Identification of residual lignin markers in eucalypt kraft pulps by Py-GC/MS

Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) has been used to characterize the residual lignin in eucalypt (Eucalypt globulus) kraft pulp during the pulping and bleaching processes. The composition and structure of eucalypt wood lignin and kraft lignin have also been studied by Py-GC/MS and C-13-nuclear magnetic resonance (NMR). Pulp samples were collected at different stages of the pulping process (after cooking, oxygen delignificat ion, and bleaching with chlorine dioxide or hydrogen peroxide). By comparis on with lignin pyrolysis products obtained from Py-GC/MS of eucalypt wood a nd kraft lignin, characteristic features of lignin in the different pulps h ave been established. The main lignin-derived markers detected in pulps wer e guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-vinylguaiacol, syringol, 4 -methylsyringol, 4-ethylsyringol, 4-vinylsyringol and trans-4-propenylsyrin gol, all of them in very low amounts. Analytical pyrolysis was also used to characterize the changes in the residual lignin after kraft pulping of euc alypt wood pretreated with two lignin-degrading fungi (Bjerkandera adusta a nd Poria subvermispora) in wood 'biopulping' experiments. In general, Py-GC /MS has shown to be valuable in the characterization of residual lignin mar kers in kraft pulps due to the sensitivity of the technique when individual -ion chromatographic profiles for selected lignin markers are used. (C) 200 1 Elsevier Science B.V. All rights reserved.