o-Quinones are thought to play a key role in the photoyellowing of mechanical pulps. The facile reaction betweeno-quinones ando-phenylenediamine to give fluorescent phenazines is examined as a possible way to detect quinonoid intermediates in pulp sheets. The method was tested ono-quinone-rich mechanical pulp sheets prepared by chemical treatment with Fremy's salt (potassium nitrosodisulphonate). The presence of photochemically generatedo-quinone groups in peroxide-bleached mechanical pulps was inferred from the fluorescence observed from o-phenylenediamine treated sheets. This fluorescence increased with increasing radiation time up to a limiting value. The quinones (but not their phenazine derivatives) are stable upon storage in the dark.
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