Published by De Gruyter

Volume 62 Issue 5

Issue of Holzforschung

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Contents
Journal Overview

Original Papers

July 1, 2008

Studies on the dehydrogenative polymerizations (DHPs) of monolignol β-glycosides: Part 4. Horseradish peroxidase-catalyzed copolymerization of isoconiferin and isosyringin

Yuki Tobimatsu, Toshiyuki Takano, Hiroshi Kamitakahara, Fumiaki Nakatsubo

Page range: 495-500

Abstract

Horseradish peroxidase (HRP)-catalyzed dehydrogenative copolymerization of guaiacyl (G)-type monolignol glycoside (isoconiferin, coniferyl alcohol γ- O -β- d -glucopyranoside, iso-G) and syringyl (S)-type monolignol glycoside (isosyringin, sinapyl alcohol γ- O -β- d -glucopyranoside, iso-S) were performed in continuous dehydrogenation mode (end-wise polymerization) to result in the formation of water-soluble lignin-like copolymers (iso-G/S-DHPs) in a homogeneous phase. The yield of iso-G/S-DHP increased with increasing iso-G content in the mixture of monomers from 23% (iso-G/iso-S 0:100) to 81% (iso-G/iso-S 50:50). The degree of polymerization (DP) of the resulting iso-G/S-DHP also increased proportionally from 7 (iso-G/iso-S 0:100) to 27 (iso-G/iso-S 50:50) as the iso-G content increased. It is obvious that iso-G plays an important role in the polymerization of iso-S. A similar tendency was also observed in conventional copolymerization of coniferyl alcohol (G-alc) and sinapyl alcohol (S-alc). The highest DP for DHP obtained in the conventional system was only ∼10 due to the heterogeneous reaction system. As the HRP-catalyzed monomer consumption rate of iso-S was greatly enhanced by addition of iso-G as a co-monomer, radical transfer from iso-G to iso-S seems to be plausible. Conventional copolymerization of G-alc and S-alc also supports this view. Spectroscopic studies and alkaline nitrobenzene oxidation analyses indicated that iso-G/S-DHPs had typical lignin structures composed of both G and S units. It was confirmed that the copolymerization behavior of the glycosides iso-G and iso-S in a homogeneous phase are well reflected by that of the monolignols G-alc and S-alc in a heterogeneous phase. Results also indicated that the presence of G-type co-monomers sensitively affects the polymerization of S-type monomers.

July 1, 2008

Studies on the dehydrogenative polymerization of monolignol β-glycosides: Part 5. UV spectroscopic monitoring of horseradish peroxidase-catalyzed polymerization of monolignol glycosides

Yuki Tobimatsu, Toshiyuki Takano, Hiroshi Kamitakahara, Fumiaki Nakatsubo

Page range: 501-507

Abstract

Horseradish peroxidase (HRP)-initiated dehydrogenative polymerizations of guaiacyl (G) and syringyl (S)-type monolignol γ- O -glucosides, isoconiferin (iso-G) and isosyringin (iso-S), which contain a hydrophilic glucosyl unit on γ-position of coniferyl alcohol (G-alc) and sinapyl alcohol (S-alc), respectively, were monitored by UV spectroscopy to study the formation of dehydrogenation polymer (DHP, lignin polymer model) in a homogeneous aqueous phase. During homopolymerization of iso-S, a new absorbance band at 325 nm ( A 325 ) rapidly increased in intensity and then gradually disappeared, whereas such stable changes in absorbance were not observed during homopolymerization of iso-G. During polymerization of iso-S, A 325 rapidly disappeared when an acid, nucleophile or reductant was added to the reaction mixture, indicating that A 325 can be attributed to S-type quinone methide intermediates (QMs). Similar to iso-S polymerization, temporary absorbance at 328 nm was observed during conventional polymerization of S-alc. We interpret this observation as follows: S-type QMs accumulated in the reaction mixture and the progress of subsequent DHP formation during oxidative polymerization of iso-S or S-alc was hindered. UV monitoring of iso-G and iso-S copolymerization revealed that the presence of iso-G promoted the disappearance of A 325 . Furthermore, S-type QMs generated in situ by iso-S polymerization disappeared more rapidly after guaiacol addition than after 2,6-dimethoxyphenol addition. The following mechanism for copolymerization of iso-G and iso-S can be proposed: G-type precursors with phenolic hydroxyl groups react readily by nucleophilic addition with the α-C of S-type QMs, and the molecular chains of DHPs increase via non-cyclic α-aryl ether bonds.

July 22, 2008

Monolignol dehydrogenative polymerization in vitro in the presence of dioxane and a methylated β-β′ dimer model compound

Anders Holmgren, Liming Zhang, Gunnar Henriksson

Page range: 508-513

Abstract

Lignin formation is believed to occur by polymerization of resonance-stabilized monolignol radicals formed by enzymatic oxidation. Recently, different hypotheses suggested that lignin polymerization is influenced by surfaces in the cell wall which can be polysaccharides or proteins. The latter is called the proteinaceous dirigent sites/template polymerization hypothesis. According to another hypothesis, lignin itself is believed to act as a template and replicate its primary structure. In this work, dehydrogenative polymerization (DHP) of the lignin precursor coniferyl alcohol was performed in vitro in the presence and absence of pinoresinol dimethyl ether (a β-β′ dimer model). Another peculiarity of the experiments was the presence of dioxane which afforded a high solubility of the reactants. The question was whether the presence of β-β′ dimer model would change the structure of the DHP formed. The DHPs were analyzed by quantitative 13 C NMR, GC-FID, and GC-MS. The dimer model as a template in the homogeneous polymerization state (in solution) did not influence the DHP structure.

July 22, 2008

Structural characterization of milled wood lignins from different eucalypt species

Jorge Rencoret, Gisela Marques, Ana Gutiérrez, David Ibarra, Jiebing Li, Göran Gellerstedt, J. Ignacio Santos, Jesús Jiménez-Barbero, Ángel T. Martínez, José C. del Río

Page range: 514-526

Abstract

The chemical structure of milled-wood lignins from Eucalyptus globulus , E. nitens , E. maidenii , E. grandis , and E. dunnii was investigated. The lignins were characterized by analytical pyrolysis, thioacidolysis, and 2D-NMR that confirmed the predominance of syringyl over guaiacyl units and only showed traces of p -hydroxyphenyl units. E. globulus lignin had the highest syringyl content. The heteronuclear single quantum correlation (HSQC) NMR spectra yielded information about relative abundances of inter-unit linkages in the whole polymer. All the lignins showed a predominance of β-O-4′ ether linkages (66–72% of total side-chains), followed by β-β′ resinol-type linkages (16–19%) and lower amounts of β-5′ phenylcoumaran-type (3–7%) and β-1′ spirodienone-type linkages (1–4%). The analysis of desulfurated thioacidolysis dimers provided additional information on the relative abundances of the various carbon-carbon and diaryl ether bonds, and the type of units (syringyl or guaiacyl) involved in each of the above linkage types. Interestingly, 93–94% of the total β-β′ dimers included two syringyl units indicating that most of the β-β′ substructures identified in the HSQC spectra were of the syringaresinol type. Moreover, three isomers of a major trimeric compound were found which were tentatively identified as arising from a β-β′ syringaresinol substructure attached to a guaiacyl unit through a 4-O-5′ linkage.

July 22, 2008

FTIR spectroscopy in combination with principal component analysis or cluster analysis as a tool to distinguish beech (Fagus sylvatica L.) trees grown at different sites

Rumana Rana, Günter Müller, Annette Naumann, Andrea Polle

Page range: 530-538

Abstract

FTIR spectroscopy was used to distinguish between beech ( Fagus sylvatica L.) trees grown at five different sites; one in middle Germany close to Göttingen (forest district Reinhausen), three located in the southwest (two in Rhineland-Palatinate: forest districts Saarburg and Hochwald, and one in Luxembourg), and one in North-Rhine Westfalia. Detailed investigation of the spectra in the fingerprint region (1800–600 cm -1 ) revealed 16 distinct peaks and shoulders, most of which were assignable to wavenumbers previously shown to represent wood compounds. Differences in peak heights and peak ratios indicated differences in wood composition of beech trees from different sites. To determine if the wood of individual trees could be distinguished, principal component analysis (PCA) and cluster analysis were performed using FTIR spectra as input data. With both PCA and cluster analysis, trees from four of the five different sites were separated. It was not possible to distinguish between trees from Saarburg and Hochwald, where similar edaphic and climatic conditions exist, while wood spectra from trees from all other areas clearly segregated. Wood collected at different positions in the stem (bottom, crown, center and outer year rings) of trees grown at the same site was not distinguishable. Therefore, FTIR spectral analysis in combination with multivariate statistical methods can be used to distinguish wood of trees from different growth habitats. Extension of this method to other species may be of great interest for wood certification, as it may be possible to distinguish wood, of a given species, originating from different regions.

July 22, 2008

Hydrothermal dissolution of mixed southern hardwoods

Mehmet Sefik Tunc, Adriaan R.P. van Heiningen

Page range: 539-545

Abstract

A hydrothermal dissolution profile of wood components cellulose, hemicelluloses, and lignin of hardwood during autohydrolysis for 100 min at temperatures from 130 to 170°C in a modified accelerated solid extraction system (Dionex ASE-100) is described. The content of cellulose, hemicelluloses, lignin, acetyl, and uronic acid groups remaining in the extracted wood were determined. The extract was analyzed for oligosaccharides and monosaccharides, lignin, acetic acid, uronic acid, furfural, and hydroxymethylfurfural. Xylo-oligomers are the predominant component in the extract at temperatures higher than 150°C. At temperatures higher than 160°C, small amounts of furfural and hydroxymethylfurfural are generated. Most of the arabinan and galactan are removed from the wood at 160°C. The xylan remaining in the wood is acetylated at the same degree as in the original wood. In the extract, the ratio of acetyl groups bound to xylo-oligosaccharides decreases with increasing temperature. The content of uronic acid groups found in the extract obtained after autohydrolysis at T ≥150°C is significantly smaller than that calculated from the decrease in uronic content of the wood.

July 1, 2008

Characterisation of fines from unbleached kraft pulps and their impact on sheet properties

Marie Bäckström, Marie-Claude Kolar, Myat Htun

Page range: 546-552

Abstract

Fines are an essential component in the papermaking process because they have a profound influence on the behaviour of the wet web and on the mechanical properties of the final sheet. Primary fines are present in the pulp prior to refining, and secondary fines are produced during refining. In the present investigation, two commercially manufactured unbleached pulps with kappa numbers of 45 and 90 were studied in terms of how they responded to refining with respect to the quality of fibre and fines. Primary and secondary fines were collected and characterised and their impact on sheet strength was evaluated by addition of known amounts to a refined and decrilled pulp. All the measured paper strength properties improved when primary and secondary fines were added. The strength improvement was generally somewhat higher in the second case. The effect was more pronounced at a higher level of addition. We attribute the main strength improvements associated with fines to improved consolidation by the creation of capillary forces between the surfaces.

July 1, 2008

Effects of refining steam pressure on the properties of loblolly pine (Pinus taeda L.) fibers

Trairat Neimsuwan, Siqun Wang, Xiaofei Philip Ye

Page range: 556-561

Abstract

Medium density fiberboard is widely used with increasing tendency in North America, particularly in the furniture sector, including door skin and cabinets. Sorption property is one of the most important factors for quality judgment. This study will present water vapor sorption behavior of fibers in the range of varying relative humidity from 11% to 89% as affected by steam pressure of thermomechanical refining in small-scale measurement. A 54-year-old loblolly pine tree was refined at 2 to 18 bar of steam pressure. Fiber properties were determined by scanning electron microscope, dynamic contact angle analyzer, wide angle X-ray diffractometer, and water activity meter. The results showed that steam pressure has a dramatic effect on sorption behavior and surface properties of the refined fiber. In conclusion, a higher rate of sorption was found in juvenile fiber at low steam pressure. Higher water activity and lower crystallinity was found at low steam pressure. The sorption isotherm of refined fiber was fitted very well by the Hailwood-Horrobin model.

July 1, 2008

Elastic deformation mechanisms of softwoods in radial tension – Cell wall bending or stretching?

Carl S. Modén, Lars A. Berglund

Page range: 562-568

Abstract

Radial softwood modulus E R is typically twice as high as the tangential modulus E T . The reason for this is unclear, although cell geometry is likely to contribute. The established hexagonal honeycomb model for prediction of E R is based on a cell wall bending mechanism only. If cell wall stretching also takes place, the dependence of E R on relative density will be different. If experimental data for E R as a function of relative density show deviations from cell wall bending predictions, this may indicate the presence of cell wall stretching. A SilviScan apparatus is used to measure density distribution. A procedure by means of digital speckle photography is then developed for measurements of local E R within the annual rings of spruce. Comparison is made between experimental data and the two expected density dependencies from cell wall bending and from stretching. The hypothesis of cell wall stretching as a contributing mechanism is supported based on the observed linear dependence of E R over a wide density range.

July 1, 2008

Fiberboard bending properties as a function of density, thickness, resin, and moisture content

John F. Hunt, Jane O'Dell, Chris Turk

Page range: 569-576

Abstract

Fibers from treetop residues of lodgepole pine ( Pinus contorta ) and recycled old corrugated containers were used to fabricate wet-formed fiberboard panels over a range of densities from 300 to 1100 kg m -3 , a thickness range from 1.3 to 4.8 mm, and phenolic resin contents from 0% to 4.5%. The panels were then tested after conditioning in 50% and 90% relative humidity (RH) environments. Density, thickness, equilibrium moisture content, bending modulus of elasticity (MOE), and modulus of rupture (MOR) were measured for each panel. Panel apparent-density increased with thickness, but this may be due to surface effects rather than true density values. The equilibrium moisture content approximately doubled for the panels in the 90% RH environment, compared to 50% RH. At 50% and 90% RH conditions, equilibrium moisture contents decreased significantly when only 0.5% resin was added and remained essentially the same with increasing resin levels. In this study, both MOE and MOR increased with approximately the square of density. MOE increased, whereas MOR showed no clear effects as thickness and resin amount increased. This research is part of a larger program for developing an understanding of panel properties for engineered three-dimensional fiberboard products.

June 25, 2008

Modification of Fagus sylvatica (L.) with 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU): Part 1. Estimation of heat adsorption by the isosteric method (Hailwood-Horrobin model) and by solution calorimetry

Andrés Dieste, Andreas Krause, Holger Militz

Page range: 577-583

Abstract

The differential heat of adsorption ( ΔH s ) of Fagus sylvatica wood modified with 0.8 M, 1.3 M, and 2.3 M solution of 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU) was determined at different equilibrium moisture contents (EMCs) by both the isosteric method, using the Hailwood-Horrobin model at 20, 30, and 40°C and by solution calorimetry. Both methods revealed that at 1% EMC, the 2.3-M modified wood releases approximately double the amount of energy as does unmodified wood. At EMC below approximately 5%, DMDHEU-modified wood appears to be more hygroscopic than unmodified wood, indicating that more OH groups are available for adsorption. The bulking effect of the cell wall and the increase of OH groups caused by the modification with DMDHEU are probably the reason for this observation. As expected, higher EMC led to a reduction of ΔH s .

June 25, 2008

Development of wooden block shear wall – Improvement of stiffness by utilizing elements of densified wood

Ivón Hassel, Pierre Berard, Kohei Komatsu

Page range: 584-590

Abstract

The objective of this research was to study the performance of a wooden block shear wall which utilizes compressed wood as a connecting element in place of the traditional metal connectors. The compressed wood was made by compressing Japanese cedar ( Cryptomeria japonica ) to a compression ratio of 63% without fixation treatment. The connecting elements, namely diamond keys (DKs), recover their radial compressed dimension when absorbing moisture. The expansion of the wood causes a tighter fit of the wood blocks, thereby improving the system stiffness. DKs work as fuses by absorbing most of the stress and damage. This allows the structure to be readjusted and reused after earthquakes. The wooden blocks are made of glued-laminated timber based on European red pine ( Pinus sylvestris ). The behavior of the wall was studied by means of a finite element method (FEM) and full-scale shear tests. The material properties were found by performing mechanical tests, using digital image analysis, and strain gauges to measure the strain. The stiffness of the wall and how it is affected by the DKs are described. The FEM provided predictions which are in agreement with experimental results of wood block wall systems. The addition of DKs increased the stiffness by up to 2.5-fold. Future improvement of FEM will include accounting for the contribution of vertical connectors and out-of-plane forces.

July 1, 2008

Significance of the heating rate on the physical properties of carbonized maple wood

Xinfeng Xie, Barry Goodell, Yuhui Qian, Michael Peterson, Jody Jellison

Page range: 591-596

Abstract

Effects of the heating rate on the physical properties of carbonized wood were investigated by comparing the dimensional shrinkage, electrical resistivity, Young's modulus, and the evolution of turbostratic crystallites in maple hardwood samples carbonized at 600°C, 800°C, and 1000°C under heating regimes of 3°C h -1 and 60°C h -1 . Important carbonized wood properties that developed at high temperature and high heating rates could also be produced at slow heating rates and lower temperatures. Furthermore, slow heating rates promoted the formation and growth of graphene sheets in turbostratic crystallites, which had a significant influence on the electrical resistivity and Young's modulus of the carbonized wood. The results indicate that the graphene sheets of turbostratic crystallites formed during wood carbonization were arranged parallel to the axial direction of wood cells and at an angle to the circumference of wood cells in the cross-sectional plane. With regard to the production of carbon products, a decrease in the heating rate may be beneficial for char properties and the prevention of crack production during manufacture of large monolithic carbon specimens from wood and wood-based materials.

July 1, 2008

Exploring Scots pine fibre development mechanisms during TMP processing: Impact of cell wall ultrastructure (morphological and topochemical) on negative behaviour

Dinesh Fernando, Geoffrey Daniel

Page range: 597-607

Abstract

A study was carried out aiming at understanding the fundamental reasons for different fibre behaviour exhibited by Norway spruce and Scots pine causing large energy consumption differences during thermomechanical pulping (TMP). Ultrastructural characterization of TMP fibres and shives, which were sampled from the two wood species after primary refining, was performed using scanning electron microscopy, transmission electron microscopy (TEM) and TEM-immunogold labelling for their morphological and topochemical properties. As expected, pine wood chips needed higher electrical energy consumption to be refined to a given Canadian Standard Freeness and it produced inferior strength properties compared to spruce. Electron microscopy (EM) observations indicated that the mechanisms of fibre development during primary refining of pine and spruce were different. The two stages of pine fibre separation and development were not concurrent. Results indicated that pine fibre defibration/fracture occurred predominantly through the compound middle lamella/S1 interphase or through the S1 layer producing lesser amounts of shives during the primary refining stage than spruce. In contrast, spruce fibres defibrated mainly through the S2 layer. Detailed EM observations on shives and pulp fibres from TMP revealed the ultrastructural characteristics associated with pine fibre cell walls. Morphological and topochemical features of the S1 layer, S1/S2 interphase, such as lignin and galactoglucomannan distribution across cell walls were explored. The ultrastructural properties are discussed in relation to the TMP parameters (i.e., electrical energy consumption) and strength data. It is concluded that ultrastructural characteristics of Scots pine fibre cell walls govern the different fibre development mechanisms and explain the negative response of this wood during TMP processing.

July 22, 2008

Pentachlorphenol migration from treated wood exposed to simulated rainfall

John Simonsen, Hua Chen, Jeffrey J. Morrell, Camille Freitag, Milo Clauson

Page range: 608-612

Abstract

The leaching of toxins from treated wood poses an, as yet, poorly quantified risk to both plant and animal life. In particular, the leaching of pentachlorophenol (PCP) into rainwater falling on treated wood over aquatic environments, such as bridges, is understudied. Computer models have been developed which predict the leaching of creosote from marine pilings. If data were available, similar models could be developed for PCP-treated bridges and the risk to waterways determined for various structural designs. Providing such data is the objective of this study, where the migration of PCP from treated wood under the influence of simulated rainfall was studied using a simulation system that delivered uniform rainfall rates over-treated wood. The runoff from the treated wood was captured and analyzed with high resolution gas chromatography combined with low resolution mass spectrometry. PCP migrated from treated wood into rainwater runoff at a fairly constant rate of approximately 0.15 g l -1 m -2 . Small non-significant deviations were observed with rainfall rate, time, and temperature. We suggest that PCP migration rates from exposed treated wood can be modeled and thereby predict the migration of PCP from this source into the environment.

June 25, 2008

Resistance of Trichoderma harzianum to the biocide tebuconazol – Proposed biodegradation pathways

Diana N. Obanda, Todd F. Shupe, W. James Catallo

Page range: 613-619

Abstract

Wood preservatives are moving from metal-based to totally organic chemical systems. A major problem with organic biocides is biodegradation by wood-inhabiting but non-decaying microorganisms during the long service expected from treated wood. While data for triazoles suggest good efficacy against a wide range of basidiomycete fungi, this class of preservatives are less effective against the ascomycetes (soft-rot fungi, molds, and stains). The objective of this study was to examine the biotransformation of tebuconazol as one of the triazoles by the mold Trichoderma harzianum . After inoculation for 21 days, 68% of the tebuconazol was degraded in vitro. MS and IR analysis of isolated metabolites indicated that the major pathway is cleavage of the triazole ring on tebuconazol. Additionally, oxidation reactions occurred on the tert- butyl moiety. The oxidation products are subsequently metabolized by acetylation. Biotransformation resulting in non-toxic degradates is one of the mechanisms employed by this fungus in tolerating tebuconazol.

Short Notes

July 31, 2008

On the variation of acid-labile aryl ether unit content in wood lignin

Xiao-Ping Guo, Yuan-Zong Lai

Page range: 527-529

July 1, 2008

Coumarins and secoiridoid glucosides from bark of Fraxinus rhynchophylla Hance

Chuan-Ling Si, Zhong Liu, Yan-Fang Su, Jin-Kyu Kim, Young-Soo Bae

Page range: 553-555

July 1, 2008

Antifungal activities of heartwood extracts of Port-Orford cedar extractives

Heng Gao, Diana N. Obanda, Todd F. Shupe, Chung Y. Hse, Dennis R. Ring

Page range: 620-623

July 1, 2008

Antifungal secoabietane dialdehyde and bisabolane-type terpenoids from the heartwood of Cryptomeria japonica D. Don

Irawan W. Kusuma, Sanro Tachibana

Page range: 624-626

Meetings

July 31, 2008

Meetings

Page range: back cover-back cover

About this journal

Objective
Holzforschung (HF) is an international scholarly journal that publishes cutting-edge research on the biology, chemistry, physics and technology of wood and wood components. High quality papers about biotechnology and tree genetics are also welcome. Rated year after year as one of the top scientific journals in the category of Pulp and Paper (ISI Journal Citation Index), Holzforschung represents innovative, high quality basic and applied research. The German title reflects the journal's origins in a long scientific tradition, but all articles are published in English to stimulate and promote cooperation between experts all over the world. Ahead-of-print publishing ensures fastest possible knowledge transfer.

Topics

Biology, chemistry, physics and technology of wood and wood components
Biotechnology and tree genetics

Article formats
Original articles, Reviews, Short notes

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