FUNDAMENTAL PROPERTIES OF MECHANICAL PULP LIGNINS .4. PHOTOSTABILIZATION OF H2O2-BLEACHED MECHANICAL PULP SHEETS

Whole phenolic and alcoholic hydroxyl groups along with p-hydroquinone sin pulp lignin were acetylated by dipping H2O2-bleached mechanical pu lp sheets in acetic anhydride at 95 degrees C for 60 min. The brightne ss of the pulp sheets increased with acetylation of the phenolic hydro xyl groups in the lignin. The acetylation of p-hydroquinones as leucoc hromophores resulted in stable brightness under irradiation with light . By dipping H2O2-bleached mechanical pulp sheets in a solution of dia zomethane at 6 degrees C for 15 days, the phenolic hydroxyl groups wer e made into methylether groups. p-Benzoquinones as chromophores in the pulp sheets were converted to colorless compounds and a remarkable in crease in brightness was observed. However, these compounds, epoxy cyc lodienones, derived from p-benzoquinones acted as new leucochromophore s with consequent slight color reversions of the pulp sheets.