Volume 65, Issue 3

No abstract available

The impact of hypochlorous acid (HOCl) treatment on a fully bleached eucalyptus kraft pulp was studied with respect to the final brightness as well as the brightness reversion under humid ageing conditions. The carbonyl contents in the pulps were determined by the CCOA method where carbazole-9-carboxylic acid [2-(2-aminooxethoxy)-ethoxy] amide (CCOA) was applied as the carbonyl-selective fluorescence label. The molecular weight distribution of cellulose and hemicelluloses was analyzed as well. The amount of carbonyl groups in pulp was observed to increase significantly after the HOCl treatment, and the carbonyl distribution in pulp to shift towards the low molecular weight fraction. Plotting the carbonyl content against the post color number (PCN) of the pulps revealed a linear correlation. Additionally, the effect of the hemicellulose content was investigated, and alkaline extraction was applied to partially remove the hemicelluloses in pulp. These hemicellulose-poor samples showed a lower reactivity with hypochlorous acid and less brightness reversion at equal carbonyl content.

It has been proposed that magnesium hydroxide can replace magnesium sulfate as a lower cost cellulose protector. This claim has been evaluated based on four commercial unbleached softwood kraft pulps. The selectivity was improved in the presence of soluble MgSO 4 , but little or no selectivity improvement was obtained when insoluble Mg(OH) 2 was applied. It was further observed that in-situ iron concentration in unbleached pulp affects selectivity of oxygen delignification, while in-situ calcium concentration affects efficiency of magnesium protection. The results favor the hypothesis of formation of a Mg-carbohydrate complex as the major mechanism of cellulose protection by magnesium. The application of a soluble magnesium compound is recommended to improve selectivity in oxygen delignification.

Kraft pulp is currently bleached largely by the elemental chlorine free (ECF) technology with oxygen, chlorine dioxide, and hydrogen as active agents. This technology brought about significant environmental improvements in relation to standard processes based on chlorine gas and hypochlorite, but there is still need for further improvements. This study presents a novel environmentally friendly bleaching stage – the so-called ‘hydrogen peroxide in supercritical carbon dioxide’, P (SC-CO2) – that can be adapted to current ECF bleaching processes, with preference in cases where hydrogen peroxide is already used. In this study, the P (SC-CO2) stage was evaluated as a replacement to the last peroxide stage of the D(EP)DP bleaching sequence and to the first peroxide stage of the D(EP)DP sequence, for an oxygen delignified eucalypt kraft-O 2 pulp. The P (SC-CO2) stage was run with 0.5% hydrogen peroxide, at 15% consistency, 70°C, and 73 bar. The reaction time was 30 min. The performances of regular P stages and the new P (SC-CO2) stage were compared. Promising results were observed with the DEP (SC-CO2) DP sequence; the P (SC-CO2) decreased kappa number from 2.7 to 2.1, and the hexenuronic acid groups from 17.0 to 12.4 mmol kg -1 . The P (SC-CO2) stage showed poor performance when applied in the D(EP)DP (SC-CO2) sequence. It is concluded that the process presents potential but requires further optimization to improve selectivity and efficiency.

Highly swellable, mechanically stable hydrogels were obtained by cross-linking different technical lignins with poly(ethylene) glycol diglycidyl ether (PEGDGE). The gelation time and the properties of the products can be controlled by the extent of pre-oxidation and the cross-linking conditions, namely the dynamic viscosity η*, storage and loss modulus (G′; G″), and loss factor tan δ. The highest free swelling capacities (FSC) of up to 50 g water per g xerogel were obtained from pre-oxidized pine kraft lignin Indulin ® AT and spruce organosolv lignin. Dynamic rheological measurements confirmed the typical rheological behaviour of gel structures, i.e. a linear decrease of dynamic viscosity about three orders of magnitude within a frequency range of 0.08 and 20 s -1 . The results furthermore revealed a good mechanical sturdiness of the cross-linked lignin hydrogels. Sandy soils supplemented with small quantities of the hydrogels were found to feature a significantly increased plant-available water content. Based on the observed effects, oligo(oxyethylene) lignins are promising materials with respect to a prolonged water retention in soils.

Mechanically stable hydrogels featuring water absorption capacities of up to 75 g H 2 O g gel -1 can be obtained by cross-linking of activated technical lignins with poly(ethylene) glycol diglycidyl ether under strong alkaline conditions. Fenton oxidation prior to cross-linking by hydrogen peroxide and catalytic amounts of ferrous chloride has been found to be superior to an alkaline H 2 O 2 pre-treatment with respect to gel formation, water sorption, and rheological properties of the resulting oligo(oxyethylene) lignin gels. Purified pine kraft lignin undergoes in the course of Fenton oxidation hydroxylation of both aliphatic and aromatic moieties. This is the main reason for the enhanced cross-linking density obtained after treatment with poly(ethylene) glycol diglycidyl ether. The oxidative changes have been demonstrated by principal component analysis of Curie point pyrograms, wet chemical methods, FT-IR, and 31 P NMR spectroscopy. Cleavage of side-chains, radical 5,5′-coupling of phenylpropane units, formation of carbonyl and carboxyl groups, and cleavage of aromatic rings were observed. These structural changes may increase or decrease the water sorption capability of the cross-linked products.

Very little is known about the occurrence of pectin in wood and it is speculated that between 10 mg g -1 and 40 mg g -1 of wood consists of pectin. The present study aimed to quantify pectin in eucalyptus wood and to determine the influence of tree species, yield potential of the site, tree age class and wood tissue type on its occurrence. Wood was hydrolysed using the Saeman procedure and the neutral and acidic monosaccharides quantified with high-performance liquid chromatography (HPLC). The d -galacturonic acid was the predominant pectic monosaccharide followed by d -galactose, l -arabinose and l -rhamnose. Through the addition of all pectic monosaccharides, it was determined that eucalyptus wood contained between 15.2 mg g -1 and 25.8 mg g -1 pectin. Wood tissue type had a major influence on the total pectin content of the samples. The cambium contained the highest concentration of pectin, reflecting more active growth. These results contribute to the understanding of wood biochemistry and can be useful in the industries producing biofuels or paper.

The macroscopic formulation of moisture transport in wood below the fiber saturation point has motivated many research efforts in the past two decades. Many experiments demonstrated the difference in steady state and transient moisture transport and the inadequacy of models derived for steady state transport when used to describe transient processes. A suitable modeling approach was found by distinguishing between the two phases of water in wood, namely bound water in the cell walls and water vapor in the lumens. Such models are capable of reproducing transient moisture transport processes, but the physical origin of the coupling between the two phases remains unclear. In this paper, the physical background on the microscale is clarified and transformed into a comprehensive macroscopic description, ending up with a dual-scale model comprising three coupled differential equations for bound water, water vapor, and internal energy, as well as a simplified microscale model for determination of the coupling term.

Mechano-sorptive (MS) strains were measured in torsion on eight loblolly pine specimens as a function of galactan content. The strains were generated by an increase of environmental humidity from 38% to 84% and were measured during an anticlockwise and a clockwise loading scheme that caused the specimen to recover its original dimensions at the end of the test. The magnitude of the MS strains was found to be independent of galactan concentration. The specimens with high and low galactan contents had different MS strains but the average of the measured data was the same. The number of observations (eight) was too small for a reliable statistical analysis to identify the regressors that are the main sources of the strain variations. The cell structure of the specimens was visualised by X-ray tomography.

Australian blackwood ( Acacia melanoxylon R.Br.) is a high-quality appearance-grade timber species native to eastern Australia. It is characterised by dark-coloured heartwood, with colour varying from pale straw to red-brown and walnut brown, and pale cream-coloured sapwood. This wide range in heartwood colour is expressed as between- and within-tree variation, and is regarded as a problem in markets where colour consistency is important. To understand the genetic and environmental control of heartwood colour, multiple colour measurements were taken from stem cores from 16 open-pollinated family collections of blackwood planted across three 19-year-old progeny trials. Data was analysed with a mixed model with within-tree variation modelled using a three-node cubic spline. Significant genetic, environmental and genetic-by-environment interactions were detected, not only in the variation in between-tree mean heartwood colour but also in the pattern of within-tree heartwood colour variation. In general, heartwood colour became darker, less yellow and more red towards the sapwood/heartwood boundary. To control the between- and within-tree heartwood colour variation in blackwood plantations, care is needed to not only select genotypes with the desired wood colour and colour variation but also site characteristics that allow expression of that colour.

The color properties of aging wood samples from historical buildings have been compared with those of recent wood samples that were heat treated at temperatures ranging from 90°C to 180°C. The results of kinetic analysis obtained by the time-temperature superposition method showed that the color change during natural aging was mainly due to a slow and mild oxidation process. In other words, heat treatment could accelerate the changes in wood color that occur during aging. In one sample, the color change ( ΔE* ab ) after 921 years at ambient temperature was almost equivalent to that of heating (artificial aging) approximately for 6.7 h at 180°C. The results have been interpreted that the aging and the subsequent change in wood color begin at the time of tree harvesting.

Thermal conductivity (ThCond), thermal diffusivity and heat capacity of Norway spruce ( Picea abies [L.] Karst.) and European beech ( Fagus sylvatica L.) have been determined for all principal directions – radial (R), tangential (T) and longitudinal (L) – depending on the moisture content (MC) and ThCond was additionally measured in 15° steps between these directions. The ThCond was determined in a guarded hot plate apparatus. For determining thermal diffusivity and heat capacity, the same apparatus was supplemented with thermocouples and the temperature evolution was evaluated numerically by a partial differential equation. The results show expectedly that ThCond increases with increasing MC, whereby the highest increment was observed in T and the lowest in L direction. ThCond is higher for beech than for spruce in all anatomical directions and the conductivity for both species is more than twice as high in L direction than perpendicular to grain. The highest ThCond is found for beech at a grain angle of approximately 15°. The lowest ThCond shows spruce at an angle of approximately 60° between T and R direction. Thermal diffusivity is similar for both species and decreases with increasing MC. Its differences with regard to the anatomical directions correlate with those of the ThCond values. Heat capacity is lower for beech than for spruce and shows a clear increase with increasing MC.

A novel air-coupled ultrasound (ACU) 120 kHz normal transmission system enabled successful imaging of bonding and saw cut defects in multilayered glulam beams up to 280 mm in height with a signal-to-noise ratio (SNR) of 40 dB. The main wave propagation paths were modeled; quasi-longitudinal and quasi-transverse modes were coupled in each lamella and the sound field was found to be shifted from the insonification axis as a function of the ring angle, leading to interference of wave paths in the receiver and to 15 dB amplitude variability in defect-free glulam. The assessment was improved with spatial processing algorithms that profited from the arbitrary scanning resolution and high reproducibility of ACU. Overlapped averaging reduced in-band noise by 15 dB, amplitude tracking captured only the first incoming oscillation, thus minimizing diffraction around defect regions, and image normalization compensated 6 dB of systematic amplitude variability across the fiber direction. The application of ACU to in situ defect monitoring was demonstrated by using multiparameter difference imaging of measurements of the same sample with and without saw cut defects. The segmentation of the defect geometry was improved significantly and the amplitude variability was reduced by 10 dB. Further work is planned to model additional insonification setups and grain and density heterogeneities.

A new optical measurement system, the main components of which are a diode-pumped solid state laser and avalanche photodiodes, was introduced to clarify the optical characteristics of wood from the viewpoint of time-of-flight near infrared spectroscopy. The sample thickness and the wavelength of input pulsed laser clearly influenced the transmitted time-resolved profile. The effective optical path length became 15 times longer than the sample thickness. The optical model based on the diffusion approximation to the radiative transfer equation proved to be useful for thick samples, which can be optically regarded as an ideal diffuser, although wood is a structural material with non-homogeneous cellular structure.

Non-destructive evaluation (NDE) methods are common for grading structural lumber with static bending as the traditional NDE method for strength. More recently, longitudinal and transverse vibration techniques have also been proposed for grading lumber. In this study, unjointed and finger-jointed sawn lumber has been evaluated by these traditional and relatively new NDE methods. In total, 188 pieces of 38 mm×89 mm black spruce lumber were tested. Of these, 40 were unjointed, 47 had 2–3 finger joints, and 101 had 5–7 finger joints. The main objective was to evaluate the reliability of the various NDE techniques in predicting the bending stiffness and tensile strength of finger-jointed lumber with different number of finger joints. Results show that all NDE methods provide stiffness values of unjointed and finger-jointed lumber that correlate well with laboratory measured static bending stiffness with R 2 values ranging from 0.76 to 0.97. Moreover, lumber with finger joints has lower bending stiffness than unjointed lumber. Based on the correlation coefficients, there is no evidence that finger joints affect the precision of the strength prediction by NDE methods.

Sludge of pulp and paper mills have natural adhesive properties. The primary sludge (PS, contains fibers) and secondary sludge (SS, contains proteins) could also be suitable for manufacturing medium-density fiberboard (MDF). Protein in SS can react with formaldehyde (HCHO), and as an additive in urea-formaldehyde (UF) resins it can reduce formaldehyde emission. Thus, SS was investigated in the present study. PS and SS were collected from two mills and characterized in terms of chemical composition, fiber length distribution, pH, and buffering capacity. MDF samples were processed according to an experimental design, in which UF resin content was reduced from 12% to 8% and replaced by SS in the range of 5%–15%. Gel time measurement showed high SS reactivity with UF resin. The SS reduced HCHO emissions by up to 68% compared to control panels, without compromising internal bond strength. The bonding effect of SS was lower than expected due to the high pH, thus the buffering capacity reduced UF performance. Moreover, sludge reduced bending performance. Dimensional stability was the greatest disadvantage of sludge panels.

Spruce wood that had been degraded by white-rot fungi ( Trametes versicolor or Ceriporiopsis subvermispora) and suffered mass losses up to 17% was investigated by transmission Fourier transform infrared (FT-IR) imaging microscopy. A significant marker during incipient simultaneous white-rot ( T. versicolor ) was the cleavage of glycosidic bonds of polysaccharides that preceded their metabolisation. Simultaneous white-rot processes were also characterised by a relative decrease of the overall lignin content and a relative accumulation of wood polysaccharides. No early marker was found for selective white-rot ( C. subvermispora ) that removes mainly lignin by an oxidative process. This feature was detected only in wood samples exhibiting mass losses higher than 12%. Furthermore, it was shown, that simultaneous and selective white-rot processes were unevenly distributed within the wood samples but quite evenly distributed within single tracheids.

Various factors were investigated that could affect the adsorption of alkyl dimethyl benzyl ammonium chloride (ADBAC) on red pine wood. An increase in ionic strength of ADBAC solution had little effect on ion exchange (chemisorption) but allowed higher hydrophobic uptake (physisorption) of ADBAC in wood. ADBAC solution containing high amounts of monoethanolamine (MEA) and Cu decreased the chemisorption of ADBAC; free MEA and Cu appear to compete with ADBAC cations for the same bonding sites in wood. When ADBAC in MEA solution was adsorbed on wood under different pH conditions, ADBAC adsorption increased with increasing pH, but was considerably lower than the cation exchange capacity of red pine. Red pine blocks were treated radially and longitudinally with alkaline copper quat solution to verify how the micelle form of ADBAC penetrates into wood. Copper penetrated evenly into 50 mm thick wood samples with little gradient with depth; however, high amounts of ADBAC were concentrated on the surface creating a steep gradient with depth. After accelerated leaching, considerable amounts of physically adsorbed ADBAC leached out, especially from the surface.

The ability of boron to diffuse from fused boron rods into surrounding wood was investigated on pentachlorophenol-treated Douglas-fir poles. Boron readily diffused into the wood surrounding the treatment holes and was present at protective levels in most poles within 1 year after application. The protected zone was generally confined to the treatment zone. Effective levels of boron were still present in this zone 15 years after treatment. Attempts to correlate the presence of decay fungi with residual boron levels indicated that these fungi were sometimes present in zones with boron at the lower threshold level of 0.5 kg m -3 boric acid equivalent (BAE), but most of the isolations could be explained by localized variations in distribution. Boron rods provided excellent long term protection against internal decay in Douglas-fir poles.

No abstract available

No abstract available