Volume 61, Issue 6

The first and the second generation of improved maritime pine ( Pinus pinaster ) have produced gains of up to 30% in stem volume, a reduction of final harvesting age by 10 years and a considerable improvement of stem straightness. The third generation will include wood quality traits for different end-uses, including pulp and fibre properties. To facilitate this goal, near infrared spectroscopy (NIRS) was used to estimate chemical composition with regard to lignin, cellulose, hemicelluloses, and extractive content, and lignin quality with regard to 4-hydroxy-phenylpropane/ g uaiacylpropane ratio. A total of 960 samples were investigated which were collected from a large number of trees (belonging to 80 families obtained by crossing 18 mothers and 20 fathers; there are 12 trees per family). Good calibration data was obtained between NIRS and wet chemistry methods (R 2 values higher than 0.9 and good precision of prediction). To complete the NIRS work, kraft cookings in small scale, fibre morphology and microdensitometry investigations were also conducted. Genetic calculations indicated that for a 1% rate of selection on mothers and fathers, genetically induced changes are possible with lignin content (−3.8%), cellulose content (+1.3%), pulp yield (+1.8%), fibre length in pulps (+0.17 mm) and wood density (+50 kg m −3 ).

For evaluation of changes in phenolic lignin units during kraft pulping and bleaching, a direct method based on UV reflectance measurements of pulp handsheets was tested. Similar trends in total phenolic hydroxyl-group contents were evident when UV reflectance results for isolated lignins and pulp sheets were compared. This direct method gave reliable results after alkaline cooking, oxygen delignification, and bleaching stages followed by alkaline extraction (DE, ZE). However, the phenolic content obtained after peroxide bleaching (QP) was over-estimated. This may be due to alkali-induced reactions during pH adjustment of the sheets for measurement concomitant with ionisation of the phenolic hydroxyl groups. Otherwise, this direct method based on UV reflectance measurements is a promising new approach for determining the total content of phenolic lignin units in pulp sheets without isolating the lignin.

Several lignin-like model compounds (vanillin, syringaldehyde, guaiacol, syringol, p -benzoquinone, naphthoquinone) and commercial softwood lignin were submitted to small charges of ozone, chlorine dioxide and hydrogen peroxide in aqueous solution under conditions simulating a final bleaching stage. In the case of ozone, the coloured quinone models were directly destroyed, whereas the phenolic models and lignin underwent a two-step decomposition mechanism: chromophores were formed at very low ozone charges, and then were destroyed with increasing ozone charge. Chlorine dioxide had hardly any effects on the quinone models, but formed coloured groups from the phenolic models and lignin. However, these were more intensely coloured and were only partially removed with higher ClO 2 charges. As for hydrogen peroxide, the colour of lignin and naphthoquinone were directly removed, at least partially, but high H 2 O 2 charges were necessary. Consequently, ozone seems to be the best reagent for final bleaching in which small chemical charges are applied. We suggest reaction mechanisms between ozone and the phenolic model compounds and p -benzoquinone that can explain the observations.

Structural modification of eucalypt pulp lignin was investigated in a totally chlorine-free (TCF) bleaching sequence including a laccase-mediator stage. This stage was applied after two oxygen delignification stages, and was followed by an alkaline peroxide stage. After two oxygen delignification stages, two more stages with a laccase mediator and alkaline peroxide were applied. The residual lignins were enzymatically isolated from the different pulps and analyzed by spectroscopic techniques and analytical pyrolysis. The latter revealed high amounts of syringyl units (>70%) in the lignins. 13 C- 1 H heteronuclear single quantum correlation (HSQC) NMR indicated high amounts of β-O-4′ inter-unit linkages (>75% side-chains). Changes in lignin composition and inter-unit linkages were demonstrated in the course of the bleaching sequence. Moreover, oxidative modification of the major syringyl units was shown by C 2,6 -H 2,6 HSQC correlations and by the presence of oxidized pyrolysis markers in pyrograms. The existence of both C α keto and carboxyl groups in the residual lignin, together with normal (C α -hydroxylated) units, was revealed by heteronuclear multiple bond correlation (HMBC) between aromatic H 2,6 and side-chain carbons. These C α -oxidized structures represent nearly 60% of total units in the lignin isolated from the enzymatically treated pulp. Analysis of residual lignin after the final peroxide stage compared with a simple alkaline treatment revealed that most of the oxidatively altered lignin was removed by the alkali used in the peroxide stage. Thus, the kappa number decreased and the final residual lignin was more structurally related to that found before the oxidative stages, although it contained less resinols and more carboxyl group-bearing units. However, the action of peroxide is necessary to attain the high brightness required (>90% ISO).

The distribution of lignin, carbohydrates, and metal ions on the surface of spruce and aspen wood tissue sections was investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The distribution patterns of metals and lignin in ray cells, vessels, and fibres were different, whereas carbohydrates were uniformly distributed across the sections of all morphological regions. In spruce sapwood, Ca, Mg, Na, K, Fe locations was more pronounced in the bordered pit tori and inner layer of ray parenchyma cells. Little lignin was detected in these regions. In spruce heartwood, the degree of lignification was low on the surfaces of bordered pit tori; however, Na and K were not detected here. In compression wood from spruce, the locations of p -hydroxyphenyl and guaiacyl units was different in cell wall layers. In aspen sapwood, the main locations of Ca, Mg, Na, K were in lumina of longitudinal parenchyma cells and in pits between vessels and ray cells. Low-intensity signals of the secondary ions assigned to lignin were found in the same morphological regions.

Three bleached and subsequently aged cellulosic pulps have been analysed for their chromophore content according to the chromophore release and identification (CRI) method. Several chromophores have been unambiguously identified, despite their very low content (ppb range). This is the first report on defined chromophoric structures isolated from bleached pulps. It is also the first application of the CRI method to cellulose I substrates, rather than to cellulose II substrates (fibres) and cellulose derivatives as hitherto performed. A common feature of the chromophores is the 2-hydroxy-[1,4]benzoquinone moiety, which is strongly stabilized by resonance or tautomerism. The structure of the chromophores indicates that oxidised carbohydrate structures act as precursor moieties, which condense upon ageing to the chromophore structures identified.

The effects of periodate oxidation on cellulose were studied by means of gel permeation chromatography (GPC) using multiple detection and carbonyl-selective fluorescence labeling according to the CCOA methodology profiling of carbonyl groups. At low degrees of oxidation, the molecular weight distribution was fully maintained. Upon more pronounced oxidation the molecular weight even increased due to cross-linking effects. More condensed structures were identified by means of light scattering. Periodate oxidation also affects crystalline regions of cellulose, as demonstrated by comparison of homogeneous and heterogeneous carbonyl labeling. Highly ordered regions in cellulose were affected by oxidation even below an oxidation degree of 2%. Two different phases for the oxidation kinetics were identified in the early stages of periodate treatments.

Pretreatment of wood or kraft pulp with endoglucanase followed by swelling in urea leaves a non-crystalline residue that can be dissolved in strong aqueous sodium hydroxide-sodium borate solution. A stepwise precipitation process employing acid and barium ions can separate lignin-carbohydrate complexes enriched in individual polysaccharides. This procedure has been applied to eucalypt and birch wood and to the corresponding kraft pulps. Thioacidolysis of the various lignin-carbohydrate complexes was used as the major analytical technique to obtain information about the structure and structural changes in lignin. A combination of thioacidolysis and size exclusion chromatography was used to obtain knowledge on the degree of depolymerisation and repolymerisation of lignin when going from wood to chemical pulp. In contrast to spruce wood and kraft pulp, complete recovery of the lignin-carbohydrate complexes could not be obtained from hardwood samples.

Cross polarisation/magic angle spinning 13 C NMR spectroscopy has been used to study structural changes in cellulose induced by the dissolving pulp process. The cellulose structure in several dissolving pulps was investigated for commercial and laboratory cooked Eucalyptus 92α and 96α. The average lateral dimension, or average thickness, of the cellulose fibril aggregates is related to the amount of surface area exposed and could be one controlling factor for the chemical reactivity of commercial dissolving pulps during modification reactions. The thickness of the cellulose fibril aggregates governs the amount of surface area present in the fibre wall, and cellulose surface material constitutes the part of the cellulose that is directly accessible to reagents. In all sample series investigated, the raw pulp was found to be less aggregated than the corresponding bleached final pulp. Furthermore, an irreversible increase in fibril aggregate width was observed on free drying for both laboratory cooked and commercial pulps. Upon rewetting with water, the freely dried 96α pulp was found to be more aggregated than the freely dried 92α pulp, although sugar analysis showed very similar carbohydrate compositions. As indicated by the molecular mass distribution, the commercial 92α pulp contained larger amounts of degraded cellulose; this may be a plausible explanation for the different behaviour of the 92α and 96α pulps during free drying.

Wood is colonised and degraded by a variety of micro-organisms, the most efficient ones are wood-rotting basidiomycetes. Microbial decay processes cause damage to wooden constructions, but also have great potential as biotechnological tools to change the properties of wood surfaces and of sound wood. Standard methods to evaluate changes in infected wood, e.g., EN350-1 1994, are time-consuming. Rapid FT-NIR spectroscopic methods are also suitable for this purpose. In this paper, degradation experiments on surfaces of spruce ( Picea abies L. Karst) and beech ( Fagus silvatica L.) were carried out with white rot basidiomycetes or the ascomycete Hypoxylon fragiforme . Experiments with brown rot or soft rot caused by Chaetomium globosum were also performed. FT-NIR spectra collected from the degraded wood were subjected to principal component analysis. The lignin content and mass loss of the specimens were estimated based on univariate or multivariate data analysis (partial least squares regression).

Three major types of paper mill sludge, primary sludge (PS), secondary sludge (SS) and de-inking paper sludge (DPS) were characterized and evaluated as adhesive fillers. Plywood panels were made of formulations with phenol formaldehyde (PF) and sludges. Panels with PF/PS and PF/SS formulations had higher dry and wet shear strengths than those made with PF/Cocob ® formulation. All wood failure values were comparable. Dry and wet shear strengths of the panels with PF/DPS formulation were comparable to those of the PF/Cocob ® panels (with Cocob ® as a commercial filler), but the former displayed a much lower wood failure value. Owing to this fact and its high ash content, DPS was not evaluated further as a potential component of adhesive formulations. Compared with SS, PS resulted in higher dry and wet shear strengths and higher wood failure values. However, granular SS was easier to disperse into the resin component than fibrous PS, and the PF/SS formulation was more easily dispensed on aspen veneer sheets than the PF/PS formulation. SS alone displayed adhesive properties with 0.87 MPa of dry shear strength, but PS alone did not exhibit any bond strength. PS and SS were further evaluated for their general thermal behavior and major functional groups using differential scanning calorimetry and Fourier transform infrared spectrometry, respectively.

In the cellular structure of wood, bound-water diffusion and water-vapor diffusion interact via sorption in a complex moisture-transportation system. At low relative humidities, moisture transport may be modeled by a Fickian diffusion equation with a good approximation. At higher relative humidities, slow sorption and faster bound-water diffusion cause effects, which have been referred to as non-Fickian or anomalous, as they cannot be modeled by one Fickian diffusion equation. Previous research has demonstrated that a set of coupled diffusion equations, namely the multi-Fickian model, can represent this behavior. The multi-Fickian model describes the combined transport of bound water and vapor and their interaction through sorption. The bound-water concentration is also influenced by sorption hysteresis. In the worst case, sorption hysteresis may result in deviations of up to 30–35% in moisture content. Hence, for a precise moisture content computation, sorption hysteresis must be taken into account. The present paper explains the relation between sorption hysteresis and multi-Fickian moisture transport, and clarifies how models for the two phenomena are coupled. To illustrate the effects, a finite element simulation, which is based on the combined model, is presented.

Rheology of wood molecular and supramolecular organization has mostly been conducted with dynamic methods, and the application of time/temperature equivalence typically requires plasticizers to observe segmental relaxation. Dry wood rheology offers the experimental advantage of easy moisture control, but only weak secondary relaxations are observed with dynamic methods. Static methods allow for the longer relaxation times in glassy polymers, and these relaxations are strongly stimulated by lower less damaging temperatures. This study describes the application of creep mode time/temperature equivalence to dry yellow-poplar ( Liriodendron tulipifera ) and southern yellow pine ( Pinus spp.). It was found that time/temperature equivalence was valid from 10–170°C, but only for specimens that received a prior 30-min thermal treatment (with minor desiccation) in the range of 100–170°C. The two woods exhibited clear differences in the temperature dependence of the dry wood creep relaxation, and in the sensitivity to free volume manipulation. These findings are believed to reflect polymer structural differences in hardwoods and softwoods indicating that creep mode time/temperature studies of dry wood may be useful for the analysis of xylem polymer behavior.

The stiffness and strength, modulus of elasticity (MOE) and modulus of rupture (MOR), as well as density, moisture content, microfibril angle and diffraction pattern coefficient of variation of azimuthal intensity profile (I CV ) was determined for 259 small clear specimens. These samples represent 38 old- and second-growth western hemlock ( Tsuga heterophylla ) trees harvested from several sites in coastal British Columbia, Canada. The data were analyzed by classic statistical regression techniques to reveal interrelations among the mechanical properties and the inherent wood properties. Simultaneously, the predictive power of artificial neural networks was evaluated with the same data set by employing several optimization techniques. Regression analysis of wood density and the flexural strength properties resulted in R 2 of 0.172 and 0.332 for MOE and MOR, respectively. The most efficient network model proved to be far superior demonstrating correlation coefficients with models for MOE ranging between 0.693 and 0.750, and the corresponding MOR models ranging between 0.438 and 0.561 in all testing phases. It is apparent that neural networks have the potential and capacity to self-train and become powerful adaptive systems that can predict the strength and stiffness of wood samples. The neural network analysis also revealed the importance level of each independent variable on both MOE and MOR properties.

The modulus of elasticity in bending and the bending strength of the face and core layer of particleboard and medium density fiberboard (MDF) were determined. Three directions of longitudinal axis of test specimens were considered: the direction of the mat forming, the direction perpendicular to it, and the direction perpendicular to the panel plane. The experiments were carried out on specimens that were prepared with strips of layers separated from the panels and glued into laminated assemblies. The bending properties of the core and face layer of the tested panels differed considerably. The core layer properties were on average more than 4 times smaller for particleboard and almost 3 times smaller for MDF. The relative differences between the bending properties were greater than the differences between the densities of the layers. The bending properties of the layers were almost isotropic in the planes of layers and very strongly anisotropic in the planes perpendicular to layers. The modulus of elasticity of the tested panels was calculated for the axis corresponding to the mat forming direction. The calculations were performed on the basis of the moduli of panel layers and based on the layered system theory. The results were compared with the modulus determined directly for entire panels. The relative difference between the compared moduli was found to be very small for both tested panels.

Wood plastic composites (WPCs) are typically composed of wood particles, thermoplastic polymers and small amounts of additives. Further improvement of WPC technology requires a better understanding of their mechanical performance and durability on the micro level. X-ray computed tomography (CT) and advanced imaging techniques can provide visualization and support characterization of the internal structure, deformation and damage accumulation in WPCs under loading and various environmental exposures. However, both wood and thermoplastics are weakly attenuating materials for X-ray and good contrast between these two components is difficult to obtain. In the present study, chemically inert gold nano-particles and micro-particles were investigated as contrast agents to improve X-ray CT scanning contrast between wood and thermoplastics. The effect of adding 1% (by wt.) gold nano- and micro-particles on the tensile properties of wood/high-density polyethylene composites was addressed. Samples with and without surfactant were tested in tension and scanned on a custom desktop X-ray CT system. It was found that the addition of gold particles did not impair the WPC tensile properties. However, some of the tensile properties were significantly affected if the surfactant was included. Gold micro-particles were shown to disperse well without surfactant and significantly improve the X-ray CT scanning contrast between wood and polymer, while gold nano-particles (without surfactant) did not disperse well and do not contribute to contrast improvement.