Structural modification of eucalypt pulp lignin in a totally chlorine-free bleaching sequence including a laccase-mediator stage

摘要: Structural modification of eucalypt pulp lignin was investigated in a totally chlorine-free (TCF) bleaching sequence including laccase-mediator stage. This stage applied after two oxygen delignification stages, and followed by an alkaline peroxide After more stages with laccase mediator were applied. The residual lignins enzymatically isolated from the different pulps analyzed spectroscopic techniques analytical pyrolysis. latter revealed high amounts syringyl units ()70%) lignins. 13C-1H heteronuclear single quantum correlation (HSQC) NMR indicated b-O-49 inter-unit linkages ()75% sidechains). Changes composition demonstrated course sequence. Moreover, oxidative major shown C2,6-H2,6 HSQC correlations presence oxidized pyrolysis markers pyrograms. existence both Ca keto carboxyl groups lignin, together normal (Cahydroxylated) units, multiple bond (HMBC) between aromatic H2,6 side-chain carbons. These Ca-oxidized structures represent nearly 60% total treated pulp. Analysis final compared simple treatment that most oxidatively altered removed alkali used Thus, kappa number decreased structurally related to found before although it contained less resinols group-bearing units. However, action is necessary attain brightness required ()90% ISO).