Volume 64, Issue 1

Ozone bleaching is a common practice in pulping, and also of eucalyptus, where it is usually applied in combination with bleaching sequences based on oxygen, hydrogen peroxide, or chlorine dioxide. Ozone has been proven to be a highly efficient and competitive bleaching chemical in terms of delignification efficiency, low costs, and reducing ecological impact. The objective of the present work was to evaluate technology with ozone/alkaline extraction (Z/E) and ozone/chlorine dioxide (Z/D) for bleaching of eucalyptus kraft pulp. Primarily, the impact of these bleaching steps on refinability and quality of pulp should be investigated. As reference, the sequence D*(EP)D (hot chlorine dioxide, extraction in presence of hydrogen peroxide, chlorine dioxide) was selected, which is considered as the state-of-the-art bleaching in elemental chlorine free (ECF) bleaching technology. Various bleaching sequences with ozone in their first step (Z/D(EP)DP, Z/D(EP)DD, Z/EDP, Z/EDD and A*Z/EDP) were found to provide kraft pulps of similar brightness and in similar yield as the reference sequence D*(EP)D. The kappa number, viscosity, and the contents of glucose and xylose, and hexenuronic acid of the pulps were also similar. In addition, the Z sequences resulted in a substantial reduction of the total chlorine dioxide consumption (more than 30.3% in all cases). The A*Z/EDP sequence, which proved to be the most efficient, yielded 87.5% ClO 2 reduction. The studied bleaching sequences also resulted in substantially improved brightness reversal with regard to the reference sequence. The sequence A*Z/EDP was also the most efficient as regards the removal or organochlorines (OX) from the pulp and their reduction in the effluents (AOX). Ozone bleaching sequences improved paper strength, especially with the A*Z/EDP sequence.

Formation of hydroxy acids and soluble lignin fragments was investigated during conventional kraft pulping of first-thinning Scots pine ( Pinus sylvestris L.) stem wood and its long-fiber outer part and short-fiber inner part. The results indicate that there are characteristic differences in the formation of hydroxy acids in these specific tissues, due to the slightly different contents of cellulose, hemicelluloses, and lignin. Notable are the differences in the formation of xylan-derived acids (2-hydroxybutanoic and xyloisosaccharinic acids) and glucomannan- and cellulose-derived acids (3,4-dideoxy-pentonic and glucoisosaccharinic acids). In contrast, no significant differences were found in the average molecular masses of the dissolved lignins in these black liquors. Finally, the black liquor from the outer part of first-thinning pine was shown to have similar properties as the black liquor from the reference mature wood material.

One kraft lignin and two lignosulfonates were oxidized in aqueous acidic solutions containing a polyoxometalate (POM). The degradations were carried out in H 2 O or MeOH/H 2 O mixtures in the presence of oxygen. The treatment with aqueous H 3 PMo 12 O 40 led to the dissolution of the studied lignins in the acidic medium (pH 1–2) and to the formation of up to 6.5 wt% vanillin and 6.2 wt% methyl vanillate based on the weight of dry lignin. The lignin oxidation products were analyzed by size-exclusion chromatography (SEC). For this purpose, a SEC method was developed, which allows the analysis of kraft lignin, lignosulfonates, and reaction products thereof without the need to remove the homogeneous catalyst. This method allows the direct observation of depolymerization and repolymerization reactions and hence the provision of a tool for studying the underlying chemistry. It has been demonstrated that the depolymerization of kraft lignin in water is accompanied by counterproductive condensation reactions. These repolymerization reactions were effectively prevented by addition of methanol, which couples competitively with lignin intermediates.

The redox enzyme laccase can lead to cross-linking of lignin molecules by oxidising phenolic end groups to resonance-stabilised radicals that can undergo radical coupling to form covalent bonds. This property has potential for many technical applications. However, laccase treatment can also lead to degradation. Experiments were performed with two laccases of different oxidation potential and pH and temperature optima. The predominant reaction following laccase oxidation is the formation of 5-5′ and 4-O-5′ bonds. If the 5-position is blocked, other reactions occur, including coupling of the 1-position and oxidation of the α-position, which aggravates cross-linking of different lignin molecules. The product profile generated by the two laccases is somewhat different, mainly because of the different pH rather than differences in enzyme activity. Reaction mechanisms and the technical and biological significance of the results are discussed.

A novel method for labelling of anionic groups on wood surfaces was developed and applied to spruce and aspen wood sections in the native state, and after acid washing and alkaline treatment. The metal ions Mg 2+ , Cu 2+ , Sr 2+ , and Zn 2+ were used as markers and their patterns of attachment to anionic groups were assessed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Sr 2+ was found to be a very suitable marker for labelling of anionic groups. In addition to ToF-SIMS, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used for semi-quantitative analysis of labelled anionic groups in wood samples. ToF-SIMS imaging of Sr 2+ -labelled anionic groups revealed abundant anionic groups in bordered pit tori and ray parenchyma cell walls in spruce wood. LA-ICP-MS revealed that the relative concentration of Sr 2+ in tori of bordered pits was approximately eight-fold higher than in fibre cell walls. After alkaline treatment the concentration of anionic groups in the fibre cell wall was approximately three-fold higher than in the original acid-washed spruce. In aspen wood, anionic groups were located mainly in pits between vessels and contact ray parenchyma cells, in ray cell walls and in certain fibre wall layers.

Many studies have successfully applied near infrared (NIR) spectroscopy to estimate important wood traits. Some of them have reported the effects of wood surfaces on NIR spectra information and their influence on the performance of the predictive model. However, limited information is available concerning the effect of sample preparation on the model performance to estimate chemical properties in Eucalyptus wood. Hence, the aim of this study was to investigate the influence of the milling procedure, particle size, and quality of the solid wood surface on the performance of the partial least squares regression to predict chemical properties of Eucalyptus urophylla wood by NIR spectroscopy. Adequate models were built to predict klason lignin content, acid-soluble lignin content, and syringyl-to-guaiacyl ratio in Eucalyptus urophylla wood. Sample preparation strongly influences the ratio of performance to deviation (RPD) of these predictive models. The effect of the sample presentation (solid or milled wood) was stronger than the effect of the particle size difference between thin and thick powder. The best calibrations were developed using NIR spectra measured on wood powder (RDP values from 1.99 to 2.97), but satisfactory calibrations were developed from NIR spectra measured on solid samples (RPD values from 1.68 to 2.16).

Multivariate statistical models capable of rapidly and accurately predicting the surface moisture content in Tsuga heterophylla were developed based on near infrared (NIR) spectra of small specimens precisely conditioned within the hygroscopic range. In an initial research phase, the applicability of NIR as predictor of surface moisture was investigated. The first derivative spectra in the range of 1300–2100 nm yielded the best results. The partial least squares regression (PLS-1) model had coefficient of determination (R 2 ) of 0.98, root mean square error of cross validation (RMSECV) of 0.97%, root mean square error of prediction (RMSEP) of 1.05%, and ratio of performance to deviation (RPD) of 7.25. In a subsequent phase, an inline pilot-plant NIR system combined with this PLS-1 model was constructed. The prediction ability of the NIR system was tested with line speeds of 0, 100, 200, and 400 mm s -1 on kiln-dried full-length lamination boards classified as “wets” after conventional kiln drying. In a calibrated range of moisture content (0–25.4%), the NIR system demonstrated R 2 values of 0.79 and 0.74, RMSEP values of 3.13 and 3.28, and RPD values of 2.18 and 1.67 at a line speed of 0 and 100 mm s -1 , respectively, regardless of the presence of knots and surface roughness. These results demonstrate that the NIR system at a line speed of 0–100 mm s -1 could be used to provide entire surface moisture distribution and to detect local moisture peaks that indicate surface wet-pockets in kiln-dried lumber destined for lamination.

Cellular distribution of coniferin in differentiating xylem of Japanese cypress ( Chamaecyparis obtusa ) was analyzed by Raman microscopy. Small blocks were collected from differentiating xylem, frozen, cut on their surface with a sliding microtome, and then freeze-dried. Scanning electron microscopy showed numerous needle-like deposits in the tracheid lumina from the beginning of the S 1 layer formation to the S 2 layer-forming stage. The Raman spectrum of the deposits in the tracheid lumen was similar to that of coniferin. The presence of coniferin in a water extract from differentiating xylem was confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy and 1 H- and 13 C-nuclear magnetic resonance spectra. Differential Raman spectra taken from samples before and after washing with water and dehydration in an ethanol showed that developing secondary walls contained coniferin during the S 2 layer-forming stage and also after S 3 layer formation. In contrast, coniferin was detected in the cell corner middle lamella during the S 2 layer-forming stage, and the differential spectra were different from that of coniferin after S 3 layer formation. The differential spectrum in this stage was similar to that of a dehydrogenation polymer of coniferyl alcohol prepared by the “zulauf” method (bulk polymerization). These results suggest that free lignin oligomers of the type bulk polymerizate might exist in the cell corner middle lamella during the S 3 layer-forming stage and can be removed from specimens during washing and dehydration. The results can be interpreted in a way that no such oligomer exists in the secondary wall during the same stage owing to endwise addition of monolignols (in analogy to a “zutropf” polymerization).

Cellulose was treated with various concentrations of 1,3-dimethylol-4,5-dihydroxyethylene urea (DMDHEU) to obtain different DMDHEU contents in the cellulose preparation. The release of sugars due to hydrolysis by a cellulase enzyme complex clearly decreased with increasing DMDHEU content. When the cellulose preparation with the highest DMDHEU content was subjected to pretreatment with Fenton's reagent (Fe 2+ , H 2 O 2 ), the sugar release increased 4.5-fold. Incubation of modified cellulose with only H 2 O 2 did not increase sugar release by cellulase. Compared to cellulose, the sugar release from milled wood powder induced by cellulase was very low but still decreased due to treatment with DMDHEU. Sole incubation of wood powder with Fenton's reagent did barely cause more sugar release compared to the storage of wood powder in buffer, but when the pretreated wood was incubated with cellulase the sugar release was higher than without pretreatment. Release of sugar from untreated cellulose in liquid cultures of the white-rot fungus Trametes versicolor was detected after 7 days and increased linearly with incubation time. Sugar release from DMDHEU-treated cellulose was much lower and was not detectable before 21 days of incubation. Total protein content in the cultures was low, but was slightly higher in the cultures of untreated cellulose. Laccase activity was not different in the presence of untreated and DMDHEU-treated cellulose after 7 and 14 days, but increased with increasing DMDHEU content after 21 and 28 days.

The effects of thinning intensity on wood structure and chemistry of Norway spruce [ Picea abies (L.) Karst.] have been studied in a long-term thinning experiment established in the 1960s in south-western Sweden. The experiment comprised datasets of unthinned control trees and trees of four thinning treatments, in which thinning operations of different intensities were carried out. These thinning operations were applied either once, three, or five times over the course of the stand rotation. Thinning intensities varied from 0% to 60% based on the stand basal area (BA) before thinning: (A) 5×20% (i.e., 20% of the BA removed five times); (B) 3×40% (i.e., 40% of the BA removed three times); (C) 1×60% (i.e., 60% of the BA removed once); and (D) 5×40% (i.e., 40% of the BA removed five times). Altogether 60 trees that were 67 years old were sampled 38 years after the treatment onset. Radial growth rate, wood density, tracheid properties, and the chemical composition of wood were studied in detail. All four thinning treatments increased growth rate and decreased wood density; however, treatment D showed the greatest change. Single, heavy thinning in treatment C resulted in unfavourable intra-stem variation in ring width and wood density. No significant differences in tracheid properties and wood chemistry were found between the treatments. We conclude that only a remarkable increase in growth rate would induce detrimental changes in tracheid properties and wood chemistry in the context of thinning.

Calcium-containing materials have been implicated in promoting wood degradation by Serpula lacrymans , but mechanisms remain unresolved. In this study, S. lacrymans and Serpula himantioides degraded pine sapwood in agar-block microcosms with one of four treatments: calcium-free, 5 mM agar CaCl 2 , high-purity gypsum (CaSO 4 ), and gypsum amended with 1% FeSO 4 . Calcium and iron availability were limited in minimal nutrient agar. At week 5, pine degradation was significantly higher for S. lacrymans in iron-amended gypsum treatments than other treatments, and the respective agar oxalate levels were also higher. Oxalate solubility was lowest in pure calcium microcosms. Scanning electron microscopy showed hyphae in contact with gypsum and precipitation of calcium oxalate. At week 15, wood degradation by S. lacrymans was severe (>60%) in both calcium-free and iron-amended treatments, but was significantly less in pure calcium treatments (≈45%). Cation analysis in week 15 wood revealed higher calcium and iron levels in treatments containing those element additions. Serpula himantioides had decayed wood equally among treatments at both harvests. Results demonstrate that calcium has an inhibiting effect – and not a promoting effect as hitherto believed – on wood degradation by S. lacrymans . It appears that oxalate and iron play a role in stimulating wood degradation by this destructive fungus.

Changes in lignin and carbohydrate content with radial direction, growth-layer number, compression wood (CW) severity, and earlywood (EW) and latewood (LW) origin are described for one near-ground position in each of a severely bent and a nominally straight ramet (tree) of a clone (genotype) of Pinus radiata . Bark-to-bark strips were taken through the pith and the longest radial dimension of the CW side of the discs. Separate EW and LW samples were obtained for most growth layers, yielding a total of 95 samples. Differences in lignin and carbohydrate content between EW and LW were large where CW formation was moderate and small where it was severe. Mannose content was consistently different in the EW and LW of opposite wood (OW) and CW. Results suggested that the inner juvenile wood of OW rings might contain either a galactose-rich galactoglucomannan or a β-1,4-galactan. Consideration of all 95 samples showed that although the contents of galactose, lignin, glucose, and mannose were linearly and strongly correlated with one another, their relationship with xylose and arabinose content was non-linear.

The reactions between constituents of alkaline copper quat (ACQ) and of wood were investigated by a tensile stress relaxation approach. Small samples were stressed and impregnated with various ACQ solutions, in which the ratios of monoethanolamine (MEA), ACQ, and didecyl dimethyl ammonium chloride (DDAC) were varied. The other parameters included temperature and concentration of the treating solutions. The stress relaxation curves of wood were recorded during the impregnation period and the effects of impregnation parameters were investigated by an orthogonal experimental design (OED). The effects of water, MEA, and DDAC on stress relaxation of the samples were also observed. The bulking effect of water was tested separately in samples treated with distilled water without stretching. The results showed that the stress relaxes dramatically in the initial period and then changes slightly over a long period, which is readily visible in double logarithmic plots of f ( t )/f (0) versus time ( t ). There are complex interactions between the components of ACQ solutions and wood matrix: (1) in rapid phase I, the splitting of the easily accessible hydrogen bonds (mainly in the amorphous hemicelluloses) are prevalent by interaction with components of ACQ solution; (2) in slow phase II, Cu penetrates deeper in less accessible regions (e.g., in paracrystalline regions of cellulose) and renders possible further relaxation. The results of range and variance analysis reveal that the molar ratio of Cu to MEA and temperature of ACQ solution have significant effects on the rate of reaction during phase I, whereas in phase II only the temperature of ACQ solution has a significant effect. The stress relaxation curves of samples impregnated in water, MEA, and DDAC all showed a quasi one phase stress relaxation rate, which suggests that phase II is mostly related to Cu in ACQ formulations. It is concluded that the formation of complexes with Cu is still the major reaction in wood although there is competition among ACQ constituents for reaction sites.

Numerical and experimental studies involving the double cantilever beam test to estimate the resistance -curve under mode I loading in wood ( Pinus pinaster Ait. – RL fracture system) are presented. Two data reduction schemes based on the specimen compliance and crack equivalent concept are proposed to obtain accurate values of fracture energy. The methods do not require crack length monitoring and mitigate the influence of scatter of wood elastic properties on the measured fracture energy. A finite element analysis to validate the proposed methodologies was performed. Good agreement was achieved in both cases, especially for one case. Experimental tests were also carried out to determine the fracture energy of this wood species. Application of both data reduction schemes provided consistent values.

The crosswise gluing of cross-laminated panels made of solid wood can cause problems when exposed to moisture variations. In the present study, the substitution of the spruce middle layer by a wood composite is tested for its influence on moisture-induced stresses and deformations in laboratory tests and numerical simulations. Furthermore, slits in the spruce middle layer were investigated. The hygroscopic warping due to a moisture gradient, stresses caused by moistening and cracks due to drying were studied. The results show larger warping in composite laminates compared to the spruce cross-laminate, which is governed by the modulus of elasticity of the middle layer. The in-plane swelling was found to be larger in composite laminates, while stresses were lower. The drying test discovered that cracks develop in the middle layer of spruce-medium density fiberboard laminates due to shear stresses and tensile stresses in the thickness direction. It was concluded that slits can be applied in the middle layer, as they have no significant influence on moisture-induced stresses but increase the thermal insulation. If the substitution of the spruce layer is required, the application of oriented strand board in the middle layer is recommended.

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No Abstract available