Volume 66, Issue 7

The purpose of this study was to review some of the existing models for delignification in kraft cooking. Data and results from earlier studies were utilized to evaluate the performance of the models of Gustafson (M G ), Purdue (M P ), Andersson (M A ) and Bogren’s method “continuous distribution of reactivity” (M Bcdr ) in terms of their ability to give a realistic description for delignification of softwood and hardwood. The M G , M P and M Bcdr were tested on lignin data obtained from cooks of Eucalyptus globulus . In this case, M P seemed to perform best, whereas the M Bcdr failed in the range of low residual lignins. M A considers the lignin subunits with various reaction speeds, and this feature improves the performance in the case of low residual lignins and helps to reflect sudden changes in cooking conditions, but the difference to the ordinary M P is moderate.

To clarify the influence of prehydrolysis on fiber characteristics, Scots pine ( Pinus sylvestris L.) wood chips were subjected to pressurized hot-water and dilute-acid prehydrolysis (0.5% H 2 SO 4 ) prior to kraft pulping to partially remove hemicelluloses as hydrolyzate. After the prehydrolysis, the wood chips were submitted to kraft pulping and the pulp was fully bleached in oxygen (O), chlorine dioxide (D), alkaline extraction (E) and chlorine dioxide (D)-sequence. Measurements with an automated optical fiber analyzer showed that prehydrolysis prior to kraft pulping caused significant changes in the fiber dimensions and morphology of the final bleached pulp. Especially, a decrease in fiber width and an increase in fiber deformations were observed compared to a reference kraft pulp. The scanning electron microscopy of handsheets supported the morphology analyses and revealed alterations also in the fiber ultrastructure. The changes in both chemical and physical fiber characteristics require attention when considering the correct processing and end-use of prehydrolysis-kraft pulp fibers.

The suitability of a new switchable ionic liquid (SIL) has been investigated as a solvent for fractionation of lignocellulosic materials. SIL was prepared from inexpensive chemicals, e.g., glycerol, CO 2 , and 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU). Fresh Nordic birch wood ( B. pendula ) was treated with the SIL for a time period of 1–5 days at 100°C and under atmospheric pressure. Upon SIL treatment, at best, 57% of the hemicelluloses were dissolved and 50% of lignins were dissolved from the native birch. The slightly fibrillated SIL treated chips contained about 55% cellulose. Up to 76% of the recovered species removed from the spent SIL liquor was originating from hemicelluloses, mainly from xylan. The spent SILs were reused for fresh wood dissolution in four consecutive cycles and each time the wood dissolution efficiency was similar. SILs could offer affordable (easy-to-synthesize) solvent systems for partial elimination of hemicelluloses and lignin from wood. SILs can also be prepared in-situ and on-site.

Chips of Norway spruce have been impregnated with Na 2 SO 3 and refined at two specific energy consumptions levels at full mill scale. The optical properties of thermomechanical pulps (TMPs) obtained were analyzed in terms of brightness, light scattering, opacity, and autofluorescence by spectral imaging. Even at low sulfite dosage (0.24% sulfite by dry weight) light absorption was reduced, and the brightness was elevated, and a clear dose-response effect was observed. Two-photon spectral imaging (TPSI) showed that sulfonation, impregnation, and refining affect the fluorescence properties differently. Compared to native wood, both processed wood chips and pulp fibers revealed blue-shifted fluorescence maxima, a characteristic of shortened conjugated systems. Two subpopulations of fibers with different optical properties were observed, and the fluorescence of one fiber population was red shifted.

The ability of commercial laccase for improvement of the physicochemical properties of sodium lignosulfonate (NaLS) without any mediator has been investigated. Surface tension, adsorption characteristics, rheological behaviors and fluidity of cement pastes were in focus. Gel permeation chromatography (GPC) shows an initial decrease and then an extensive increase of molecular weight (MW) of NaLS after incubation with laccase. Parallel to MW decrement, the content of phenolic groups is increasing, while an MW increment has the opposite effect. The UV-Vis spectra and the zeta potential of NaLS do not indicate further modification of the substitution pattern on the aromatic ring. The surface tension of NaLS and the adsorbed amount of NaLS on MgO particles is elevated after laccase treatment. The electrostatic attraction between MgO particles and NaLS is the main driving force during this adsorption process. The dispersion efficiency of laccase modified NaLS on the MgO slurry and cement paste is improved.

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to determine the distribution of metal elements in single wood fiber of kraft pulp. Calibration procedures for quantitative analysis of metals in single fibers (SFs) by LA-ICP-MS technique were also developed. Calibration curves were constructed by using matrix-matched standards prepared from (a) cellulose powder washed with 0.05 M EDTA, (b) unbleached softwood pulp washed with 0.05 M EDTA and nitric acid. Calibration materials were prepared by doping the washed cellulose powder and the washed unbleached softwood pulp with standard solutions with increasing concentrations of the elements of interest (Co, Mg, Cu, Na, K, Mn, Zn, Ni, Ca, and Fe). Quantitative determination of the metals in single wood fiber was based on the calibration curves resulting from both the doped cellulose pellets and the doped SFs. The determination of the absolute concentration of elements in a single wood fiber by LA-ICP-MS is still difficult, but in this study, it was demonstrated that the information about the metal distribution can be obtained easily, and their semiquantitative determination is possible.

The white-rot fungus Trametes versicolor and brown-rot fungi Coniophora puteana , Gloeophyllum trabeum , and Postia placenta have a potential to produce a range of hydrolytic enzymes participating in the degradation of lignocellulosic materials. In the colonization of untreated and thermally modified wood blocks wheat bran-containing medium (WBA) greatly favored the secretion of xylanase by C. puteana and both endoglucanase and xylanase expression by T. versicolor , although rather higher carboxymethyl cellulase activity of C. puteana was observed on the malt extract-based medium (malt extract-containing agar (MEA). Coniophora puteana and T. versicolor are able to actively colonize and degrade the untreated pine and birch wood blocks. The mycelium applied on blocks in the form of pellets was more aggressive in wood degradation in comparison with the colonized mycelium. WBA favored the dry matter loss during the initial stages (10–20 days) of pine wood colonization; however, MEA further promoted more rapid wood degradation. The main finding was that the thermal treatment of birch wood was accompanied by a low degree of fungal colonization and increased durability against the fungal attack in spite of the high cellulase and xylanase activities. Thermal modification of wood was not toxic to the fungi because it did not disturb the secretion of the hydrolytic enzymes involved in wood degradation. The thermally modified hollocellulose is probably less susceptible to the enzymes involved in the degradation of polysaccharides or less accessible to hydrolytic enzymes due to the change of the cell wall structure.

This paper is the final part of a series reporting on the penetration (P) and bonding behaviour of urea-formaldehyde (UF) resins of different viscosities based on different degrees of condensation (DCs). The various resins were applied onto radial and tangential wood surfaces, and solid wood assemblies were prepared by hot pressing. P t and P r were observed by evaluation of photomicrographs of the bond lines. The mean and maximum depth of penetration was inversely proportional to the DC. The average depth of P t was found to be slightly higher than P r because of the abundance of pits on the radial walls. However, the maximum P was higher in radial direction, due to the elliptic shape of vessels in poplar as well as due to rays improving the resin flow. The lap shear strength (σ m ) of the same bonded assemblies was determined. Despite the fact that the wood failure always was very high, the σ m increased with the better penetration of the resins with low viscosity. The higher strength values measured has been interpreted as a fortification effect of the interphase by bulk resin penetration, as cell wall penetration cannot be expected due to the large size of such resin molecules.

Soy-based resins have recently attracted great attention as adhesives in the wood composite industry. This article is focusing on hydrolysis and modification of soy protein concentrates to formulate soy-based resins for wood composites. The soy-based resins have been evaluated in terms of bondability on wood substrates and bonding performance in plywood products. The performance of plywood was found to meet the relevant CSA standard (Canadian Standard Association) requirements under both of dry and wet conditions, if the soy-based resins were obtained from low hydrolyzed soy flour. Hydrolysis is an effective and efficient tool for reducing the viscosity of soy resins. However, hydrolysis also reduces the bond strength of soy-based resins as hydrolysis cleaves the macromolecules of soy proteins into smaller molecules. Modified soy-based resins have a certain potential for production of interior- and exterior-used plywood.

Exploration of damage accumulation and reliable prediction of the fatigue lives of laterally loaded, nailed timber joints, are important to proper engineering design of wood structural systems subjected to earthquakes, cyclones/hurricanes or other loads causing fluctuating force flows in such joints. Failure of nailed timber joints typically involves the combination of yielding at plastic hinges in nail and/or the crushing of wood under nails. Force-based criteria can predict the static strength of such joints but cannot reliably predict fatigue behaviour because that depends on loading history and the dissipation of energy within plastic nail hinges and/or crushed wood. In this study, the failure modes, damage accumulation and fatigue life of nailed timber joints subjected to reversed cyclic loads under load-control condition were studied. The results showed that there are two failure modes of nailed timber joints, i.e., ductile failure of nails when the applied load level was higher than 85% of the static maximum load to failure ( P max ) and brittle failure when the applied load level was <85% of P max . The damage accumulation involved three phases, i.e., damage initiation, damage propagation and failure. Fatigue life of nailed joints under reversed cyclic loads was modelled by an energy criterion that separated dissipated energy into non-damaging and damaging components demarcated by the fatigue limit. This approach replicated the behaviour of nailed joints tested at 20 load levels of fully reversed repetitive cyclic loading.

The applicability of the flexural vibration test to determine the elastic constants of glued laminated timber (GLT) composed of five wood species (ash, Fraxinus spaethiana Lingelsh.; balsa, Ochroma pyramidale Urban.; Japanese cedar, Cryptomeria japonica D. Don; Japanese red pine, Pinus densiflora Sieb. et Zucc.; Sitka spruce, Picea sitchensis Carr.) has been investigated. GLT models were prepared from four laminae with dimensions of 30 (R)×5 (T)×300 (L) mm 3 . The suitability of Japanese cedar for inner layers in GLTs was tested by flexural vibration test to determine the elastic constants of the laminae and the glued laminated timber. The Young’s and shear moduli were calculated by the Goens-Hearmon regression method based on the Timoshenko theory of bending (TGH method), and the results were compared with the estimated values based on the Young’s and shear moduli measured individually of each lamina. The simple lamination theory was found to be applicable for Young’s modulus but not to shear modulus. The result obtained based on the lamination theory from the shear strain energy was similar to that obtained by the TGH method.

Heartwood detection for Scotch pine ( Pinus sylvestris ) is possible via several different methods, such as X-ray and infrared cameras. X-ray systems are often very expensive and need huge modifications of sawmill equipment for implementation. Infrared cameras are more affordable but can only be applied for fresh samples with high water content. This article describes a novel imaging method for heartwood detection for Scotch pine, which is based on the fluorescence information emitted of pinosylvin type stilbene and its monomethyl ether. Fluorescence imaging is a low-cost method for measuring heartwood content in real time on an industrial line. The method is applicable for fresh and dried samples. This paper will show the results of fluorescence matrices of Scotch pine. Measurements were made with a bispectrometer system to obtain suitable wavelengths for the excitation and detection of fluorescence. A reliable measuring system is described, which is suited for on-line measurements on an industrial line. An algorithm will also be presented, which is useful for quantification of heartwood and sapwood.

The antagonistic potential of Trichoderma spp. for biological control of wood-damaging fungi was investigated in the present paper. In vitro assays to investigate antifungal characteristics of Trichoderma spp. were conducted with various wood-damaging fungi. Exo-chitinase activity of the isolates was also measured. Three typical wood decayers and three sap-stainers served as target fungi. The antagonistic abilities of each Trichoderma species differed markedly according to the target fungus. The growth inhibition rates shown by the non-volatile metabolites against the wood decayers reached 100% for Trichoderma harzianum KUC1459. The antibiotics produced by Trichoderma dorotheae KUC5027, a recently reported species of Trichoderma , revealed strong antagonistic effects against sap-stainers. Trichoderma gamsii KUC1747 effectively inhibited the growth of all wood-damaging fungi in dual culture tests. The exo-chitinases of Trichoderma longibrachiatum KUC1540, Trichoderma aureoviride KUC1335, and T. harzianum KUC1459 showed significantly high activity.

The purpose of this study was to compare the reaction chemistry of micronized copper and alkaline copper treatments with wood and to determine how fast copper is solubilized during the reaction between the acidic functionality in wood and the basic copper carbonate (CuCO 3 ). Copper species produced in wood by various treatment methods were analyzed by electron paramagnetic resonance (EPR) spectroscopy. The effects of time and solution concentration on the spectral parameters of copper complexes in sawdust treated with copper sulfate solutions were examined, followed by study on the structure and the rate of formation of the copper complexes in sawdust treated with basic CuCO 3 suspension. The study further attempted to identify the soluble copper species formed in wood during treatment with micronized copper preservatives. Comparisons were made among the fixed copper complexes in wood treated with micronized copper preservatives, copper sulfate solutions, basic CuCO 3 suspensions and alkaline copper solution. The results showed rapid formation of fixed copper complexes in wood treated with aqueous suspensions of basic CuCO 3 . These complexes can resist leaching, and they have similar stereochemistry to those formed between wood and copper sulfate. This finding supports the premises that soluble copper is generated during the treatment of sawdust with basic CuCO 3 , and it can bond to wood cell components by migrating into the cell wall in a manner similar to other soluble copper species. Such copper complexes formed are different from those of alkaline copper treated wood, which can be easily distinguished by EPR.

There are numerous chemotypes of Cinnamomum osmophloeum in Taiwan, each of which generates an identical profile of volatile secondary metabolites. Cinnamaldehyde is the major constituent of C. osmophloeum and its quantity varies between strains. The cinnamaldehyde-type C. osmophloeum contains abundance of cinnamaldehyde, which is an economically important product, which can be gained from the leaf essential oil. Here, the genes involved in cinnamaldehyde biosynthesis have been investigated and four candidate genes, phenylalanine ammonia-lyase ( CoPAL ), 4-coumarate: coenzyme A ligase 1 and 4 ( Co4CL1 and Co4CL4 ), and cinnamoyl-CoA reductase ( CoCCR ), were selected as potential molecular marker typical for the cinnamaldehyde chemotype. Cinnamaldehyde was increased in Co4CL1 , Co4CL4 , and CoCCR transgenic plants. The results showed that the cinnamaldehyde and non-cinnamaldehyde chemotypes can be distinguished by a single nucleotide polymorphism in the substrate binding pocket region of Co4CL4, at residue 378 of Co4CL4. This polymorphism could be used as a potential molecular marker for identification of strains of C. osmophloeum , which belong to high-yield cinnamaldehyde producer type. In addition, this finding might provide a suitable strategy for biosynthesis of bioactive metabolites in the future.

No abstract available.