LIGNIN INHIBITS AUTOXIDATIVE DEGRADATION OF CELLULOSE

We studied autoxidation of lignin-containing and lignin-free pulps, in itiated by the water-soluble radical initiator 2,2'-azobis(amidinoprop ane)dihydrochloride (ABAP). A fully-bleached, softwood kraft pulp, tre ated with 0 . 3 M ABAP and 140 kPa oxygen for 48 h (20% solids, pH 7, 60 degrees C), experienced an 80% reduction in cellulose degree of pol ymerization (DP), and lost 40% of its zero-span tensile strength. No d iscolouration occurred. In contrast, there was virtually no change in cellulose DP or zero-span tensile strength, but considerable discolour ation for a lignin-containing pulp (peroxide-bleached thermomechanical pulp) under the same conditions. We propose that, under these conditi ons, the discolouration of lignin is a manifestation of its antioxidan t properties.