.