The sawmill industry is a very important link in the Mozambique forest products value chain, but the industry is characterized by undeveloped processing technology and high-volume export of almost unrefined logs. The low volume yield of sawn timber has been identified as a critical gap in the technological development of the industry. To improve the profitability of the industry, there is thus a need to develop methods and techniques that improve the yield. In this paper, different positioning of logs prior to sawing and the possibility of increasing the volume yield of crooked logs by bucking the logs before sawing have been studied. A computer simulation was used to study the cant-sawing and through-and-through sawing of the logs to determine the volume yield of sawn timber from the jambirre (Millettia stuhlmannii Taub.) and umbila (Pterocarpus angolensis DC.) species. The optimal position, i.e. the position of the log before sawing that gives the highest volume yield of sawn timber for a given sawing pattern when the positioning parameters, offset, skew and rotation, are considered gave a considerable higher volume yield than the horns-down position. By bucking very crooked logs and using the horns-down positioning before sawing, the volume yield can be of the same magnitude as that obtained by optimal positioning on full-length (un-bucked) logs. The bucking reduces the crook of the logs and hence increases the volume yield of sawn timber.

To increase understanding of breakdown strategies for Mozambican timber, simulations were carried out using different sawing patterns that can be alternatives to the low degree of refinement performed for export today. For the simulations, 3D models of 10 Jambirre and 5 Umbila logs were used. The log shape was described as a point cloud and was acquired by 3D-laser scanning of real logs. Three sawing patterns (cant-sawing, through-and-through sawing, and square-sawing) were studied in combination with the log positioning variables skew and rotation. The results showed that both positioning and choice of sawing pattern had a great influence on the volume yield. The results also showed that the log grade had an impact on the sawing pattern that should be used for a high volume yield. The volume yield could be increased by 3 percentage points by choosing alternative sawing patterns for fairly straight logs and by 6 percentage points for crooked logs, compared to the worst choice of sawing pattern.

This study investigated the effect of the positioning of the log before sawing on the volume yield of sawn timber from tropical hardwood species. Three positioning parameters were studied, the offset, skew, and rotation, combined with two sawing patterns of cant-sawing and through-and-through sawing. A database consisting of two tropical hardwood species with very different outer shapes, jambirre (Millettia stuhllmannii Taub.) and umbila (Pterocarpus angolensis DC.), was used to simulate the sawing process. The result of the simulation revealed that, according to the combined effect of offset, skew, and rotation positioning, the positioning of the log before sawing is extremely important to achieve a high volume yield of sawn timber. The positioning parameter that has the highest effect on the volume yield is the rotation, and the variation in the volume yield associated with a deviation in the positioning can reduce the volume yield of sawn timber by between 7.7% and 12.5%.

The hygroscopic nature of wood leads to large moisture fluctuations in the material that may influence the mechanical performance of glued wood products. Adhesives based on bone, fish and hide have a long tradition for the gluing of wood and can be found in wooden structures in our cultural heritage. In this study, selected sorptive and mechanical properties of animal adhesives have been compiled and compared to those of synthetic polyurethane adhesives. Bone, fish and hide adhesives show a high moisture uptake at high relative humidity, which confirms the low moisture resistance of such adhesives. The modulus of elasticity and ultimate tensile strength of the films based on animal adhesives are considerably reduced when the moisture content is increased.

Most of the cracks are caused by changes in temperature and relative humidity which lead to shrinkage and swelling of the wood and thereby induce stresses in the structure. How these cracks influence the strength of the wooden structure, especially the shear strength, is not well understood. However, it is reasonable to expect that cracks have an impact on the shear strength as they preferably run along the beams in the direction of grain and bond lines. The purpose of this study was to investigate the load-bearing capacity of cracked glulam beams and to find a model that could predict the failure load of the beams due to the cracks. Three-point bending tests were used on glulam beams of different sizes with pre-manufactured cracks. An orthotropic elastic model and extended finite element method was used to model the behaviour of the cracked beams and to estimate the load-bearing capacity. The conclusions were validated by numerical simulations of the mechanical behaviour of three-point bending of glulam beams with different crack locations. The crack initiation load was recorded as the failure load and compared to the experimental failure load. The results of the compaction simulations agree well with the experimental results.

Laminated veneer products consist of veneers bonded together with adhesive into apredetermined shape. Since wood is a hygroscopic material and also anisotropic bynature, laminated veneer products are especially shape-sensitive to changes in moisturecontent. A deviation from the intended shape is a problem for both the manufacturersand users of the final products and annually such deviations cause great economic lossesin the manufacturing industry.To illustrate the influence of moisture on distortion and shape stability, studies havebeen performed in industrial conditions and in a laboratory environment. Veneers ofbeech and birch and a seat shell moulded from these veneers were used in the study.Distortion, i.e. spring-back, position and twist, has been determined directly aftermoulding and during subsequent moisture and drying cycles.The distortion follows more or less slavishly the changes in relative humidity around theproduct. The distortion is generally small directly after moulding but, after the laminateshave been exposed to a variation in relative humidity, the distortion increases. Some ofthe problems of poor shape stability that may arise later in the bending process can bereduced if attention is paid to moisture content and fibre orientation already in theproduction of the veneer.To achieve good shape stability of laminated veneer products in practice, the followingshould be followed by the manufacture industry:• develop cooperation with suppliers of veneer and set requirements of veneerwith regard to deviation of the fibre orientation, and require that the veneer bedried and conditioned to a moisture content consistent with production,• control incoming veneers with respect to fibre orientation and moisture content,• plan warehousing of veneers and ensure adequate conditioning, and• consider the orientation of the veneers and the species.

A laminated veneer product (LVP) consists of veneers bonded together with adhesive under pressure into a predetermined shape and, in general, under increased temperature to shorten the curing time of the adhesive. The process is commonly used in furniture design to manufacture complex forms such as thin shells. In the industrial production of LVP and when the ready- for-use components are exposed to climate variations, rejection due to distortion of the laminates is a major problem. The shape stability depends on a variety of material and process parameters, and this study has focused on the influence of fibre deviation in a single veneer. Recent research on the shape stability of LVP and how distortion is influenced by various material and production parameters is presented. A finite-element model for LVP is introduced and the use of this modelis exemplified by predicting the shape of a LVP with fibre distortion in a single veneer. The results show that it is possible to improve the shape stability of LVP if knowledge of various material and process parameters is implemented in the manufacturing process, and that a simulation based on a model of the wood material can be helpful in estimating the risk of an undesired deformation of the product.

A shortcoming of the laminated bending process is that the product may become distorted after moulding. This study focused on the influence of fibre orientation deviation for individual veneers on the distortion of a moulded shell. The distortion of 90 cross-laminated shells of the same geometrical shape, consisting of seven peeled birch veneers, were studied under relative humidity variation. All the veneers were straight-grained in the longitudinal-tangential plane, but to simulate a deviation in fibre orientation, some of the individual veneers were oriented at an angle of 7° relative to the main orientation of the other veneers in the laminate. A finite element model (FEM) was applied to study the possibility of predicting the results of a practical experiment. The study confirms the well-known fact that deviation in fibre orientation influences shape stability. The results also show how the placement of the abnormal veneer influences the degree of distortion. From this basic knowledge, some improvements in the industrial production were suggested. However, the FE model significantly underestimated the results, according to the empirical experiment, and it did not show full coherence. The survey shows the complexity of modelling the behaviour of laminated veneer products under changing climate conditions and that there is a great need to improve the material and process data to achieve accurate simulations. Examples of such parameters that may lead to distortion are density, annual ring orientation in the cross section of the veneer, the orientation of the loose and tight sides of the veneer, and parameters related to the design of the moulding tool.

To ensure success in the production of laminated veneer products, it is necessary to acquire a sound basic understanding of the behaviour of the wood, and to understand the inherent reactions of wood to adhesive, heat, moisture, strain and stress. This can ensure an efficient wood utilization and promote the development of new processes and products that take advantage of the visco-elastic nature of wood. A shortcoming of the laminated bending process is that the products may become distorted after moulding and during use. In this study, we have examined how the performance of laminated veneer products can be improved through the implementation of basic knowledge of wood in the design and production process. The results show that the material and process parameters and storage in a changing relative humidity have a clear impact on distortion. Fibre orientation of the veneers in the moulded assembly was the most critical parameter to control. Fibre deviations mainly resulted in twist of the product. A moisture content in one veneer deviating from that of the rest of the veneers in the assembly before moulding resulted in distortion of the laminated veneer products both after moulding and during use. To decrease the negative effect of fibre orientation and moisture content on shape stability, the veneer should be straight-grained and well-conditioned to a moisture level adapted to the use of the final product. Special care should also be taken to orientate the veneers during assembly before moulding.

There is an increasing need to update and correct information about product geometry in the wood manufacturing industry. Changes in machinery or personnel can be the cause of that need. Manual measurement takes time and diff erent ways of digitizing the geometry of the products have therefore been developed.In this study, two methods (3D-coordinate measurement and optical scanning) have been tested together in order to determine the position of a product in relation to the processing machine, and to optically scan the product geometry. The aim was to identify and evaluate methods to digitize product geometry into a CAD-model for the wood industry. Th e seat shell measured was fitted in the CNC-machine where the processing later would be performed.The methodology used has made it possible to create a CAD-model from the physical model. Based on the experience from this methodology, it would be recommended to continue by creating of a tool that minimizes the need for after processing, i.e. the adjustment of certain coordinates manually.

Laminated bending of veneers mean that dried, thin veneers or thin wood sheets are glued together under influence of pressure and eventually increased temperature. At the same time the product is given its desired shape, most often curved. This thermo hydro mechanical process offers several benefits. For example thick bends of small radiuses of any species of wood may be formed and poor quality wood containing knots, splits and other defects may be utilised. Laminated bends can usually be set more readily and made to conform better to the shape of the form than similar bends of solid wood. Further no softening treatment is generally required before the pieces are bent. However, there are also disadvantages e.g. more technical skill and better equipment are usually required than for solid wood bending. The presence of glue may be somewhat detrimental to the machines used for the final cleaning up of the bent pieces. Further the glue lines which are usually visible on the sides may be an aesthetical unappreciated effect [1],[2].The quality of the laminated bended veneer products are obtained as an interaction between the process, the veneers and the glue [3]. In industries designing and producing these products it is of interest to obtain better understanding of how processing- and material parameters affect the product quality. With an improved understanding of the material and processing parameters it may be possible to increase the efficiency of wood utilisation and promote the development of new processes and products that manipulate the viscoelastic nature of wood. In particular the possibilities to obtain narrower radius of curvature and better possibilities of bending in more than one plane would be advantageous.This study has focused on the moisture content (MC) and the grain angle orientation in the veneers. These two specific aspects were assumed to have a great influence on spring-back and distortions of the laminated bended veneer products. Spring-back and distortions were therefore studied in separate tests where MC and the grain angle orientation was varied separately in manufactured laminated bended wood products. After manufacturing the products were exposed to variations in humidity and temperature whereupon the spring-back and distortions were measuredThree tests were performed. For the first and the second test a seat shell was selected as test product, figure 1a. To the third test another product was selected, figure 1b. This product was a small bookshelf. The company producing this shelf had experienced large problems considering distortions of this product. Further the product was very simple in shape with only one bend and therefore suitable for measurements.In the first test the influence of MC of the veneers was investigated. In the second and third test the influence of grain angle of the veneers was studied.For the study veneers of birch and beech were selected in the production. For the first and third study only birch veneers were used. The veneers were initially conditioned to equilibrium moisture contents (EMC) according to setups in different test groups. For the first study a test group was also built up from veneers taken directly out of production to study the industrial conditions. The seat shells in this test group contained veneers conditioned to EMC 4 %, except for the surface veneers that had been stored in the production hall. The humidity and temperature conditions in this room corresponded to MC 7 %.The manufacturing of the products were performed in industrial conditions. In the tests the products were built up from a number of veneers and the studied factors were varied between the veneers in a controlled manner.The results from the first test showed that the MC of the veneers influenced the spring-back and the distortions. A large moisture gradient between veneers and especially unsymmetrical placements of these in the construction were especially critical. The results from the second and third tests showed that grain angle deviation has large effect on the distortions of the products. Even a small grain angle deviation as in study two (5°) resulted in large problems with distortions. The study also showed that when crossing two or more veneers with deviating grain angles there were cases when these faults interacted and multiplied the distortions. In production grain angle deviations can be a result of inaccurate placement of the veneers during pressing, incorrect cutting of the veneers, inherent from the growth of the tree or a combination of these factors. Deviations of the grain angle were, however, shown to have only small effects on spring-back.

A shortcoming of the laminated bending process is that the products may become distorted after moulding and during use. In this study, we have examined the influence of different UF-adhesive systems, adhesive distribution, and veneer properties such as species, moisture content, and fibre orientation. Two different species were studied: beech (Fagus silvatica L.) and birch (Betula pubescens Ehrh.). Distortion was determined directly after moulding and after storage in a changing relative humidity. The aim of the work was to study how the above-mentioned material and process parameters influence the distortion. The results show that the material and process parameters and the storage in a changing relative humidity had a clear impact on distortion. Fibre orientation, differences in moisture content between veneers, and the moisture gradient in the final product are identified in this study as being the most important parameters influencing the distortion and shape stability of laminated veneer products

A shortcoming of the laminated bending process is that the products may become distorted after moulding and during use. Annually, significant financial losses have incurred in the furniture and interior design industries as a result of distorted products. In this study, we have examined the influence of deviation of fibre orientation of individual veneers on distortion of a moulded shell to find ways to improve shape stability of laminated veneer products.Ninety cross-laminated shells, consisting of 7 veneers of Birch (Betula pubescens Ehrh.) with a total thickness of 3.6 mm, were studied. The in-plane dimensions of the veneer were 400x660 mm. All the veneers were straight-grained, but to simulate deviation in fibre orientation some of the individual veneers were oriented 7 degrees relative to the main orientation of the other veneers in the laminate. Distortion was determined directly after moulding and after storage in a changing relative humidity.The results show the well-known fact that deviation of fibre orientation of the veneers in the laminate influences the shape stability of the product. The results from this study, however, also show how the placement of the abnormal veneers in the laminated veneer products influences the degree of distortions. From this basic knowledge some improvements for production of laminated veneer products were suggested.

One of the most important quality aspects of a laminated veneer product is its shape stability under changing relative humidity (RH). This study aimed to establish an understanding of how the orientation of individual veneers in the laminate, i.e., orientation according to fibre orientation and orientation of the loose (the side with ‘lathe checks’) or tight side of the veneer, affects the shape stability. Three-ply laminates from peeled veneers of beech (Fagus sylvatica L.) were studied. The four types of laminate were the following: loose sides of all veneers in the same direction (cross and parallel centre ply) and loose sides of the outer veneers facing inward (cross and parallel centre ply). Four replicates of each type yielded 16 samples. The samples were exposed to RH cycling at 20% and 85% RH at 20°C, and the shapes of the samples were determined. The shape stability was influenced by the veneer orientation. Laminations with the middle veneer perpendicular to the top and bottom veneer (cross-laminated) showed the best shape stability, especially when the loose sides of the veneers were oriented the same direction. In parallel-laminated veneers, the laminates with opposite directions of the loose sides in the two outermost veneers showed the best shape stability. The major explanation of the behaviour of the laminates is that the loose side expanded more than the tight side from the dry to the humid climate, which was shown by optical 3D deformation analysis (ARAMISTM). After RH cycling, the laminates with cross plies showed visible surface checks only when the tight side was facing outwards.

A major problem in the manufacture of three-dimensional laminated veneer products (LVP) is damage due to stretching and/or buckling of the veneer. To reduce or eliminate this problem, veneer densification or adding a strengthening layer to the veneer can be an alternative. To study how veneer modification influences the veneer-to-adhesive bond strength, three methods of modification were studied in relation to an unmodified reference veneer: (1) densified veneer, (2) veneer pre-bonded with paper and hot melt adhesive (HMA), (3) veneer pre-bonded with non-woven polypropylene (NW) fabric glued to the veneer (a) with a urea formaldehyde (UF) adhesive, (b) with a mixture of UF and polyvinyl acetate (PVAc) adhesive, and (c) with a PVAc adhesive. Densification, pre-bonding with paper, and NW with UF/PVAc adhesive mixture resulted in no or only a slight decrease in strength of the bond-line compared to the reference. NW glued with UF or PVAc adhesive showed a considerable reduction in the strength of the bond-line. The climatic cycling had no significant influence on the bond strength.

To improve the resistance of wood to biological decay the Maillard reaction between introduced amines and wood cell-wall polymers can be utilised. However, initial studies in wood modification showed almost complete leaching of bicine and tricine from treated wood and the loss of beneficial effects. The objective of this study was to assess whether possible reactions of bicine or tricine with wood could be further enhanced and reaction products stabilised through the addition of glucose and/or citric acid. Thus, Scots pine sapwood specimens were impregnated with tricine or bicine, with or without glucose and citric acid, and then heated to a temperature of 160°C. The dimensional stability, degree of chemical leaching and mechanical properties were assessed. Overall, it was concluded that neither the presence of glucose nor citric acid did appear to enhance the reactivity of tricine or bicine. Anti-swelling efficiency (ASE) of 50% was observed for combined treatments of bicine/tricine and citric acid but the leaching resistance originated mainly from citric acid and glucose, with no indication for the retention of bicine or tricine. The presence of citric acid led to a strongly reduced modulus of rupture. 

Wood is a renewable, bio-based material with a mixture of different properties and qualities, used in numerous applications. Beside many species with high wood qualities several species suffer due to a number of disadvantages, where low hardness and abrasive resistance are characteristic for low-density species. This paper presents examples of on-going European research projects and industrial processes mostly related to wood densification methods. Wood densification is a classical thermohydro-mechanical (THM) wood treatment process, through which density is increased by mechanical compression of wood perpendicular to the grain, by impregnation of cell lumens or cell walls with solutions or melted substances (resins, waxes), or by a combination of both. The purpose is to produce newly designed and engineered materials and products with new property profiles, which would potentially find new markets. In general, the THM processes consist of three stages: plasticization of the wood cells, followed by the actualcompression, and finally solidification of the compressed wood in order to prevent elastic spring-back and the moisture-induced set-recovery. The wood densification process refers but is not limited to solid wood and might apply to whole wood pieces, or to local areas within given pieces only. Another THM method is the mechanical compression of wood parallel to the grain, which leads to a product with high flexibility. A European wood research network, represented by the authors of this contribution, has extended experience in many wood modification processes, as demonstrated through ongoing researches and case studies in this paper

The drying of Eucalyptus nitens is a troublesome process as the species is extremely prone to drying defects. This paper reports ongoing research toimprove the understanding of surface checking and cell collapse in Chilean grown Eucalyptus nitens during drying. Computed tomography (CT) scanning was used as a powerful tool for studying the internal changes in the wood-material during the drying process. Different levels of temperatures have been tested with the same equilibrium moisture content (EMC) conditions and low air velocity. The results confirm that a low drying temperature and a low air velocity, which results in a slow rate of drying, reduce internal cell collapse and surface checking .

Medical computer tomography (CT) uses dual-energy x-ray absorptiometry (DXA) for basis material differentiation. DXA is based on the different interactions between x-ray photons and the scanned material based on the energy of the x ray, the effective atomic number of the material components, and their electron density. Considering wood and water as the only components of a wood specimen at a given moisture content (MC), DXA has been suggested for quantification of the wood-water proportion and thus for the determination of MC. Such an approach can provide great improvements and advantages in the use of CT technology in the sawmill industry, for example, detection of fresh knots in sapwood and optimization of timber drying. However, the approach in wood science is recent and still presents doubts. This study tries to clarify the possibilities of dual-energy CT for estimation of moisture in wood through the approach of the ratio method, which has been used as the theoretical basis for establishing the feasibility of the DXA in wood science and which is often used for differentiation between components of a scanned material. Two-dimensional x-ray measurements were confronted with theoretical calculations. The theoretical calculations show that the attenuation of water and wood at different acceleration voltages differs enough to apply the ratio method, but the practical experiments cannot prove it. The authors suggest that the inhomogeneity in wood introduces large errors that cause misleading results. Also, the equipment providing measurements of photon count could present different results.

During the drying of sawn timber, hydrostatic tension forces within the cell may exceed the compressive strength perpendicular to the grain of the thin cell wall and the cell then collapses. This phenomenon is common in hardwoods such as Sequoia sempervirens, Thuja plicata, Tsuga heterophylla, Juglans nigraand many species of eucalyptus and oak. Usually, this leads to severe surface deformation, and both surface and internal checking(honeycombing) may occur. The quality of the final product is lowered by these cracks and deformations. The aim of this study was to investigate, by CT-scanning samples throughout the drying process, whether it is possible to detect when and how cracking and deformation occurs and develops in specimens of Eucalyptus nitens. Based on this knowledge, better drying schedules can be developed to improve the yield and ensure a higher quality of the sawn timber. Three specimens, one specimen in each drying run, of Eucalyptus nitens were used for the tests. Their cross-sectional dimensions, prior to drying, were 105x23 mm2 and their length was 70 cm. A specially designed laboratory drying kiln that fits within the gantry of a Siemens Somatom Emotion medical CT-scanner was used (Fig. 1). With this equipment, it is possible to scan the inside of the kiln without interrupting the drying process.

Computed tomography (CT) during drying of sawn timber is an excellent non-destructivetechnique to study the moisture flux as a function of drying time. In this study, a climatechamber combined with a medical CT- scanner has been used for non-destructive studies ofdensity changes in sawn timber during drying and conditioning.Green sawn timber contains large amounts of water and has to be dried before it can befurther processed and used in various building applications. The most common dryingmethod is convective air-circulation drying in large industrial kilns, where the relativehumidity (RH) of the hot circulating air is gradually reduced until the timber reaches thetarget moisture content (MC).Drying of sawn timber is driven by the existence of a difference in MC between the coreand the surface, so that moisture moves from the wet inner region towards the drier outerregion. During the early capillary stages of drying, the drying rate is high while, at the laterstages when all liquid water has evaporated, the drying rate is slow and diffusioncontrolled.At the end of the drying process, the timber surface is always drier than its core.In addition to this moisture gradient, internal stresses develop within the cross section withcompression stresses in the timber surface and tension in the inner regions. To avoidunwanted distortions, both these stresses and the moisture gradient, need to be eliminatedbefore the timber is further processed. This is achieved in a final conditioning stage withinthe drying process by moistening the circulating air through steaming or water spraying.The aim of the present work was to optimize the conditioning stage by developing amethod for studying of moisture gradients, deformations and internal and externaldimensional changes in sawn timber during the conditioning phase by using a CT-scannercombined with a drying unit for in-situ measurements of moisture flow.The results show that it is possible to detect the moisture gradient between the surface andcore of the timber with satisfactory reliability, but not the internal and external dimensionalchanges. However, this method creates a potential for increasing the knowledge andunderstanding of the conditioning phase and makes it possible to optimize and develop thisstep in the drying process to improve the yield and ensure a higher quality of the sawntimber.

X-ray computed tomography (CT), which was introduced in the medical field in the early 1970s, is also a powerful tool for the non-destructive measurement of dynamic processes in wood. For more than 20 years, CT has been used in wood research at Luleå University of Technology. The uniqueness of the CT equipment means that processes such as drying, modification, water absorption, internal and external cracking and material deformation can be studied in temperature- and humidity-controlled environments. The data recorded by the CT during the process is converted into two- or three-dimensional images that for instance can show dynamic moisture behavior in wood drying.This paper gives an overview of the possibilities of using CT in timber construction research, and shows examples of applications and results which can be particularly difficult to achieve using other methods. A specific focus is on studies on wood products for construction, and how to deal with different material combinations such as wood and metal.The practical application of the result is that CT-scanning, combined with image processing, can be used for non-destructive and non-contact 3-D studies of exterior constructions elements during water sorption and desorption, to study swelling and shrinking behaviour, delamination phenomena, crack development, etc.

Industrial drying of sawn timber is a process driven by a difference in moisture content (MC) between the core and the surface as moisture moves from the wet inner region towards the drier surface. After drying, the timber surface is always drier than its core, and stresses have developed within the wood volume. If the timber is to be further processed, these stresses and the moisture gradient need to be reduced to avoid unwanted distortion, i.e. the timber needs to be conditioned. Conditioning is usually accomplished by exposing the timber to a hot and humid climate after the drying regime. The conditioning regime is essential for timber quality, and it is energy and time consuming; therefore of interest for optimisation. This research was a case study where for the first time the MC during conditioning was studied in an X-ray computed tomography (CT) scanner. The aim was to test a previously developed algorithm and investigate the influence of MC and heartwood-sapwood proportion on the effectivity of the moisture equalisation in 30 mm thick Scots pine boards. The MC was estimated from CT data acquired during the drying and conditioning of the boards in a lab-scale kiln adapted to a medical CT scanner. Results show that the algorithm can provide relevant data of internal MC distribution of sawn timber at the pixel level. Furthermore, for the drying schedules studied, the conditioning at low MC (8%) does not need to be longer than 3 h, while higher MC (18%) requires a longer conditioning.

The estimation of the pixel-wise distribution of the moisture content (MC) in wood using X-ray computed tomography (CT) requires two scans of the same wood specimen at different MCs, one of which is known. Image-processing algorithms are needed to compensate for the anisotropic distortion that wood undergoes as it dries. An alternative technique based on dual-energy CT (DECT) to determine MC in wood has been suggested by several authors. The purpose of the present study was to evaluate the hypothesis that DECT can be used for the determination of MC in real time. A method based on the use of the quotient between the linear attenuation coefficients (μ) at different acceleration voltages (the so-called quotient method) was used. A statistical model was created to estimate the MC in solid sapwood of Scots pine, Norway spruce and brittle willow. The results show a regression model with R2 > 0.97 that can predict the MC in these species with a RMSE of prediction of 0.07, 0.04 and 0.11 (MC in decimal format) respectively and at MC levels ranging from the green to the totally dry condition. Individual measurements of MC show an uncertainty of up to ±0.4. It is concluded that under the conditions prevailing in this study, and in studies referred to in this paper, it is not possible to measure MC with DECT.

X-ray computed tomography (CT), which was introduced in the medical field in the early 1970s, is also a powerful tool for the non-destructive measurement of dynamic processes in wood. For more than 20 years, medical CT has been used in wood research at Luleå University of Technology. The uniqueness of the CT equipment allowsprocesses such as drying, modification; water absorption; internal and external cracking; and material deformation to be studied in temperature- and humidity-controlled environments. The data recorded by the CT scanner during the process is converted into two or three dimensional images that, for instance, can show dynamic moisture behaviour in wood drying and crack formation. This paper provides an overview of the possibilities of using CT in bio-composite research, and shows examples of applications and results that can be particularly difficult to achieve using other methods. A specific focus is on studies on wood products that use combinations with materials such as metal and especially about how to deal with the difficulties that this entails.The practical application of the result is that CT scanning, combined with image processing, can be used for non-destructive and non-contact three-dimensional s tudies of exterior construction elements during water sorption and desorption, to study parameters such as swelling and shrinking behaviour; delamination phenomena; and crack development.

The use of cross-laminated timber (CLT) as a construction material for high-rise timber buildings has increased in the recent years especially in Europe and North America; a trend that is expected to continue. The CLT-elements will often be finished with an impermeable layer, whether it is walls, floors and, especially, roof. In Sweden, often no weather protection is used during the construction of the building, allowing the wood to be exposed to liquid water and relaying on later atmospheric conditions to dry the timber prior to finishing. The Swedish building regulations require a maximum surface moisture content (MC) of 18% before assembly of the elements and a maximum surface MC of 16% before the wood is covered. This could drive to high levels of MC within the CLT while the surface is already dry, which is a highly possible scenario in the case of high buildings where sun and wind create good conditions for a fast surface drying. At the same time, the regulation requires control of MC to be made with an electrical pin-type MC-meter, which is problematic because its reliability lays in part on the device reaching a certain penetration into the wood. The measurement of surface MC could thus be erroneous and the risk for mould development would be high even if the regulations are strictly followed. If a CLT with a too high moisture level are covered with an impermeable surface layer, the moisture is trapped within the CLT and may cause microbiological degradation that could be problematic to correct later on.An update in the regulation requirements is recommended, but such update must be based on a proper understanding of how moisture can be distributed in CLT and other wood-based building material during outdoor construction.

This project aims to establish amethod to study (1) the effect of liquid-water-exposure time on the MC distribution of Spruce timber boards, but that could potentially be used in other wood-based building materials as well, and (2) the drying process under emulated outdoor conditions. The focus is set on those elements that are laid horizontally or with a very low inclination, such as floors and roofs. Sections of methacrylate are glued to the internal side of 43 x 200 mm planed spruce timber, allowing the wood to be exposed to standing water under a period of several days. CT images of different cross sections are taken periodically so that the evolution of MC profile can be monitored. The hypothesis is that the suction of liquid water will not be large and that it can dry quickly once the exposure to liquid water ends, but also that a MC gradient will develop beneath the surface which, under drying, may create regions of high MC that may be unnoticed by measuring with pin-type MC-meters.

X-ray computed tomography (CT) is a powerful tool for the non-destructive study of dynamic moisture processes in wood and other bio-based materials. In the CT facilities at Luleå University of Technology, it is possible to study wood-moisture relations such as water absorption, drying and related material deformation under a temperature- and humidity-controlled environment.An increase in the use of bio-based materials in building construction has led to an increased interest in capillary phenomena in these materials, because of an increasing number of moisture-related damage in timber and hybrid-timber buildings. This article shows some examples of how different bio-materials used in construction interact with liquid water over time. The overall purpose has been to develop the CT technique as a powerful tool for the determination and visualization of capillary flow that can be a base for modelling and an increased understanding of moisture flow in new bio-based building materials.Early-stage observation of the behaviour of different traditional and new bio-based building materials shows that CT scanning, combined with image processing, has a high potential to be used in performing non-destructive and non-contact tests that can help to increase the knowledge of water-material interactions and develop building materials with an optimized performance.

Auto-adhesion is a phenomenon that is in general related to the manufacture of wood-basedfibreboards, e.g. to the Masonite process or similar processes based on lignocellulosic raw materials.Auto-adhesion as a mechanism for the bonding of solid wood or veneer has not met with the sameindustrial success, but interest is increasing for environmental reasons and as a result of theincreasing cost of adhesives in wood products. The temperature in the laminate is crucial for the autoadhesionprocess that will result in bonding between veneers during hot-pressing. This paper presentsa model for the temperature evolution during the hot-pressing of a porous material, which wasdeveloped and verified for a five-veneer beech laminate pressed at a temperature of 250°C and apressure of 6MPa in an open system for 280 seconds. The result shows good agreement between themodel and the experimental temperature data during the hot-pressing. It can be concluded that a goodcontrol of the temperature evolution during the manufacture of adhesive-free veneer boards is of majorimportance to reach the target properties of the product.

Five-ply self-bonded boards were obtained by pressing beech veneers parallel to the grain without additional adhesives, steam or pre-treatment. Fifteen different combinations of pressing parameters were tested, including temperature (200°C, 225°C and 250°C), pressure (4, 5 and 6 MPa) and pressing time (240, 300 and 360 seconds). Due to severe pressing conditions, the new product showed a higher density and different properties compared to a conventionally glued laminated wooden board. The self-bonding quality was assessed through dry shear strength tests, through a three-point bending test and a water-soaking test at 20°C. The dimensions in the cross section of the boards were measured after soaking in water. Results show that the choice of pressing parameters affects all the mechanical and physical properties tested. A statistical analysis revealed that the pressing temperature is the most influential parameter. Boards pressed at 200°C delaminated rapidly in water, whereas boards pressed at 225°C delaminated only at core-positioned layers after 48 hours and boards pressed at 250°C did not delaminate at all in water. Compared to panels pressed at lower temperatures, boards pressed at 250°C had the highest density, a higher shear and bending strength and a lower water absorption.

Laminated self-bonded densified boards were obtained by pressing five veneers of beech(Fagus sylvatica L.) parallel-grain-oriented, without adhesive and without surface activation. Theboards were pressed according to an experimental design based on fifteen different combinations ofpressing parameters: temperature (200, 225, and 250°C), pressure (4, 5, and 6MPa), and time (240,300, and 360s). The image of the 40 board edges (radial sections) was analysed with ImageJ softwarein the red-green-blue (RGB) colour space. Brinell hardness tests were also performed. The resultsshow an almost linear relation between the brightness values (defined as the arithmetic mean of theRGB channels) and the Brinell hardness. It is suggested that brightness is a predictor of strength forself-bonded laminated boards.

A self-bonding phenomenon takes place when five layers of beech (Fagus SylvaticaL.) veneers are pressed at temperatures higher than 200ºC. If the pressing temperature between veneer surfaces reaches at least 225ºC during pressing and if the pressure applied is optimal, water-resistant bonds are formed between veneers. This study investigates the relation of thickness reduction (marker of compression) and mass loss (marker of heat treatment intensity) to boards quality. The effect of water and water vapour on the bondings between veneer in boards pressed at 200, 225 and 250ºC is studied. The conclusion is that pressing 5 layers of 2 mm rotary-cut beech veneer parallel-fibered at 225ºC, 5 MPa and 300 s leads to a thickness reduction of 33.4 % and mass loss of 1.23 %; in such boards bondings are not resistant to liquid water but are resistant to vapour after one adsorption-desorption cycle. When pressing at 250ºC, 5 MPa and 300 seconds, the thickness reduction is 50% and the mass loss 4%; in such boards no delamination was observed when soaked in water. Boards pressed athigher temperature show lower hygroscopicity. Their equilibrium moisture content (EMC) rangedbetween 3.6 and 7%. Based on the results of this study it ishypothesised that the decay resistance of self-bonded boards will increase when increasing the severity of the hot-pressing.

This study evaluated the capability of nuclear magnetic resonance (NMR) technology based on small portable magnets for in situ studies of the local moisture content in wood. Low-field and low-resolution [1H]NMR with a unilateral permanent magnet was used to monitor and map the moisture content of wood cladding materials of various types in a spatially resolved manner. The results show that portable NMR equipment based on small open-access permanent magnets can be successfully used for non-invasive monitoring of the moisture content in various extended wood specimens. The moisture content was measured with a depth resolution of 0.2 mm and a maximum penetration depth of 3 mm. This makes the technique suitable for in situ local moisture content measurements beneath a coating layer in the cladding, for example, and it is also possible to relate the moisture level to specific properties of the wood material.

The purpose of this study has been to identify and clarify the challenges to be faced in order to make more efficient use of wood in the production of timber houses in factories. This includes anexample of the current payment capacity of the timber-house manufacturers in order to obtain wood for trusses and wall frames which is more adapted for their production. This article also describes the history and the outlook of the Swedish single-family timber housing industry. In brief, the article provides a basic understanding of the conditions of the single-family timber housing industry in Sweden. The companies in the case study reported very little waste related to quality discrepancies in the cutting of sawn timber for trusses and wall frames, achieving a volume yield of 93% or more. The study also shows that 2/3 of the cost of producing these components is associated with the raw material and 1/3 of the cost with processing. Companies should therefore maintain a high volume yield in their wood processing, and they should ensure that the quality specifications for the sawn timber used in the production are correctly related to the wood’s intended use. These figures also suggest that a company’s ability to pay for components is about 30% higher than the price of sawn timber.

Ska trä öka sin konkurrenskraft måste trähusföretag och virkesleverantörer bli bättre på att både ställa och uppfylla kravspecifikationer. Idag kan materialspill och felleveranser uppgå till närmare en femtedel av virkeskostnaden.Trähusbranschen står inför ett antal utmaningar. Avgörande är att kunna producera attraktiva bostäder till en kostnad som inte är högre än att människor har råd.Trähusföretagen utnyttjar inte fullt ut material och metoder som är anpassade för en effektiv produktion av hus i fabrik. I den kontexten får träets miljöfördelar en underordnad betydelse i konkurrensen med andra mindre miljömässigt uthålliga material.

This study concerns the development of a method for surface modification based on the hot-and-cold bath process. In the experiments the wooden boards were first heated in an oven and after that they were immediately soaked in a cold chemical solution. This procedure allowed the chemicals to penetrate partially into the wood without using pressure equipment. In this study copper, furfuryl alcohol and phenol formaldehyde based solutions were used. The impregnation resulted in modified layers below the wood surfaces representing a trade- off between the full-bulk modification and surface coating of wood. It is concluded that the method can be developed further for potential industrial use to produce e.g. flooring, cladding or decking.

The objective of this study was to investigate the possibility of using X-ray computer tomography (CT) for measuring average moisture content (MC) and shrinkage of biological products that are dried as granular materials. Three different biological materials were dried simultaneously under the same drying conditions, namely, spruce sawdust and two species of mushrooms. The results showed that moisture content values within approximately ±1% of the oven-dry values and linear relationships between shrinkage and MC can be obtained without any calibration factor and a limited number of CT-images.

Mathematical models are essential for the development of schedules for the air-circulation drying of timber in Swedish sawmills, but earlier models have been shown to be conservative leading to longer drying times than necessary. In the current study, macroscopic (macro) X-ray computed tomography (CT) has been used in both the development and validation of a finite element (FE) model, to enable the macro-CT aided FE modelling of the nonlinear transient moisture flow in wood. The model uses more advanced theory than has previously been used in Swedish sawmills, by incorporating a surface emission coefficient to simulate the surface resistance to moisture flow. A single piece of Norway spruce [Picea abies (L.) Karst.] timber was subjected to that part of a traditional kiln-drying schedule, which is associated with diffusion-driven moisture transport. The incorporation of macro-CT data into the FE model resulted in a more realistic representation of the board’s geometry, the initial moisture state, and the definition of material parameters. It also led to a better simulation of flow speed and moisture gradient, especially the asymmetric MC development within the cross section throughout the drying process.