Bark Lignin Research Articles

Characterization of Milled Wood Lignin (MWL) in Loblolly Pine Stem Wood, Residue, and Bark

Milled wood lignin samples from Loblolly pine stem wood, forest residue, and bark were isolated and characterized by quantitative (13)C and (31)P nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), and gel permeation chromatography (GPC) for molecular weight determination. Results from (13)C NMR show the stem wood and forest residue samples have similar functional group contents. However, the bark has fewer methoxyl groups, β-O-4 structures, dibenzodioxocin, and side chains than the other two lignins. The bark lignin has the highest amounts of p-hydroxyphenyl (h) and C-5 condensed lignin, stem wood has the lowest, and the residue lies between. (31)P NMR analysis indicates that bark lignin contains more C-5 substituted phenolics and fewer aliphatic hydroxyl groups than the lignin isolated from stem wood or residue. The molecular weight distribution analysis indicates the bark lignin has higher weight-average molecular weight (M(w)) and polydispersity index than the lignin recovered from stem wood or residue.

Bark decay by the white-rot fungus Lentinula edodes: Polysaccharide loss, lignin resistance and the unmasking of suberin

Abstract The chemical composition of oak bark during growth of Lentinula edodes was studied to assess the transformation of lignin, suberin, tannin and structural polysaccharides. Oak logs (Quercus alba) were decayed by L. edodes over 8 years, during which time they were sampled at five intervals (30, 40, 66, 77, 101 months). Elemental analysis (C, H, N and O), solid-state 13C NMR as well as off-line thermochemolysis in the presence of tetramethylammonium hydroxide (TMAH) with gas chromatography-mass spectrometry were used in the characterization of fresh and degraded barks. Solid-state 13C NMR analysis showed that cellulose and xylans were the main structural components of fresh bark but that L. edodes caused a 46% decrease in polysaccharide content and that loss of crystalline and non-crystalline cellulose regions occurred in parallel. The decrease in cellulose content was accompanied by a relative increase in the proportion of methylene carbon from suberin. The aromatic region of the spectra revealed a loss of a shoulder at 145 ppm attributed to tannins after 30 months decay; in contrast the aromatic content remained unaltered, suggesting that highly structured tannins were degraded in preference to lignin. Chemolytic treatment with TMAH confirmed moderate changes in guaiacyl and syringyl acid-aldehyde ratios with growth indicating that the fungus had not caused extensive oxidative side chain alterations. The ratio of syringyl to guaiacyl units ( S / G ) in fresh oak bark was lower at ∼0.6 than that previously reported for oak sapwood ( S / G > 1 ) and a slight decrease in S / G values was observed with fungal decay. The resistance of bark lignin as compared to sapwood lignin is attributed in part to the inhibiting effect of tannins and suberin on fungal growth.

Eucalyptus bark lignin substituted phenol formaldehyde adhesives: A study on optimization of reaction parameters and characterization

AbstractThe major adhesive resin worldwide used in the manufacture of plywood is phenol formaldehyde resole (PF) resin. The raw material for this kind of adhesive is derived from petroleum oil. Because of rising prices of crude oil and the scarcity of petroleum products, their replacement by natural resource–based raw material has become a necessity. In the present work, the possibility of replacing phenol in PF resin with lignin was explored. The parameters for preparation of bark lignin substituted PF (LPF) adhesive, such as lignin concentration, formaldehyde to phenol molar ratio, catalyst concentration, reaction time, and reaction temperature, were optimized. It was found that up to 50 wt % of phenol can be substituted by lignin to give an LPF adhesive with better bonding strength compared to that of control PF resin. Prepared resins were characterized using IR, DSC, and TGA. IR spectra of LPF adhesive showed structural similarity with that of PF adhesives. Thermal stability of LPF adhesive was found to be lower compared to that of control PF (CPF) adhesive. DSC studies revealed a lower curing temperature for LPF resin than that for CPF resin. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3514–3523, 2004

Chemical characterisation of bark and of alkaline bark extracts from maritime pine grown in Portugal

The chemical composition of maritime pine ( Pinus pinaster) bark and of alkaline bark extracts has been investigated with bark from trees grown in Portugal. Bark is composed of lignin and polyphenolics (ca. 44%), polysaccharides (ca. 39%), dichoromethane, ethanol and water extractives (ca. 17%) and ashes (ca. 1%). The lignin content determined by the Klason method, after the extraction of polyphenolics (tannin-rich fraction) from the bark by alkali solution, is 33.2%. Cellulose content is about 24%. Hemicelluloses (about 15% of bark dry weight) are suggested to be predominantly composed of arabinoglucuronoxylans and minor amounts of galactoglucomanans. The bark lignin is composed by p-hydrophenylpropane and guaiacylpropane units in proportions of 20:80. The condensed tannins are constituted mainly by catechin-type structural units. The direct extraction of bark with aqueous alkaline solutions yields extracts which contain sugars, lignin and condensed tannins. The number average molecular weights ( M n) of alkaline extracts are in the range 1000–1500. The composition and M n of extracted substances depends on the alkaline extraction conditions.

Characterization of the major components in bark from five Japanese tree species for chemical utilization

Characterization of the major components in bark from five Japanese tree species, Pinus densiflora, Larix leptolepis, Cryptomeria japonica, Fagus crenata, Quercus mongolica, was performed from a viewpoint of chemical utilization. Relatively high yields of formaldehyde-condensable polyphenols were obtained from the bark of P. densiflora (22.5%) and L. leptolepis (20.8%) by 1% NaOH extraction. The alkali insoluble residue contained large amounts of neutral sugars (26.1%–40.7%) in comparison with untreated bark. Glucose was generally the dominant sugar in the residue, although the major neutral sugar content in F. crenata was xylose. By successive treatment with 1% NaOH and acid chlorite, a marked decrease in lignin content was observed in P. densiflora. In the other tree species, bark lignin was resistant to acid chlorite treatment to a certain extent.

Structural Characterization of the Bark and Core Lignins from Kenaf (Hibiscus cannabinus)

Dioxane and milled wood lignins were isolated from the core and bark of kenaf (Hibiscus cannabinus), variety Salvador. These lignins were characterized by 13C and 1H NMR, FTIR, and UV spectroscopies, permanganate oxidation, and alkaline hydrolysis followed by GC and GC-MS analysis of the released products and by functional groups analysis. The permanganate oxidation and alkaline hydrolysis was also applied to “in situ” lignins. Isolated and “in situ” lignins showed significant differences in composition and structure. Strong structural differences were observed between bark and core lignins, suggesting their different biosynthetic routes. The β-O-4 type linkages are the main interunit linkages and are more abundant in bark than in core lignin. The core lignin is more “condensed” and shows higher contents of β-β plus β-5 linkages than those in the bark lignin. Permanganate oxidation showed that both core and bark “in situ” lignins are HGS-type lignins with HGS proportions of 15:66:19 and 12:56:32, respectively (H including coumarate structures in the case of core lignin). Coumarates represent about 50% of the H units of core lignin and are absent in bark lignins. The presence of suberin-like aliphatic chains covalently bound to lignin was suggested for bark lignin. Keywords: Lignin; kenaf; Hibiscus cannabinus; 13C NMR; 1H NMR; UV spectroscopy; FTIR spectroscopy; permanganate oxidation; phenolic acids

The Effect of Lignin and Bark Wounding on Susceptibility of Spruce Trees to Dendroctonus micans

The effect of lignified stone cell masses (lignin) and mechanical wounding of bark on gallery formation and oviposition by the spruce bark beetle, Dendroctonus micans, was determined in plantations of Norway and Sitka spruce. When beetles were implanted onto trees that varied in bark lignin concentration, there was a significant negative relationship between lignin and adult gallery size. Only a few larval galleries were established, all of them on trees with a low lignin concentration. Results confirm the importance of lignin as a preformed defence in living trees. Adults excavated significantly larger galleries in wounded than unwounded bark. Most larval galleries were also established in wounded bark. The concentrations of nitrogen, carbohydrate, and resin and the moisture content of wounded and unwounded bark were measured at the beginning of the experiment. A number of significant changes were induced by wounding, including an increase in the concentration of nitrogen and starch, and decreases in the moisture content and the concentration of free sugars. There was no overall effect of wounding on resin content of bark, although concentrations were significantly lower in new than old wounds. An increase in the nutritional quality of bark following wounding appears to be the main factor influencing attacks on wounded trees by D. micans.

Structure and composition of sweet sorghum stalk components

Stem bark and pith of sweet sorghum were analyzed with reference to their sucrose, simple reducing sugars, cellulose, hemicelluloses, lignin and associated phenolic acids contents. Moreover, lignin monomeric units (guaiacyl and syringyl) engaged in non-condensed structures were characterized by thioacidolysis, whereas cell wall associated phenolic acids ( p-coumaric and ferulic acids) were estimated by alkaline hydrolysis at 170°C. The results obtained showed that bark and pith are heterogeneous as far as their chemical composition and the structure of their chemical components are concerned. In particular, the pith content in water soluble sugars is twice as high compared with the one in the bark, whereas bark is enriched in lignocellulosic fibres. Bark lignin is twice as important in content and less condensed in structure compared to pith lignin. p-Coumaric acid is the predominant p-hydroxycinnamic acid associated to the cell walls, whereas ferulic acid is present in significant quantities.

Chemical composition and structural features of the macromolecular components of Hibiscus cannabinus grown in Portugal

Different morphological regions of Hibiscus cannabinus plants grown in Portugal were submitted to chemical composition studies. General chemical composition was determined by established methods. The polysaccharides were fractionated by successive extractions of holocellulose with aqueous KOH solutions. The sugar composition was determined by hydrolysis of polysaccharides followed by gas chromatography (GC) analysis of neutral sugars and spectrophotometric determination of uronic acids. In situ lignins and milled wood lignins (MWL) were characterised by permanganate oxidation followed by GC and GC-MS (mass spectrometry) analysis of the methylated oxidation products. The results of general chemical analysis have evidenced the different relative abundance of holocellulose, lignin, proteins, extractives and ashes in bark, core and foliage, at different stages of maturity. About 70–80% of the core hemicelluloses (about 20% o.d. material) was easily extracted with 5% KOH aqueous solutions against 60–70% (about 15% o.d. material) for the hemicelluloses of the bark. This hemicellulose fraction was composed mainly by glucuronoxylans with high content of uronic acids (xylose: uronic acid: 3–5: 1 for bark and 5–10: 1 for core). The hemicellulose fraction extracted with 24% KOH aqueous solutions was composed mainly by glucuronoxylans (80–90%) and glucomannans (10–15%). The results obtained by the permanganate oxidation method indicated that kenaf lignins are H-G-S type with approximate H: G: S molar proportions of (9–13): (55–60): (27–34) in bark and (14–20): (57)-(74): (12–23) in core, which evidences a high content of H and G units and a relatively low content of S units when compared with traditional dicotyledons. The relative proportion of H, G and S units as well as the structural features of lignins depends on the stage of maturity and on the morphological region of the plant. Kenaf lignins present a lower degree of condensation when compared with traditional wood lignins.

The Influence of Genetic and Environmental Factors on a Quantitative Defensive Trait in Spruce

1. Lignified stone cell masses in Spruce bark are an important physical defence against insects and fungi and in Sitka Spruce and this defensive trait was influenced by both genetic and environmental factors. Single-tree, family and provenance mean heritability of the trait were 0.22, 0.68 and 0.79-0.95 respectively. 2. There was a distinct, clinal, increase in bark lignin with increasing latitude of provenance origin. Relative differences in bark lignin content between provenances were similar at four sites but absolute amounts were strongly site dependent. 3. Tree growth also varied systematically between provenances and differed between sites but we found no compelling evidence of a direct trade-off between growth and this quantitative defence. 4. Variation in growth and defence between provenances appeared to reflect, independently, climatic limitations in the native habitat.

Comparative study of Caribbean pine (Pinus caribaea L.) wood and bark dioxane lignin

The objective of this paper was to depict some differences between Caribbean pine bark and wood lignin. Gas chromotography (GC) of nitrobenzene oxidation products of extracted wood and bark meals and of corresponding dioxane lignins was performed. The isolated lignins were submitted to IR and UV spectrometry, gel permeation chromatography and differential thermo-gravimetry. The data obtained indicate differences in the contents of condensed bis-guaiacyl structures in the lignins. Contents of phenolic hydroxyl and α-carbonyl groups in both lignins do not markedly differ. There are also certain differences in the thermostability and the molecular weights of compared dioxane lignin preparations.

The comparison of chemical and structural differences of Caribean pine (Pinus caribea L.) wood and bark lignin

The presented paper deals with some chemical properties of Caribean pine wood and bark lignin. In order to obtain necessary data, the following operations and analyses were performed: dioxane lignin isolations, determination of Klason lignin, determination of methoxyl, carboxyl and phenolic hydroxyl groups in dioxane lignins and the nitrobenzene oxidation of both compared lignins and of the risidues remaining after dioxane lignins extraction. The oxidation products were analysed by GLC. The experimental data show that there are moderate differences between compared lignins.

The mechanism of the formation of quinonic acids in the oxidation of the bark of the Siberian larch. II

1. It has been shown by chemical and physicochemical methods of analysis that the oxidation of bark lignin by atmospheric oxygen in nitric acid is accompanied by oxidative-condensation and oxidative-hydrolytic processes.

Determination of Total Lignin, Extraneous Substances and Polysaccharides in Bark and Wood ofAcacia penninervis.II. Polysaccharides and Summative Analysis

Article Determination of Total Lignin, Extraneous Substances and Polysaccharides in Bark and Wood of Acacia penninervis. II. Polysaccharides and Summative Analysis was published on January 1, 1974 in the journal Holzforschung (volume 28, issue 6).

Determination of Total Lignin, Extraneous Substances and Polysaccharides in Bark and Wood ofAcacia penninervis.I. Lignin and Extraneous Substances

Determination of Total Lignin, Extraneous Substances and Polysaccharides in Bark and Wood ofAcacia penninervis.I. Lignin and Extraneous Substances