Volume 64, Issue 4

Commercial aspen wood chips were treated with hot water (autohydrolysis) and with alkali to extract part of the hemicelluloses. The extracted residues and an unextracted wood (control) were subjected to pulping based on the alkaline sulfite anthraquinone (ASA) and alkaline sulfite anthraquinone methanol (ASAM) methods to afford pulps useful for paper production with the same degree of delignification. Unlike the autohydrolysis residue, the alkali extracted residue was shown to favor subsequent pulping in terms of pulping yield, charges of chemicals, cooking times and properties of pulps. The experimental conditions and results are discussed.

Drying and rewetting of Pinus radiata sapwood latewood was studied by synchrotron wide angle X-ray scattering in transmission mode. Scattering from cellulose was interpreted in terms of chains distributed on a monoclinic lattice. Drying wood material to below the fibre saturation point resulted in decreased spacing between adjacent cellulose polymers within the hydrogen-bonded sheets of chains, and also decreased the monoclinic angle. The changes were partly reversed when the dried wood was rewet, but accumulated through multiple cycles of oven-drying and rewetting. No changes were observed in the fibre repeat distance, thus the distortion of the crystal lattice was not attributed to mechanical stresses associated with drying. Instead, the changes were attributed to formation of intrachain hydrogen bonds at dehydrated crystallite surfaces, causing conformational changes within the cellulose chains and increasing the density of packing. The results help account for the hysteresis observed in moisture desorption-adsorption isotherms during wood material drying and rehydration.

Hot-pressing wood, particularly in the production of wood composites, generates significant “native” (wood-based) formaldehyde (FA), even in the absence of adhesive. The level of native FA relates directly to the time and temperature of hot-pressing. This native FA dissipates in a relatively short time and is not part of the long-term FA emission issue commonly associated with hydrolyzing urea-formaldehyde bonds. This paper demonstrates that the common desiccator/chromotropic acid method is very specific for FA and is not influenced by other volatile compounds set free from wood during hot-pressing. Furthermore, it is shown that particleboard produces native FA at high levels even in the absence of adhesives or in the presence of one type of no-added formaldehyde (NAF) adhesive. Soy-based adhesives suppress native FA emission and provide low FA emission levels in both the short and long term. This study highlights an often overlooked aspect that should be considered for emission testing: standardizing the time and conditions employed immediately after pressing and prior to the onset of emissions testing. Addressing this issue in more detail would improve the reliability of correlation between data obtained by rapid process monitoring methods and emission measurements in large chambers.

Enthalpies of reaction for the initial steps in the pyrolysis of lignin have been evaluated at the CBS-4m level of theory using fully substituted β-O-4 dilignols. Values for competing unimolecular decomposition reactions are consistent with results previously published for phenethyl phenyl ether models, but with lowered selectivity. Chain propagating reactions of free radicals with a closed-shell dilignol are dominated by structures in which extensive electron delocalization occurs.

The effect of three different commercial cellulase treatments applied on softwood bleached kraft pulp before the refining step was studied. Disc refining was applied under similar conditions as usual in paper mills. Two cellulase treatments allowed an energy saving of 20% to reach a given drainage index or breaking length. Water retention value (WRV), which characterizes the water absorption inside the fibre wall, was increased by the cellulase treatment. However, tear index losses were observed upon enzyme treatment. The third cellulase did not have an impact either on any parameters of the refining or on the pulp properties, except WRV. Viscosity measurements showed that the two first cellulases have strong endoglucanase activities but are lacking exoglucanase activities. Probably, endoglucanase activity weakens the fibre structure by generation of weak points or kinks. This hypothesis would explain the important cutting and fibrillation phenomena observed in the case of these two cellulases. It can be concluded that cellulase treatment could save 20% of electrical energy needed for refining, i.e., 50 kWh t -1 , if a paper quality with a high tensile resistance but lowered tear strength is acceptable.

Red oak wood ( Quercus rubra L.) samples were submitted to an enzymatic treatment with a commercial mixture of hemicellulases aiming at the selective depolymerization and removal of the hemicelluloses. Mechanical properties of treated samples were characterized and compared with untreated samples at two hierarchical levels. At the macrolevel, tensile properties revealed to be less sensitive to degradation of the cell wall matrix compared to compression and hardness properties. Results obtained through indentation at the microlevel indicated that hardness and the so-called reduced modulus of treated wood were significantly lowered. Accordingly, hardness and reduced elastic modulus have proven to be most sensitive to modification of the cell wall matrix by reducing the content of hemicelluloses. It is proposed that transversal and shear stresses, which are mainly carried by the cell wall matrix, are additional parameters having strong effects on elastic modulus obtained by nanoindentation. Micromechanical modeling was employed to confirm the observed changes. There is consistency between the measured and the modeled properties, obtained at both the microlevel and the macrolevel of wood.

A statistical lattice model was developed to investigate the energy associated with damage and failure of wood. The model incorporates several important morphological aspects of wood such as grain direction, early wood percentage and grain geometry. The model was developed to investigate progressive damage under enforced boundary displacements and has been adapted to predict fracture energy related phenomena. In this particular study, notched specimens were loaded in uniaxial tension while monitored by a passive acoustic emission (AE) measurement system. The energy associated with the mechanical damage was measured by the AE instruments and compared with the energy released by ruptured elements in the lattice model. Cumulative energy release was tracked as a function of specimen load and deformation in both model and experiment. A ratio was established between the cumulative AE energy released at the first drop in load and the cumulative fracture energy released when the model load-deformation relationship becomes significantly non-linear. An additional ratio was established between the total fracture energy measured prior to 50% of peak strain and the total fracture energy measured prior to peak strain. The magnitudes of these energy release ratios vary owing to a change in failure modes between the short model and the larger specimens; however, the shape of the AE energy release curve up to failure coincides well with that predicted by the model simulations.

The interaction of wood with water is a primary factor for degradation of the substrate. Organosilicons are known to behave like a water repellent, thus they are in discussion as protecting agents for wood used outdoors. In the present paper, the influence of water on organosilicon treated material was investigated. Solid Scots pine sapwood was impregnated or treated superficially with low concentrations of organosilicons and evaluated for several water related characteristics. The results confirm the water repellent properties of organosilicons as the polysiloxane film increases the contact angle between water and the wood substrate. However, they do not influence the total uptake of moisture but can change the rate at which moisture is taken up, and as such, prolong the service life of the substrate. In general, impregnated specimens behave better than dipped ones. To gain more insight in the exact behavior, continuous moisture uptake experiments are needed in real outdoor exposure tests.

The water vapour sorption behaviour of Sitka spruce was analysed based on the parallel exponential kinetics (PEK) model. The PEK model deconvolutes the sorption kinetics curve into two exponential kinetics processes (fast and slow) which have characteristic times and moisture contents associated with them. The sorption kinetics was examined at different temperatures enabling the determination of activation energies for the sorption kinetic processes throughout the hygroscopic range (from 5% to 95% relative humidities). The physical interpretation of the PEK model is also discussed.

Scots pine ( Pinus sylvestris L.) sapwood was treated with glutaraldehyde (GA) and magnesium chloride (MgCl 2 ) as a catalyst. The effects of treating conditions on the mechanical properties were examined. The weight percent gain (WPG) of thin veneer strips after leaching was highest at pH 4.0–4.5 and tensile strength measured in zero-span strength and finite-span strength decreased with decreasing pH in a range of 3.5–5.5. Sole treatment with MgCl 2 also gradually decreased the tensile strength up to 25% with decreasing pH. At a fixed GA concentration (1.2 M), increasing MgCl 2 concentration linearly diminished tensile strength. Conversely, increasing GA at a fixed MgCl 2 concentration (1.5%) displayed the same effect, whereas in both cases zero-span strength loss was higher than finite span-strength loss. GA treatment of Scots pine sapwood stakes did not affect the modulus of rupture and the modulus of elasticity, but significantly reduced work to maximum load in bending and impact bending strength indicating embrittlement of wood. At the same time, compression strength increased with increasing WPG of GA. It is assumed that embrittlement caused by hydrolysis and crosslinking of cell wall polymers is compensated by enhanced compression strength thereby resulting in unchanged bending strength.

Scots pine sapwood was treated with various concentrations of glutaraldehyde (GA) and magnesium chloride as a catalyst in aqueous solutions. The weight percent gains (WPGs) attained after leaching were 1.0%, 8.6%, 13.7%, and 21.9%, respectively. The treatments reduced the equilibrium moisture content at 90% RH up to 30% compared with the untreated controls. Capillary water uptake of wood was also restrained by GA treatment (8.6% WPG) resulting in water reduction effectiveness of approximately 50% in both radial and tangential direction after 244 h. Wood blocks treated to the highest WPG (22%) attained 70% anti-swelling efficiency (ASE). High ASE values were caused by cell wall bulking through incorporation of GA in the cell wall and as a result of reduction of the maximum degree of swelling in water, i.e., through crosslinking of cell wall polymers. During 10 water submersion and drying cycles, untreated and GA treated specimens displayed equal weight losses indicating that mainly wood constituents were washed out. These cyclic water submersion tests also caused approximately 10% reduction in ASE in samples treated to higher WPG. Magnesium chloride as a catalyst for the reaction of GA imparts wood similar water related properties as sulphur dioxide catalysis of GA treatment, but the application of MgCl 2 is much easier to perform in practice.

Longitudinal bending creep during desorption, which is also referred to as mechano-sorptive creep, was measured under various desorption conditions for moso bamboo ( Phyllostachys pubescens ) to clarify the effect of the conditions and the specimen part. The results showed that the mechano-sorptive effect appeared not only in wood but also in bamboo, and that its effect was reduced by an increase in the volume fraction of the bundle sheath in the cross-sectional area. The results of this experiment suggest that mechano-sorptive behavior is related to the amorphous matrix in bamboo components.

Sitka spruce ( Picea sitchensis ) is the most widely planted commercial tree species in the United Kingdom and Ireland. Because of the increasing use of this species for construction, the ability to predict wood stiffness is becoming more important. In this paper, a number of models are developed using data on cellulose abundance and orientation obtained from the SilviScan-3 system to predict the longitudinal modulus of elasticity (MOE) of small defect-free specimens. Longitudinal MOE was obtained from both bending tests and a sonic resonance technique. Overall, stronger relationships were found between the various measures of cellulose abundance and orientation and the dynamic MOE obtained from the sonic resonance measurements, rather than with the static MOE obtained from bending tests. There was only a moderate relationship between wood bulk density and dynamic MOE (R 2 =0.423), but this relationship was improved when density was divided by microfibril angle (R 2 =0.760). The best model for predicting both static and dynamic MOE involved the product of bulk density and the coefficient of variation in the azimuthal intensity profile (R 2 =0.725 and 0.862, respectively). The model parameters obtained for Sitka spruce differed from those obtained in earlier studies on Pinus radiata and Eucalyptus delegatensis , indicating that the model might require recalibration before it can be applied to different species.

The critical stress intensity factor of mode I ( K Ic ) obtained by single-edge-notched bending (SENB) tests of wood was experimentally and numerically analyzed. A double cantilever beam (DCB) test was also conducted and the results were compared with those of SENB tests. The K Ic value was obtained by introducing an additional crack length into the equations used for analyzing the SENB test of isotropic material when the initial crack length ranged from 0.1 to 0.6 times the depth of the specimen.

Caesalpinia echinata Lam. (pau-brasil) is a Brazilian tree with symbolic character for Brazilian forestry, which is at risk of extinction because of illegal logging activities and exportation as raw material for bows of string instruments. Additional studies are required to select substitutes for pau-brasil, i.e., other wood species are being sought with potentially suitable characteristics for bow manufacture. The present paper is dedicated to the evaluation of six native Brazilian woods by comparing their anatomical features, specific gravity, speed of sound propagation, and dynamic modulus of elasticity in relation to the corresponding properties of C. echinata that are considered as standard for bow manufacture. The results showed that length, diameter, lumen diameter, and wall thickness of fibers are the most important variables contributing to specific gravity. Additionally, ray dimensions influenced sonic velocity. The values of dynamic modulus of elasticity are directly related to dimensions of rays and fibers. Among the six woods included in this study, Dipteryx spp., Handroanthus spp., and Hymenaea spp. were considered as the best alternatives to C. echinata wood as sources of bow construction. The bows from the first two woods were already tested by professional musicians and their suitability was certified. The Diplotropis spp. wood also showed promising characteristics. Mezilaurus itauba and Astronium lecointei do not have the necessary properties for bows.

A novel protocol for non-destructive assessment of green density and moisture content via increment cores was validated for young (8–10 years) and mature trees (36 years) of radiata pine ( Pinus radiata D. Don.). Initial procedures involved comparing 5- and 12-mm cores with fresh disks taken from young trees at breast height and felled during the winter, as well as methods for rehydrating the wood cores. Subsequently, the best method (12-mm cores) was validated with material collected in summer from both young and mature trees. The protocols developed require separate processing of sapwood and heartwood, and soaking the sapwood for 24 h to replace the moisture lost while coring. For young trees, bark-to-pith 12-mm cores accounted for between 64% and 66% of variation in green density of sapwood and between 51% and 72% of saturation percentage, as measured by destructively sampled disks. For mature trees, the average of two sides of 12-mm bark-to-bark cores accounted for 73% of variation in green density of sapwood, and 56% of saturation percentage as measured by destructive wedges. One or both sides of a bark-to-bark core accounted for between 72% and 80% of variation in whole-section green density, and between 70% and 79% of variation in sapwood percentage. The number of heartwood rings was better predicted from the average of two sides of the cores (R 2 of 0.71). Whole-tree values (lower two logs) for sapwood green density and saturation were better predicted from the average of both sides of the bark-to-bark core (R 2 of 0.76 and 0.57, respectively). Whole-tree values for whole-section green density could be predicted either by one side or two sides of the cores (R 2 for 1 or 2 sides of 0.77 and 0.81). Finally, whole-tree sapwood volumetric percent was better predicted by the average of two sides of the cores (R 2 of 0.81).

Logs of eastern red cedar, Juniperus virginiana L., with well-developed bands of light-colored wood (“included sapwood”) within heartwood can be unsuitable for sawn wood products. This finding is in contrast to published information that the “included sapwood” is (1) a heartwood anomaly rather than sapwood and (2) its occurrence is not a reason to exclude this type of wood from commercial use. The alternative view presented here is that “included sapwood” is wound-initiated discolored wood which is the starting point for wood decay in living trees and which has adversely altered wood properties before the development of decay symptoms. Our study of the patterns of discoloration and decay, electrical resistance properties, elemental analysis, wood acidity, solubility in dilute NaOH, total phenol content, and tests of wood decay resistance indicated that the so-called included sapwood was discolored wood. This light-colored discolored wood had no greater decay resistance than sapwood, a common finding in other tree species in which “included sapwood” is found. Half the sample disks sent to our laboratory had symptomatic decay within the bands of light-colored discolored wood bounded by a phenol-enriched protective layer on the bark side and phenol-enriched heartwood on the pith side of the band. This ring-rot, even in its pre-symptomatic stage, can cause problems during processing for sawn wood products. Therefore, logs with well-developed bands of light-colored discolored wood should be considered high-risk material for some products, although they could be useful for others.

Tebuconazole, didecyldimethylammonium chloride (DDAC), and boric acid are co-biocides frequently added to copper-based wood preservative systems. Although the performance thresholds of these biocides are well known, there is currently little information on the effects of subthreshold loadings of the co-biocides on common wood decay fungi. We tested five strains of Postia placenta on white pine cubes ( Pinus strobus ) treated with subthreshold retentions of tebuconazole, DDAC, or boric acid. No stimulatory effects were observed on blocks treated with DDAC or boric acid. Decay stimulation, as measured by weight loss, occurred between loadings of 1.0×10 -5 to 1.0×10 -3  kg m -3 on blocks treated with tebuconazole. This effect should be taken into account during the design and use of wood preservative systems containing this fungicide.

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