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.     

Characterisation of the Monomeric Composition ofin situWheat Straw Lignins by Alkaline Nitrobenzene Oxidation: Effect of Temperature and Reaction Time

The effect of temperature and time on the recovery yield of the products of alkaline nitrobenzene oxidation of in situ lignins in wheat straw internodes and corresponding leaves were studied. The results showed that significant variations in the yields of aromatic aldehydes ( p -hydroxybenzaldehyde, vanillin and syringaldehyde) as well as hydroxycinnamic acids ( p -coumaric and ferulic acids) arise from changes in the temperature and the reaction time. The conditions for maximum yield depend on the aldehyde concerned. For example, the yield of p -hydroxybenzaldehyde increases with increasing temperature and reaction time. This phenomenon could be attributed to the low relative reactivity related to the specific electronic structure of the non-methoxylated units and/or to the existence of specific condensation reactions involving the p -hydroxyphenyl aromatic ring. Finally, the results indicate a much higher complexity of Grami-neae lignins compared to those derived from hardwoods and softwoods.     

Pyrolytic and hydrogenolytic degradation studies on lignocellulosics,pulps and lignins

Wood and MWL's from beech, spruce, bamboo as well as teak wood and teak-HCl-lignin were subjected to analytical pyrolysis (Py), using the off-line approach, and to hydrogenolysis (Hy). Gas chromatography-mass spectrometry (GCMS) was used for product identification and assignment as derivatives from 4-hydroxy-phenyl-propane, guaiacylpropane and syringylpropane basic units followed by capillary gas chromatography (GC) for quantitative determination of the phenolics. The results are compared with those of nitrobenzene oxidation and quantitative FTIR-spectroscopy. Py-GC and Hy-GC experiments were also used for the characterization of residual lignins in kraft and alkaline-sulphite-anthraquinone-methanol (ASAM) pulps from beech, pine and sugar cane bagasse. Analytical pyrolysis of biomass, both in on-line and off-line approach, is well suitable for lignin classification even without previous lignin isolation. Hydrogenolysis is more recommendable for the characterization of residual lignins in pulps.     

Lignin in wheat internodes. Part 1: The reactivities of lignin units during alkaline nitrobenzene oxidation

The alkaline nitrobenzene procedure for determining lignin building units has been applied to wheat internodes. The effect of reaction time and temperature on the rate of reaction has been measured and the nature of the aldehyde and acid products determined by gas-liquid chromatography. Survival factors for individual phenolic compounds were determined and found to be in the range 0.85–4.99, and were constant for each compound under the reaction conditions (c 6 % nitrobenzene in 2 M NaOH, 170°C, 2 h in a stainless steel pressure vessel), optimised for maximum recovery of products using wood and wheat internode meals. The reaction products fiom 24 monomeric and dimeric lignin model compounds were quantitativety determined to provide information on the susceptibility of various lignin structures to alkaline nitrobenzene oxidation. The results of these and earlier studies by other authors suggest that at the higher temperature a heterolytic reaction mechanism is operating on nitrobenzene oxidation conditions. On nitrobenzene oxidation, ferulic and p-coumaric acids survived in amounts which allowed the procedure to be used, with appropriate correction factors, to determine the nature and amount of these cinnamic acids associated with walls of grasses.     

Analytical pyrolysis and FTIR spectroscopy of fossil Sequoiadendron giganteum (Lindl.) wood and MWLs isolated hereof

Recent and fossil woods from the genus of Sequoiadendron, as well as their milled wood lignins were investigated by means of FTIR spectroscopy and pyrolysis GC/MS technique. Though almost same in appearance the differences in band intensities of FTIR-spectra reveals the distinctly increased aromatic character and the oxidation in fossil specimens. More detailed information about the changes in old wood were obtained by analytical pyrolysis, which delivers degradation products with shortened side chains and more saturated units relating to fossil lignin.     

Accretion reactions of octanal catalyzed by sulfuric acid: product identification, reaction pathways, and atmospheric implications

Atmospheric accretion reactions of octanal with sulfuric acid as a catalyst were investigated in bulk liquid-liquid experiments and gas-particle experiments. In bulk studies, trioxane, alpha,beta-unsaturated aldehyde, and trialkyl benzene were identified by gas chromatography-mass spectrometry as major reaction products with increasing sulfuric acid concentrations (0-86 wt%). Cyclotrimerization and one or multiple steps of aldol condensation are proposed as possible accretion reaction pathways. High molecular weight (up to 700 Da) oligomers were also observed by electrospray ionization-mass spectrometry in reactions under extremely high acid concentration conditions (86 wt%). Gas-particle experiments using a reaction cell were carried out using both high (approximately 20 ppmv) and low (approximately 900 ppbv) gas-phase octanal concentrations under a wide range of relative humidity (RH, from < 1% to 50%, corresponding to > 80 wt% to 43 wt% H2SO4) and long reaction durations (24 h). One or multiple steps of aldol condensation occurred under low RH (< 1% and 10%, > 80 wt% and 64 wt% H2SO4, respectively) and high octanal concentration (approximately 20 ppmv) conditions. No cyclotrimerization was observed in the gas-particle experiments even under RH conditions corresponding to similar sulfuric acid concentration conditions that favor cyclotrimerization in bulk studies. No accretion reaction product was found in the low octanal concentration (approximately 900 ppbv) experiments, which indicates that the accretion reactions are not significant as expected when the gas-phase octanal concentration is low. A kinetic analysis of the first-step aldol condensation product was performed to understand the discrepancies between the bulk and gas-particle experiments and between the high and low octanal concentrations in the gas-particle experiments. The comparisons between experimental results and kinetic estimations suggest that caution should be exercised in the extrapolation of laboratory experiment results to ambient conditions.     

Die Verwendung von Ablaugenlignin bei der Herstellung von Holzwerkstoffen

Lignins occurring in the spent liquors of pulp mills constitute large potentials as raw materials for wood adhesives. As a polyphenol, lignin contains reactive sites for condensation with formaldehyde or intramolecular reactions leading to cross-linked, insoluble resins. However, condensation reactions of this type need high temperatures or mineral acids. Another procedure consists of radical cross-linking by oxidative coupling. Up to now these procedures have not found technical application, due to corrosion and other problems. In contrast, up to 25% of conventionally used phenolic resin adhesives can presently be substituted by technical spent sulfite liquor.     

Zum Aufschluß von Kiefern-Kernholz nach dem Sulfitverfahren

Pine heartwood can not be pulped under strongly acid sulfite conditions, because condensation reactions between pinosylvin and lignin will cause a high reject content. Pinosylvin, isolated from pine heartwood, was treated under sulfite conditions at pH values between 1.7 and 4.2. It could be shown, that at low pH-values a great part of the pinosylvin remains undissolved, while at higher pH-values sulfonation and polymerisation reactions contribute to the solubility of pinosylvin. If a mixture of milled-wood-lignin and pinosylvin is treated under conditions of a magnefite cook (pH 4.6), lignosulfonates and a sulfonated watersoluble reaction product of pinosylvin and MWL is created. Pulping pine heartwood under strongly acid conditions using a process with two temperature phases (160 and 135 °C) leads to a pulp with a kappa number of 37 and a reject content of 10%.     

Reactive Maillard intermediates leading to coloured products — 5-hydroxymethyl- and 5-(1,2-dihydroxyethyl)-3(2H)-furanone

In the course of the Maillard reaction, labile sugar degradation products are formed that are susceptible to secondary reactions and therefore have a decisive influence on the product spectrum. Such reactive intermediates may be transformed into stable derivatives with trapping reagents, and thus be protected from further reactions. Secondary processes may also be forestalled if the primary products are removed from the reaction mixture by high-vacuum distillation. By this procedure, 5-hydroxymethyl- and 5-(1,2-dihydroxyethyl)-3(2H)-furanone have been identified directly from Maillard reaction mixtures for the first time. The activated methylene group of these 3(2H)-furanones can easily enter into condensation reactions. The coloured condensation products in turn react with primary amines to pyrrolinone derivatives, which may also contribute to the colouring observed in non-enzymatic browning.     

Effect of fixation time on leaching of copper-ethanolamine based wood preservatives

Fixation in copper-ethanolamine treated Norway spruce wood is finished in the first or in the second week after impregnation depending on the concentration of wood preservatives used. However, copper losses increased after four weeks of fixation again, presumably due to lignin depolymerisation caused by ethanolamine.     

Ethanol extractives of fossil Sequoia wood

Except for small amounts of neutral compounds, the ethanol extracts from fossil Sequoia wood contained over 80% polymeric substances. The bulk of materials was separated into fractions by column chromatography and investigated by means of UV- and FTIR spectroscopy. According to the results the polymeric products are a type of Brauns lignins. Both spectroscopic data revealed considerable changes in. composition and constitution of lignin.     

Die Rolle des Holzes als Chemierohstoff und Energieträger

Apart from the most important technical and economic utilization of cellulose in pulping, papermaking and in the production of cellulose derivatives, macromolecular wood components offer the production of a wide range of chemicals hitherto derived from fossil material, particularly from petroleum. For example ethanol can be produced, which is used for chemical and energetic purposes and may serve as basic material for a number of synthetic polymers. Compounds like furfural, xylitol, acetic acid as well as yeasts and proteins can be derived from polyoses. Technical lignins have a wide range of application due to their dispersing, binding, and surface-active propertics. Special chemical and thermal lignin degradation reactions yield products such as phenols, hydrocarbons, organic acids and important solvents.     

Effect of fixation time on leaching of copper-ethanolamine based wood preservatives

Zusammenfassung Fixation in copper-ethanolamine treated Norway spruce wood is finished in the first or in the second week after impregnation depending on the concentration of wood preservatives used. However, copper losses increased after four weeks of fixation again, presumably due to lignin depolymerisation caused by ethanolamine.      

工业木素的氨化反应研究及其进展

从反应的影响因素、产物的氮键类型和结构等方面,介绍了木素氧化氨解过程可能的反应机理,并详述了国内外关于工业木素氧化氨解工艺及其相应产品应用的研究进展,为我国工业木素资源的农业利用提供科学依据。     

Monitoring OH-initiated oxidation kinetics of isoprene and its products using online mass spectrometry

A novel technique has been developed to simultaneously monitor the kinetics of the OH radical-initiated oxidation of isoprene and formation and oxidation of its products (methyl vinyl ketone, methacrolein, 3-methylfuran, and formaldehyde) using online mass spectrometry. The kinetics of isoprene and its products were investigated at 323 K and at 1 atm total pressure. The responses of 30 representative ions for isoprene and its products were monitored during the reaction, and their concentration profiles were calculated by linear algebraic equations, which resolve the measured mass spectra of representative ions into the responses of individual target organics, and by calibrations, which converted the responses to individual target concentrations. Using this method, yields of methyl vinyl ketone, methacrolein, and 3-methylfuran at 323 K were measured to be 14.4+/-0.1%, 19.0+/-0.2%, and 2.9+/-0.2%, respectively, in excellent agreement with previously reported yields under NOx-free conditions. The reaction kinetics of isoprene and its oxidation products measured by the experimental procedure developed in this study were compared with those estimated by a kinetic model of isoprene oxidation. The observed methacrolein concentrations as a function of time were reproduced reasonably well by this model, while the observed methyl vinyl ketone concentration could be reproduced by including secondary reactions of some of the hydroperoxide products of isoprene oxidation. The observed 3-methylfuran concentrations could be reproduced using secondary cyclization reactions of some of the 1,4-hydroxycarbonyl products of isoprene oxidation. These results suggest that under low NOx conditions reactions of some of the hydroperoxides and hydroxycarbonyls produced from the OH-initiated oxidation of isoprene may be a significant source of methyl vinyl ketone and 3-methylfuran in the atmosphere.     

Antioxidant activity of water-soluble Maillard reaction products

Maillard reaction products (MRP) results from a condensation reaction between amino acids (or proteins) and reducing sugars or lipid oxidation products, and MRP exhibit in vitro antioxidant activities. The objective of this study was to determine antioxidant activities of water-soluble MRP from the reaction between histidine (His) and glucose (Glu) by using the oxygen radical absorbing capacity (ORAC_PE) assay with phycoerythrine. Heating His–Glu mixture at 100 °C up to 30 min did not generate MRP with antioxidant activity. However, significant formation of MRP with ORAC_PE values of 0.25, 0.43, and 0.44 μmol Trolox equivalent/mg reaction mixture was observed when the mixture was heated at 120 °C for 10, 20, and 30 min, respectively. Heating the mixture at 120 °C over 30 min reduced the peroxyl radical scavenging activity of the MRP, possibly due to the degradation of antioxidant MRP formed in the earlier stages of the reaction. In conclusion, MRP obtained from His–Glu mixture possesses peroxyl radical scavenging activity, and this activity can be quantified by the ORAC_PE assay.     

Wood nails to fix softwoods: characterization of structural deformation and lignin modification

Softwoods can be nailed with high density solid wood like Santos Rosewood (Machaerium scleroxylon) or nails made of densified laminated beech wood composite by hammering or shooting, for example with air nail guns, without pre-drilling. Shooting with about 30 m/s causes friction between nail surface and softwood matrix, heating up the interface to temperatures high enough to soften lignin. Re-condensation of softened lignin causes wood welding which doubles pull out strength in comparison to wood nails fixed without wood welding. Changes in lignin UV-absorption within the single cell wall layer and deformation of main anatomical features of spruce wood tissue are characterized by scanning UV microspectrophotometry (UMSP) whereas structural deformations of spruce wood tissue are revealed by X-ray micro-computed tomography (µ-CT).     

Changes on Content,Structure and Surface Distribution of Lignin in Jute Fibers After Laccase Treatment

Effect of laccase treatment on the content, structure, and surface distribution of lignin in jute fibers were fundamentally investigated. Four percent lignin was removed from jute fibers via the laccase treatment. The residual lignin in the laccase-treated jute fibers showed increased molecular weights, which indicated polymerization between lignins on jute fibers. Meanwhile, the phenolic hydroxyl content in lignin decreased during the laccase oxidation accompanied by demethylation of methoxyl groups and generation of carbonyl groups. Due to the degradation and subsequent polymerization of lignin by laccase, the bulgy lignins on jute fiber surfaces were redistributed, which made the surface neat and glossy.     

The boron fixation to the cellulose, lignin and wood matrix through its reaction with protein

This paper is an attempt to determine the actual boron adsorption and retention in wood and its isolated components: cellulose and lignin. The rate of boron retention in cellulose, lignin and wood powder of Scots pine Pinus silvestris L. was investigated using denaturing properties of protein contained in reaction solutions. Both animal and plant origin protein was used in this study. In order to determine the reactivity of the analyzed formulation the reactions of cellulose, lignin and wood powder with protein borates were carried out. The aim of the analyses was also to compare methods of protein denaturation: thermal and chemical with the use of tannic acid solution. The obtained products were subjected to water extraction at 20 °C. Boron content in the solid and water extracts was analyzed using atomic absorption spectrometry (AAS). The results showed that the method of protein denaturation played the crucial role in the rate of boron retention. The type of protein used in the reaction solution had also significant effect on the boron retention.