OBSERVATION OF QUINONOID GROUPS DURING THE LIGHT-INDUCED YELLOWING OF SOFTWOOD MECHANICAL PULP

Unbleached and alkaline hydrogen peroxide bleached black spruce (picea mariana) stone groundwood samples were irradiated with a weak light source over a period of six days in an effort to probe the early photochemical events occurring during the light-induced brightness reversion. Samples withdrawn at daily intervals were subjected to oxyphosphorylation with trimethyl phosphite to label ortho-quinones and other chromophoric species with phosphorus. The solid-state P-31 NMR spectra of these samples revealed the rapid formation of ortho-quinones during the early phase of irradiation, followed by a dramatic reduction of these species at latter phases. The data suggests that during the early photochemistry, ortho-quinones are produced in high yield pulps, which subsequently react creating other more complex chromophores which do not possess the quinonic character.