Showing papers in "Holzforschung in 2009"

Cell wall features with regard to mechanical performance. A review. : COST Action E35 2004-2008 : Wood machining - Micromechanics and fracture

Abstract: The mechanical performance of wood and wood products is highly dependent on the structural arrangement and properties of the polymers within the fibre cell wall. To improve utilisation and manufact ...

Colour in thermally modified wood of beech, Norway spruce and Scots pine. Part 1: Colour evolution and colour changes.

Abstract: Colour evolution and colour changes were analysed from surface images of small specimens of three thermally-modified timber species using the CIEL*a*b* colour space. Upon heat exposure, the wood substance became orange and then approached grey irrespective of species; this was accompanied by a steady reduction in lightness. Colour changes were similar in the three woods at any given level of heat-induced weight loss (WL), whilst changes in the three coordinates of the CIEL*a*b* space in function of WL were different regardless of the wood species. For DL*, the profile was curvilinear and monotonous, while Da* and Db* bear a complex, non-linear profile. In turn, DE* was found to be highly influenced by the behaviour of DL*. It is proposed that DE* in thermally modified wood originates from chemical changes in the main wood polymers, more so in lignin than in polysaccharides, due to the darkening of the lignin itself. This was associated with the generation of chromophoric groups, mainly the increase in carbonyl groups appearing in the Fourier transform infrared spectra of lignin between 1710 and 1600 cm -1 , particularly the emergence of quinone species.

HSQC-NMR analysis of lignin in woody (Eucalyptus globulus and Picea abies) and non-woody (Agave sisalana) ball-milled plant materials at the gel state 10th EWLP, Stockholm, Sweden, August 25–28, 2008

Abstract: Abstract In situ analysis of lignin by 2D NMR of whole plant material was carried out by swelling finely ball-milled samples in deuterated dimethylsulfoxide (DMSO-d6 ) and sonicated so that a gel was formed in the NMR analysis tube. Solution HSQC NMR spectra of different plant materials representative for hardwood (Eucalyptus globulus), softwood (Picea abies), and non-woody plants (Agave sisalana) are presented here. The spectra show signals corresponding to those of the main plant constituents, such as lignin and polysaccharides. The lignin signals were assigned by comparing the HSQC spectra of the whole plant materials with the HSQC spectra of their respective milled-wood lignins (MWLs). In general terms, the major lignin structural features, such as the relative abundances of the main lignin substructures, the syringyl/guaiacyl ratios and the extent of γ-acetylation of the lignin side-chain observed in the HSQC spectra of the whole plant materials, matched those obtained from the HSQC spectra of the isolated MWLs. Therefore, this technique, which needs only minor amounts of lignocellulosic material and minimal sample preparation, can be useful for the rapid screening of plant lignins without the need for tedious and time-consuming lignin isolation procedures.

Orientation of the wood polymers in the cell wall of spruce wood fibres.

Abstract: The mechanical and physical properties of wood fibres depend to a large extent on the orientation of the polymers, mainly the cellulose microfibrils, within the supramolecular structure of the cell wall. Under moist conditions, the arrangement within the polymer matrix may play a dominant role for mechanical properties in general and, especially, in the transverse direction. In this context, it is of special interest to determine the orientation of glucomannan and xylan, being the essential components of softwood hemicelluloses, and of lignin in wood fibres. Fourier transform infrared (FTIR) microscopy was used to examine the orientation of the main wood polymers in transversal and longitudinal direction of spruce fibres. We investigated fibres made from a thermomechanical pulp, in which the outer fibre wall layers were removed by mechanical action, and chemically delignified fibres. The polarised FTIR measurements indicated that glucomannan and xylan appear to have a parallel orientation with regard to the orientation of cellulose and, in all probability, an almost parallel orientation with regard to the fibre axis. Lignin was found to be less oriented in the fibre wall, although its arrangement is not fully isotropic. In the longitudinal direction of the fibres, there were no significant changes in the molecular orientation of the studied polymers.

Kraft lignin as feedstock for chemical products: The effects of membrane filtration

Abstract: The use of technical lignins as feedstock for chemical products will require improvements in purity, molecular mass distribution, and thermal behavior. Therefore, industrial black liquors from kraf ...

Relations between chemical changes and mechanical properties of thermally treated wood 10th EWLP, Stockholm, Sweden, August 25-28, 2008

Abstract: Abstract Thermal treatments of wood (Fagus sylvatica and Fraxinus excelsior) were examined. The temperature load on wood causes characteristic changes in the chemical composition, which were determined by means of several defined methods. The results confirm that in addition to the degradation of polyoses lignin, known as the thermally most stable compound, also shows significant thermal alterations. In addition, mechanical properties of the specimens were examined in order to correlate these results with the effects of chemical changes of thermally treated wood. It was shown, e.g., that the decomposition of the polyoses can affect the strength properties both positively and negatively.

TEMPO-mediated oxidation of softwood thermomechanical pulp

Abstract: Abstract A softwood thermomechanical pulp (TMP) was suspended in water and oxidized with sodium hypochlorite and catalytic amounts of sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) at pH 10. When the NaClO addition levels were 20–26 mmol g-1 of the TMP, the yields of water-insoluble TEMPO-oxidized TMPs fractions were approximately 40%. Sugar composition and other analyses revealed that most of the lignin and hemicellulose components in the TMP were removed as water-soluble fractions by the oxidation. Thus, almost pure TEMPO-oxidized celluloses can also be prepared from TMP, although the addition levels of NaClO are much higher than for the TEMPO-mediated oxidation of pure celluloses. The water-soluble fractions were analyzed by NMR, showing that polyuronic acids formed from glucomannan and cellulose by oxidation were the main compounds. The water-insoluble fractions of TEMPO-oxidized TMPs prepared with NaClO of 20–26 mmol g-1 had carboxylate contents of approximately 1.2 mmol g-1, and had the same cellulose I allomorph and the same crystal widths as in the original TMP. Transparent and highly viscous gels were obtained by disintegration of these TEMPO-oxidized TMPs in water, and the gels consisted of individual nanofibers 4–6 nm in width. Thus, TEMPO-oxidized cellulose nanofibers can also be prepared from TMP.

Catalytic hydrogenolysis of ethanol organosolv lignin.

Abstract: The production of ethanol based on lignocellulosic materials will bring about the coproduction of significant amounts of under-utilized lignin. This study examines the potential of conventional heterogeneous and novel homogeneous catalysts for the selective cleavage of the aryl-O-aryl and aryl-O-aliphatic linkages of ethanol organosolv lignin to convert it from a low grade fuel to potential fuel precursors or other value added chemicals. The development of hydrogenolysis conditions that effectively increase the solubility of lignin were initially examined with Ru(Cl)(2)(PPh3)(3) and demonstrated the ability to decrease the molecular weight and enhance the solubility of the lignin polymer. Later studies examined several heterogeneous and homogeneous hydrogenation catalysts at optimized reaction conditions resulting in 96.4% solubility with Ru(Cl)(2)(PPh3)(3), increase in H/C ratio with Raney-Ni, Pt/C and extensive monomer formation with NaBH4/I-2. The changes in molecular structure of lignin were followed by size exclusion chromatography, qualitative and quantitative NMR spectroscopy and elemental analysis. These studies demonstrated that aryl-O-aryl and aryl-O-aliphatic linkages could be cleaved and the hydrogenated lignin had a decrease in oxygen functionality and the formation of products with lower oxygen content.

Cellulosic aerogels as ultra-lightweight materials. Part 2: Synthesis and properties.

Abstract: Ultra-lightweight cellulose aerogels can be obtained inthree steps: (1) preparation of a cellulose solution inmolten N -methylmorpholine- N -oxide monohydrate(NMMOOH 2 O) at 110–1208C and casting of the viscousmass into moulds; (2) extraction of the solidified castingswith ethanol to initiate cellulose aggregation and toremove NMMOOH 2 O so that the fragile, fine-porous tex-ture of cellulose II is largely retained; and (3) drying ofthe lyogel using supercritical carbon dioxide (scCO 2 ).According to this approach, cellulosic aerogels were pre-pared from eight commercial cellulosic materials andpulps and analysed for selected chemical, physicochem-ical and mechanical parameters. The results reveal thatall aerogels obtained from 3% cellulose containingNMMOOH 2 O melts had a largely uniform mesoporousstructure with an average pore size of ;9–12 nm, sur-face area of 190–310 m 2 g -1 , and specific density of0.046–0.069 g cm -3 , but rather low mechanical stabilityexpressed as compressive yield strain of 2.9–5.5%. Allsamples showed viscoelastic behaviour, with Young’smodulus ranging from ;5to10Nmm

Micromechanics of creep and relaxation of wood. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

Abstract: Wood, like all polymeric materials, shows viscoelastic behaviour. The time dependent behaviour of wood depends on material anisotropy, temperature, moisture and stresses. To predict the behaviour of wood, numerous mathematical models have been developed largely relying on experimental results. In this paper, time dependent viscoelastic behaviour of wood is reviewed under constant and cyclic climatic conditions, separately. More emphasis is given on results obtained in recent years on the behaviour of thin wood tissues, single fibres, thermo-viscoelasticity of wood, influence of hemicelluloses and the modelling of the effect of transient moisture at the molecular level on the mechanical response.

Oxidative modifications of cellulose in the periodate system - reduction and beta-elimination reactions.

Abstract: The conversion of cellulose to dialdehyde cellulose (DAC) by treatment with aqueous periodate was studied by the CCOA method, which is a combination of gel permeation chromatography and carbonyl-selective fluorescence labeling. The beta-alkoxy-elimination reaction underalkaline conditions was used as a diagnostic tool to address the regioselectivity of the oxidation at low degrees of conversion. The oxidation proceeded by random oxidant attack; cluster-like or isolated oxidation patterns were excluded. The beta-alkoxy-elimination proceeded as a competitive process during reduction of DAC by sodium borohydride. Reduction was thus inevitably accompanied by a significant loss in molecular weight. The borohydride treatment decompacted the molecules by reducing the aldehyde groups and destroying hemiacetal crosslinks. As a result, highly flexible chains were produced.

Modeling xylan solubilization during autohydrolysis of sugar maple wood meal: Reaction kinetics

Abstract: Abstract The objective of this work was to study the kinetics of hemicelluloses extraction during hydrothermal pretreatment of sugar maple wood meal. Pretreatment was conducted in a batch reactor at 145–185°C with reaction times up to 8 h and with liquor to solid ratio of 20:1. Under these conditions, hemicelluloses were selectively solubilized and little degradation (approximately 6–9% of the initial amount) of cellulose and lignin was observed. A kinetic model was developed. It was supposed that there are no diffusion limitations and that the reaction rate constants have first-order kinetics with Arrhenius-type temperature dependence. The model proposes the formation of xylose directly from wood xylan as well as from xylooligomers formed in the liquid phase by the hydrolysis of xylan. The model is able to correlate satisfactorily experimentally measured yields of residual xylan, xylooligomers, xylose, and furfural obtained during the pretreatment.

Colour in thermally modified wood of beech, Norway spruce and Scots pine. Part 2: Property predictions from colour changes.

Abstract: Abstract In the woodworking industry, image analysis is routinely used for quality control and for matching and classification during various processes. An extension of these automated systems for the prediction of physical properties of thermally modified wood (TMW) is enticing, because to date there is no generalised procedure for the quality assurance of TMW. In this work, the feasibility of predicting 13 physical parameters from the analysis of colour changes is demonstrated using small thermally modified specimens of three wood species. Simple linear regression models for anti-swelling efficiency, nominal density, heat-induced weight loss and 10 strength parameters in six forms of stress were all very or highly significant, with R2 statistics for the best predictor from 0.24 to 0.94. ΔE* was found to be a better predictor than ΔL* for most properties. Multiple linear regression with 11 colour variables increased the prediction ability of most models in terms of R2, although these improvements varied with the property and species concerned. The best models altogether were obtained by partial least squares regression, with relative prediction error values >0 in all cases. Our results demonstrate that physical properties of small specimens of TMW can be efficiently predicted with only one after treatment measurement of colour in the CIEL*a*b* colour space by means of image analysis of TMW surfaces. We anticipate that our approach would be a starting point for more refined modelling of physical properties of larger wood members and other properties of interest in TMW (e.g., decay resistance).

Fracture behaviour of wood and its composites. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

Abstract: Abstract Fracturing of wood and its composites is a process influenced by many parameters, on the one hand coming from the structure and properties of wood itself, and on the other from influences from outside, such as loading mode, velocity of deformation, moisture, temperature, etc. Both types of parameters may be investigated experimentally at different levels of magnification, which allows a better understanding of the mechanisms of fracturing. Fracture mechanical methods serve to quantify the fracture process of wood and wood composites with different deformation and fracturing features. Since wood machining is mainly dominated by the fracture properties of wood, knowledge of the different relevant mechanisms is essential. Parameters that influence the fracture process, such as wood density, orientation, loading mode, strain rate and moisture are discussed in the light of results obtained during recent years. Based on this, refined modelling of the different processes becomes possible.

Changes in wood-water relationship due to heat treatment assessed on micro-samples of three Eucalyptus species

Abstract: Abstract Wood-water relationship of untreated and heat-treated wood was studied. Specimens of Eucalyptus grandis, E. saligna, and E. citriodora were submitted to five conditions of heat treatment: 180°C and 220°C with air; 220°C, 250°C, and 280°C with N2. The wood-water relationships were accurately studied in a special device, in which the moisture content (MC) of the sample was measured with a highly sensitive electronic microbalance placed in a climatic chamber. The dimensions of the sample were collected continuously without contact by means of two high-speed laser scan micrometers. Sorption curves and shrinkage-MC relationships were observed. To study the effects of heat treatment, the following parameters were also determined: fiber saturation point (FPS), wood anisotropy (T/R ratio), shrinkage slope, reduction in hygroscopicity, and anti-shrink efficiency (ASE). The physical properties were significantly affected only at 220°C and above. At heat temperature levels higher than 220°C, the reduction in hygroscopicity and ASE are higher than 40% and continue to be reduced with increasing temperature level. This work also demonstrates that heat treatment does not change the slope of the curves “shrinkage vs. MC”, proving that heat treatment affects the domain of alterations in wood properties, but not the behavior within this domain.

Quantitative chemical indicators to assess the gradation of compression wood

Abstract: A chemistry-based parameter has been sought for determining the gradation of compression wood (CW), i.e., the severity, in tissues of Pinus radiata wood. Fluorescence microscopy was the reference for characterisation of the tissues containing CW. The collected material contained CW of varying severity, beginning with normal wood (NW containing no CW), continuing with material with some features of CW (CW of mild severity, MCW) and ending up with a material with pronounced features of CW (CW of high severity, SCW). Matching opposite wood (OW) was also included in the study. The chemical analyses included lignin determination, sugar analysis in the acid hydrolysate, thioacidolysis, 31 P-NMR spectroscopic analysis and steric exclusion chromatography of thioacidolysis products. As the severity of CW changed progressively from NW through MCW to SCW, all chemical parameters changed concurrently. In particular, levels of galactose and lignin increased, while those of glucose and mannose decreased. The amounts of p-hydroxyphenyl b-ethers released by chemical degradation and uncondensed p-hydroxyphenyl C-9 units also increased at elevated CW severity levels. The amounts of galactose and the p-hydroxyphenyl content of the lignin correlated linearly with lignin for CW samples. The chemical differences between CW and OW in the stem, branch and seedling were similar, i.e., they are independent of the morphological origin of the sample. Parameters based on the p-hydroxyphenyl unit content appear the most suitable chemical indicators of CW severity, as they are least sensitive to the sample’s morphological origin and their response to CW severity is high.

Cutting forces in wood machining – Basics and applications in industrial processes. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

Abstract: The data available in the literature concerning wood cutting forces permits to build models or to simulate the main wood machining processes ( milling, sawing, peeling, etc.). This approach contributes to a better understanding of formation of wood surfaces and chips and the data may be helpful to optimise cutting geometry, reduce tool wear, improve tool material, and to size tool-machines. The models may also be useful for industrial application in two ways: ( 1) providing data to optimise the settings for a given operation ( batch approach), and ( 2) building predictive models that could be the basis of an online control system for the machining processes ( interactive approach). A prerequisite for this is that numerous machining tests on different wood materials are performed based on experiences with different kind of tools and experimental devices. With a focus on potential industrial applications, the emphasis of this review was on the wood peeling process, which is a very demanding special case of wood cutting. Although not so many industrial machines are equipped with expensive force sensors, there is a lot of high quality information available about cutting forces which may be useful to improve the scientific or technological knowledge in wood machining. Alternative parameters, such as vibration or sound measurements, appear to be promising substitutes in the praxis, particularly to feed online control systems of any wood cutting process.

Comparison of mechanical properties of thermally modified wood at growth ring and cell wall level by means of instrumented indentation tests

Abstract: Abstract Thermal modification is a well established method to improve the dimensional stability and the durability for outdoor use of wood. Unfortunately, these improvements are usually accompanied with a deterioration of mechanical performance (e.g., reduced strength or higher brittleness). In contrast, our investigations of the hardness properties in the longitudinal direction of beech wood revealed a significant improvement with thermal modification. Furthermore, we applied instrumented indentation tests on different hierarchical levels of wood structure (growth ring and cell wall level) to gain closer insights on the mechanisms of thermal treatment of wood on mechanical properties. This approach provides a variety of mechanical data (e.g., elastic parameters, hardness parameters, and viscoelastic properties) from one single experiment. Investigations on the influence of thermal treatment on the mechanical properties of beech revealed similar trends on the growth ring as well as the on the cell wall level of the wood structure.

Revisiting the transition between juvenile and mature wood: a comparison of fibre length, microfibril angle and relative wood density in lodgepole pine

Abstract: Abstract In an attempt to examine the dynamic inter-relationship among wood density and fibre traits [tracheid length and microfibril angle (MFA)] in lodgepole pine (Pinus contorta), 60 trees were sampled in three age classes from four sites in central British Columbia. Breast height discs were taken and relative wood density was measured along two radii. Tracheid length was assessed on isolated 5-year increments from pith to bark at breast height for each tree. MFA was determined every 50 μm and the 5-mm composite intervals from pith to bark per disc at breast height were used in the analysis. Segmented regression was employed to identify the “juvenile to mature wood” transition point, which revealed transition ages of 31, 18 and 15 for wood density, fibre length and MFA, respectively. These traits were related to primary growth, expressed as area increment, ring width, percent earlywood and height increment during the juvenile wood phase. Comparisons of wood and fibre traits showed a higher congruence between the time of transitions for fibre length and MFA (Pearson correlation coefficient 0.52) than that between fibre length and wood density (0.07), and MFA and wood density (0.16). The cessation of early rapid radial increment growth terminated before wood and fibre transitions to mature wood occurred. Fibre length was significantly, but not strongly, related to ring width and percent earlywood (0.35 for both). The duration of juvenile fibre production was not significantly related to height growth.

Hierarchical modelling of microstructural effects on mechanical properties of wood. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

Abstract: Wood exhibits a hierarchical architecture. Its macroscopic properties are determined by microstructural features at different scales of observation. Recent developments of experimental micro-characterisation techniques have delivered further insight into the appearance and the behaviour of wood at smaller length scales. The improved knowledge and the availability of increasingly powerful micromechanical modelling techniques and homogenisation methods have stimulated rather comprehensive research on multiscale modelling of wood. Linking microstructural properties to macroscopic characteristics is expected to improve the knowledge of the mechanical behaviour of wood and to serve as the basis for the development of innovative wood-based products and for biomimetic material design. Moreover, understanding fundamental aspects of wood machining requires multiscale approaches which can take into account the heterogeneity, anisotropy and hierarchies of wood and wood composites. In this review, recent developments in the field of hierarchical modelling of the hygroelastic behaviour of wood are discussed, and a short outline of the theoretical background is given. Much focus is placed on composite micromechanical models for the wood cell wall and on multiscale models for wood resting upon hierarchical finite element models and on the application of continuum micromechanics, respectively. These models generally lead to the specification of equivalent homogeneous continua with effective material properties. Finally, current deficiencies and limitations of hierarchical models are sketched and possible future research directions are specified.

Extractives in bark of different conifer species growing in Pakistan

Abstract: Abstract The amount and composition of lipophilic and hydrophilic extractives, including proanthocyanidins, has been analysed as a first screening in the bark of six Pakistani coniferous tree species, namely Pinus wallichiana, Pinus roxburghii, Pinus gerardiana, Abies pindrow, Taxus fuana and Cedrus deodara. The predominant lipophilic extractives were common fatty and resin acids, fatty alcohols and sterols. In all bark samples, short-chain fatty acids were more abundant than long-chain fatty acids. Generally, the amount of free fatty acids was also larger than the amount of triglycerides. Oleic acid was the most common fatty acid, except in C. deodara, where lignoceric acid dominated. The largest amounts of fatty acids and fatty alcohols were found in P. wallichiana and P. gerardiana. P. gerardiana contained an exceptionally large amount of resin acids, approximately 3% of the bark weight, compared to the other species. The amount of free sterols was approximately at the same level or larger than the amount of steryl esters in most samples. In addition to proanthocyanidins, different known lignans, stilbenes, ferulates and flavonoids were generally predominant amongst the hydrophilic extractives. Resveratrol glycoside was abundant in P. wallichiana, while C. deodara and P. gerardiana contained large amounts of lignans and lignan derivatives. All bark extracts contained large amounts of proanthocyanidin-related catechin and its derivatives. Furthermore, C. deodara and P. roxburghii contained quite large amounts of taxifolin. In particular, P. wallichiana and A. pindrow are potential rich sources of proanthocyanidins, representing approximately 16% and 5% of the bark weight, respectively.

Alteration of the pore structure of spruce (Picea abies (L.) Karst.) and maple (Acer pseudoplatanus L.) due to thermal treatment as determined by helium pycnometry and mercury intrusion porosimetry

Abstract: Abstract The pore size distribution in wood affects sorption and transport of moisture. In the present paper, the pore structure of spruce and maple was examined in untreated and thermally modified samples. The relative humidities of the specimens were 33%, 43%, 53%, and 76%. Tests were carried out by helium pycnometry and mercury intrusion porosimetry. The results clearly show that thermal treatments change the apparent density, pore structure, and pore size distribution. Measurements by the mercury intrusion porosimetry indicated that the influence of various environmental conditions (humidity, temperature) on the porosity and pore size distribution is small.

Protection mechanisms of DMDHEU treated wood against white and brown rot fungi

Abstract: Abstract The resistance of beech and pine wood blocks treated with 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU) against Trametes versicolor and Coniophora puteana increased with increasing weight percent gain (WPG) of DMDHEU. Full protection [mass loss (ML) below 3%] was reached at WPGs of approximately 15% (beech) and 10% (pine). Untreated and DMDHEU treated blocks were infiltrated with nutrients and thiamine prior to fungal incubation and it was observed whether the destruction or removal of nutrients and vitamins during the modification process has an influence on the ML caused by the fungi. This study revealed that no considerable differences were found. Then, the cell wall integrity was partly destroyed by milling and the decay of the fine wood powder filled into steel mesh bags was compared to that of wood mini-blocks. The purpose of this study was to examine whether the effects of surface area, cell wall bulking, and reduction in micro-void diameters play a role in decay resistance. The ML caused by the fungi, however, also decreased with increasing WPG and showed comparable patterns similar to the case of mini-blocks. ML of powder bearing the highest WPG appeared to be caused by losses in DMDHEU during fungal incubation. For brown rotted wood, the infrared absorption ratios at 1030 cm-1 and 1505 cm-1 revealed decreasing decay of polysaccharides with increasing WPG of treated wood.

Effect of surface modification of beech wood flour on mechanical and thermal properties of poly (3-hydroxybutyrate)/wood flour composites.

Abstract: Poly (3-hydroxybutyrate) (PHB), a biodegradable polymer from the polyhydroxyalkanoate biopolyester class, was filled with 20% beech wood flour (WF) to form completely biodegradable films. In the present study, the influence of surface modification of wood flour was investigated on the interfacial adhesion of PHB/WF composites. In addition to a hydrothermal pretreatment, sodium hydroxide and stearic acid were used as surface modifiers. Direct measurement of interfacial adhesion was carried out by mechanical testing and dynamic mechanical analysis. Thermal properties, degree of crystallinity of PHB/WF composites were determined by differential scanning calorimetry. Effects of sodium hydroxide and stearic acid treatment on the adhesion of PHB/WF interface were feeble when no hydrothermal pretreatmentwas applied. Nevertheless, surface modifiers applied on hydrothermally pretreated WF significantly improved the WF/PHB interface adhesion.

A single point NMR method for an instantaneous determination of the moisture content of wood

Abstract: Nuclear magnetic resonance (NMR) enables an instantaneous determination of the proton density in liquids and is thus convenient for determining the moisture content (MC) of wood. We demonstrated that the MC of a wood sample can be determined instantaneously on the basis of its mass (m) and the amplitude of its NMR freeinduction-decay (FID) signal. The measurement is based on the assumption that the only liquid in the wood is water and that the relationship between the amplitude of the FID signal (S) and the mass of the water (mw) in the sample is linear, i.e., Ss km wqk9 (m-mw), and can be precisely calibrated for a given NMR probe and NMR spectrometer setup (in our case ks105 AU g-1 and k/k9 s34). With the FID signal converted into the mass of water, the MC is calculated as: MCs(S- mk 9)/(m k-S). After the initial calibration of the FID signal with respect to the content of water, the correctness of the method was verified on samples of different wood species with various MCs. The results confirmed that the proposed method is comparable in terms of accuracy and reliability to the gravimetric method, regardless of the species of wood. As the method is instantaneous, it might become the method of choice in applications where a short measurement time combined with a high accuracy is demanded.

Topochemical investigations of cell walls in developing xylem of beech (Fagus sylvatica L.).

Abstract: Formation and lignification of xylem cells in mature beech (Fagus sylvatica L.) trees growing in a forest site in Slovenia (46 degrees N, 14 degrees 40' E, 400 m a.s.l.) were studied on the cellular and subcellular level. Samples containing the cambial zone and developing xylem were taken from six beech trees every week throughout the 2006 vegetation period. Cell wall thickening and lignification in individual cell wall layers and cell types were determined by light microscopy, cellular UV-microspectrophotometry and transmission electron microscopy, respectively. Cell division started between the 18th and the 24th of April 2006. Lignification began in the newly formed xylem tissue on the 2nd of May. After 1 month, the developing earlywood portion contained fully differentiated vessels with completed wall deposition and lignification, and differentiated fibres and axial parenchyma became visible after 2 months. At the end of cambial cell division on the 9th August, the differentiation of the most recently formed fibres in the terminal zone of the growth ring continued for approximately 4 weeks. This indicates that the process of lignification in earlywood is slower than in latewood. The high temporal resolution of the investigated processes and the combination of the above-mentioned microscopic techniques provides a detailed insight into the process of cell wall thickening and lignification of woody tissue in beech.

Ozone pretreatment of lignocellulosic materials for ethanol production: improvement of enzymatic susceptibility of softwood.

Abstract: Abstract In order to utilize lignocellulosic biomass as a feedstock for bioethanol, ozone pretreatment was conducted on Japanese cedar sawdust and three other lignocellulosic wastes. Successful lignin degradation was accomplished by ozone pretreatment of the Japanese cedar sawdust and over 90% of polysaccharides were converted to monomeric sugars by enzymatic saccharification. This ozone pretreatment was also effective with other lignocellulosics, such as Hinoki cypress sawdust, lumber and board wastes. Ethanol production by simultaneous saccharification and fermentation of the ozone pretreated Japanese cedar sawdust was also successful. It was shown that ozone pretreatment increases enzymatic susceptibility and enables the production of ethanol from lignocellulosic biomass.

Non-destructive determination and quantification of diffusion processes in wood by means of neutron imaging

Abstract: Diffusion processes in samples of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies [L.] Karst.) were determined and quantified by means of neutron imaging (NI). The experiments were carried out at the neutron imaging facility NEUTRA at the Paul Scherrer Institute in Villigen (Switzerland) using a thermal neutron spectrum. NI is a non-destructive and non-invasive testing method with a very high sensitivity for hydrogen and thus water. Within the scope of this study, diffusion processes in the longitudinal direction were ascertained for solid wood samples exposed to a differentiating climate (dry side/wet side). With NI it was possible to determine the local distribution and consequently the total amount of water absorbed by the samples. The calculated values scarcely differ from those ascertained by weighing (≤3%). The method yields profiles of the water content over the whole sample, thus allowing the local and temporal resolution of diffusion processes within the sample in the main transport direction (longitudinal). On the basis of these profiles, it was possible to calculate the diffusion coefficients along the fibre direction according to Fick's second law.

Air permeability in longitudinal and radial directions of compression wood of Picea abies L. and tension wood of Fagus sylvatica L.

Abstract: The air permeability in longitudinal and radial directions of compression wood in spruce (Picea abies) and tension wood in beech (Fagus sylvatica) was compared with that of the corresponding normal wood. The primary aim of the present study was to explain why the reaction woods dry more slowly than the normal woods in the domain of free water. A number of boards conventionally dried to an average final moisture content of 12% were chosen to perform the measurements. Bordered pits on the radial walls of longitudinal tracheids in the compression and normal wood and intervessel or intervascular pits in the tension and normal wood were also examined. The reaction wood of both species is less permeable than the normal wood, both in longitudinal and radial directions. The difference in permeability was more pronounced between compression and normal wood of spruce, especially in longitudinal direction. From an anatomical point of view, this is likely related to some differences in anatomical characteristics affecting the airflow paths, such as the pit features. Such results can explain the difference in drying kinetics of the reaction and normal woods in the capillary regime of drying.

Properties of wood surfaces – characterisation and measurement. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

Abstract: Abstract Wood surfaces might be considered as geometrical structures combined with position dependent chemical properties. It is possible to access surface properties only from a methodical point of view, e.g., by measuring roughness, colour, surface energy and other features. This type of characterisation remains incomplete because it does not account for the complex interactions of the properties, which are caused by the machining process. A better approach might be to describe the surface as a system of time dependent properties including the history of machining operations performed for a specific purpose. This work presents the advancements in the understanding of wood surfaces achieved in the course of the COST Action E35. The interaction between raw material, machining, and techniques of measurement will be discussed in terms of surface characteristics including the tactile properties of wood surfaces.