Showing papers in "Holzforschung in 2004"

Comparative Analysis of Inactivated Wood Surfaces

Abstract: The surface inactivation of two wood species, yellow poplar (Liriodendron tulipifera) and southern pine (Pinus taeda), was studied following high temperature drying. Surface analysis involved X-ray photoelectron spectroscopy, sessile drop wettability and fracture mechanics of the adhesively-jointed surfaces. The results showed that wood drying at high temperature (i.e., >160 to 180°C) caused modifications in surface composition. The oxygen to carbon ratio (O/C) decreased and the ratio of carbon atoms bonded to other carbon or to hydrogen atoms vis-a-vis carbons bonded to oxygen atoms (i.e., the C1/C2 ratio) increased with drying temperature. In addition, the contact angle increased with the temperature of exposure, but decreased with time. A dependence on wood species was evident: southern pine surfaces always exhibited higher contact angles than yellow poplar. Also, the rate of contact angle decline with time, dθ/dt, was found to vary with surface composition: this rate corresponded to O/C ratio-changes, especially in the case of southern pine. Southern pine was most susceptible to inactivation particularly when bonded with PF adhesive. Yellow poplar surfaces did not show significant inactivation when exposed to drying temperatures below ca. 180°C. The results are explained by a relative enrichment of wood surfaces with non-polar substances, hydrophobic extractives and volatile organic compounds that become visually evident during the drying process at temperatures above ca. 160°C. Little change was observed if drying temperatures remained below 150°C.

The use of organo alkoxysilane coupling agents for wood preservation

Abstract: Corsican pine (Pinus nigra) sapwood was treated with methanolic solutions of two organo alkoxysilanes ([γ-(methacryloxy)propylx] trimethoxy silane (TMPS), or vinyl trimethoxy silane (VTMS)). Various treatment parameters were studied in order to determine the optimum method for obtaining a stable weight percentage gain. For TMPS, it was found that best results were obtained when a free-radical initiator was used in conjunction with the silane. This indicates that polymerisation of this species occurs via the pendant methacryloxy moeity, a result confirmed by solid-state nuclear magnetic resonance studies of the treated wood. For VTMS, wood moisture content had a profound influence upon the weight percentage gain due to treatment, with higher weight percentage gains obtained as wood moisture content was increased. This indicates that polymerisation in this case occurred via the formation of silanol groups to form siloxane linkages. Solid-state NMR confirmed that the double bond of the organo-functional group was intact after polymerisation had occurred. Modified wood samples were then prepared using optimised treatments for each silane. The wood was prepared to a variety of weight percentage gains and the effect of treatment on the dimensional stability and decay properties of the treated material studied. Treatment of Corsican pine sapwood with the two organo-alkoxy silanes, resulted in only moderate increases in dimensional stabilisation, with anti shrink efficiency values (after 5 water-soak/oven-dry cycles) no greater than 40%. Treatments were found to be relatively stable to hydrolysis. Some differences were observed in the effectiveness of the two silanes in providing protection. Full decay protection required high treatment levels with the silanes.

Eco-composite from poly(lactic acid) and bamboo fiber

Abstract: Bamboo fiber-filled poly(lactic acid) (PLA) eco-composites were prepared by mechano-chemical compositing with bamboo fiber (BF)-esterified maleic anhydride (MA) (BF-e-MA) in the presence of dicumyl peroxide as a radical initiator. Tensile properties of the composites were improved by adding BF-e-MA and the dicumyl peroxide. A sufficient effect of the addition on the tensile property of the composites was observed even in the presence of the dicumyl peroxide of 0.25%. However, the composites with BF-e-MA usually showed a higher activation energy for thermal flow, indicating that their flow became more difficult, because molecular motions were rather suppressed by cross-linking of BF-e-MA with the PLA matrix resin. The crystallization temperature of PLA became higher by the addition of BF and BF-e-MA in non-isothermal crystallization. It was confirmed by scanning electron microscope and polarizing microscope observation that interfacial properties between BF and PLA were improved after the addition of BF-e-MA. A diffusion coefficient (D) of water in the PLA/BF composites with BF-e-MA was smaller than that in the composites without BF-e-MA. An equilibrium water-sorption amount (M∞) was higher in the order of composites without BF-e-MA>composites with BF-e-MA>pure PLA.

Use of near infrared spectroscopy to predict the mechanical properties of six softwoods

Abstract: The visible and near infrared (NIR) (500-2400 nm) spectra and mechanical properties of almost 1000 small clear-wood samples from six softwood species: Pinus taeda L. (loblolly pine), Pinus palustris, Mill. (longleaf pine), Pinus elliottii Engelm. (slash pine), Pinus echinata Mill. (shortleaf pine), Pinus ponderosa Dougl. ex Laws (ponderosa pine), and Pseudotsuga menziesii (Mirb.) Franco (Douglas fir) were measured. Projection to Latent Structures (PLS) modeling showed that the NIR spectra of these softwoods could be used to predict the mechanical properties of the clear-wood samples. The correlation coefficients for most of these models were greater than 0.80. All six softwood species were combined into one data set and a PLS model was constructed that effectively predicted the strength properties of any of the individual softwoods. Reducing the spectral range to between 650 and 1050 nm only causes a slight decrease in the quality of the models. Using this narrow spectral range enables the use of smaller, faster, lighter, less expensive spectrometers that could be used either in the field or for process control applications.

Homogeneity in cellulose crystallinity between samples of Pinus radiata wood

Abstract: Wood was sampled from 22 locations in 3 Pinus radiata trees and characterized by solid-state 13 C NMR spectroscopy. Values of a cellulose crystallinity index were confined to the range 0.486 to 0.541 despite inclusion of earlywood and latewood, compression wood and opposite wood, juvenile wood and mature wood. The mean value was 0.515 and the standard deviation was 0.015. Highest crystallinity was associated with relatively slow radial growth, with a correlation coefficient of R= -0.79 for a linear least-squares fit against ring width. The NMR results were consistent with published studies based on X-ray peak widths. Crystallinity indices based on X-ray peak heights or areas have shown wider ranges of variation, attributed to differences in cellulose content rather than cellulose crystallinity.

Estimation of Pinus radiata D. Don tracheid morphological characteristics by near infrared spectroscopy

Abstract: Eight Pinus radiata D. Don increment core samples were selected from a total of 32 cores for the development of calibrations for several tracheid morphological characteristics: coarseness, perimeter, radial and tangential diameter and wall thickness. Near infrared (NIR) spectra, obtained from the radial-longitudinal face of each core in 10-mm sections from pith to bark, were used to develop the calibrations. Calibrations for coarseness and wall thickness were excellent, with coefficients of determination (R 2 ) of 0.91 and 0.89, respectively. Calibrations for the remaining characteristics were weaker (R 2 ranged from 0.65 to 0.69). To test the predictive ability of the calibrations, two intact P. radiata increment cores (core A and B) were selected from the same set as the calibration samples. NIR-predicted tracheid coarseness and wall thickness were in strong agreement with measured (SilviScan-determined) values. Radial patterns of variation (NIR-predicted, measured) closely followed each other for both cores, but coarseness and wall thickness were underestimated for core B. Tracheid tangential perimeter was well predicted with R 2 of 0.69 (core A) and 0.79 (core B). Relationships for the remaining characteristics were weak. Collection of NIR spectra in smaller increments, to capture more of the variation, may improve calibration.

Changes in the lignincarbohydrate complex in softwood kraft pulp during kraft and oxygen delignification

Abstract: Three kraft pulps in the kappa number range between 50 and 20 and the same pulps oxygendelignified to similar lignin contents (kappa approximately 6) were analyzed for lignincarbohydrate complexes ...

Ionic liquids in wood preservation

Abstract: In this study ionic liquids (3-alkoxymethyl-1-methylimidazolium tetrafluoroborates and hexafluoro-phosphates) are successfully used for wood preservation. These liquids are new biocides as well as new solvents which penetrate wood well. The prepared ionic liquids with an alkoxymethyl substituent, which consisted of 7, 8 or 9 carbon atoms, exhibited fungicidal activity against Coniophora puteana (Schum.: Fr.) Karst., Trametes versicolor (L.: Fr.) Pilat and Sclerophoma pityophila (Corda) v. Hohn. The effective and lethal doses were measured by the agar-plate method. In their activity against wood degrading fungi, ionic liquids such as 1-methyl-3-octyloxymethylimidazolium and 1-methyl-3-nonyloxymethylimidazolium tetrafluoroborates were comparable with commercially available benzalkonium chloride and didecyldimethylammonium chloride. Ionic liquids both with and without DDAC penetrated into Scots pine wood very well.

The effects of initial spacing on wood density, fibre and pulp properties in jack pine (Pinus banksiana lamb.)

Abstract: Relationships between basic tree and wood properties, and species, seed source, geographic location, site conditions and management decisions are very complex. The objective of this study was to quantify the effects of forest management practices on wood density, fibre and pulp properties in jack pine, one of the most important commercial species in Northern America. A better understanding of the relationship between initial spacing and wood and end-product quality should help define improved forest management strategies required to produce quality wood and products in the future. On the basis of the oldest jack pine initial spacing trial established in 1941 by the USDA Forest Service, this study examined the impact of four different initial spacing trials on tree growth, wood density, fibre and pulp properties of jack pine. The results clearly show that initial stand spacing has a significant effect on all of these properties, and thus it is possible to improve yield and wood and pulp fibre properties of jack pine through stand density regulation. Additionally, a positive effect of pre-commercial thinning on fibre properties was also demonstrated. As a consequence of these results, basic prescription information for decision-making in the establishment of jack pine plantations with desirable pulp properties can be elucidated.

Effect of wood acidity and catalyst on UF resin gel time

Abstract: Knowledge of pH and buffering capacity of raw fiber materials is important for understanding the effects of raw material on the curing rate of urea formaldehyde (UF) resin, used for panel manufacturing, especially with some less-desirable wood materials such as bark, top, and commercial thinnings. The effects of pH and buffering capacity as well as catalyst content on the gel time of UF resin were investigated. The results obtained from this study indicate that bark has a lower pH value as well as higher acid and alkaline buffering capacities than wood of the same species due to their extractives. The pH values of the raw fiber materials studied decrease with increased absolute and relative acid buffering capacity due to the increased absolute acidity mass in the solution. At lower levels of added catalyst, the effect of raw material pH on UF resin gel time is significant, while it is insignificant at higher catalyst contents. This may be due to the acidity of wood, which is the main acid catalyst source of the mixture at lower levels of added catalyst, while at higher levels, catalyst is the main source. With higher catalyst contents, all studied raw materials mixed with UF resin result in a longer gel time than does UF resin alone.

Bioactive phenolic substances in industrially important tree species. Part 2: Knots and stemwood of fir species

Abstract: Knots, i.e. branch bases inside tree stems, in fir trees contained remarkably higher concentrations of lignans, oligolignans, and juvabiones than the adjacent stemwood. Eight fir species were analysed (Abies sibirica, A. lasiocarpa, A. balsamea, A. alba, A. amabilis, A. veitchii, A. sachalinensis, and A. concolor). The amount of lignans could in some knots exceeds 6% (w/w) and the knots generally contained 20-50 times more lignans than the stemwood. However, there were large variations, not only between species but also even between knots in the same tree. Secoisolariciresinol was the predominant lignan in all knots. The lignans occur in free form in the knots and are easily extracted with polar solvents. In addition to the lignans, oligomeric aromatic substances, mainly sesquineo- and dineolignans, and juvabiones were accumulated in the knotwood. Secoisolariciresinol, but also lariciresinol (Abies alba) and 7-hydroxymatairesinol (A. amabilis), could be extracted in large scale from fir knots at pulp and paper mills. The ready availability of large amounts of lignans and oligolignans now enables research to assess their bioactivity and provide the base for applications in medicine and nutrition, or as natural antioxidants and antimicrobial agents in various technical products.

A biopulping mechanism : creation of acid groups on fiber

Abstract: We investigated how biopulping modifies chemical and physical properties of wood and how these changes affect the properties of the resulting fiber. Mechanical and chemical testing revealed wood cell changes during 2 weeks of colonization by Ceriporiopsis subvermispora. Typical mechanical properties, such as modulus of elasticity and maximum load, tracked reductions in energy needed for mechanical refining to pulp. The data indicate the fiber saturation point of spruce increased from 29% to 42% during biopulping. At the same time, titratable acid groups increased up to 62%. Chemical analysis showed that oxalic acid esters were produced in the wood during biopulping in sufficient amounts to account for the increase in acid groups. The benefits of biopulping - energy savings and increased handsheet strength - as well as other physical property changes are consistent with the mechanism we propose: biopulping increases the acid group content of wood.

Artificial weathering of tropical woods. Part 2: Color change

Abstract: This paper describes the change in diffuse reflectance Fourier transform infrared (DRIFT) and ultraviolet-visible (UV-Vis) diffuse reflectance spectra of the following eight tropical woods during artificial weathering up to 600 h in relation to their color changes, especially to yellowing: Amnurana acreana, Acacia auriculiformis, Dipterocarpus spp., Eucalyptus marginata, Eucalyptus robusta, Shorea spp. and Tabebuia spp. with relatively high and low specific gravity. For A. acreana, A. auriculiformis, Dipterocarpus spp. and both Tabebuia spp., Δb * (yellowing) increased with exposure up to 50 h, and decreased above 50 h. For E. marginata, E. robusta and Shorea spp., on the other hand, both Δa * (shift to red) and Δb * decreased with increased exposure time. For woods in which Δb * increased, the Δb * showed a positive dependence on the difference in relative intensity ratio of a band at 1740 cm -1 to that at 2900 cm -1 (ΔD 1740 /D 2900 ) in DRIFT spectra of specimens before and after exposure. This result indicated that the increased band at 1740 cm -1 played a significant role in the increased Δb * . Then again, also for woods in which Δb * decreased, the ΔD 1740 /D 2900 increased, but was not related to the Δb * . The ΔD 1740 /D 2900 for woods in which Δb * decreased had a positive relationship to the difference in remission function at 410 nm (ΔF(R∞) 410 ) in UV-Vis diffuse reflectance spectra for specimens before and after exposure, while woods in which Δb * increased were independent of the ΔF(R∞) 410 . Therefore, it is suggested that woods in which Δb * increased and decreased differ from one another in the contribution to the increase in the band at 1740 cm -1 , resulting in either an increase or decrease of Δb * .

Bioactive phenolic substances in industrially important tree species. Part 1: Knots and stemwood of different spruce species

Abstract: Knots (i.e., branch bases inside tree stems) in spruce trees contained remarkably higher concentrations of lignans and oligolignans than the adjacent stemwood. The amount of lignans in some knots exceeded 10% (w w -1 ) and some knots contained hundreds of times more lignans than the heartwood in the same tree. However, there were large variations between different species and even between different knots in the same tree. 7-Hydroxymatairesinol was the predominant lignan in knots of Picea abies, P. glauca, P. koraiensis, P. mariana, and P. omorika, while liovil and secoisolariciresinol dominated in P. sitchensis and P. pungens. The lignans occur in free form in knots and are easily extracted with polar solvents. In addition to the true lignans, especially the knots contained large amounts of lignan-related oligomeric aromatic substances, here called oligolignans, consisting of three or four phenylpropane units. 7-Hydroxymatairesinol, but also other lignans, could be extracted in large scale from spruce knots at pulp and paper mills. Other potentially important lignans could be produced from 7-hydroxymatairesinol by semisynthesis. The ready availability of large amounts of lignans and oligolignans now enables research to assess their bioactivity and provide the basis for applications in medicine and nutrition or as natural antioxidants and antimicrobial agents in a variety of technical products.

Identification of volatile organic compounds (VOCs) from bacteria and yeast causing growth inhibition of sapstain fungi

Abstract: This paper describes an experiment to identify volatile organic compounds (VOCs) from a range of three bacteria and one yeast strain that had previously been shown to be inhibitory to selected sapstain fungi. The bacteria and yeast were cultured on two media, malt extract (ME) and tryptone soya (TS) and the VOCs trapped on chromatographic adsorbant before being analysed by Integrated Thermal Desorption - GC-MS. Since sapstain fungi were only inhibited by VOCs produced on the TS media, it was possible to use Principle Component Analysis to highlight the individual VOCs that are most likely to be responsible for the inhibition. A number of ketones together with dimethyl disulphide and dimethyl trisulphide were highlighted. The importance of VOC production by organisms during the biological control of sapstain is discussed.

Oligolignans in Norway spruce and Scots pine knots and Norway spruce stemwood

Abstract: Oligolignans present in substantial amounts in Norway spruce and Scots pine knots were characterised. The hydrophilic knotwood substances were extracted and different chromatographic methods were applied to obtain fractions for analysis by GC, GC-MS, HR-EI-MS, LC-ESI-MS, NMR, and FTIR. β-O-4-Linked guaiacylglyceryl ethers of hydroxymatairesinol (la, lb, lc), secoisolariciresinol (II), lariciresinol (III), isolariciresinol (IV), lignan A (V), liovil (VI), conidendrin (VII), and pinoresinol (VIII) were identified in the spruce knotwood extract and β-O-4-linked guaiacylglyceryl ethers of nortrachelogenin (IX) and secoisolariciresinol (II) in the pine knotwood extract. The structures of allo-hydroxymatairesinol-4'-guaiacyl-glyceryl ether (la), hydroxymatairesinol-4-guaiacylglyceryl ether (lb), hydroxymatairesinol-4'-guaiacylglyceryl ether (Ic), secoisolariciresisinol-4-guaiacylglyceryl ether (II), and lariciresinol-4'-guaiacylglyceryl ether (III) were determined via GC-MS, HR-MS, and 1 H and 13 C NMR analyses. The structures of (la), (lc), (IV), (V), (VI), (VII), and (IX) have not been reported earlier. Spruce stemwood, both heartwood and sapwood, also contained oligolignans in small amounts. In addition, some dilignans with four phenylpropanoid units were tentatively identified in the hydrophilic knotwood substances.

Changes in the surface properties of wood due to sanding

Abstract: Spruce and beech wood specimens were sanded with four different grain sizes. Surface morphological and chemical changes were determined by roughness measurement, surface free energy determination according to acid-base theory and X-ray photoelectron spectroscopy. An analysis model was proposed to describe chemical changes due to sanding and the data were analysed according to it. It could be shown that spruce and beech behave similarly over a wide range and that chemical changes are non-linear functions of grain size and thus surface roughness. A maximum of surface free energy and a maximum of carbon C1s sub-peak ratio (ratio of carbon bonded to a single non-carbonyl oxygen to carbon bonded only to hydrogen or other carbon atoms) was found for middle grain size.

Production of 2,5-dimethoxyhydroquinone by the brown-rot fungus Serpula lacrymans to drive extracellular Fenton reaction

Abstract: The brown-rot fungus Serpula lacrymans MAFF 420003 was grown in a liquid culture medium containing 0.5% carboxymethyl cellulose (CMC) and 1% glucose as carbon sources. Although little extracellular cellulase was secreted, the fungus produced an oxidized quinone-type chelator, 2,5-dimethoxy-1,4-benzoquinone (2,5-DMBQ). The concentration of 2,5-DMBQ in the medium reached a maximum of 90 μM after a month of cultivation. S. lacrymans could reduce 2,5-DMBQ to 2,5-dimethoxyhydroquinone (2,5-DMHQ), thus a biological Fenton reaction was adopted by the fungus. The changes in the molecular weight distribution of CMC and arabinogalactan were analyzed after the addition of 2,5-DMHQ and Fe 3+ . CMC was apparently depolymerized by the reaction, but the same reaction conditions showed no significant effect on arabinogalactan. These differences suggest the specificities of the biological Fenton reaction via 2,5-DMBQ toward soluble polysaccharides. In addition, the crystallinity index of α-cellulose did not decrease as a result of the reaction with 2,5-DMHQ and Fe 3+ . These results provide indirect evidence that S. lacrymans employs a biological Fenton reaction mediated by a quinone-type chelator, and preferentially degrades amorphous regions of cellulose rather than crystalline regions in the non-enzymatic cellulose degradation.

Antifungal activity of constituents from the heartwood of Gmelina arborea: Part 1. Sensitive antifungal assay against Basidiomycetes

Abstract: Antifungal activity of constituents from the heartwood of the Malaysian Gmelina arborea against Trametes versicolor and Fomitopsis palustris was investigated. A sensitive bioassay system for antifungal activity against basidiomycetes was developed which uses a medium in which homogenized hyphae were dispersed. Ethyl acetate-solubles from the heartwood showed the highest activity against both fungi, although the activity against F. palustris was quite weak. Spots exhibiting antifungal activity against T. versicolor were specified by autobiography of ethyl acetate-solubles, and five constituents were isolated and identified as (+)-7'-O-ethyl arboreol, (+)-paulownin, (+)-gmelinol, (+)-epieudesmin and (-)-β-sitosterol. The four lignans showed antifungal activity, whereas β-sitosterol did not. From the comparison of antifungal activity, it was concluded that the piperonyl nucleus contributed to the activity of lignans. Of the four lignans isolated, gmelinol appeared to be an important antifungal constituent, since it was rich in the heartwood of G. arborea. Furthermore, the synergism by coexistence of these five compounds was confirmed.

Chemical reaction of maritime pine sapwood (Pinus pinaster Soland) with alkoxysilane molecules: A study of chemical pathways

Abstract: The chemical modification of maritime pine sapwood (Pinus pinaster) with alkoxysilanes was studied according to three different pathways: carbamoylation with 3isocyanatopropyltriethoxysilane, etherification with 3glycidoxypropyltrimethoxysilane and alcoholysis of n-propyltrimethoxysilane Grafting was confirmed by weight percent gain calculations (WPG), infrared spectroscopy (FTIR) as well as 13 C and 29 Si NMR CP MAS analysis Signals of the grafted groups in the different spectra were assigned and the reactivity of the trialkoxysilane moieties towards wood was discussed Experiments with model wood blocks showed that the reactions investigated occurred within the wood cell walls Grafted chemicals were found to be relatively stable with regard to water leaching but only slight dimensional stabilisation was noted after treatment

Effects of refining on the fibre structure of kraft pulps as revealed by FE-SEM and TEM : Influence of alkaline degradation

Abstract: The aim of the study was to evaluate the effect of refining on the ultrastructure of spruce pulp fibres. Pulps with different molar masses of cellulose (estimated as intrinsic viscosity) were studi ...

Carbohydrate structures in residual lignin-carbohydrate complexes of spruce and pine pulp

Abstract: Residual lignin carbohydrate complexes (RLCC) were isolated enzymatically from spruce and pine pulp. The RLCCs contained 4.9–9.4% carbohydrates, with an enrichment of galactose and arabinose compared to the original pulp samples. The main carbohydrate units present in all studied RLCCs were 4-substituted xylose, 4-, 3- and 3,6-substituted galactose, 4-substituted glucose and 4 and 4,6-substituted mannose. These units were assigned to carbohydrate residues of xylan, 1,4- and 1,3/ 6-linked galactan, cellulose and glucomannan. RLCCs of surface material and the inner part of spruce kraft pulp fiber were compared to obtain information on the heterogeneity of layers of the fiber wall. The 1,4linked galactan was the major galactan in RLCC of fiber surface material of spruce kraft pulp. Towards the inner part of the fiber, the proportion of 1,3/6-linked galactan increased relative to 1,4-linked galactan. This finding is presented for the first time. 1,3/6-Linked galactan structures are suggested to have a role in restricting lignin removal from the secondary fiber wall. RLCCs of three different alkaline pine pulps were studied before and after oxygen delignification to evaluate differences resulting from the cooking method. The pulps were conventional kraft pine pulp (PCK), a polysulfide/ anthraquinone pine pulp (PPSAQ) and a soda/anthraquinone pine pulp (PSoAQ); all were cooked to approximately kappa number 30. Small differences were found in the carbohydrate structures of the unbleached pulps. The study indicated that the RLCC of unbleached PSoAQ pulp contained longer oligomeric carbohydrate chains and less branched 1,3/6-linked galactan residues than the RLCCs of unbleached PCK and PPSAQ pulps. The RLCC of the unbleached PSoAQ also contained more 1,4-linked glucose units suggesting a greater number of linkages of lignin to cellulose in the PSoAQ pulp than in the other two pulps. All RLCCs of oxygen-delignified pulps had more non-reducing ends and less 1,3/ 6-linked galactan than the corresponding RLCCs of the unbleached pulps. The RLCC of the oxygen-delignified PSoAQ pulp had a higher ratio of 1,4-galactan to 1,3/6linked galactan and shorter xylan residues than the RLCCs of oxygen-delignified PCK and PPSAQ pulps.

Variation in microfibril angle in Eucalyptus clones

Abstract: The microfibril angle of the S 2 layer in wood fibres is an ultra-microscopical feature that influences important properties affecting the utilisation of timber. However, this characteristic is as yet little studied, and this is especially true of the genus Eucalyptus. The microfibril angle of the S 2 layer of the secondary wall was measured in fibres taken from eight-year-old trees of 11 Eucalyptus clones growing in four sites in Brazil. The overall mean microfibril angle measured was 8.8°. While the angle seemed to decrease slightly from pith to bark in a non-linear fashion, this decrease was not statistically significant. The microfibril angle showed statistically significant differences between sites and between clones, although the broad sense heritability of the microfibril angle was low (h 2 =0.293). Various theories attempt to explain the microfibril orientation, but we conclude that environmental stresses play an important role in defining the angle in Eucalyptus wood.

Nondestructive estimation of tracheid length from sections of radial wood strips by near infrared spectroscopy

Abstract: The use of calibrated near infrared (NIR) spectroscopy for predicting tracheid length of Pinus taeda L. (loblolly pine) wood samples is described. Ten-mm sections of 14 P. taeda radial strips were selected and NIR spectra obtained from the radial longitudinal face of each section. The fibers in these sections were characterized in terms of arithmetic and length-weighted mean tracheid length using a fiber quality analyzer, and calibrations with NIR spectra were developed for both measures of tracheid length. Relationships were good, with coefficients of determination (R2) of 0.88 for arithmetic tracheid length and 0.96 for length-weighted tracheid length. The accuracy of NIR predicted length-weighted tracheid length was sufficient for ranking purposes.

Internal stresses in the cross-grain direction in glulam induced by climate variations

Abstract: Results are presented from an experimental investigation to determine internal stress states perpendicular to grain in glulam induced by moisture variations. The stresses are determined by measuring the released strains before and after cutting. Stress distributions are determined for specimens seasoned in constant humidity, specimens exposed to an artificial single climate change, specimens exposed to cyclic climate change and for specimens exposed to natural climate outdoors under shelter. Results for seasoned specimens show that internal stresses exist in glulam without the presence of moisture gradients. Stresses in specimens with an induced moisture gradient become larger when moistening from a specific climate A to another climate B than when drying from B to A. Tests in an outdoor sheltered climate show large variations in strains and stresses. The tensile stress level in the inner part of the glulam cross section exceeds the characteristic strength of 0.5 MPa during a period of approximately 80 days.

Solid wood joints by in situ welding of structural wood constituents

Abstract: Mechanically-induced wood flow welding, without any adhesive, is here shown to rapidly yield wood joints satisfying the relevant requirements for structural application. The mechanism of mechanically-induced vibrational wood flow welding is shown to be due mostly to the melting and flowing of the amorphous polymer materials interconnecting wood cells, mainly lignin, but also some hemicelluloses. This causes the partial detachment of long wood cells and wood fibres and the formation of an entanglement network in a matrix of melted material which then solidifies. Thus, it forms a wood cell/fibre entanglement network composite having a molten lignin polymer matrix. During the welding period, some of the detached wood fibres no longer held by the interconnecting material are pushed out of the joint as excess fibre. Cross-linking chemical reactions of lignin and of carbohydrate-derived furfural also occur. Their presence has been identified by CP-MAS 13 C NMR. These reactions are, however, relatively minor contributors during the very short welding period. Their contribution increases after welding has finished, explaining why relatively longer holding times under pressure after the end of welding contribute strongly to obtaining a good bond.

The creep of wood destabilized by change in moisture content. Part 2: The creep behaviors of wood during and immediately after adsorption

Abstract: The fluidity of wood remarkably increases during moisture changes. This phenomenon is termed mechano-sorptive creep. The mechanism of mechano-sorptive creep has been studied, including a previous report by our group. Here, creep tests in bending were carried out for wood during and immediately after adsorption of moisture and after a long moisture conditioning. The effects of the rate of moisture adsorption on creep were also examined. The results and conclusions are as follows: (I) Greater creep occurred immediately after the adsorption process as compared with that after a long moisture conditioning, whereas much greater creep occurred during the same adsorption process, similar to the case of drying. Therefore, during the changes in moisture, not only destabilization but also stabilization should occur simultaneously, so that the wood during the changing process is in a remarkably unstable state. (II) Smaller creep occurred immediately after a slower adsorption as compared with that immediately after a more rapid adsorption. This suggests that wood is more stabilized during a slower versus a more rapid adsorption process. However, difference in creep between the final stages of the slower and the more rapid adsorption process was scarcely found. This is considered to result from the difference in degree of stabilization caused by the different duration of both adsorptions. In other words, this result is only an outward appearance. (III) Greater creeps were recognized during larger changes in moisture content (Au) during the adsorption processes corresponding to the drying process. Therefore, mechano-sorptive creep depends not only on Au but also on the range of relative humidity (RH). Larger stabilization was found during the changing process of larger Au.

Ultrastructure of iodine treated wood

Abstract: Iodine staining has been used to study the orientation of cellulose microfibrils in wood using light microscopy. The aim of this work was to understand the exact nature of the staining reaction with iodine and to provide insight into the properties and organisation of the wood cell wall. Based on transmission electron microscopy it is apparent that precipitation of the iodine following treatment with nitric acid results in the formation of crystal cavities within the cell wall, which follow the orientation of the cellulose microfibrils. There is no evidence that iodine precipitates within drying checks as previously speculated. High resolution confocal reflectance microscopy of crystal cavity orientation indicates that the microfibril arrangement within pit borders can be both spiral and circular. Crystal cavities are much more abundant within the S1 layer than elsewhere. All of the cells examined had crystal cavities in the S1 region, which may be related to the reduced lignification at the S1/S2 boundary resulting in greater porosity of the cell wall at this location. Within the S2 region, clusters of crystal cavities are randomly distributed and occur in widely varying numbers among adjacent cell walls, suggesting variations in the porosity of the S2 wall within and among adjacent tracheids. Cavities form preferentially within more electron lucent regions of the cell wall. The random nature of crystal cavity formation within S2 clusters probably reflects the underlying random nature of the cell wall nanostructure. We conclude that iodine staining can provide important clues to the nanostructural properties of tracheid cell walls.

Artificial weathering of tropical woods. Part 1: Changes in wettability

Abstract: Changes in the wettability of eight species of tropical woods during artificial weathering up to 600 h are discussed from the aspect of chemical and structural changes in their surfaces: Amnurana acreana, Acacia auriculiformis, Dipterocarpus spp., Eucalyptus marginata, Eucalyptus robusta, Shorea spp., and Tabebuia spp. with relatively high and low specific gravity. On the whole, the wettability of specimens decreased upon irradiation up to 20 h; above that they increased. Changes in wettability during artificial weathering differed according to wood species. The IR spectra suggest that the specimen surfaces after irradiation for 600 h result in a cellulose-rich layer, and therefore the increase in wettability during artificial weathering can be explained in terms of the increase in hydroxyl groups originating from both the exposed cellulose and adsorbed water. However, the difference in wettability exists between species even after the surface develops a cellulose-rich layer. The stereoscopic micrographs showed the development of cracks for all of the specimens after irradiation for 600 h, and differences in their magnitudes according to species. From these results, the differences in wettability between species were estimated to be due to the structural changes on the surface during artificial weathering, whereas the increase in wettability was due to the chemical changes.

Changes in the fiber wall during refining of bleached pine kraft pulp

Abstract: The effect of refining on the fiber wall was studied for bleached kraft pulp fractions from pine first thinnings and pine sawmill chips. Hydrocyclone fractionation of both pulps produced fractions enriched in earlywood and latewood fibers. Some external fibrillation but no changes in fiber wall thickness were observed for the thin-walled earlywood fibers during refining. Refining the thick-walled latewood fibers led to extensive external fibrillation and a decrease in fiber wall thickness. The pore structure of the fiber wall opened up during refining for all pulp fractions. Earlywood fibers were more porous than latewood fibers, and fibers from first thinnings more porous than those from sawmill chips. The earlywood fibers from first thinnings had more large pores than the other fiber fractions. In the region of the smaller pores, the pore volume did not change significantly with refining, whereas in the region of the larger pores it increased markedly. In all the fractions investigated, specific hydrolytic enzymes hydrolyzed cellulose more easily after refining. This is an indication of an increase in cellulose surface area and/or disordering of cellulose as a result of refining, probably due to local disorder of the cellulose in the fibril aggregates. Bonding developed most strongly for the earlywood fiber fraction from first thinnings. This is concluded to be due to a combination of fiber dimensions and fiber wall porosity.