The effects of oxidative alkaline extraction stages after laccase(HBT) andlaccase(NHAA) treatments - An NMR study of residual lignins

Two laccase-mediator systems (LMS) were performed with 1-hydroxybenzo-triaz ole (HBT) and N-acetyl-N-phenylhydroxylamine (NHAA), as the mediators, on a southern softwood conventional kraft pulp with an initial kappa of 33.8. T he LMSHBT and LMSNHAA treated pulps were then subjected to various reinforc ed alkaline extraction stages with oxygen (E+O), peroxide (E+P), and peroxi de/oxygen (E+P+O). The kappa data suggested that both LMSHBT and LMSNHAA ar e effective at delignifying kraft pulps. However, under the conditions empl oyed in this study, a greater level of delignification was obtained with an LMSHBT stage than with an LMSNHAA stage. The viscosity measurements confir med the selectivity of LMS. Oxidative reinforcement of the alkaline treatme nts was beneficial for regaining the loss in brightness from LMS when the m ediator was either NHAA or HBT. P-31 NMR spectral analysis of phosphitylate d residual lignins revealed a greater enrichment of carboxylic acid groups after an LMSHBT than after an LMSNHAA stage. Depletion of free phenolic gro ups was evident after either an LMSHBT or an LMSNHAA treatment. However, it was greater after an LMSNHAA stage.