Oskar Faix

Determination of lignin content of Eucalyptus globulus wood using FTIR spectroscopy

FTIR spectroscopy was used to quantitatively determine lignin in Eucalyptus globulus wood. A total of 40 wood samples from a 9 year old provenance trial was divided into two independent sets for calibration and validation. Lignin contents, as determined by the acetyl bromide method, ranged from 23 % to 34 % o.d. extractive-free wood. Spectra were recorded with the KBr pellet technique and twelve peaks between 1800cm -1 to 800cm -1 used for calibration by linear regression. The best calibration fit (R 2 =0.98) was obtained with the 1505 cm -1 peak from lignin and the 1157 cm -1 peak from polysaccharides as a reference. The standard error of calibration (SEC), and the standard error of prediction (SEP) calculated with the validation set, were very low. A linear regression of FTIR measurements proved strong enough to predict lignin content with a very high coefficient of determination. The accuracy of FTIR techniques allows its use in large scale breeding programmes to assess wood lignin content with considerable less effort and shorter time than using wet-lab methods, once a reliable calibration is performed for the species.

Determination of tree to tree variation in syringyl/guaiacyl ratio of Eucalyptus globulus wood lignin by analytical pyrolysis

Abstract High syringyl/guaiacyl ratios (S/G ratios) are advantageous for pulping. Analytical pyrolysis was applied to Eucalyptus globulus wood to measure S/G ratios and assess its potential in forest breeding programmes. Samples were collected from five trees of two provenances grown in three sites. After peak assignment, relative peak areas were calculated for carbohydrate, guaiacyl and syringyl type degradation products. Lignin derived products account on average for 21% of the total identified area. The average S/G ratio of trees was 2.0, ranging from 1.5 to 2.6. The analysis of variance for the S/G ratios showed that provenance and tree were highly significant sources of variation accounting for 48 and 27% of the variation, respectively. Site had no influence but ‘site×provenance’ interaction was significant and accounted for 16% of the variation. The error associated with the method represented only 6% of the variation. Analytical pyrolysis proved reproducible and sensitive for the measurement of the natural variability of E. globulus with regard to lignin composition. The pyrolytic determination of the S/G ratios is recommended as an evaluation trait in breeding programmes for pulpwood production.

Artificial Ageing of Wood Monitored by DRIFT Spectroscopy and CIE L*a*b* Color Measurements 1. Effect of UV Light

The effect of UV irradiation up to 200hrs was monitored on five wood species (Picea abies, Pinus sylvestris, Larix decidua, Populus euramericana, Robinia pseudoacacia) by spectro colorimetry and diffuse reflectance infrared Fourier transform (DRIFT) spectrometry. The CIE L * a * b * color calculations exemplified the rapid change of total color difference (ΔE * ) in the first 25 to 50hrs of irradiation. All samples exhibited yellowing, i.e. a pronounced steep shift to positive Δa * values in the Δa * , Δb * coordinate system. Robinia p. showed an additional shift to redness, i.e. towards positive Δb * values. The colored compounds developed could be removed by water extraction only to a moderate extent. Thus it was concluded that the yellow color was mainly due to oligomeric chromophores, arisen probably from leuco chromophores of the lignin moiety of wood. In agreement with the literature, DRIFT measurements revealed the preferred degradation of aromatic structures and the formation of nonconjugated carbonyl and carboxyl groups. The DRIFT spectra indicate dehydration, oxidation to carboxyl groups and the formation of lactones or other esters. It was demonstrated by spectral subtraction that the increasing carbonyl bands consisted in the case of softwoods of two sub-bands with equal intensity at 1763 and 1710 cm -1 . The formation carbonyl bands of the hardwoods obeyed different rules. The formation of conjugated carbonyl groups below 1700 cm -1 was observed only to a limited extent. The carboxyl group containing photodegradation products could easily be removed by water extraction. This was interpreted that the oxidized compounds did not necessarily contribute to the formation of colored compounds. The plots of DRIFT band intensities, derived from baseline corrected and normalized spectra, vs. the irradiation time revealed pronounced intensity changes in the first 50 hrs of irradiation. The coherent intensity profiles were beveling above 100hrs of irradiation.

Degradation of gymnosperm (Guaiacyl) vs. angiosperm (syringyl/guaiacyl) lignins by Phanerochaete chrysosporium

This study examined the relative degradabilities of guaiacyl and syringyl/guaiacyl lignins by the white-rot fungus Phanerochaete chrysosporium Burds. Synthetic syringyl/guaiacyl lignin (Cpin syringyl units) was depolymerized much more rapidly than synthetic guaiacyl lignin (Cp), although the two were oxidized to CO2 at the same rate. Milled wood lignin or birch, labeled with H at Ce, was also depolymerized more rapidly than similarly labeled spruce milled wood lignin. During degradation two to three times äs much of both the synthetic and natural guaiacyl lignins became mycelium-bound äs the syringyl/guaiacyl lignins. This result is interpreted to reflect a greater resistance of the guaiacyl lignins. Collectively, our results point to a more facile initial degradation of the syringyl/guaiacyl type of lignins. This finding helps explain the more rapid degradation of angiosperm wood than gymnosperm wood by white-rot fungi.

Quantitative Analysis of Cork (Quercus suber L.) and Milled Cork Lignin by FTIR Spectroscopy, Analytical Pyrolysis, and Total Hydrolysis

Quantitative Analysis of Cork (Quercus suber L.) and Milled Cork Lignin by FTIR Spectroscopy, Analytical Pyroiysis, and Total Hydrolysis By A.V. Marques, H. Pereira, D. Meier, and O. Faix Institute Superior Engenharia Lisboa, Departamento Quimica Organica, R. Conselheiro Emidio Navarro, P-1399 Lisboa, Portugal Universidad Tecnica de Lisboa, Departamento de Enghenharia Florestal, Tapada da Ajuda, P-1399 Lisboa, Codex, Portugal Bundesforschungsanstalt für Forstund Holzwirtschaft, Institut für Holzchemie und chemische Technologie des Holzes, D-21027 Hamburg, Germany

Determination of Carbonyl Groups of Six Round Robin Lignins by Modified Oximation and FTIR Spectroscopy

The carbonyl group content of six round robin lignins, which were distributed in the scientific community 1990-1991, has been determined by a modified oximation. In this technique, the reaction occurs at higher temperature (80°C) than usual (25°C) and the oximating mixture contains besides hydroxylamine hydrochloride also triethanolamine (TEA) in excess. The latter shifts the chemical equilibrium towards a fully oximated product. The portion of TEA not consumed in oximation is titrated with HCI either by potentiometric titration to pH 3.3 or by high frequency conductometric titration. Both titration techniques give similar results. The modified oximation yields essentially higher CO contents than the traditional one. A correction technique is presented which is necessary for lignins containing carboxyl groups. The corrected CO contents show an excellent correlation (r 2 = 0.99) with the normalized area of the total carbonyl region of the FTIR spectra. This measure. obtained through division of the integral between 1840 and 1550cm -1 by the absorbance at 1600cm -1 , allows the reproduction of the results of CO group determination by modified oximation. Several correlation equations are presented and problems of CO group determination in lignins are discussed.

Isolation and characterization of a guaiacyl lignin from saponified cork of Quercus suber L.

Extractive-free cork from Quercus suber L. has been submitted to depolymerisation by sodium methoxide in methanol (transesterification) from which a saponified cork (CORK sap ) in a yield of 34.4% was obtained. From CORK sap a milled cork lignin (MCL sap ), an ether soluble part, and a lignin carbohydrate complex (LCC sap ) were isolated, with the respective yields of 11.9%, 0.54%, and 0.79% (based on CORK sap , corresponding to 4.1%, 0.19% and 0.27% based on original cork). The isolates were characterized by FTIR spectroscopy, analytical pyrolysis (Py-GC-FID), elemental analysis, OMe determination, molecular weight determination, and acid hydrolysis followed by monomeric sugar analysis. The elimination of aliphatic suberinic acids of cork before MCL isolation was helpful to obtain a pure sample. MCL sap was essentially free of suberinic acids and its carbohydrate content was around 5%. It was demonstrated for the first time that milled cork lignin belongs to a guaiacyl-type lignin which is very similar to spruce lignin containing up to 98% guaiacyl units, 1% 4-hydroxy-phenylpropane units, and approx. 1-2% syringyl units. The total hydrolysis of LCC sap followed by sugar analysis yielded 8.3 % arabinose and 0.7% xylose.

Structural Characterization of Cork Lignin by Thioacidolysis and Permanganate Oxidation

Summary Quercus suber L. milled cork lignins obtained from extractive-free cork (MCL) and from saponified cork (MCLsap) were characterized by thioacidolysis and KMnO4 oxidation. These techniques and the previously used analytical pyrolysis revealed that cork contains a guaiacyl lignin (G lignin) with 94–96% guaiacyl-, ca. 3% syringyl-, and 2–3% of 4-hydroxyphenyl-propane units. The total yields of degradation products in thioacidolysis and KMnO4 oxidation experiments were lower in comparison to those of a spruce milled wood lignin (MWLspruce) suggesting a higher cross-linking in the G-lignin of cork. The higher frequency of “condensed” structures (having C-C or C-O-C linkages to aromatic rings) in cork lignin was also manifested in the relative abundance of various aromatic acids obtained by KMnO4 oxidation. The cork lignin (MCLsap) contains only low amounts (ca. 2%) of covalently bonded suberinic acids. Numerous free aliphatic suberinic acids were detected and identified in the ether soluble part of MCLsap. Ferulic acid was not liberated by thioacidolysis, pointing at an in situ acylation. We suggest that the major part of the aromatic domain in cork is a G-lignin but that it includes also another structural moiety with higher H-unit content and linked by thioacidolysis resistant bonds.

Thioacidolysis of enzymatic dehydrogenation polymers from p-hydroxyphenyl, guaiacyl and syringyl precursors

Lignin polymer models (DHPs) were obtained from p-coumaryl, coniferyl and/or sinapyl alcohols under conditions simulating the end-wise or the bulk polymerization modes. Their structures were characterized by thioacidolysis followed by Raney nickel desulfuration in order to investigate the correlative variations of DHP structures with polymerization mode and precursor type. Whatever the precursors. addition rates and final concentrations of monolignols in the dehydrogenative medium appeared discriminatory enough to give rise to end-wise and bulk type DHPs. the former mimicking less imperfectly native lignins. The behavior of the p-hydroxyphenyl precursor. less easily oxidized, is influenced by the presence of other types of precursors. Polymerized alone, it gives rise to a very condensed polymer. In contrast, when copolymerized with G and/or S precursors. it is efficiently involved in labile bonds. H units of the copolymers are mainly terminal units with free phenolic groups, in synthetic DHPs as well as in native lignins.

Determination of Monosaccharide Composition of Eucalyptus globulus Wood by FTIR Spectroscopy

Summary FTIR spectroscopy was used to estimate monosaccharide content in Eucalyptus globulus wood, using the natural variability of the species for calibration and validation of the method . A total of 38 samples from 9 year old trees from provenance trials was used. The composition ranged for glucose from 43.2% to 59.5%, for xylose from 9.4% to 17.8%, for galactose from 0.5% to 5.4%, for mannose from 0% to 2.8%, and for rhamnose from 0.3% to 0.8%, based on extractive-free dry wood. The multivariate analysis gave in general, better results with increased R2, lower SEC and SEP errors, although the univariate method also gave good fits with high coefficient of determination (R2) based on remaining data once outliers were removed. FTIR techniques may be used in large scale breeding programmes to measure wood monosaccharide composition with considerably less effort and in shorter time than wet-lab methods, once a reliable calibration has been made for the species.