Residual extractives in aspen kraft pulps and their impact on kappa number and Klason lignin determination

We investigated the impact of residual extractives on lignin determination by lignin content difference between unextracted and extracted pulps, residual extractives analysis, and lignin content contribution from model extractive compounds. There were two different kinds of extractives in aspen kraft pulp. The extractives impacting on kappa number determination were well removed in oxygen delignification; these were mainly unsaturated fatty acids. However, the extractives impacting on Klason lignin determination were largely resistant to oxygen delignification; these were mainly saturated fatty acids, sterols, and hydrocarbons. Oxidation of unsaturated fatty acids was the main reaction in oxygen delignification. These trends were confirmed by simulation of lignin content determination with three model extractive compounds (β-sitosterol, linoleic acid, and palmitic acid). The publication of this article was made possible by an Emachu Research Fund. The authors are grateful for the fund.     

Changes of major chemical components in larch wood through combined treatment of drying and heat treatment using superheated steam

The effects of the combined treatment of drying and heat treatment using superheated steam (SHS) were studied relative to the changes of the major chemical components in larch wood. The green lumber was dried and heat-treated in SHS conditions of 250 °C and 0.5 MPa for 18 h, and the relative percentage contents of sugars, lignin, and extractives were investigated and compared with the relative percentage contents in the lumber heat-treated in hot air conditions of 250 °C and atmospheric pressure for 18 h. After both heat treatment methods, the relative percentage contents of xylan, mannan, galactan, and arabinan were greatly decreased, whereas that of the Klason lignin was increased, additionally that of glucan and extractives remained almost unchanged. Lignin may bind with furan compounds decomposed from hemicellulose following heat treatment, thus contributing to the increase in the apparent relative percentage contents of the Klason lignin. In addition, the condensate collected in the condenser after combined drying and heat treatment using SHS was investigated qualitatively and quantitatively by high-performance liquid chromatography (HPLC). A large amount of furfural and acetic acid decomposed from hemicellulose was detected and some sugar components composed of cellulose and hemicellulose were detected in the liquid condensate.     

Chemical characteristics of surfaces of hardwood and softwood deteriorated by weathering

The factors that cause weather-induced deterioration of wood surfaces were determined by chemical and spectroscopic analyses. Albizzia (Paraserianthes falcata Becker.) and sugi (Cryptomeria japonica D. Don) were exposed to two temperate conditions of natural weathering with and without rainfall and to accelerated conditions of artificial weathering coupled with ultraviolet (UV) light irradiation and water flashing. Infrared spectroscopic analysis showed that the oxidative reaction of lignin was observed under all conditions of weathering for both wood species. However, a marked decrease in lignin and hemicellulose content were recognized when albizzia woods were exposed to weathering with water. Lignin content in the softwood sugi did not decrease as much as in albizzia even in the presence of water, but the modification of lignin macromolecules was assumed to be accelerated by water, as seen by electron spin resonance spectroscopy. These results showed that the presence of water promotes the weathering deterioration of wood under UV irradiation.     

Spectroscopic analysis of the role of extractives on heat-induced discoloration of black locust (Robinia pseudoacacia)

Abstract

To investigate the role of extractives on heat-induced discoloration of wood, samples of black locust (Robinia pseudoacacia) wood flour were extracted with various solvents prior to heat-treatment. Analysis of their color parameters and chromophoric structures showed that the chroma value of the unextracted sample decreased while that of the extracted sample increased after heat-treatment. Both samples showed broad diffuse reflectance UV-Vis (DRUV) absorption bands with maxima around 360–380 nm after heat-treatment due to the formation of conjugated double bonds, carbonyl functionalities, and quinoid structures. Compared with the unextracted sample, the dominant chromaticity of the extracted samples hypochromatically shifted and the peak became narrower. This result showed that extractives contribute mostly to the reduction in the light reflection on heat-treated wood. In addition to extractives, lignin and hemicellulose also contributed to the formation of color substances upon heat-treatment. The increase in C₃/C₂ ratio in X-ray photoelectron spectroscopy (XPS) spectra signified the oxidation reactions in the heating process. The increase in O₁/O₂ for extracted sample after heat-treatment and changes in DRUV and Fourier transform infrared spectroscopy (FTIR) spectra support the hypothesis that discoloration can also arise from the degradation of hemicellulose and the condensation reactions of lignin.     

Impact of thermal modification on color and chemical changes of spruce and oak wood

Thermal modification of wood is an environment-friendly alternative method for improving several properties of wood without the use of chemicals. This paper deals with the examination of color and chemical changes in spruce (Picea abies L.) and oak wood (Quercus robur F.) that occur due to thermal treatment. The thermal modification was performed at 160, 180, and 210 °C according to thermowood process. The color changes were measured by the spectrophotometer and described in the L*a*b* color system. Chemical changes were examined by wet chemistry methods, infrared spectroscopy and liquid chromatography. During the experiment, oak samples showed smaller color changes than spruce samples at all temperature values. During thermal modification, the content of cellulose, lignin, and extractives increases; however, the hemicellulose content drops by 58.85% (oak) and by 37.40% (spruce). In addition to deacetylation, new carbonyl and carboxyl groups are formed as a result of oxidation. Bonds in lignin (mainly β-O-4) and methoxyl groups are cleaved, and lignin is condensed at higher temperatures.     

Nondestructive estimation of wood chemical composition of sections of radial wood strips by diffuse reflectance near infrared spectroscopy

The use of calibrated near infrared (NIR) spectroscopy for predicting the chemical composition of Pinus taeda L. (loblolly pine) wood samples is investigated. Seventeen P. taeda radial strips, representing seven different sites were selected and NIR spectra were obtained from the radial longitudinal face of each strip. The spectra were obtained in 12.5 mm sections from pre-determined positions that represented juvenile wood (close to pith), transition wood (zone between juvenile and mature wood), and mature wood (close to bark). For these sections, cellulose, hemicellulose, lignin (acid soluble and insoluble), arabinan, galactan, glucan, mannan, and xylan contents were determined by standard analytical chemistry methods. Calibrations were developed for each chemical constituent using the NIR spectra, wood chemistry data and partial least squares (PLS) regression. Relationships were variable with the best results being obtained for cellulose, glucan, xylan, mannan, and lignin. Prediction errors were high and may be a consequence of the diverse origins of the samples in the test set. Further research with a larger number of samples is required to determine if prediction errors can be reduced.     

Influence of the chemical composition of kenaf bast and core on the alkaline pulping response

The bast and core of kenaf,Hibiscus cannabinus L., have markedly different chemical components and alkaline cooking responses. The bast had about double the hot-water extractives content and only about half the lignin content of the core. The core contained a large amount of hemicellulose, mostly composed of xylan. The lignin structures of bast and core were also quite different: The former had a significant abundance of syringyl structures. Evidence showed that the bast was much more easily delignified than the core. When the bast and core were cooked together in alkaline condition, the pulp yields at the same kappa number were higher than those of the individual pulpings of bast and core. The bast-core pulping gave a positive effect on the yield of bast pulp in the sodaanthraquinone and kraft pulpings. On the other hand, kenaf was abundant in the hot water extractives. These extractives consumed alkali during cooking to a relatively large extent but acted as a protector of hemicellulose and slightly increased the pulp yields.Part of this paper was presented at the 48th and 49th Annual Meetings of the Japan Wood Research Society, Shizuoka, April 3–5, 1998 and Tokyo, April 3–5, 1999     

Effect of acetylation on the chemical composition of hornbeam (Carpinus betulus L.) in relation with the physical and mechanical properties

Common hornbeam (Carpinus betulus L.) is a highly underused wood species despite its great hardness, strength, wear-resistance and toughness. It is mainly used as firewood in Hungary because of its wood defects, irregular shape and low-dimensional stability. These wood defects and small breast height diameter result in a low yield. It is non-durable outdoors as it tends to turn grey, crack and be attacked by wood-decaying organisms. Indoors it lasts for hundreds of years. One technology that could improve the stability and durability properties is acetylation. Hornbeam was acetylated with the Accoya® method under industrial conditions. The aim of this research was the assessment of acetylation affecting the chemical properties of hornbeam wood and how these are related to the change in physical and mechanical properties. Main wood constituents (cellulose, hemicellulose, Klason lignin, extractives and ash content) were determined and compared. Chemical parameters related to the degradation of structural polymers were also evaluated (total phenolic and soluble carbohydrate contents, pH and buffering capacity, furfural, levulinic acid, formic acid, acetic acid). Structural changes in acetylated wood and in the Klason lignin fraction were also assessed using FTIR spectroscopy.     

Genetic variability of growth and wood chemical properties in a clonal population of Eucalyptus urophylla × Eucalyptus grandis in the Congo

Thirty-four Eucalyptus urophylla × Eucalyptus grandis hybrids were evaluated with a view to selecting for improved growth and wood-quality traits for plantations in the Congo. Height, circumference at breast height and volume were measured at 12, 27, 37, 49 and 60 months. Lignin content, the syringyl/guaiacyl ratio and total extractives content were predicted by near-infrared spectroscopy using wood powder samples collected from trees at breast height. While wood chemical properties were stable and under strong genetic control, growth traits were not. The genetic correlation between lignin content and growth was weak and negative, whereas the environmental correlation was also weak but positive. The genetic improvement of E. urophylla × E. grandis clones, based on growth features, leads to a limited decrease in lignin content and syringyl content and to a limited increase in extractives content.     

Discolouration of birch wood: analysis of extractives from discoloured surface of vacuum-dried European white birch (Betula pubescens) board

A discolouration that appeared on the surfaces of a European white birch (Betula pubescens) board during vacuum drying was studied by means of colour measurements (CIEL*a*b*), elemental analysis and the analysis of extractives. The discoloured surface layer of the dried board contained substantially more methanol-soluble extractives than did the light-coloured part (50.7 mg g⁻¹ vs. 26.7 mg g⁻¹ dry wood), and the colour difference (ΔE* _ab 20.0) between the two extracts was notable. Characterization by means of GC and ¹³C NMR spectroscopy showed that the extracts contain sugars (mainly glucose and fructose), low-molecular-weight phenolic compounds, proanthocyanidins, Brauns’ lignin and fatty acid esters. Concentrations of sugars, low-molecular-weight phenols, proanthocyanidins and Brauns’ lignin were higher in the discoloured surface layer than in the light-coloured part. The yellowness of the surface layer was associated with the accumulation of low-molecular-weight phenolic extractives, and the redness with Brauns’ lignin and possibly proanthocyanidins.     

Chemical characterization of six mangrove species in Bangladesh

Lack of data especially pertaining to the chemistry of mangrove wood species makes it difficult to prepare successful plans for their conservation and to use mangroves as a source of wood fiber. In this paper, chemical characterizations of the six main mangrove species of Bangladesh [namely Keora (Sonneratia apetala), Geoa (Excoecaria agallocha), Bine (Avicennia alba), Sundari (Heritiera fomes) Pashur (Xyloccarpous mekongests), and Kakra (Bruguiera gymnorhiza)] were investigated. The chemical results revealed that these species contain high percentages of dichloromethane followed by methanol extractives. Methanol extracts in Pashur, Sundari, and Bine were higher than 10%, which indicates high percentage of tannin material. The total lignin content in these species was higher than 25%, except for Gewa (23.6%) and Pashur (21.3%), which is higher than that of the normal range of hardwood. The pentosan content in these six species was within the range of 19.4–22.8%. The α-cellulose content in Keora and Gewa was acceptable for pulp production, but the others were lower than the normal range of hardwood. Alkaline nitrobenzene oxidation showed that all these species had a very high syringaldehyde to vanillin (2.6–5.0) ratio except Keora (1.6). Surprisingly, rhamnose is the main constituent with xylose of hemicelluloses of these six mangrove species. The ash content in these six mangrove wood species was also higher than that in normal hardwood.     

Influence of accessory substances,wood density and interlocked grain on the compressive properties of hardwoods

Wood samples of nine tropical hardwoods from Peru and sugar maple wood from Quebec were selected to perform moisture sorption tests associated with parallel-to-grain and tangential compression tests using a multiple step procedure at 25°C. Cold-water and hot-water extractives, sequential cyclohexane (CYC), acetone (ACE) and methanol (MET) extracts, ash content (ASH), wood density and interlocked grain (IG) were evaluated on matched samples too. Wood density corrected for the accessory substances was by far the major factor positively affecting the compressive properties of tropical hardwoods. The total amount of accessory substances is required in order to establish better relationships between physico–mechanical properties and density of tropical hardwoods. For a given wood density, the ultimate stress in parallel-to-grain compression was higher in tropical hardwoods than in temperate hardwoods. However, the compliance coefficients for both types of woods were quite similar. Sequential extraction with organic solvents was the most suitable method for evaluating the effect of extractives on compressive properties of tropical hardwoods. The CYC and ACE fractions did not contribute to variation in these mechanical properties. The substances dissolved in MET affected positively the compliance coefficient s ₁₁ in parallel-to-grain compression and negatively the compliance coefficient s ₃₃ in tangential compression. The IG decreased the compliance coefficient s ₁₁ but also decreased the ultimate stress in parallel-to-grain compression. Finally, variations in compressive properties that were due to changes in equilibrium moisture content (EMC) were clearly influenced by wood density; denser woods were more sensitive to changes in EMC than lighter woods.     

Activities of some enzymes of lignin formation in reaction wood of Thuja orientalis and Metasequoia glyptostroboides 2

Summary To elucidate biochemical features leading to p-hydroxyphenyl-rich lignin in gymnosperm reaction wood the activities of the following five enzymes involved in the biosynthesis of p-hydroxyphenyl lignin were compared in reaction and opposite woods: phenylalanine ammonialyase (EC 4.3.1.5), cinnamate 4-hydroxylase (EC 1.14.13.11), p-hydroxycinnamate: CoA ligase (EC 6.2.1.12), cinnamyl alcohol dehydrogenase (EC 1.1.1.-) and peroxidase (EC 1.11.1.7). The enzyme activities in the reaction woods of Thuja orientalis and Metasequoia glyptostroboides were remarkably higher than those in the opposite woods, reflecting the higher contents of p-hydroxyphenyl lignin in reaction wood.This work was partly supported by the Grant-in-Aid for Scientific Research (548047) from the Ministry of Education, Science and Culture of Japan. We thank the Ministry of Education for the support     

Chemical characterization of Pinus halepensis sapwood and heartwood

ABSTRACT

This paper describes the chemical composition of sapwood (SW) and heartwood (HW) of Pinus halepensis Mill stem. Extractives were first isolated by accelerated solvent extraction and then analysed by gas chromatography-mass spectrometry (GC-MS). The cellulosic polysaccharide content present in the pre-extracted wood samples was determined with acid hydrolysis and GC. The hemicelluloses content was determined with acid methanolysis and GC. Free monomers were additionally analysed by GC. The amount of lignin was determined gravimetrically by the Klason lignin method and the acid-soluble lignin was determined by a UV method. Formic and acetic acids in wood were determined after alkaline hydrolysis and analysed by HP-SEC. It was found that lipophilic and hydrophilic extractives were more abundant in heartwood (1.6% and 2.5%) than in sapwood (1.1% and 1.8%). Celluloses content was higher in sapwood (42.5%) than in heartwood (39.7%), whereas lignin, hemicelluloses and sugar monomer contents were more abundant in heartwood (28.9%, 26.8% and 0.3%) than in sapwood (28.0%, 24.5% and 0.2%). The variation in acetic and formic acids and ash contents between sapwood (0.7%, 0.2% and 0.5%) and heartwood (0.6%, 0.1% and 0.4%) was small. The acetylation degrees were found to be slightly similar in sapwood (0.4) and heartwood (0.3).     

Comparative study of organic solvent-soluble and water-soluble lipophilic extractives from wheat straw 2: spectroscopic and thermal analysis

As a continuing study of six organic solventsoluble lipophilic extractives and one water-soluble lipophilic extract from wheat straw, seven extracts were further compared using Fourier transform-infrared (FT-IR) analysis,¹H and¹³C nuclear magnetic resonance (NMR) spectroscopy, and thermal analysis. In the FT-IR spectra of two-thirds chloroform/one-third methanol, methyltertbutyl ether (MTBE), hexane, petroleum ether, and dichloromethane extracts, a strong band at 1746cm^–1 is indicative of the ester carbonyl of triglycerides or steryl esters or waxes, whereas the occurrence of carboxylic carbonyl of free fatty acids or resin acids at 1712–1719 cm^–1 is verified in the spectra of two-thirds toluene/one-third ethanol and hot water extracts. Signals at 187.9,178.4, and 173.3 ppm in the¹³C NMR spectrum of MTBE extract correspond to carbonyl groups of resin acids, fatty acids, and fatty acid/steryl esters, respectively. All the extractives were to varying degrees thermally unstable at a temperature of about 200°C, and the melting temperature occurred at about 54°C.     

Modelling moisture-related mechanical properties of wood Part I: Properties of the wood constituents

Summary By starting with simple concepts of the molecular structure and building up through the various levels of organisation in the wood cell wall it is possible to construct a model that simultaneously predicts the variation with moisture content change of both the longitudinal Young's modulus and longitudinal shrinkage of wood. To do this it is first necessary to define the stiffness and swelling characteristics of the lignin, hemicellulose and cellulose constituents of the wood as moisture content changes. It is suggested here that it is the bound fraction of the sorbed water that is responsible for the changes in swelling stress as well as for change in stiffness in the lignin and hemicellulose. The magnitudes of the stiffness of each of the constituents appear to be quite closely circumscribed by experimental values for longitudinal Young's modulus and shrinkage of wood and it is apparent that the stiffness characteristics of the in situ constituents are compatible with available experimental evidence for extracted lignin and hemicellulose and for native cellulose.     

Analysis of chemical changes in Picea abies wood decayed by different Streptomyces strains showing evidence for biopulping procedures

The present study is focused on analysing the suitability of different Streptomyces strains for biomechanical pulping purposes using spruce wood (Picea abies) as substrate. After 2 weeks of incubation, no apparent variations in lignin Klason content of treated woods were detected compared with the control. However, the increase in acid-soluble lignin fraction pointed out chemical alterations in lignin moiety. Through Py-GC/MS analysis enrichment in cellulose and lignin molecule modifications were detected in treated woods. The increase in the relative abundance of the most G-type phenol units with a higher oxidation degree suggests that some oxidation occurred in the lignin C3-alkyl chain. In addition, the decrease in the phenylmethane + phenylethane/phenylpropane (phC1 + ph C2/ph C3) ratio would indicate the ability of Streptomyces strains to breakdown the C3-alkyl chain linkages once carbons had been oxidized. From this study it could be concluded that the assayed strains are able to produce a delignification of spruce wood which may improve mechanical pulping processes.     

高地钩叶藤材化学成分含量分析

为构建棕榈藤材材性数据库,提升棕榈藤材高附加值加工利用水平,文章以高地钩叶藤为研究对象,对其主要化学成分含量进行测定和分析。结果表明,高地钩叶藤材综纤维素、酸不溶木质素、α-纤维素、半纤维素、苯-醇抽提物、热水抽提物、冷水抽提物、1%NaOH抽提物及灰分含量的均值分别为67.98%、16.72%、43.91%、24.38%、9.78%、18.85%、15.02%、38.60%和1.46%。径向上,综纤维素、α-纤维素、酸不溶木质素及灰分含量均为藤皮>藤中>藤芯;而半纤维素、冷水抽提物、热水抽提物、苯-醇抽提物及1%NaOH抽提物含量均为藤芯>藤中>藤皮。轴向上,综纤维素、α-纤维素、酸不溶木质素及灰分含量最大值均在中部,而半纤维素及4种抽提物含量最大值均在梢部。酸不溶木质素和α-纤维素含量最小值在梢部,综纤维素、半纤维素及灰分含量最小值在基部,冷水抽提物、苯-醇抽提物及1%NaOH抽提物含量最小值均出现在基部以上2 m处,而热水抽提物含量最小值在中部。     

Compositional and structural characteristics of residual biomass from tropical plantations

Many products and abundant wastes from tropical plantations, such as latex, palm oil, and coconut production due to replantation, are waiting effective utilization. Nonutilized tropical biomass — oil palm (Elaeis guneensis Jacq.), coconut (Cocos nucifera L.) coir dust and coir fiber, and rubber (Hevea brasiliensis) wood — were analyzed for chemical and structural characteristics of wall polysaccharides and lignin. Coconut coir dust is mostly composed of middle lamella and is separated from coir fiber, which is composed of secondary walls. These were supported by lignin content, and structural characteristics of wall polysaccharides and lignin. The chemical and spectroscopic characteristics of walls of rubber xylem were similar to those of typical temperate angiosperm woods. Oil palm frond was significantly rich in arabinoxylan, and numerous acetyl groups were substituted to the arabinoxylan. Lignin of oil palm frond and wall polysaccharides of coconut coir dust are substituted with hydroxybenzoic acids with ester and ether linkages. Some p-hydroxybenzoic acid substituted to the wall polymers of coconut coir dust would contribute to the formation of associations between polysaccharides and lignin. Based on the above results it is suggested that coconut coir fiber and rubber wood are suitable resources for chemical pulp production for paper-making, but oil palm frond is not.     

Changes of chemical properties and the water vapour sorption of <Emphasis Type="Italic">Eucalyptus pellita</Emphasis> wood thermally modified in vacuum

The aim of this study was to evaluate the chemical composition and the dynamic water vapour sorption properties of Eucalyptus pellita wood thermally modified in vacuum. For this purpose, wood samples were thermally modified in a vacuum oven at 160–240 °C for 4 h. Chemical composition were investigated by wet chemical analysis, elemental analysis, as well as Fourier transform infrared (FTIR) analysis, and dynamic water vapour sorption properties were evaluated by dynamic vapour sorption apparatus. The results showed that holocellulose and alpha-cellulose contents decreased and lignin and extractives contents relatively increased during the heat process. Elemental analysis showed a reduction in hydrogen content and an increase in carbon content. FTIR analysis indicated that the degradation of hemicellulose and condensation reactions of lignin occurred. In addition, the thermo-vacuum resulted in a reduction in the equilibrium moisture content of wood during the adsorption or desorption process. And the sorption hysteresis had a decreasing trend with increasing treatment temperature. The development of the hygroscopicity was related to the increase in the relative content of lignin, the degradation of the carbonyl groups in xylan and the loss of carbonyl group linked to the aromatic skeleton in lignin after heat treatment.