A one-pot catalysis combining laccase with Cu(salen) for selective removal of refractory lignin units during oxygen delignification of bamboo kraft pulp

The catalysis is an alternative to extend the delignification of pulp with molecular oxygen. This work thus focused on the delignification selectivity and selective removal of refractory lignin units by the one-pot catalysis combining laccase with Cu(salen) after oxygen delignification of bamboo kraft pulp. The one-pot catalysis showed a higher efficiency than the single-catalyst catalysis in relation with delignification selectivity and pulp brightness. The determination of the molecular weight showed that the combined catalysis remarkably enhanced the cleavage of connection bonds in pulp lignin. Furthermore, the quantitative analysis of the refractory linkages with 2D-HSQC- and P-31-NMR techniques indicated that the 5-5', beta-5' and beta-beta' units were removed by the one-pot catalysis to a large extent, following the corresponding order of cleavage reactivity. This rationalization was further theoretically confirmed by using the 5-5' model compound method.