Spectral and photophysical properties of thermomechanical pulps bleached with the use of acidified and alkaline hydrogen peroxide

We characterized spruce thermomechanical high-yield pulps subject to a variety of non-delignifying hydrogen peroxide treatments. Apart from standard technological analysis, spectral and photophysical properties of the sample pulps were evaluated using steady-state diffuse reflectance spectroscopy and time-resolved emission and diffuse reflectance spectroscopy with sub-microsecond time resolution. The steady-state diffuse reflectance spectra allow to obtain a more complete information as compared to standard brightness measurements, as they include the data from the UV-A zone, crucially determining the yellowing rates of the respective paper products. Time-resolved emission and diffuse reflectance results provide additional information on the amount and reactivity of photoactive groups present in the pulp, which also affect the yellowing rates of the paper products. The best characteristics were registered for the pulp sample prepared using a two-stage hydrogen peroxide brightening, with the preliminary acidic and the final alkaline treatment, which can be recommended for industrial implementation.