The kismet of residual lignins during LMS delignification of high-kappa kraft pulps

A series of laccase-mediator treatments (LMS) with 1-hydroxybenzotriazole ( HBT) and N-acetyl-N- phenylhydroxylamine (NHAA) (Fig. 1) as the mediators w ere performed on a laboratory prepared southern softwood conventional kraft pulp (kappa # 75.4). Subsequent to the LMS treatments, the treated pulps w ere subjected to various oxidatively reinforced alkaline extraction stages (E*). The kappa results suggested that both LMSHBT and LMSNHAA treatments d elignified this high-kappa pulp. The E* stages were beneficial in counterin g the darkening effect observed after the LMS treatments. Structural change s in residual lignins isolated before and after laccase-mediator (LMSNHAA ( E*) and LMSHBT (E*)) treatments were explored. The spectral analysis of pho sphitylated residual lignins revealed an increase in carboxylic acid conten t and a depletion of phenolic hydroxyl groups in non-condensed at C-5 ligni n moieties. Aliphatic hydroxyl groups were substantially decreased when NHA A was used. Overall, it appears that LMSHBT and LMSNHAA treatments on high- kappa kraft pulps primarily attack phenolic hydroxyl groups in non-condense d at C-5 lignin structures.