Composition and structure of organosolv lignins from four eucalypt species

Lignins were extracted from different species using organosolv process (ethanol/water). Obtained organosolv lignins were characterised by various methods to determine their composition, structure and functional groups with the purpose of evaluating their potential use for obtaining value-added compounds. The purity of organosolv lignins was determined. The total phenols content and the antioxidant power were analysed in order to know the reactivity of lignins. The ratio S/G was determined by nitrobenzene oxidation. In addition, molecular weight distribution, infrared spectroscopy and thermo gravimetrical analysis were carried out in order to determine the physical and chemical properties of organosolv lignins. Obtained organosolv lignins have very high purity and low sugar and inorganic contamination. All organosolv lignins samples have high polydispersity, and lignin from grey ironbark wood had the highest molecular weight average. Among the organosolv lignins, lemon-scented gum showed the highest average value of S/G ratio and the lowest average value of total phenols.     

Effective combinations of functional groups in chemically modified kraft lignins for reduction of aluminum toxicity

Plant growth tests were performed with radish (Raphanus sativa var. radicula Pers.) in culture solutions containing low molecular weight compounds in the presence of aluminum to determine the types of functional groups in kraft lignin (KL) modified with ozone and alkali that contributed to reducing aluminum toxicity. The low molecular weight compounds used in this study contained carboxyl, formyl, methoxyl, alcohol hydroxyl, and phenolic hydroxyl groups. The compounds that had adjacent two carboxyl groups (oxalic acid), carboxyl/alcohol hydroxyl groups (glycolic acid), or carboxyl/formyl groups (glyoxylic acid) were effective in reducing aluminum toxicity. Malonic acid, having two carboxyl groups, also reduced aluminum toxicity. The ability of ozone-treated KLs to reduce aluminum toxicity was considered to be partly due to these chemical structures. Protocatechuic acid, having two adjacent phenolic hydroxyl groups, was also effective in reducing aluminum toxicity. This indicated that the effectiveness of the alkaline-treated KL was partly due to its catechol structure. This report was presented in part at the 58th Annual Meeting of the Japan Wood Research Society, Tsukuba, Japan, March 2008     

Formation of a complex with aluminum by ozone-treated kraft lignins and their low molecular weight fragments

The formation of a complex with aluminum by low molecular weight compounds and saponified ozone-treated kraft lignins was evaluated based on the decrease in pH of their solutions on the addition of 0.1 M AlCl₃. Decreases in pH were observed with the solutions containing compounds having adjacent carboxyl groups (oxalic acid), carboxyl/alcoholic hydroxyl groups (glycolic acid), carboxyl/formyl groups (glyoxylic acid), and phenolic hydroxyl groups (protocatechuic acid) on the addition of 0.1 M AlCl₃. The malonic and phthalic acids, having two carboxyl groups, were also effective. These results show that the compounds were effective in forming complexes with aluminum. This finding corresponds to the fact that aluminum toxicity is reduced by formation of a complex with aluminum, except in phthalic acid. The chemical structures stated above in ozone-treated kraft lignins contribute, at least partly, to the complex with aluminum. The pH of solutions containing saponified ozone-treated kraft lignins and alkaline-treated kraft lignin decreased more than that without modified kraft lignins on the addition of 0.1 M AlCl₃, showing that they were effective in forming a complex with aluminum. The high molecular weight part of saponified ozone-treated kraft lignin was effective in forming a complex with aluminum and in reducing its toxicity.     

The effect of aging on lignins of wood

Summary Samples of different wood species varying in age from 900 to 4400 years and stored during this period under different conditions were analyzed for their lignin content. Lignins isolated from the samples were investigated by IR-spectroscopy. It could be shown that lignin in wood undergoes oxidative changes which lead to a decrease in the amount of lignin isolated by the hydrochloric acid procedure. at Hamburg-Lohbrügge.DAAD Visiting Professor Fellowship to study and do research at the Bundesforschungsanstalt für Forst- und Holzwirtschaft at Hamburg-Lohbrügge.Dedicated to Karl Kratzl on the occasion of his 60th anniversary     

Sulfuric acid bleaching of kraft pulp 1: Bleaching of hardwood and softwood kraft pulps

To develop a new nonchlorine bleaching technology, hardwood and softwood kraft pulps, before and after oxygen-alkali predelignification, were treated with dilute sulfuric acid solutions (pH 1.0-1.8) at 100°C for 1 h and then extracted with aqueous sodium hydroxide at 70°C for l h. Hardwood kraft pulp was successfully bleached. The delignification selectivity was similar to that seen with oxygen-alkali bleaching; and it was greatly enhanced by the addition of sodium nitrate and sodium nitrite. The sulfuric acid bleaching can replace the presently adopted oxygen and chlorine stages if the additives are allowed. This bleaching process was also effective for oxygen-bleached hardwood kraft pulp, but it was less effective for softwood kraft pulp and oxygen-bleached softwood kraft pulp. The effectiveness of the addition of sodium nitrate and sodium nitrite was more apparent for softwood kraft pulp than for hardwood kraft pulp.Part of this report was presented at the 7th International Symposium on Wood and Pulping Chemistry, Beijing, July 1993     

Chemical aspects of kraft pulping

Summary Kraft pulping is interpreted in chemical terms on the basis of results from extensive qualitative and quantitative model experiments. In essence, the behavior of lignin is explained as a competition between degradation reactions, mainly involving aryl ether cleavage with participation of neighboring groups, and condensation reactions, comprising conjugate addition of carbanions to quinone methide intermediates. The initial phase of technical delignification is tentatively ascribed to the cleavage of - and -aryl ether bonds in phenolic lignin units, whereas the cleavage of -aryl ether bonds in non-phenolic lignin units is considered to be the rate-determining reaction of the bulk phase. The residual phase may possibly be attributed to the rupture of C-C linkages and to aryl ether cleavage without neighboring group participation. Experimental support for these correlations is provided. The interplay of the various lignin reactions, illustrated in a summarizing scheme, explains some known observations in kraft pulping.Attention is drawn to analogies between reactions involved in the degradation of carbohydrates and those reponsible for the degradation of lignin. From the chemical standpoint, therefore, the selectivity of delignification is due to differences in the reactivity of the wood polymers, rather than to differences in the mechanisms of the degradation reactions. This fact explains the limitations of selective delignification.Parts of this work have been reported at the Fifth Planary Meeting of the International Academy of Wood Science on Copenhagen, Denmark, June 19, 1976, and at the ACS meetings in Appleton, Wisc., May 17–19, 1978, and Honolulu, Hawaii, April 1–6, 1979     

Sulfuric acid bleaching of kraft pulp III: reactivity of kraft pulping-resistant structures under acidic conditions

To investigate the bleaching mechanism, a lignincarbohydrate complex (LCC) model compound, a vinyl ether-type lignin model dimer, and a hexeneuronic acid model compound were treated with dilute sulfuric acid of different pHs. Beech kraft pulp and red pine kraft pulp were also treated with dilute sulfuric acid and then extracted with aqueous alkali. The amount of hexeneuronic acid degradation products in acid effluents and lignin dissolved in alkali effluents were determined. It was found that the benzyl ether-type LCC bond and the vinyl ether bond in lignin were effectively cleaved under the pH where sulfuric acid bleaching of kraft pulp was effective. Hexeneuronic acid group was also effectively degraded during sulfuric acid bleaching. In beech kraft pulp bleaching, both lignin removal and hexeneuronic acid removal contributed to the kappa number reduction. In red pine bleaching, the contribution of hexeneuronic acid removal was negligible, and most of the kappa number reduction was achieved by the lignin removal.Part of this report was presented at the 9th International Symposium on Wood and Pulping Chemistry, Montreal, July 1997     

Differences in biosyntheses of guaiacyl and syringyl lignins in woods

Summary Metabolic differences in the formation of guaiacyl and syringyl lignins were explained in terms of the different functions of O-methyltransferases and reducing enzymes which participate in methylation and reduction of the hydroxycinnamic acid intermediates in the biosynthetic pathway of these two types of lignins. Sinapyl alcohol was dehydrogenated with peroxidase and H₂O₂ under various reaction conditions. Chemical properties of the dehydrogenation polymers (DHPs) formed were characterized, and the possible occurrence of syringyl lignin in hardwood was discussed. DHP and dimers of p-coumaryl alcohol were also characterized and discussed in relation to the formation of grass lignin which contains p-hydroxyphenyl propane as an additional lignin monomer.The authors are indebted to Messrs. Y. Nakamura and H. Kuroda in this Division and Mr. T. Yamasaki at Kagawa University for their cooperation in the course of these investigations     

Effect of severe thermal treatment on spruce and beech wood lignins

? The structure, proportion and mode of assembly of lignin, celluloses and hemicelluloses have marked effects on the reaction mechanisms during thermal treatment and therefore have a strong influence on the quality of the final product. The effect of treatment conditions, including severe conditions (up to 553 K) and treatment duration (up to 8 h) on the structure of native spruce and beech lignins was studied.

? Lignin content was determined by the Klason method and lignin structure was evaluated by thioacidolysis.

? The results highlighted the strong reactivity of the native spruce and beech lignins towards severe heat treatments. The distinct susceptibility of syringyl (S) and guaiacyl (G) units towards thermal treatment is confirmed by comparing the data for beech and spruce samples. The most severe treatment of spruce wood (280 °C) induced a dramatic enrichment in lignin content together with the almost complete disappearance of G lignin units, whereas a more moderate treatment substantially changed lignin structure by degradation reactions that affect the p-hydroxyphenyl (H) and G lignin units similarly.

? Thioacidolysis revealed that the thermal treatment induces the appearance of vinyl ether structures in spruce lignins. The decreased yield of the G and S thioacidolysis monomers reflects the progressive disappearance of G and S lignin units only involved in β-O-4 bonds and the formation of condensed linkages in proportions related to treatment severity. In severe conditions, β-O-4 linked S units are more degraded than their G homologues.

     

Studies on the delignification of spruce wood by organosolv pulping using SEM-EDXA and TEM

Summary Samples of spruce wood derived from various stages of organosolv pulping were studied by SEM-EDXA and TEM. During the first stage (methanol-water) the lignin content of the secondary walls decreased slowly, whereas in the compound middle lamellae only the reactivity of lignin increased. During the subsequent stage (methanol-NaOH) the delignification proceeded fast in both layers but the residual lignin content in the compound middle lamellae remained higher than in the secondary walls.     

The detection of muconic acid type structures in oxidized lignins by13C NMR spectroscopy

Summary ¹³C NMR spectroscopic studies of spruce oxygen-organosoly lignins indicated the presence of muconic acid type structures. This confirms previous chemical analysis which reached the same conclusion. Resonances of the muconic acid structures in the NMR spectra of oxidized lignins were assigned using a model compound.     

Variation of the phenolic hydroxyl group content in wood lignins

Summary The phenolic hydroxyl group content of wood lignin has been determined in situ by a periodate oxidation method for four softwood and six hardwood species. Hardwood lignins, in contrast to softwood lignins, showed a significant variation among different species in this functional group content which decreased with an increase in the proportion of syringyl units in the wood lignin.Financial support from the Empire State Paper Research Associates is greatly appreciated     

Screening of wood-rotting fungi for kraft pulp bleaching by the Poly R decolorization test and biobleaching of hardwood kraft pulp byPhanerochaete crassa WD1694

From among 419 wood-rotting fungi 10 were selected by the Poly R decolorization test, and their ability to bleach hardwood kraft pulp was assayed. Of the 10 selected, 6 fungi (i.e.,Phanerochaete crassa WD1694 and F150;Pleurotus pulmonarius PSC-H, PSC-M, and PSC-T;and Pleurotus species A119) showed much higher bleaching ability thanPhanerochaete chrysosponum BKMF1767 orTrametes versicolor WD1670, both of which are well-known high ligninolytic fungi.P. crassa WD1694 had the highest bleaching ability among the selected strains, and it increased the pulp brightness from 28 to 54, with a corresponding decrease in kappa number from 16 to 6 after 10 days of cultivation and alkali extraction. MnP was a predominant ligninolytic enzyme ofP. crassa WD1694 during the biobleaching.This research was presented in part at the 46th Annual Meeting of the Japan Wood Research Society, Kumamoto, April 1996