Colour and UV-Visible Absorption Spectra of Mechanical and Ultra-High Yield Pulps Treated with Alkaline Hydrogen Peroxide, 1991 International Mechanical Pulping Conference Proceedings

Stone ground wood, SGW, thermomechanical pulp, TMP, and chemithermomechanical pulp, CTMP were treated with 50% charge of alkaline hydrogen peroxide on OD pulp at 30°C and constant pH for times of up to 300

hours. During the initial stages of alkaline hydrogen peroxide bleaching chromophores that absorb light at

wavelengths in the range 360 to 460 nm are oxidized to chromophores, coniferaldehyde and quinonoid, that absorb light at wavelength < 300="" nm="" to="" increase="" is0="" brightness="" and="" l*="" and="" decrease="">

There are chromophores in the lignin of SGW and TMP, which after the initial brightness increase, rapid undergo a further slow reaction with peroxide resulting in a decrease in the remaining yellowness (b*) by 25% with no corresponding increase in whiteness (L*) or IS0 brightness. This result is attributed to the slow oxidation of the aromatic carbonyl groups by the large excess of alkaline hydrogen peroxide.