ON THE BEHAVIOR OF SPRUCE THERMOMECHANICAL PULP LIGNIN DURING HYDROGEN PEROXIDE BLEACHING

Lignins were isolated from spruce TMP and hydrogen peroxide bleached T MP (BTMP) by means of enzymatic hydrolysis with cellulases in yields o f 67 and 78%, respectively. In addition, the TMP lignin, TMP EL, was s ubjected to a treatment with bleaching agent to obtain a bleached lign in, TMP ELB. The three lignin samples were all characterized by thioac idolysis and C-13-NMR spectroscopy. Comparison of these lignin samples provided evidence about the behaviour of lignin towards alkaline hydr ogen peroxide bleaching. It has been demonstrated that the bleaching d oes not affect the overall structure of lignin. The only one major cha nge of the lignin moiety is elimination of coniferaldehyde end structu res, which would be an important contribution to the brightening of pu lp.