Lignin-carbohydrate bonds in a lignin-carbohydrate complex isolated from spruce

Summary The origin of the lignin-carbohydrate bonding in a lignin-carbohydrate complex isolated by a modified Björkman procedure is discussed. The results obtained from sugar analysis, methylation analysis, deuterium labelling of reducing end groups and gel permeation chromatography are used to evaluate different proposed models for the lignin-carbohydrate bonding.I wish to express my gratitude to Dr. Bengt Lindgren for valuable discussions, to Stiftelsen Nils and Dorthi Troedssons Forskingsfond for financial support and Dr. Antomy Bristow for linguistic revision     

Structural changes of residual lignin in softwood kraft pulp treated with manganese peroxidase

Structural changes of residual lignin in unbleached softwood kraft pulp (SWKP) during manganese peroxidase (MnP) treatment were investigated to obtain some understanding of the biobleaching action of SWKP with MnP treatment. Alkaline-extracted lignin from darkened SWKP by MnP showed more intense color and contained moreo-quinone than that from control SWKP. However, no difference in the conjugated-carbonyl was observed between the lignins from MnP-treated and control SWKP. The nitrobenzene oxidation analysis revealed that oxidative condensation of non-condensed lignin in SWKP occurs during an early stage of MnP treatment. These observations were supported by the model experiment in which the lignin prepared from control SWKP was subjected to MnP treatments three times, and the changes of color and functional groups in the lignin were determined after each treatment. These results suggested that an increase ino-quinone and the condensation reaction of non-condensed lignin in SWKP are responsible for the characteristic darkening of SWKP during MnP treatment. It was also ascertained that darkened lignin was degraded and brightened by repeated MnP treatments.     

Proteins in Norway spruce thermomechanical pulp

Two methods of cytochemical staining using Coomassie dye and Cu⁺-bicinchoninic acid, respectively, showed that there are proteins in thermomechanical pulp (TMP) of Norway spruce. Protein isolated from TMP was analyzed for amino acid composition. There was about twice the amount of acidic amino acid material compared with basic amino acids, and the presence of glucosamine indicated that the isolated polypeptides also contained glycoproteins. The presence of proteins in ray cells and fiber tracheids in TMP adds to the chemical heterogeneity of the structurally complex high-yield pulp.     

Isolation of lignin from spruce by acidolysis in dioxane

Summary Acidolysis of spruce wood (Picea abies) corresponded to a pseudo-first order reaction mechanism. While anhydrous methanolis a better medium for wood acidolysis than anhydrous dioxane, after addition of 10% water dioxane became about twice as effective as methanol. The results are discussed in terms of acidity functions (H), solubility parameters and condensation effects. Infrared spectra of dioxane lignins showed a similar re-arrangement of side chain carboxyl groups from to position, as was observed previously during acidolysis in methanol.     

The occurrence of non-cyclic benzyl ether bonds in lignin

Summary The structure of the non-cyclic benzyl aryl (-0-4) ethers 4 and 5, proposed by Freudenberg and Friedmann (1960) and recently boubted by Leary (1980), is discussed on the basis of previously published experimental results. Further evidence in favor of the occurrence of non-cyclic -0-4 bonds in lignin is provided. A critical comment is, however, given on the formation of non-cyclic -0- bonds in lignin according to Leary (1980).     

The occurrence of benzyl non-cyclic ether bonds in lignin

Summary A reply to the note by Nimz (1981) on the occurrence of benzyl non-cyclic ether bonds in lignin.     

Comparison between 10,000-year old and contemporary spruce lignin

Wood from white spruce Picea glauca that had been preserved by rapid burial in lake sediments 10,000 years ago, was investigated and compared to a contemporary reference white spruce wood. The 10,000-year old sample appeared to have an intact primary cell wall and middle lamella, whereas the carbohydrate monomer distribution, and microscopic images showed that the secondary wall was at least partially removed, indicating that this structure had been selectively attacked by bacteria. The Klason lignin amount in the aged spruce was found to be 60%. The relative lignin monomer content in the aged spruce was 9% lower than that of the reference wood, showing that there were fewer β-O-4′ linkages in the aged sample. This finding was supported by SEC analysis of the thioacidolysed samples as a larger proportion of lignin oligomers were observed in the aged spruce than in the reference material. This indicates a somewhat greater number of condensed bonds in the aged spruce than in the reference spruce sample. Quantitative ¹³C NMR analysis and HSQC techniques applied on milled wood lignins (MWL) revealed no significant structural differences between the aged spruce and the reference.     

Characteristics of lignin obtained from steam-exploded softwood with soda/anthraquinone pulping

Lignins were obtained from a mixture of softwood sawdust using a hydrolytic pretreatment and a subsequent soda-anthraquinone delignification/pulping stage. Their potential uses and the effect of the pretreatment conditions on the yield (% of recovered lignin from black liquors) and chemical composition of isolated lignins were evaluated. The severity factor used combined the temperature and time of the hydrolytic process in a single ordinate (R_o). The severity range was modified from log R_o = 2.6 to log R_o = 4.6 and the pulping conditions were constant throughout the experiments. The effect of the cooking time on the chemical composition of precipitated lignins was also studied between 135–170 min for original (non-pretreated) material. Yield, elemental analysis, molecular weight distribution, Fourier transform infrared spectra (FTIR), structure, and the methoxyl and aliphatic/aromatic alcohol content of the various lignins, were compared.     

Distribution of structure and lignin within growth rings of Norway spruce

A radial core from a Norway spruce (Picea abies (L.) Karst.) estimated to be about 107 years old was cut from a board and was analyzed for density and microfibril angle (MFA). Furthermore, cell geometry, wall thickness and lignin distribution were analyzed on three selected growth rings in detail. Intra-ring differences in the density profiles are also true for cell wall thicknesses as well as radial and tangential lumen diameters. A higher MFA was found for earlywood with a slow decrease toward the latewood region. The lignin was found to remain rather constant throughout the growth rings, which suggests a constant chemical composition of the cell wall material within the growth ring. From the recorded datasets on a cellular level, it can be concluded that the main adaptation regarding structure–property relationships toward the optimization of water transport and mechanical stability is mainly achieved at the cell level.     

Sorption of kraft lignin from spent liquors on pulp fibres

In this investigation, the sorption of kraft lignin (KL) from spent liquors, membrane filtrated and model KL liquors on fully bleached softwood kraft pulp fibres, was studied. The time, temperature and alkalinity during the sorption experiments were chosen to reflect the conditions of black liquor impregnation of chips before the cooking operation. The amount of sorbed KL was estimated by brightness and kappa number measurements. A linear correlation between the k value and the kappa number was found. Among the parameters investigated, the concentration of metal non-process elements was found the most crucial for the sorption of KL on pulp fibres under black liquor impregnation. The influences of KL concentration, metal ion profile and KL molecular weight distribution on the KL sorption behaviour under black liquor impregnation are discussed.     

Oxidative cleavage of lignin aromatics during chlorine bleaching of kraft pulp

Methanol liberation and methoxyl loss during chlorine bleaching of softwood kraft pulp were quantitatively investigated to estimate the degree of structural modification of lignin aromatics. An increase in the chlorine multiple led to enhanced methoxyl loss from lignin. Our result, using pH-adjusted chlorine water (pH 5.7), by which chlorination under oxidation-favorable conditions was achieved, strongly supported the importance of the oxidation reaction by chlorine during delignification and lignin degradation. It was also suggested that methanol can be produced not only via catalytic hydrolysis by chlorine but via oxidative cleavage of the ether bond as well. The infrared spectrum of chlorolignins suggested that chlorine oxidation can open aromatic rings to muconic acid derivatives without cleaving ether bonding of the methoxyl group. No straight relation between the methoxyl content and the kappa number of chlorinated pulps was shown. The methoxyl content of bleached kraft pulps subjected to successive chlorination and alkali extraction showed a good relation with the kappa number. This means that almost all the portions of the oxidatively modified lignin structure were successfully removed during these treatments, and the aromatic structures of residual lignin in chlorinated and alkali-extracted pulps were thought to remain intact.Part of this paper was presented at the 46th Annual Meeting of the Japan Wood Research Society, Kumamoto, April 1996; the 10th International Symposium on Wood and Pulping Chemistry, Yokohama, June 1999; and the 67th Pulp and Paper Research Conference, Tokyo, June 2000     

木质素合成关键酶基因与造纸植物转基因改良应用研究

木质素是自然界数量仅次于纤维素的自然有机物质,但在造纸业中是主要的污染来源。木质素生物合成过程十分复杂,涉及了大量酶体系。综述了木质素合成途径中的关键调控酶特性及其基因调控情况,从培育低木质素、易降解木质素的造纸植物为出发点,分析了这些关键基因在转基因造纸植物应用中的潜力和存在的主要问题,并提出了应从改变植物体内木质素含量、改变木质素单体构成比例这两个方面进行转基因的研究思路。     

Structural studies on the chemical bonds between lignins and carbohydrates in spruce wood

Summary A lignin-carbohydrate material from black spruce (Picea mariana) was treated with a hemicellulase mixture. The carbohydrates in the remaining material were studied by the following methods. a) Treatment with 0.1 M NaOH in the presence of sodium borohydride followed by selective hydrolysis of the furanosidic bonds, b) Smith degradation (periodate oxidation followed by mild acid hydrolysis). The results obtained indicate that lignin is bound to all types of sugar units in the hemicelluloses. For arabino-4-O-methylglucuronoxylan, linkages to the side-chain units seem to dominate. The links to the 4-O-methylglucuronic acid units are ester bonds, probably benzyl ester bonds. Those to the other sugar units in the hemicelluloses are ether bonds, probably benzyl ether bonds. The results suggest, furthermore, that fractions of cellulose are linked to lignin.The authors are indebted to Dr. H. H. Brownell, Ottawa, Canada, for a gift of extracted black spruce wood meal, and to Professor Bengt Lindberg, Stockholm, Sweden, for the use of glc equipment in his laboratory     

The occurrence of p-hydroxyphenylpropane units in the middle-lamella lignin of spruce (Picea abies)

Summary A sieving technique has been developed for the separation of middle-lamella fragments. The middle-lamella fraction as well as the whole wood and compression wood from Picea abies have been analysed by nitrobenzene oxidation and acidolysis in order to determine the content of p-hydroxyphenylpropane units in the middle-lamella lignin. These analyses revealed only traces of p-hydroxyphenylpropane units in the whole wood and in the middle-lamella fraction but considerable amounts were found in compression-wood lignin. This points to the fact that middle-lamella lignin is of guaiacyl nature and that earlier results reporting high proportions of p-hydroxyphenylpropane units in the middle lamella-lignin may be due to the inclusion of compression wood in the fraction studied. The acidolysis experiments further indicate that the middle-lamella lignin has fewer uncondensed -0-4 aryl ether structures than the whole wood lignin.The skilful technical assistance of Mrs. Britta Samuelsson and Mr. Johan Lindberg is highly appreciated. The author also thanks Dr. Knut Lundquist for supplying some of the reference compounds, and Dr. Hanne-Lise Hardell for help with the microscopic pictures     

Heterogeneity of lignin concentration in cell corner middle lamella of white birch and black spruce

Summary Raman microprobe spectroscopy was used to study the concentration of lignocellulosics in the cell corner middle lamella. Spectra obtained from 1.6 m regions, from 30 cell corner middle lamellae of both birch and spruce, showed the presence of lignin. However, the relative concentration of lignin to cellulose varied considerably. These results corroborate the view expressed in previous reports of the need for caution in using the lignin concentration values of cell corner middle lamella as a internal reference for studying the variation of lignin concentration in other morphological regions of the cell wall, such as secondary cell wall layers.The use of trade or firm names in this publication is for reader information and does not imply endorsement by the U.S. Department of Agriculture of any product or service     

The effect of isolation method on the chemical structure of residual lignin

Two methods are used for the isolation of residual lignin: acidolytic and enzymatic hydrolysis. Recently a two-step procedure that is a combination of enzymatic and acidic hydrolyses was proposed. In this paper, the structures of residual lignins isolated by these three methods are compared. Enzymatic hydrolysis gave lignin with the highest yield (83%); however, it contained high amounts of carbohydrates and protein. The molar mass of enzymatic lignin was the highest, indicating that no cleavage of lignin occurred. Acidolysis gave a significantly lower lignin yield (40%), but this lignin was practically free from impurities. The -aryl ether and lignin-carbohydrate linkages cleaved during the isolation, which was manifested in the decreased molar mass of the lignin as well as in increased phenolic hydroxyl group content. The new two-step isolation procedure gave properties between the preparations of enzymatic and acidolytic hydrolyses. The lignin yield was high (78%), but it contained some impurities, although less than the enzymatic lignin. The lignin-carbohydrate linkages cleaved to some extent, but the -aryl ether linkages remained intact.Y. Sun also affiliated with the Pulp and Paper Research Institute of Canada (PAPRICAN), Pulp and Paper Research Centre, McGill University.     

Chemical structural elucidation of total lignins in woods I: fractionation of the lignin in residual wood meal after extraction of milled wood lignin

Residual wood meal after extraction of milled wood lignin (WMEM) ofEucalyptus globulus was extracted with alkali and LiCl/N,N-Dimethylacetamide (DMAc). These agents dissolve mainly hemicellulose and cellulose, respectively. The extractability of WMEM in alkali solutions was influenced by the degree of swelling of the cellulose. Under good swelling conditions, considerable amounts of cellulose and lignin were extracted with the hemicellulose. Maximum extractability was about 60% of the WMEM under optimum conditions (3 M or 5 M LiOH or 3M NaOH solution). Some portion of cellulose was extracted with LiCl/DMAc at room temperature. Thus, lignin inE. globulus WMEM was divided into three fractions: hemicellulose-lignin fraction, cellulose-lignin fraction, and insoluble-lignin fraction.Part of this work was presented at the 49th annual meeting of the Japan Wood Research Society, Tokyo, April 1999; and at the 50th annual meeting of the Japan Wood Research Society, Kyoto, April 2000     

Distribution of lignin interunit bonds in the differentiating xylem of compression and normal woods of Pinus thunbergii

The lignification process and lignin distribution at different stages of cell wall differentiation in the secondary xylem of compression and normal woods of Pinus thunbergii were investigated by thioacidolysis and subsequent desulfuration. We prepared 50-µm-thick, contiguous tangential sections of pine shoots, cut from the cambial zone through to mature xylem. In compression wood, uncondensed guaiacyl (G) and p-hydroxyphenyl (H) lignins were deposited simultaneously from early to late stages of lignification. The various types of G-G, G-H, and H-H dimers were detected in compression wood, and the ratio of G-H and H-H dimers to total dimers increased as lignification proceeded. In contrast, uncondensed and condensed H units were detected in trace amounts in normal wood. Significant differences in the relative distributions of lignin interunit linkages were not observed between compression and normal woods or between differentiating and mature xylems in either compression or normal woods.Part of this report was presented at the 10th International Symposium on Wood and Pulping Chemistry, Yokohama, June, 1999     

Studies on milled wood lignin from spruce Part II. Electron microscopic observations on the milled wood

Summary Wood samples that had been ball-milled and extracted with dioxane under various conditions were observed in the scanning electron microscope. Ball milling causes not only a reduction in size of the cells and cell walls but also an internal disruption of the particles. The intensity of milling has a larger influence on the particle size than a prolongation of the milling time. A direct relation was established between particle size and the previously determined yield of purified milled wood lignin.Submitted by Erwin-Riesch-Stiftung zur Förderung der wissenschaftlichen Forschung.     

Influence of pulping variables on the properties of Elaeis guineensis soda pulp as evaluated by response surface methodology

Response surface methodology with central composite design was used to investigate the influence of pulping conditions, viz. cooking temperature, time-at-temperature and alkali charge for alkaline pulping of oil palm empty fruit bunch fibres, on the properties of the pulp and paper obtained (screened yield, Kappa number, tensile and tear indices). Quadratic models consisting of the three independent variables were found to accurately describe the pulping of this material with correlation between the actual and predicted values of the response variables having a relatively good degree of R². The delignification of oil palm empty fruit bunch fibre can be achieved with ease using sodium hydroxide as the sole cooking agent to about 30–45% yield with the process greatly enhanced by an increase in temperature. Although, a relatively low temperature (about 160°C) within the limits of pulping time (60–120 min) and of alkali charge between 20 and 30% is generally sufficient.