The effects of oxidative alkaline extraction stages after laccaseHBT and laccaseNHAA treatments -: An NMR study of residual lignins

Two laccase-mediator systems (LMS) were performed with 1-hydroxybenzo-triazole (HBT) and N-acetyl-N-phenylhydroxylamine (NHAA), as the mediators, on a southern softwood conventional kraft pulp with an initial kappa of 33.8. The LMSHBT and LMSNHAA treated pulps were then subjected to various reinforced alkaline extraction stages with oxygen (E+O), peroxide (E+P), and peroxide/oxygen (E+P+O). The kappa data suggested that both LMSHBT and LMSNHAA are effective at delignifying kraft pulps. However, under the conditions employed in this study, a greater level of delignification was obtained with an LMSHBT stage than with an LMSNHAA stage. The viscosity measurements confirmed the selectivity of LMS. Oxidative reinforcement of the alkaline treatments was beneficial for regaining the loss in brightness from LMS when the mediator was either NHAA or HBT. P-31 NMR spectral analysis of phosphitylated residual lignins revealed a greater enrichment of carboxylic acid groups after an LMSHBT than after an LMSNHAA stage. Depletion of free phenolic groups was evident after either an LMSHBT or an LMSNHAA treatment. However, it was greater after an LMSNHAA stage.