Volume 56, Issue 5

To study the effect of growth rate on fibre characteristics and their variations in Norway spruce, trees were sampled in a nutrient optimisation experiment in northern Sweden. Data was collected from 24 trees (40 years old) from fertilised and control plots after 12 years of annual nutrient application, as well as from older trees outside the experimental area. Fibre length, fibre diameter, cell wall thickness, lumen diameter and cell wall percentage were measured from every third annual ring at breast height and at a height of 4 m. Fibre properties, as well as their standard deviation, were closely related to ring number and distance from the pith. Intra-ring variation of fibre characteristics was high compared to their variation between trees. Fertilisation reduced fibre length and cell wall thickness, but increased fibre and lumen diameter in rings of the same age. The difference in fibre width, cell wall thickness and lumen diameter between fertilised and control trees was less apparent, but a greater difference in fibre length was found between the treatments with regard to distance from the pith. There was a similar effect of fertilisation on fibre properties in early- and latewood. The effect of enhanced growth rate was less pronounced at a height of 4 m (near the pith) than at breast height (in older rings). It was demonstrated that it is possible to model intra-tree variability of fibre characteristics using ring width and cambial age as independent variables. Models presented are, however, limited by the relatively young age of the sample trees used.

Growth stress (growth strain) in trees is usually evaluated using either a strain gauge or a dial gauge to measure the strain release. We summarize the techniques used to assess growth stress and compare the two methods. The dial gauge method measures change in distance between two pin targets when growth stress is released by sawing two grooves; from this the strain released is calculated. The absolute values of the strain released depended on whether the two grooves were sawn inside or outside the pin targets: the values in the first case were approximately twice those in the latter. If the grooves were sawn outside the pin targets, the values for the strain released were about the same as with the strain gauge method, in which the strain released by sawing a groove at each end of a strain gauge is measured. The released strain values were consistent when the strain gauge was glued to the outer surface of the secondary xylem after first fully removing the differentiating xylem. To release most of the surface growth stress and maximize released strain values, the optimal distance between the ends of the strain gauge and the grooves cut to release the growth stress was 3 to 5 mm, and the optimal depth of the groove was 5 to 10 mm. Most of the growth stress was released immediately when the grooves were sawn.

UV absorbers were microwave-grafted onto copper-amine (Cu-MEA) treated maple. The so-treated wood was weathered with UV light for various periods of time. Two weathering cycles were used: one with only an irradiation step using a 175W medium pressure mercury lamp of wavelength higher than 300 nm and a second with irradiation and a water spray step. The surface color and the surface roughness were monitored and the biological performance of the UV absorbers grafted on copper amine-treated maple evaluated as well. ∆E, the total color change was measured and it increased from 0 to 14.7 after 317 h weathering for untreated maple. For Cu-MEA treated and UV absorbers grafted on the surface, the values of ∆E range from 0.7 to 5.7. The higher values of ∆E for both treated and untreated samples were associated with the weathering cycle with the water spray step, suggesting that water plays an important role in the wood discoloration. However, the microwave grafting of UV absorber on Cu-MEA treated maple did not prevent or reduce the formation of rough surface or inhibit the biological performance of Cu-MEA. This laboratory study indicates that phenolic UV absorbers can be microwave grafted on maple to improve the color stability.

The concentration of individual resin acids and the equilibrium moisture content at a relative humidity of 100% were studied in brown-rot resistant and susceptible Scots pine ( Pinus sylvestris L.) heartwood. About 90% of the resin acids in the heartwood were of the abietane type, abietic acid being the most abundant. The concentration of resin acids was higher in the decay-resistant heartwood than in the decay-susceptible heartwood. Resin acids are presumably in part responsible for the decay resistance of Scots pine heartwood. However, no clear relationship was found between the concentration of resin acids and the equilibrium moisture content. The role of resin acids may also be ascribed to mechanisms other than their hydrophobic properties alone. The reasons for the slight differences in moisture content between the decay classes require further study.

Nine abietane-type diterpenes were isolated from the heartwood of Taiwania cryptomerioides and their structures identified by spectral analyses. Among these nine compounds, six diterpenes were isolated for the first time from T. cryptomerioides , including 6,7-dehydroferruginol, 6α-hydroxysugiol, 5,6-dehydro-6-hydroxysugiol, 11-hydroxyferruginol, secoabietane dialdehyde and isohinokiol. We suggest that abietane-type diterpenes are the dominant diterpenes in the heartwood of T. cryptomerioides . A possible biosynthesis pathway is proposed. In addition, a 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay was performed to evaluate the antioxidant activity of these diterpenes. This study demonstrates that ferruginol exhibits the strongest antioxidant activity among the diterpenes isolated from T. cryptomerioides heartwood.

Four flavonoid compounds, ((+)-taxifolin, (+)-aromadendrin, quercetin and (−)-naringenin), from Japanese larch ( Larix leptolepis ) wood were heated at 170 ℃C for 60 min at pH=3.46 (hydrothermolysis treatment). Alphitonin, four taxifolin steric isomers and quercetin were recovered from the treatment of (+)-taxifolin, and maesopsin, four aromadendrin steric isomers and kaempferol from (+)-aromadendrin. The reaction products from (−)-naringenin were found to be a mixture with (+)-naringenin. Quercetin was not changed by the treatment. Possible pathways for the formation of these products are discussed.

The influence of reaction time, reaction temperature and acid concentration on the yield and characteristics of FORMACELL aspen lignins were investigated. 18 samples were quantitatively isolated from the black liquor by precipitation. The samples were analysed regarding their contents of carbohydrates, methoxyl and ester groups. All samples had low carbohydrate contents and the amount of methoxyl and ester groups was continuously reduced under more severe pulping conditions. Molar mass distributions and glass transition temperatures were determined. Molar masses of lignins were continuously reduced during pulping resulting in low weight average molar masses from 2.500–3.200 g/mol. Glass transition temperatures varied from 123.6 to 154.5°C, depending on the reaction conditions. Comparison of the thermograms with those of the lignins from the Kraft or Sulfite process confirmed that in the FORMACELL process a very uniform lignin with few impurities is obtained.

The effect of solvent on yield and properties of ethanol-alkali pulps from Arundo donax L. was studied. Selectivity of pulping was significantly improved with increase in solvent proportion in the cooking liquor. A rise in ethanol concentration from 20 to 60% (by vol.) increased pulp yield from 44.0 to 48.9%, while decreasing residual lignin from 5.0 to 3.0%. Ethanol addition had a positive effect on preservation of carbohydrate complex against degradation in alkaline medium. Intrinsic viscosity of cellulose was improved up to 35% and xylan content increased from 8.6 to 12.1% with increase in ethanol concentration from 20 to 60%. The preservation of minor non-cellulosic polysaccharides with solvent addition was also observed. The papermaking properties of ethanol-alkali pulps were best for 20% ethanol content. An increase in solvent charge led to a drop in burst, tear and tensile pulp strength. Solvent addition assisted the conversion of glucuronic to hexenuronic acids, whereas the content of HexA in ethanol-alkali pulps of Arundo donax (about 10 μmol/g) was substantially lower than reported for kraft pulps from wood.

The effect of the partial removal of xylan on unbleached and bleached birch kraft pulps was investigated by Fourier transform infrared (FTIR) microspectroscopy and the resulting data were analyzed by multivariate data analysis, i.e. , principal component analysis (PCA) and maximum likelihood principal component analysis (MLPCA). Isolated model substances (xylan, cellulose and lignin) were used to calibrate these methods. Clear chemical changes in the relative proportions of the main constituents and functional groups on the pulp fiber surface were observed as a function of the amount of xylan removed. In addition, due to the partial removal of xylan, indications of some physical changes were observed.

Thermal modification is a technique to produce wood with increased dimensional stability and lower equilibrium moisture content. 2 H NMR relaxation measurements and pulsed field gradient (PFG-NMR) methods are non-invasive spectroscopic techniques that can be used to measure the response of liquid confined in porous materials and yield information on the size and distribution of the pores. These methods were used to study the structure and changes in structure of thermally modified Scots pine wood. The 2 H longitudinal relaxation measurements of wood samples at different moisture contents showed different relaxation times and relaxation time distribution in the thermally treated samples. The effect of the thermal treatments on the cell size in wood samples was studied by PFG-NMR measurements with different dwell times. The PFG-NMR measurements showed no clear change in the cell dimensions of the thermally modified samples compared with control samples taken from the same log.

Magnetic resonance imaging delivers excellent, high-resolution spatial images of damp or wet wood that can supply information on internal defects of logs to optimise cutting patterns. In normal wood, the image contrast of magnetic resonance images is primarily influenced by the distribution of moisture content within the specimen. In the case of fungal attack, it is also affected by the inherent Spin-Lattice (T 1 ) and Spin-Spin (T 2 ) relaxation times. We investigate changes in relaxation times in beech wood ( Fagus sylvatica L.) caused by fungal attack ( Coniophora puteana (Schum.) Karst.) over 6 weeks. In addition, loss of compressive strength and mass loss were tested, allowing comparison to conventional methods. Magnetic resonance imaging showed superior sensitivity in detection of early stage of fungal decay in comparison to mass or strength loss assessment.

Wood density measurement is related to several factors that influence wood quality. In this paper, a CT image calibration procedure which allows image quantification in terms of dry bulk density is presented for three different X- and gamma-ray energies (28.3, and 59.5, and 662.0 keV). The mass attenuation coefficients measured for a set of eight wood species did not vary significantly, allowing a single calibration for determination of bulk density of air-dried wood samples at each energy. The equation for bulk density calibration obtained was validated using a second set of twelve wood species. Comparison of bulk density determined by CT images, using the calibration procedure proposed, with values obtained by gravimetric methods, presented a very good linear correlation coefficient (R 2 =0.94). The main advantage of CT imaging over conventional techniques for wood bulk density determination is that it allows detection and quantification of heterogeneities and internal defects. At the sub-millimetric spatial resolution level, it is possible to identify morphological and structural aspects of wood samples.

A model of wood drying under isothermal conditions taking into consideration coating of the surface of a specimen is presented in this paper in a two-dimensional formulation. The influence of the surface coating degree as well as geometrical shape of a wood specimen on the dynamics of drying is investigated. Exponentials, describing the dependence of the halfdrying time on the degree of coating of the edges, as well as on the ratio of the width to the thickness of the transverse section of specimens from the northern red oak ( Quercus rubra ), are presented for drying from above the fiber saturation point. This paper describes the conditions of usage of the two-dimensional moisture transfer model in contrast to the one-dimensional model for accurate prediction of the drying process taking into consideration the coating of edges of specimens having a rectangular transverse section. A measure of reliability of the one-dimensional model to predict the wood drying process of sawn boards is introduced in this paper.

This paper deals with the intermolecular forces in the system wood-solid coating, which primarily condition the stability of the system. Further, it points out a series of secondary factors that significantly distort the results of interactions between surface forces; not only influencing the phase boundary wood-coating material in the liquid phase, but also negatively impacting the wood-solid coating system stability.

The contact angle of water on wood rises sharply as the wood approaches dryness. The general shape of the rise can be reproduced through thermodynamic calculations that consider the presence of extractives on the surface. SEM work confirms that extractives move progressively to the surface with increasing drying temperature. Other factors such as pore closure also contribute to surface hydrophobicity. The temperature profile within a stack of flakes during accelerated pressing shows a break at 100°C when flakes dried at high temperature are processed. Moisture is known to be driven from the outer layers of the stack to the core during early pressing. If the flake surface is hydrophobic then this moisture would film on the surface rather than penetrate into the flake. Subsequent evaporation of the moisture would lead to high pressure. Hence, flakes dried at high temperature should be more prone to delamination. High-temperature drying also promotes VOC emissions and there should be operational and environmental benefits to drying at lower temperature.