Chemical structures and thermochemical properties of bagasse lignin

1 Introduction Agricultural residues are an important renewable bio- mass resource. The annual production is more than 600 million tons in China. With the reduction of fossil fuel resources, the new trend is to acquire chemicals and energy from renewable resources. To produce green chemicals and clean fuels by developing bio- mass, biorefinery technology is one of the more promising technologies and objectives. Bagasse consists of cellulose, hemicellulose and lignin. Earlier studies have sho…     

Reactivity of a condensed–type lignin model compound in the Mannich reaction and preparation of cationic surfactant from sulfuric acid lignin

 The chemical conversion of phenolized sulfuric acid lignin (P-SAL), prepared from sulfuric acid lignin (SAL) by phenolation with sulfuric acid catalyst, to novel cationic surfactant was investigated. To elucidate the chemical reactivity of the P-SAL to a Mannich reaction, 1-guaiacyl-1-p-hydroxyphenylethane (I) as a simple phenolized sulfuric acid lignin model compound was reacted with dimethylamine and formaldehyde. Quantitative analysis of the products by gas-liquid chromatography suggested that the p-hydroxyphenyl nucleus was more reactive than the guaiacyl nucleus. The Mannich reaction of SAL with dimethylamine did not yield a soluble cationic surfactant, but P-SAL produced water-soluble cationic surfactant in a quantitative yield. The Mannich reaction products (MP-SAL) of P-SAL had 1,3-dimethylaminomethyl groups/C₉-C₆. The results of the surface tension measurements showed that the decrease in surface tension of MP-SAL was much larger than that of lignosulfonate as a commercial surfactant from lignin.     

Rapid assessment of coniferous biomass lignin–carbohydrates with near-infrared spectroscopy

The main objective of this research was to construct accurate near-infrared reflectance (NIR) models of wood chemistry. Wet chemistry procedures and high-performance liquid chromatography methods were employed to analyze the chemical composition of southern pine. The NIR spectra were collected from 21 wood samples, which were milled down to different particle size classes. NIR calibration and prediction models were established using two modeling methods with different pretreatments. Furthermore, the spectrum range used in the NIR models was refined to achieve higher prediction accuracy. Results showed that NIR model precision could be improved considerably by decreasing the particle size to a very fine powder coupled with a targeted spectrum range. Superior prediction models for lignin and holocellulose content were constructed, while models for extractives and cellulose contents were also strong.     

The mechanism of the Mäule colour reaction introduction of methylated syringyl nuclei into softwood lignin

Summary Ezo spruce (Picea jezoensis) wood meal and milled wood lignin were successively reduced with sodium borohydride, methylated with methanol-HCl, oxidized with Fremy's salt, reduced with sodium dithionite, and methylated with diazomethane. Permanganate oxidation of the treated milled wood lignin showed that 0.08–0.1/C9 units of 3,4,5-trimethoxyphenyl groups were introduced into the softwood lignin. Although hardwood meal (beech, Fagus crenata) methylated with diazomethane gave a purple-red colour with the Mäule test, the treated softwood meal gave only a dark brown colour. The aromatic nuclei of lignin were broken down by the Mäule treatment. The consumption of permanganate by treated softwood lignin was higher than by hardwood lignin, which suggests that the guaiacyl nuclei were broken down severely. It is proposed that the purple-red colour obtained from methylated hardwood lignin with the Mäule colour test is generated by reaction of syringyl groups which were liberated by -ether cleavage under the permanganate oxidation conditions.     

Characterization of Brauns’ lignin from fresh and vacuum-dried birch (Betula pendula) wood

Brauns’ lignins present in the methanol extracts of fresh birch (Betula pendula) xylem and of sawn birch board subjected to vacuum drying were characterized by ¹H and ¹³C NMR spectroscopy (1D and 2D), IR spectroscopy, gel permeation chromatography (GPC) and colour measurements (CIELab) in order to find out whether Brauns’ lignin could contribute to the colour change of sawn timber that occurred during vacuum drying. The two Brauns’ lignin samples contained about equal amounts of syringylpropane and guaiacylpropane units linked with β-O-4 and β–β side-chain structures. Molecular weight of the Brauns’ lignin of vacuum-dried birch board (acetylated: 5,200 g mol⁻¹) was higher than that of the Brauns’ lignin of fresh birch wood (acetylated: 4,400 g mol⁻¹). The Brauns’ lignin of vacuum-dried wood was also clearly darker and more prominently yellow and red; between the Brauns’ lignin samples was 23.59. The differences in the molecular weights and colours suggest that the Brauns’ lignin underwent a chemical change during vacuum drying of the wood and that this change may have affected the colour of the wood.     

Isolation of lignin–carbohydrate bonds in wood. Model experiments and preliminary application to pine wood

A novel method for analysis of benzylic ether type lignin–carbohydrate bonds has been developed by using model compounds. Four diastereomers of model compound 3-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-3-(methyl -d-glucopyranoside-6-O-yl)-1-propanol (GGMGP), were ozonized in acetic acid/water/methanol 16:3:1 for 1h at 0°C. The product from ozonation of each diastereomer was saponified and the corresponding -etherified tetronic acid (TAMGP) was isolated using ion exchange chromatography. Minor amounts of methyl -d-glucopyranoside (MGP) and small amounts of a gluconic acid etherified with tetronic acid (TAGLCA), tetronic acid, gluconic acid, and glyceric acid were detected in the product mixture of ozonated benzylic ether type model compounds. The results suggest that a benzyl ether bond between lignin and carbohydrate is rather stable during the ozone treatment. Acid treatments with sulfuric acid or trifluoroacetic acid of the derived TAMGP led to cleavage of the glucosidic bond but only a small amount of products (tetronic acid and glucose) resulting from cleavage of the -ether bond were formed. The successful chemical treatments were used for studies of benzylic ether bonds in Japanese red pine. The results suggest the presence of benzylic ether bonds to polysaccharides in the wood.Part of this paper was presented at the 10th International Symposium of Wood and Pulping Chemistry (ISWPC), Yokohama, 1999; the 11th ISWPC, Nice, 2001; and as a rapid comunication in J Wood Sci (2000) 46:263–265     

Studies of enzymatic oxidation of TMP-fibers and lignin model compounds by a Laccase–Mediator-System using different 14C and 13C techniques

In this work, the results of the enzymatic oxidation of TMP-fibers (thermomechanical pulp) and a well-structured lignin model compound, the dehydropolymer (DHP), were investigated by different ¹⁴C and ¹³C methods, caused by a Laccase–Mediator-System (LMS). These methods are the nuclear magnetic resonance spectroscopy (¹³C-NMR) with DHP (unmarked) and the determination of the ¹⁴CO₂ release of ¹⁴C-marked DHP and TMP-fibers. The ¹³C-NMR measurements were chosen to analyze the structural changes of the LMS-treated DHP model compounds and TMP-fibers qualitatively and quantitatively. The data of ¹⁴CO₂ release give an explanation of the demethylation of DHP and TMP-fibers. The effect of the LMS is shown by comparing the results in respect of DHP and TMP-fibers, which were only treated with laccase and of an inactivated LMS as the control. Comparing the results of the ¹³C-NMR method, in particular the use of the Mediator during the enzymatical treatment, showed significant changes in the structure of the DHP. Also, the TMP-fibers were materially influenced by the LMS. The analysis of the ¹⁴CO₂ release data of the ¹⁴C-marked DHP and TMP-fibers revealed that the rate of ¹⁴CO₂ increases in the ¹⁴C-2 atom as well as in the O¹⁴CH₃ group within the first hour of Laccase–Mediator incubation. Therefore, the ¹⁴CO₂ release from the DHP was higher than from the TMP-fibers.     

Semi-quantitative method to evaluate the α-carbonyl content in lignin

A method to estimate the content of -carbonyl structures in lignin was developed. This method consists of two successive treatments: NaBD₄ treatment of pulp to reduce an -carbonyl structure in lignin, and nitrobenzene oxidation. NaBD₄ was used to convert an -carbonyl structure to a deuterium-labeled hydroxymethine structure. The ratio of D-vanillin [(HO)(H₃CO)C₆H₃CDO] to H-vanillin [(HO)(H₃CO)C₆H₃CHO] or that of their syringyl analogues obtained by nitrobenzene oxidation was used as the measure of the content of -carbonyl structure. Model experiments demonstrated that when sodium hydroxide was used as alkali for the nitrobenzene oxidation, the retention of deuterium at the side chain -position was very low due to the displacement of deuterium with hydrogen by an unknown reaction mechanism. In order to depress this unexpected displacement, the reaction conditions of the nitrobenzene oxidation were modified. The modified nitrobenzene oxidation employs 0.5mol/l of lithium hydroxide as a reaction medium instead of 2.0mol/l sodium hydroxide. By this modification, this method could successfully trace the formation and the degradation of the -carbonyl structure in milled wood lignins.This paper was presented in part at the 11th International Symposium on Wood and Pulping Chemistry, Nice, France, June 2001 and at the 46th Lignin Symposium, Kyoto, Japan, November 2001     

Synergistic contribution of hydrosulfide and carbonate anions to the β-O-4 bond cleavage of lignin model compounds in a green liquor pretreatment for enzymatic hydrolysis of lignocellulosic materials

To examine why green liquor (GL) pretreatment of lignocellulosic materials effectively facilitates enzymatic saccharification under conditions milder than those of a common alkaline cooking process, dimeric β-O-4 type lignin model compounds with and without free phenolic hydroxyl group were reacted in several alkaline solutions including a model solution of GL, which mainly contains Na₂CO₃ and Na₂S. The β-O-4 bond of the phenolic model compound was cleaved with a sufficient rate in the model solution of GL. The β-O-4 bond cleavage of the non-phenolic model compound was more frequent in the model solution of GL than in other alkaline solutions. These results suggest that β-O-4 bonds present in lignocellulosic materials are effectively cleaved in a GL pretreatment. It was also suggested that HS^? and CO₃ ^2? synergistically contribute to the β-O-4 bond cleavage of the non-phenolic model compound under GL pretreatment conditions.     

Characteristic fragment ions from lignin and polysaccharides in ToF–SIMS

Different model compounds for lignin, hemicelluloses and pectins were studied by time-of-flight secondary-ion mass spectrometry (ToF–SIMS). Mass spectra of Klason lignin from normal and compression spruce wood, aspen wood and wheat straw were compared. Spectra of brominated spruce and aspen wood sections showed fragment ions attributed to brominated guaiacyl and syringyl units in lignin at m/z 215, 217, 229 and 231, and m/z 245, 247, 249 and 261, respectively. Spectra of mono-, oligo- and polysaccharides showed fragment ions at m/z 127 and 145 characteristic for hexose units, and ions at m/z 115 and 133 characteristic for pentose units. The same ions were detected in spectra of delignified spruce and aspen wood sections. Labelling of anionic groups by Sr²⁺ ions followed by ToF–SIMS analysis showed that pectins were present at specific locations on the surfaces of spruce and aspen wood sections still after delignification with hydrogen peroxide in acetic acid.     

Establishment of in vitro culture of Populus euphratica Olivier

The purpose of our study was to establish a regeneration system for micropropagation of Populus euphratica Olivier. On the basis of an analysis of plant leaf mineral nutrients, a special medium was proposed, called MP2. In optimizing media for in vitro plant cultures including MS, B5 and MP2 media we employed hormones, auxin IAA, cytokine benzyladenine (BAP) and gibberellic acid (GA) in our factorial experiments on media. Adventitious shoots were derived from cuttings of adult plants taken from Xingjiang, west China, on selected media with MP2 0.5 mg·L-1 BA 0.1 mg·L-1 NAA. The shoots were elongated on a medium with 0.25 mg·L-1 BAP, 0.1 mg·L-1 NAA and 2 mg·L-1 GA and were then rooted on a medium with 0.2-0.5 mg·L-1 IBA. All the media were incorporated with 30 g·L-1 sucrose and an adjusted pH at 6.3.     

Specific degradation ofβ-aryl ether linkage in synthetic lignin (dehydrogenative polymerizate) by bacterial enzymes ofSphingomonas paucimobilis SYK-6 produced in recombinantEscherichia coli

Sphingomonas paucimobilis SYK-6 produces unique and specific enzymes, such as-etherases,O-demethylases, and ring fission dioxygenases, for lignin degradation. Cleavage of arylglycerol--aryl ether linkage is the most important process in the lignin metabolic pathway ofS. paucimobilis SYK-6. We reported the genes (ligD, ligE, ligF) for enzymes that cleaved-aryl ether linkage of dimeric compounds in previous studies. In this study we synthesized the fluorescent high-molecular-weight lignin (UBE-DHP) by dehydrogenative polymerization. We investigated the-aryl ether cleavage ability of these enzymes produced in recombinantEscherichia coli. When UBE-DHP was incubated with LigF, 4-methylumbeliferone was released as a result of-aryl ether cleavage of O-methylumbelliferyl--hydroxypropiovanillone (compound III) incorporated in UBE-DHP. Here, we report that-etherase ofS. paucimobilis SYK-6 can be expressed inE. coli and is able to cleave the-aryl ether linkage in synthetic high-molecular-weight lignin.     

Revisiting the mechanism of <Emphasis Type="Italic">β-O</Emphasis>-4 bond cleavage during acidolysis of lignin IV: dependence of acidolysis reaction on the type of acid

The dependence of the acidolysis reaction of a C₆-C₃ dimeric nonphenolic β-O-4 type lignin model compound, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl) propane-1,3-diol (veratrylglycerol-β-guaiacyl ether, VG), on the type of acid applied was examined using three different acids [0.2 mol/l HCl, 0.2 mol/l HBr, and 0.1 mol/l (0.2 N) H₂SO₄ in 82% aqueous 1,4-dioxane at 85°C]. In the HCl system, the major reaction modes of the corresponding benzyl cation-type intermediate (BC), which is produced by protonation of the α-hydroxyl group of VG and successive release of the water molecule, are the abstraction of the β-proton and hydride transfer from the β-to the α-position. The liberation of formaldehyde from the γ-hydroxymethyl group of BC is the predominant reaction mode in the H₂SO₄ system. Apparently, an unknown reaction mode or modes is operative in the early stage of the HBr system that causes rapid disappearance of VG accompanied by the quantitative formation of 2-methoxyphenol without affording the common counterpart of a Hibbert’s ketone, 1-hydroxy-3-(3,4-dimethoxyphenyl) propan-2-one. The reaction mode in the HBr system changes with the progress of the reaction and is the same as that in the HCl system after the early stage.     

Properties of Wood/Montmorillonite Nanocomposites

INTRODUCTIONWood possesses many special properties, such asbeautiful grain, natural color, high strength-to-weightratio, good electricity and heat insulation; and it can beeasily processed, glued or dyed. It is biodegradable,recyclable and environmental-friendly (Wang Tianminet al. 2002). But as a biomaterial, it also has intrinsicdefects as easy decaying, burning and deforming,which largely limits its usage. Nano science andtechnology opens a completely new way to developwood composites…