Volume 57, Issue 1

Mass accumulation dynamics in earlywood and latewood cell walls of larch from northern regions of Central Siberia are investigated and correlations among cell mass of different tree-ring zones, radial tracheid sizes and tree-ring width are found. A linear relationship exists between cell wall mass and radial cell size. The deviation of cell mass from the regression line (index of mass deviation) and the mean density of the respective tree-ring zone are similarly functionally dependent on the radial cell size and reflect the realization of the potential determined during the period of cell formation. There is a critical value of larch tree-ring width in relation to cell mass. For the tree-rings with width less than this critical value the difference in the mass of earlywood and latewood cells increases with decreasing tree-ring width.The cell wall mass correlates with the monthly temperatures of June and July. Under favorable growing conditions tracheids with similar mass of cell walls are formed in earlywood and latewood, while under unfavorable conditions cell wall mass accumulation in latewood is severly limited. A comparative analysis of the cell wall mass in earlywood and latewood indicates that mass accumulation is independent of the switching processes from earlywood production to the production of latewood.

Loss in bending strength of wood has been shown to be a more sensitive measure of decay than is weight loss. Using modulus of rupture as the decay criterion is problematic for oriented strandboard (OSB) because of variation in mechanical properties due to particle orientation and size. Moreover, the small specimen size required for such tests increases the variance in mechanical properties. This study compared the variance in bending strength of ASTM D1037 standard-sized specimens and small specimens from two samples of commercial OSB. The small specimens were found to have a significantly higher level of variance in bending strength than the standard-sized specimens. A simple method of sorting the specimens based on strand orientation on the tensile surface significantly reduced the level of variance measured. The effects of differing levels of variance on the size, design and limitations of the experimental study are presented.

The major part of the wood cell wall consists of parallel-aligned cellulose fibrils. Locally, pits connecting adjacent cell walls disturb the fibril arrangement. The local fibril orientation around these mechanically weak points is crucial for the mechanical stability of the cell. In some softwood species like spruce, the pit apertures at junctions of tracheids and cross-running ray parenchyma cells are elongated and slit-like. The pit orientation has often been assumed to directly reflect the fibril orientation. In this paper we use X-ray microdiffraction to determine the local microfibril angle (tilt angle versus the cell axis, MFA) in single tracheid walls of Norway spruce in the vicinity of pit apertures. The results from microdiffraction are compared with the pit orientation observed under the light microscope.Whereas a good correlation was found in thick-walled latewood cells from the stem and compression wood, large discrepancies occurred for thin-walled earlywood cells. A simple mechanical model that could explain the different situation in earlywood and latewood is presented.

The reactivity of a fungal laccase to lignin of six different spruce kraft pulps with kappa numbers ranging from 15 to 110 was studied. Enzymatic oxidation of lignin was investigated by monitoring the oxygen consumption in a suspension of the pulp and the number of radicals generated in the pulp, as measured by electron paramagnetic resonance spectroscopy. The laccase catalyzed oxidation of lignin in kraft pulp followed a double exponential function. This indicates the presence of two types of substrates oxidized by the enzyme at different rates. The two substrates were interpreted as lignin located on the surface of the pulp fibers and as lignin in the cell wall. A linear relationship was found between the kappa number of the pulps and the observed first-order rate constant for oxidation of substrate in the cell wall. Quantification of free radicals in the pulp showed a linear dependence on the lignin content and the number of free radicals generated upon oxidation with laccase.

The hydrophilic and lipophilic extractives in the heartwood of knots from 7 Norway spruce trees were analysed by GC, GC-MS and HPSEC. The knots contained extremely large amounts of lignans, 6–24% (w/w), with hydroxymatairesinol comprising 65–85% of the lignans. Even the knots of the young trees contained 4–8% (w/w) of lignans. The variation in the amount of lignans was large among knots, both within a single tree and between trees. In addition to the lignans, knots also contained 2–6% (w/w) of a complex mixture of lignan-like compounds with 3, 4 and even up to 6 phenyl propane units, here called oligolignans. The amounts of lignans in the knots were similar in the radial direction from the pith into the outer branch, but decreased dramatically outwards in the branch, almost disappearing after 10–20 cm. The ratio of the 2 epimers of hydroxymatairesinol differed between different knots and even within the knot. A new spruce lignan, nortrachelogenin, or its enantiomer, wikstromol, was detected in knots from trees in northern Finland as opposed to samples from southern Finland. The amount of lipophilic extractives was small compared to the amount of hydrophilic extractives in the knots. Five of the dead knots contained more resin acids and free diterpenyl alcohols than ordinary stemwood. In the other knots, the amount of lipophilic extractives was on the same level as stem heartwood. The stem sapwood contained larger amounts of esterified fatty acids than the knots.

Electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry (MS) and size exclusion chromatography (SEC) was utilised for analysis of milled wood lignin (MWL) and lignin model compounds degraded by thioacidolysis. MS and SEC showed that thioacidolysis was an efficient method for degradation of the β-O-4 bond in lignin. Moreover, the molecular weight of thioacidolysed pinoresinol and MWL were analysed using matrix assisted laser desorption ionisation time-of-flight mass spectrometry. Tandem MS was successfully applied for the structural determination of thioacidolysed pinoresinol with and without acetylation of the product. The MS results of thioacidolysis on MWL resulted in the identification of a tetrameric lignin structure containing a 5-O-4, 5-5, β-1 linkage pattern.

Peroxymonophosphoric acid (Pp) has been shown to be an excellent delignification chemical for kraft pulps. However, the reaction mechanism of Pp with lignin has not been elucidated. Therefore, the reactions of Pp with non-phenolic lignin model compounds have been investigated at 70 and 90°C and compared to those of peroxymonosulfuric acid (Px). Pp and Px appear to follow similar reaction pathways, however, the reaction kinetics are significantly different. Both Pp and Px react with 1,2-Dimethoxy-4-methyl-benzene as electrophiles, with aromatic hydroxylation being the main initial reaction. For 1-(3,4-Dimethoxy-phenyl)-ethanone, both Px and Pp react via the Baeyer-Villiger reaction, in which the initial step is nucleophilic attack by the peracid.The reaction with 1-(3,4-Dimethoxy-phenyl)-ethanol occurs primarily via carbocation formation followed by subsequent reactions with the peracid. Changes in pH dramatically affect the reaction rates of Pp with all the model compounds investigated, whereas with the exception of the Baeyer-Villiger reaction, changes in pH did not affect the Px reactions. Below pH 2, Pp is a better electrophile than Px, but above pH 2, Px is better. In addition, while Px remains reactive, Pp is not reactive at pH above 7 for the model compounds investigated.

In peroxymonosulfuric acid bleaching, the presence of hydrogen peroxide is dependent on the reaction conditions and the conversion ratios used to generate the peroxy acid. Substantial amounts of hydrogen peroxide may be present in the reaction system under certain conditions. An understanding of the reactions of hydrogen peroxide under these conditions would be beneficial. Therefore, several simple lignin model compounds were reacted with acidic hydrogen peroxide, pH 1-3, at 70°C. In all cases the phenolic lignin model compounds reacted much faster than their non-phenolic counterparts. In fact, the extent of reaction was very much dependent on the structure of the lignin model compound. The α-hydroxyl compounds, 4-(1-Hydroxy-ethyl)-2-methoxy-phenol and 1-(3,4-Dimethoxy-phenyl)-ethanol, reacted faster than the corresponding α-carbonyl compounds with both reacting much faster than the aromatic compounds, with simple alkyl substituents. A new reaction mechanism for α-hydroxyl compounds is proposed, in which benzyl carbocation formation is followed by nucleophilic addition of hydrogen peroxide. Unlike the mechanisms proposed in the past, no evidence of aromatic hydroxylation via perhydronium ion was observed. The reactivities were very pH dependent, in that higher reactivity was associated with lower pH. Decreasing pH further increased the amount of condensation products identified, such that condensation was competitive with degradation. These condensation reactions were also present under the Caro's acid bleaching conditions at pH below 2. However, under all conditions the reactivity of acidic peroxide was found to be much less than that of peroxymonosulfuric acid.

The localisation of glucomannan on the surface of Norway spruce kraft pulp fibres with varying glucomannan (GM) contents (10.3 and 3.8%) was studied using immunogold labelling, rapid freeze deep etching (RFDE) followed by metal replication and transmission electron microscopy (TEM). The ultrastructure of P, S1 and S2 of pulp fibres with low hemicellulose content tended to be more compact than that of pulp fibres with high hemicellulose content, suggesting aggregation of cellulose microfibrils upon hemicellulose removal. The degree of immunogold labelling visualised as globular structures was similar for the two pulps, despite the large difference in total glucomannan content. Thus, no correlation between the bulk and surface contents of glucomannan was found. The globular structures were heterogeneously located along the cellulose macrofibrils (fibril aggregates) and their frequency varied greatly within and between TEM micrographs.

A new method for the quantitative preparation of pulp representative lignin-carbohydrate complexes (LCC) has been developed, in which LCC has been systematically prepared at quantitative yield, fractionated and qualitatively determined. At least 90% of residual lignin in softwood kraft pulp is proposed to be chemically bonded to carbohydrates. A major part of LCC (92%) in softwood kraft pulp was observed between lignin, xylan and glucomannan, whereas a minor part (8%) was linked to cellulose. Half of the hemicelullosic LCC is a lignin-glucomannan complex. The other half is lignin-xylan complex and xylan-lignin-glucomannan complex. Thus, part of the residual lignin in softwood kraft pulp crosslinks xylan and glucomannan. The proposed linkages are of covalent type. At most 10% of the residual lignin is not bonded covalently to carbohydrates.

The lack of a suitable method on an industrial scale has so far restricted the use of bleaching of solid wood in the woodworking industry. In this study, a new method ‘Wood-Brite™’, based on bleaching solid wood blocks with hydrogen peroxide solution, was investigated. According to our measurements, the lightness of all the wood species studied could be increased and the increase could be controlled by the intensity of peroxide treatment. Differences were observed in the change of chroma and hue of different wood species. Redness usually decreased regardless of the treatment intensity, except with teak, in which it increased markedly. At every treatment intensity, the yellowness of originally light birch wood decreased, but in other wood species it increased.

Three mono-chlorinated compounds derived essentially from glucuronoxylan were identified as the major components of the ethyl acetate extract from chlorine dioxide bleaching filtrates of E. globulus kraft pulp; one of them is reported for the first time. It was demonstrated that these components are responsible for an important fraction of the total AOX of the filtrates. The ecological risk associated with these compounds is expected to be negligible since they are easily degraded and not detected in the final mill effluent.

A numerical method is proposed to predict the stochastic dispersion of data that unavoidably occurs in a real drying process. The method is based on the use of discrete frequency distribution curves to predict a random variation on some parameters of the process and is applied to the case of radio frequency vacuum (RFV) drying of wood. Experimental data of RFV drying of western hemlock timbers were used to obtain the numeric values of the stochastic parameters and their standard deviation. A mathematical model was designed to simulate the final moisture content dispersion on hypothetical examples. Results were quantified using three indices: average, range and standard deviation.

In this paper, bending creep test results from high-temperature (HT) dried Norway Spruce timber are presented. The results are compared with creep tests of conventional low-temperature (LT) dried timber. The HT drying was performed at 115°C and the LT drying was performed at 70°C. The creep tests were performed in a varying climate with 20°C and 30–90% relative humidity. A total number of 24 specimens, 45 × 70 × 1100 mm, were loaded in bending during approximately 240 days. Both the HT-dried and the LT-dried material were cut from the same four trees to have as equal raw material as possible for the two drying methods. The results show smaller bending creep deformations of HT-dried timber (approximately 30%) as compared to the LT-dried timber. The variation in magnitude of creep for HT-dried timber was equal to or smaller than for LT-dried timber. Additionally, the variation in deformation between the moisture cycles was smaller for HT-dried timber. These observations indicate a less pronounced mechano-sorptive effect for HT-dried timber. The free shrinkage in the grain direction was significantly smaller for the HT-dried material than for the LT-dried material.

Stochastic optimization with the simulated annealing method (SA) is performed on a violin top made of Norway spruce ( Picea Abies ). A numerical example is presented which shows that it is possible, through changes in thickness variables, to compensate for changes in vibration properties caused by a variation in the material parameters in the top. A material model is also presented for the blank which considers the influence of density variations in the annual rings, the cellular structure of wood and reinforcement from the wood rays.

A water prehydrolysis-soda pulping sequence for the preparation of dissolving pulps from oil palm fibre (empty fruit bunches) was investigated using a response surface methodology (RSM) statistical experiment design. Five response variables of screened yield, Kappa number, α-cellulose, viscosity and ash content were statistically analyzed with respect to the three input variables of pulping temperature (T), time-at-temperature (t) and alkali level (A), while keeping the prehydrolysis conditions constant. Optimum conditions were: T = 161°C, t = 100 min and A= 26.1%. Values predicted by RSM for screened yield, Kappa number, α-cellulose, viscosity and ash content at the optimum are 31.2%, 6.0, 96.9%, 16.1 cps and 0.15%, respectively. These values were experimentally verified and very close agreement between experimental and predicted values was obtained.