EFFECT OF OZONE ON PULP COMPONENTS APPLICATION TO BLEACHING OF KRAFT PULPS

The effect of ozone on softwood kraft pulp was investigated. Cellulose oxidation and depolymerization were characterized by the measurement of carbonyl and carboxyl groups, the determination of the molecular weight distribution and viscosimetry. Strength properties were found to be closely related to the average degree of polymerization while optical properties were linked to the amount of carbonyl groups. Lignin oxidation was followed by C-13 NMR. The high reactivity of lignin toward ozone explains its protecting effect during ozonation. Any alkaline stage and particularly a peroxide stage (P) carried out after ozonation (Z) led to a severe depolymerization of the cellulose molecules. This was explained by the presence of the carbonyl groups on cellulose. This problem could be solved by applying a reductive stage with sodium borohydride (B) after ozonation and before P, Bleaching sequences like OZBP (O for oxygen treatment) were proposed.