Abstract
We studied autoxidation of lignin-containing and lignin-free pulps, initiated by the water-soluble radical initiator 2,2′-azobis(amidinopropane)dihydrochloride (ABAP). A fully-bleached, softwood kraft pulp, treated with 0·3 m ABAP and 140 kPa oxygen for 48 h (20% solids, pH 7, 60°C), experienced an 80% reduction in cellulose degree of polymerization (DP), and lost 40% of its zero-span tensile strength. No discolouration occurred. In contrast, there was virtually no change in cellulose DP or zero-span tensile strength, but considerable discolouration for a lignin-containing pulp (peroxide-bleached thermomechanical pulp) under the same conditions. We propose that, under these conditions, the discolouration of lignin is a manifestation of its antioxidant properties.
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