Observation of quinonoid groups during the light-induced yellowing of softwood mechanical pulp

Abstract

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 Samples withdrawn at daily intervals were subjected to oxyphosphorylation with trimethyl phosphite to labelortho-quinones and other chromophoric species with phosphorus. The solid-state³¹P NMR spectra of these samples revealed the rapid formation ofortho-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.