1997 Volume 51 Issue 2 Pages 358-366
In order to learn the effectiveness of pyrolysis-gas chromatography (Py-GC) on the characterization of chemically or biologically modified lignin, decayed hardwoods and kraft-cooked hardwoods were subjected to Py-GC as a tool for the convenience lignin analysis tool. The selected guaiacyl pyrolysis products (guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-vinylguaiacol, eugenol, vanillin, rans-isoeugenol and trans-coniferyl alcohol) and their syringyl analogue (syringol, 4-methylsyringol, 4-ethylsyringol 4-vinylsyringol, 4-allylsyringol, syringaldehyde, trans-4-propenylsyringol and trans-sinapyl alcohol), as the main lignin-derived compounds, were determined using each absolute calibration factors to flame ionization detector. The results were compared with those by the alkaline nitrobenzene oxidation.
European beech (Fagus silvatica) woods were decayed by a brown-rot fungus (Tyromyces palustris) or a white-rot fungus (Coriolus versicolor), and beech (Fagus crenata) woods were cooked with kraft liquor. Residual lignin contents of wood samples were measured by the Klason lignin methods. Lignin was analyzed by Py-GC and the alkaline nitrobenzene oxidation method quantitatively without isolation from woods. The yields of the pyrolysis products were obtained on the basis of the residual lignin in decayed woods, and changes in the yields and their relative compositions during the decay for 180 days were investigated. The molar ratios of syringyl type pyrolysis products to guaiacyl ones (S/G ratios) measured by Py-GC were compared with the molar ratios of syringaldehyde to vanillin (S/V ratios) obtained by the nitrobenzene oxidation.
(1) In pyrolysis of 180 days-decayed woods by Tyromyces palustris, the yields of trans-coniferyl alcohol and trans-sinapyl alcohol sharply decreased.
(2) In those by Coriolus versicolor, the yields of trans-coniferyl alcohol and trans-sinapyl alcohol decreased, and relative compositions of guaiacoland syringol clearly in-creased.
(3) For decayed woods by Coriolus versicolor, the yields of syringyl type pyrolysis products decreased more rapidly than those of guaiacyl ones with increase of decaying days. The S/G ratios measured by Py-GC were in good agreement with the S/V ratios obtained by the nitrobenzene oxidation.
(4) In pyrolysis of kraft-cooked woods, the yields of trans-coniferyl alcohol and trans-sinapyl alcohol decreased, and relative compositions of guaiacol and syringol increased.
(5) The S/G ratios of residual lignin in kraft-cooked woods decreased with increase of cooking time, and those were in good agreement with the S/V ratios.
