The Light-Induced Yellowing of Paper Studied by Second-Derivative DRIFT Spectroscopy

The light-induced yellowing of the surface of paper made from a Eucalyptus regnanschemimechanical pulp has been studied by using second-derivative diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy in the region 1550 to 1800 cm−1. The observed reflectances were transformed to Kubelka-Munk units and the second derivatives obtained. Use of the second derivative technique has resulted in reduced bandwidths, enabling bands such as that at 1612 cm−1arising from exocyclic C=C bonds in lignin to be resolved from the broad envelope of the strong C=C ring stretching band at 1591 cm−1. The improved resolution has enabled the effects of UV light on the population of potential chromophoric C=0 and C=C groups in paper surfaces to be studied more precisely.