Volume 65, Issue 6

The morphological and chemical characteristics of cell walls govern the response of wood fibre to mechanical pulping processes and thereby influence the energy efficiency of the process and determine most pulp and paper properties. A study has been carried out at the microstructural/ultrastructural level of fibre cell walls by means of a newly developed Simons’ staining (SS) method and scanning electron microscopy to characterize thermomechanical pulps (TMPs) produced under different refining conditions. The SS method allows assessment and quantification of pulp fibre development during the process in terms of cell wall delamination/internal fibrillation (D/IF) under different process conditions, and the degree of D/IF can be statistically evaluated for different TMP types. In focus was never-dried Norway spruce TMP from primary stage double-disc refining running in a full-scale mill, where specific refining energy was varied at different refining pressure levels. Improved energy efficiency was gained at the same tensile index level when applying high pressure (temperature). Under conditions of high pressure and refining energy, a significant enhancement of the degree of D/IF of pulp fibres was observed. The surface ultrastructure of these fibres exhibited an exposed S2 layer with long ribbon-type fibrillation compared to pulps produced with lower pressure and energy input. A given TMP type can be classified in the categories of high-severity and low-severity changes and quasi-untreated concerning the degree of D/IF of its fibres. The relative proportions of these are important for the development of pulp properties such as tensile strength. The presence of higher amounts of fibre fractions in the categories high D/IF and low D/IF will improve the tensile index of a TMP.

The aim of this work was to improve the dewatering characteristics of thermo-mechanical pulp (TMP) through enzymatic treatment without any significant reduction of the quality of the end product. The cellulose and hemicellulose content of TMP was altered by means of enzymatic treatments using different purified cellulases and hemicellulases as well as commercial enzyme preparations, in order to clarify the target carbohydrate components affecting the dewatering of TMP. The effects of enzymatic treatments on the properties of the pulp as well as its forming, pressing and drying were studied by lab scale measurements. An increased dewatering rate of TMP was observed in initial drainage, wet pressing and drying laboratory experiments, as a result of various enzymatic treatments. Interestingly, both cellulose and galactoglucomannan components in TMP were found to affect the dewatering properties of the pulp, and a greatest improvement in dewatering could be obtained with a combined treatment with an endoglucanase type of cellulase and mannanase.

The driving force for pulp and paper industry is to develop new technologies with less impact to the environment. In this context, the successful approach in the present paper was the substitution of sodium hydroxide during peroxide bleaching of thermomechanical pulp (TMP) by magnesium hydroxide or magnesium carbonate. Looking at brightening development, thioacidolysis showed that Mg-based processes eliminated less coniferaldehydes than NaOH-based bleaching. Moreover, 19 F NMR analysis showed slightly more residual quinone in lignin isolated from NaOH-based bleached pulp than lignin extracted after Mg-based bleaching. Replacing NaOH by Mg-based compounds affected the strength properties of the paper: tensile index was 10% lower than conventional bleached paper, probably due to Mg 2+ adsorption on the acid groups of fibers. However, the brightness reversion of Mg-based bleached paper decreased by about two ISO points during photoageing under sunlight. X-ray photoelectron spectroscopy supported the conclusion that Mg-based bleaching caused less re-deposition of lignin and extractives onto the fiber surface compared to the conventional process resulting in less light-induced yellowing.

Spruce wood chips were produced under well-controlled conditions in a laboratory wood chipper at spout angles of 30°, 40°, and 50° at a cutting rate of 20 m s -1 and with a nominal chip length of 25 mm. The chips were then refined under thermomechanical pulp (TMP) conditions in a pilot refiner plant. The pulp properties such as freeness, average fiber length, and shives content were determined and evaluated as a function of specific energy consumption. For a first stage refining and for a freeness value of 350 ml, a decrease in specific electrical energy consumption could be achieved by performing the wood chipping at a spout angle of 50° as compared to 30° which is the spout angle commonly used. A patent application regarding this method has been filed and is pending. It is realized that a freeness value is not directly indicative of any quality measure, such as, for example tensile index and light scattering coefficient but the obtained results can be interpreted to be promising. Further studies are needed regarding the impact of the modified chipping process.

The goal was to determine local mechanical properties inside of oriented strand board (OSB) based on a realistic morphology-based finite element (FE) model and data acquired from a physical test performed on the same material. The spatial information and local grayscale intensity from CT-scans obtained from small OSB sample was transformed into a 2D regular morphology-based FE mesh with corresponding material properties. The model was then used to simulate the actual compression test performed on the specimen using simplified boundary conditions. The simulated strain fields from the model were compared with the actual strain field measured on the specimen surface during the compression test by means of a full-field optical method, named digital image correlation (DIC). Finally, the original set of material properties was adjusted by an iterative procedure to minimize the difference between the simulated and the measured strain data. The results show that the developed procedure is useful to find local material properties as well as for morphological modeling without the need of segmentation of the image data. The achieved results serve as a prerequisite for full 3D analyses of the complex materials.

The combined bound water and water vapour diffusion of wood is of great interest in the field of building physics. Due to swelling stresses, the steady-state-determined diffusion coefficient clearly differs from the unsteady-state-determined diffusion coefficient. In this study, both diffusion coefficients and the water vapour resistance factor of Norway spruce ( Picea abies [L.] Karst.) and European beech ( Fagus sylvatica L.) were investigated for the principal anatomical directions (radial, tangential and longitudinal) and in 15° steps between these directions. The values were determined with the cup method as the basic principle. The unsteady-state-determined diffusion coefficient is, independent of the direction, about half that of the steady-state-determined diffusion coefficient. Both diffusion coefficients are about two to three times higher for spruce than for beech. They are up to 12 times higher in the longitudinal direction than perpendicular to the grain for spruce, and up to 15 times higher for beech. With increasing moisture content, the diffusion coefficients exponentially increase. The water vapour resistance factor shows converse values to the diffusion coefficients.

This paper describes the investigation of the oxygen plasma treatment of enzymatic hydrolysis lignin (EHL) that was obtained from the lignocellulosic ethanol production pro- cesses. The application of EHL as a natural binder for biocomposite product manufacturing was in focus. To understand the effects of oxygen plasma treatment, the chemical changes on the surface of EHL were evaluated by Fourier transform infrared (FTIR) spectroscopy, X-ray photo-electron spectroscopy (XPS), and electron spin resonance (ESR) spectroscopy. Adding EHL into the cotton-stalk fiberboards has a beneficial effect on physical and mechanical properties. Moreover, adding oxygen plasma-treated EHL produced a 69.2% increase of internal bond strength (IB), a 78.2% increase of modulus of rupture (MOR), and a 49.8% reduction of thickness swelling (TS). The bonding improvement was probably due to the generation of more oxygen-related functional groups and free radicals on the surface of EHL after the oxygen plasma treatment.

Only small amounts of additives are needed to formulate one-component polyurethane (1C PUR) adhesives for various applications. The current study illuminates the effects of the formulation on the mechanical properties of pure adhesives, on the one hand, and their performance in bonded wood joints on the other. Tensile shear tests on bonded wood joints, tensile tests on adhesive films, and nanoindentation measurements in the interphase region of the bond were performed. Analyses by means of infrared, atomic force, and electron microscopy provided the explanatory basis for the results obtained. Additionally to laboratory made 1C PUR, unmodified commercial 1C PUR, melamine-urea-formaldehyde (MUF), and phenol-resorcinol-formaldehyde (PRF) were tested for comparison. The results obtained confirm that the mechanical properties of 1C PUR adhesives are significantly affected by their prepolymer composition. The adhesive formulation by means of additives, on the other hand, does not affect the mechanical properties but is to a large extent responsible for the bonding performance.

Current compression perpendicular-to-grain (C ⊥ ) design values for wood members are based on mean stress obtained from ASTM D143 specimen. The standard ASTM test with metal on wood bearing has limited applicability in modern construction assemblies with C ⊥ loading scenarios. Previous work has shown that end-bearing conditions and wood-on-wood C ⊥ bearing is a more severe case as opposed to load applied over central area and metal-on-wood bearing. This study evaluated C ⊥ behavior of typical assemblies used in construction, in which members experience C ⊥ stresses near their longitudinal-end through wood-on-wood contact. These included assembly of the bottom chord of a truss bearing on the top plate of a wall (BC assembly) and assembly of the compression chord of a shear wall bearing on the bottom plate (BP assembly) of a wall. Three different BC assemblies were tested with varying aspect ratios (height/width) of the bottom chord (B.C.) member. For each test assembly, paired ASTM tests of the main member (bottom chord member in BC tests, and bottom plate member in BP tests) were conducted. The assembly stresses at 1 mm deflection were always lower than the corresponding ASTM stresses at the same deflection. Due to varying assembly depths, 1 mm deflection was a poor criterion for determining C ⊥ stress values. For B.C. members, when loaded tangentially, they buckle in the direction of annual ring curvature. High aspect ratios accentuate this effect. Expectedly, the tendency to buckle and the probability of total failure in the assembly increase with increasing aspect ratio. This behavior was not observed in the ASTM tests.

Wood properties, including bending stiffness and strength, basic density and microfibril angle were experimentally obtained for six aspen and six hybrid poplar clones grown in Western Canada. Data analysis attempted to establish a relationship between wood mechanical properties and intrinsic wood attributes by means of artificial neural networks (ANN) and ε-regression support vector machines (ε-rSVM) employing a 5-fold cross validation approach (5-fold CV). Initial results for strength were acceptable, but require further improvement. Estimations of stiffness results (MOE) were inferior to those of strength (MOR) due to the fact that in several regression cases, the developed model worked well for narrow windows of data, but failed on a large scale due to the high variations in the values of the input data vectors. In such cases, the result is probably the development of regression with uneven performance throughout the input data set, and therefore the modeling capacity is poor. To avoid this predicament, different neural networks with one output neuron were developed in order to estimate either the stiffness or the strength, and at the same time the approximation capabilities of ε-rSVM were employed. In both methods, 5-fold CV was carried out in order to attain a more generalized solution by eliminating the boundary effect phenomena and by avoiding local behavior of the global support vector regression. The resultant models were evaluated by common metrics. The best ANN for the estimation of strength in combination with 5-fold CV, was a modular back propagation with average R 2 =0.70, and mean root mean square error (MRMSE) equal to 0.19 and mean average percent error (MAPE) equal to 12.5%. The Gaussian kernel 5-fold CV ε-rSVM estimated MOR with similar accuracy. The best 5-fold CV ANN for MOE estimation was a feed forward back propagation one, with average R 2 =0.60, MRMSE equal to 0.23 and MAPE equal to 41.5%, which was better than all other kernel methods employed.

The impact of drying on the structure of the never-dried hardwood cell wall was studied at nanometer level by means of wide- and small-angle X-ray scattering (WAXS, SAXS), and at micrometer level by X-ray microtomography (μCT). Never-dried silver birch, European aspen and hybrid aspen samples were measured by WAXS in situ during drying in air. The samples included juvenile and mature wood, as well as normal and tension wood to allow comparison of the effects of different matrix compositions and microfibril angles. The deformations of cellulose crystallites and amorphous components of the cell wall were detected as changes in the cellulose reflections 200 and 004 and amorphous halo in the WAXS patterns. Especially, the width of the reflection 004, corresponding to the cellulose chain direction, increased due to drying in all the samples, indicating an increase of strain and disorder of the chains. Also, the cellulose unit cell shrank 0.2–0.3% during drying in this direction in all the samples except in hybrid aspen tension wood. According to the SAXS results of silver birch, the distance between micro-fibrils decreased during drying. It was detected by μCT that the mean cross-sectional maximum width of the parenchymatous rays decreased from that of never-dried to air-dried birch by roughly 16%.

It is a commonly accepted notion that the equilibrium moisture content (EMC) of wood at a given relative humidity (RH) is highest during initial desorption of green wood due to an irreversible loss of hygroscopicity during the 1 st desorption. The basis for this notion is investigated by assessing how drying and saturation procedures influence the differences between the 1 st and the 2 nd desorption curves for Norway spruce ( Picea abies (L.) Karst.) sapwood. The study establishes 1 st and 2 nd desorption isotherms for a variety of initial conditions and it covers the RH range from 60.1% to 99.9%. The state of the water is not affected by oven-drying and rewetting as demonstrated by time domain low field NMR relaxometry. The results challenge the conclusions of earlier studies and indicate that in these studies the 2 nd desorption was initiated at much too low EMC and therefore fails to describe a boundary desorption isotherm. Instead, it becomes an intermediate desorption isotherm starting at the adsorption boundary curve and crossing over to eventually meet the desorption boundary curve. The results also show that vacuum drying at room temperature only gives a modest loss of hygroscopicity compared to the green state. Conversely, oven-drying at 103°C results in a more significant loss of hygroscopicity, except for RH above 96% where an increase in EMC surprisingly is seen.

The degradation of several Asian bamboo species by white-, brown-, and soft-rot fungi was investigated under laboratory conditions by means of different test methods. Severe deterioration was caused by all three fungi types. The bamboo species differed in durability. Samples from 6 months young culms decayed more than older ones. There were no significant differences between 1- and 3-year-old culms. Samples taken from the culm top were more vulnerable to decay than those from the bottom. Wet bamboo samples with soil contact were especially degraded by the white-rot fungus Schizophyllum commune , whereas the brown-rot fungus Coniophora puteana produced the greatest mass loss in drier samples. The sealing of bamboo crosscut ends reduced the rate of decay.

Molecular methods are emerging also as useful tools for wood protection studies. The aim of the present study was to evaluate quantitative real-time polymerase chain reaction (qPCR) as a tool for investigating details of the colonization pattern of basidiomycete decay fungi in wood samples after 6 years of soil exposure. Samples of Pinus sylvestris L. (heartwood without treatment), furfurylated P. sylvestris sapwood and Cu-HDO treated P. sylvestris sapwood was in focus. The qPCR method based on basidiomycete DNA content in the wood had the highest sensitivity, while the ergosterol assay was more sensitive than the chitin assay. Visual rating was compared with laboratory analyses and was found to be correlating well with qPCR. This study demonstrates that qPCR in combination with microscopy provides relevant data about basidiomycete colonization in wooden material.

No abstract available