2006b) Chemical characterization of eucalypt pulp lignin during totally chlorine free bleaching including a laccase-mediator stage: 2D-NMR, FTIR and Py-GC/MS of enzymatically-isolated residual lignins

Chemical modification of residual lignin isolated from eucalypt pulp after the different stages of a TCF sequence including a laccase-mediator stage was investigated by FTIR, Py-GC/MS and 2D-NMR (using HSQC, HSQC-TOCSY and HMBC). The enzymatic treatment resulted in strong oxidative modification of a lignin fraction, which could be removed under alkaline conditions enabling a final increase of brightness by hydrogen peroxide. In addition to changes in the ratios between syringyl and guaiacyl units and between β-O-4, syringaresinol and phenylcoumaran substructures, formation of acetosyringone and muconate terminal units were observed during the TCF sequence due to oxidative breakdown of lignin side-chains and aromatic nuclei respectively. I