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This paper deals with the optical observation and evaluation of the swelling of beech wood samples (Fagus sylvatica L.) during gaseous ammonia treatment. The pressure level was varied in several experiments from ambient pressure to almost saturated steam pressure at isothermal conditions at 20°C. The initial moisture content of the wood was oven-dried and also conditioned (65% RH/ 20°C). All experiments were carried out in a self-developed experimental set-up. It consisted of three parts: a pressure vessel with a glass pane at the top, a camera with additional lighting above it and an algorithm for the semi-automatic evaluation of the data. Parallel investigation of the maximum swelling in water of specimens of the same origin showed that ammonia leads to a higher swelling in tangential direction (up to 23%). The swell-inhibiting influence by the wood rays can be observed on the basis of the comparison to the water swelling in radial direction. Furthermore, the results visualise the change in crystal structure from cellulose I to ammonia-cellulose I.

The vibrational properties of spruce (Picea abies Karst.) and European beech (Fagus sylvatica L.) were investigated in this study in dependence on the relative humidity (RH). The RH was measured at 20 °C ranging from oven-dried to 85%. For the evaluation of the vibrational properties the dynamic modulus of elasticity E’ and the damping coefficient tan δ were measured at 7 climate steps. The same samples used for the vibrational tests were afterwards mildly thermally modified at 180 °C and measured at the same climate steps. Both wood species were compared and evaluated considering the property changes (E’, tan δ, sorption isotherms and volume swelling) due to the thermal modification. The chosen modification resulted in a marginal change in the vibrational properties of spruce, whereas the properties of beech were clearly changed. The vibrational properties of beech could be improved in the usual RH range (35–85%) due to this thermal modification. For spruce, it was concluded that a mild modification, conducted in this study, is not suitable for improving the vibrational properties. Further conclusions concerning the underlying causes as well as the use in musical instruments were drawn.

Bark on trees protects the plant against environmentally adverse conditions as well as fungi and insect attacks. There are different chemical substances, mostly in the outer bark of trees, which can stop fungi from developing. Bark as a by-product of wood plantations is available in high quantity and can serve as an excellent source for the production of eco-fungicides. In the presented article, bark of various poplar clones from two short-rotation coppices (SRC) in Poland and Germany was examined to determine the chemical composition, the possible extraction of potential fungicides (terpenes, aromatic and phenolic substances), and influence of their extracts on slowing the growth of mold fungi. It was proved that the content of the fungicidal substances depends strongly on the clone type. Two methods of extraction—Soxhlet and batch—were compared to obtain fungicidal extracts. Fungicidal substances were found in extracts gained with both approaches. Triterpenes, fatty acids, aldehydes, and alcohols were primarily the active fungicides in the Soxhlet extracts, whereas phenolic substances act as fungicides in the batch extracts.

The aim of this work is to establish a bending test method as evaluation criteria for mechanical properties (strength and modulus of elasticity) of veneers. The bending test is one essential and ea...

In this study, the relatively new picture frame method applied to wood is compared with three established shear test methods, namely the experimental modal analysis, the square plate twist method and the torsion test. For the investigations, the wood species European beech (Fagus sylvatica L.) and spruce (Picea abies L. Karst.) were used and the shear tests were conducted in LR and RL direction. The results show comparable shear moduli for beech and spruce in the range of 931–1289 Nmm−2 and 495–842 Nmm−2, respectively. In contrast to the theory of linear elastic orthotropic materials, significant differences in the results of the picture frame method between LR and RL direction were observed for spruce.

The mechanical properties of cured wood adhesive films were tested in a dry state by means of nanoindentation. These studies have found that the application of adhesives have an effect on the accuracy of the hardness and elastic modulus determination. The highest values of hardness among the tested adhesives at 20 °C have condensation resins: MF (0.64 GPa) and RPF (0.52 GPa). Then the decreasing EPI (0.43 GPa), PUR (0.23 GPa) and PVAc (0.14 GPa) adhesives. The values of the elastic modulus look a little bit different. The highest values among the tested adhesives at 20 °C have EPI (11.97 GPa), followed by MF (10.54 GPa), RPF (7.98 GPa), PVAc (4.71 GPa) and PUR (3.37 GPa). X-ray micro-computed tomography was used to evaluate the adhesive joint by the determination of the voids. It has been proven that this value depends on the type of adhesive, glue quantity and reactivity. The highest values of the void ratio achieve the PUR (17.26%) adhesives, then PVAc (13.97%), RRF (6.88%), MF (1.78%) and EPI (0.03%). The ratio of the gaps increases with the higher joint thickness. A too high proportion of voids may weaken the adhesive joint. Validerad;2023;Nivå 2;2023-01-01 (johcin)

During the manufacture of veneer based moulded parts, veneers move against one another. Friction is caused due to this movement. Different conditions, such as gluing or fibre direction, could influence the friction coefficients and thus the moulding process. For a better understanding of the manufacturing process of veneer based moulded parts, it is important to know which parameters influence friction and friction coefficients. In this paper, results of friction investigations are presented. Thereby the moisture content of the used veneers was varied as well as the fibre direction. Considering the manufacture conditions, the investigations were also conducted with glue-coated veneers. The results prove an influence of fibre direction but this influence depends on moisture content., Tijekom proizvodnje furnirskih otpresaka furniri se gibaju jedan nasuprot drugome. Zbog toga gibanja nastaje trenje. Različiti uvjeti kao što su lijepljenje i smjer protezanja vlakanaca mogu utjecati na faktor trenja, a time i na proces izrade otpresaka. Za bolje razumijevanje procesa proizvodnje furnirskih otpresaka važno je znati koji čimbenici utječu na trenje i faktor trenja. U ovom su radu prezentirani rezultati istraživanja trenja između furnira. Varirani su sadržaj vode upotrijebljenih furnira, kao i smjer protezanja vlakanaca. Uzimajući u obzir i proizvodne uvjete, istraživanje se provodilo i s furnirima premazanim ljepilom. Rezultati su potvrdili utjecaj smjera protezanja vlakanaca, ali taj utjecaj ovisi o sadržaju vode u furniru.

In the field of lightweight construction, the use of natural fibers as reinforcement in composites has been increasingly discussed. Additionally, the damping properties of natural fibers are known from fiber materials such as fiber insulation boards. In the scope of the work presented here, the focus is on identifying the potential of natural fibers for lightweight structures with high vibration damping capacity. For this purpose, test specimens made of flax fiber-reinforced and glass fiber-reinforced thermoplastic composites were manufactured and characterized. Contrary to expectations, the flax fiber-reinforced composite exhibited an almost isotropic damping characteristic. A comparison of the damping and stiffness properties determined by measurement confirms the high potential of natural fiber-reinforced materials for lightweight structures with high damping.

A new method for the determination of shear modulus and shear strength is presented in this study using a shear or picture frame. A shear frame in accordance with DIN SPEC 4885 is in other fields, such as fibre reinforced composites, state of the art. Here, a square test specimen with recessed corners is held in the shear frame and subjected to a quite uniform shear deformation state. To determine the shear modulus and the shear strength, tensile load acting on the shear frame and the associated shear strain are measured. This method has the advantage of simultaneous determination of the shear modulus and the shear strength. Thin square wooden plates of European beech (Fagus sylvatica L.) were tested in all anatomical directions. The results show good accordance with literature values. The highest values of shear modulus and shear strength were yielded for the LR plane, followed by the values in the LT plane. The tests in the RT plane clearly resulted in the lowest values.

Untreated and thermally modified woods of cherry, service tree, pear and plum were investigated as potential substitutions for Indian rosewood in guitar making. Acoustic properties such as dynamic modulus of elasticity, dynamic shear modulus in LR-plane and loss coefficient as an indicator for damping were determined by means of experimental modal analysis and the mechanical properties by means of static bending and hardness test. The swelling behavior was also investigated. The results suggest that cherry and service tree could be used as alternative back and side material and plum and service tree may also be used for fingerboards. Thermal modifications at 160 °C for 8 h improve swelling behavior, mechanical properties, but damping was slightly increased for cherry and pear. No significant change of Brinell hardness was observed owing to thermal modification.

Water vapor sorption surface areas and sorption energies of untreated and thermally modified Norway spruce [Picea abies (L.) Karst.], sycamore maple (Acer pseudoplatanus L.) and European ash (Fraxinus excelcior L.) were investigated by means of dynamic vapor sorption (DVS) measurements and excess surface work (ESW) evaluation method, respectively. Adsorption and desorption experiments in the hygroscopic range and desorption tests from water saturation were conducted. Thermodynamically, ESW is the sum of the surface free energy and the isothermal isobaric work of sorption. From the amount adsorbed in the first minimum a specific surface area similar to the BET surface area can be obtained. The results show that untreated spruce has a significantly higher specific water vapor sorption surface and sorption energy compared to both hardwoods maple and ash. Thermal modification of the woods leads to a significant reduction of water vapor sorption surface and sorption energy. The determined surface area and energy are higher in desorption direction than in adsorption direction, whereby the highest values in desorption direction from water saturation, especially for maple and ash, were obtained. The surface areas calculated by means of the ESW method are similar to the surface areas calculated by means of the BET method, particularly in adsorption direction.

This paper deals with comparative studies of bending behavior of untreated and modified European beech (Fagus sylvatica L.), European oak (Quercus spp.) and black locust (Robinia pseudoacacia L.). The modification of the woods included both ammonia treatment and ammonia treatment in combination with mechanical densification. For each ammonia treatment, pure gaseous ammonia was used. The investigations were conducted by means of three-point bending tests. The bulk density increases significantly due to ammonia treatment and, furthermore, due to additional mechanical densification. The modulus of rupture is not affected by ammonia treatment. Additional mechanical densification, however, leads to a strong increase in the strength and stiffness. The deflection behavior changes in such a way that the ammonia treatment leads to an increase in deflection, and the additional mechanical densification further reinforces this trend.

This research investigated the effect of different fractions of commercial wood flour (Type c100 from JRS, Germany) on mechanical and physical properties of wood-polymer composites (WPC). The fractions were named regarding the mean lengths of their particles in µm; 80, 130, 255, 405 and 485. The composite samples were manufactured with 30 wt% of wood flour fractions of all five groups as well as the not fractionated flour, and 70 wt% of cellulose propionate (CP). The melt mass-flow rate (MFR) of the different granules, tensile strength, and modulus of elasticity, flexural strength, flexural modulus and the impact strength of the injection molded specimens as well as the water uptake were determined in this study. WPCs with the specific size range used in this investigation exhibited improved strength and modulus of elasticity in tensile and flexural tests, compared to pure CP. Using fraction 255, the mechanical properties increased the most. Tensile strength rose by 28 and 13% compared to CP and to WPC with the not fractioned wood powder, respectively. Fraction 255 increased flexural strength by 33 and 5% compared to CP and WPC with the not fractioned flour. The MFR (tested at 190 °C with 7.16 kg) of WPC_255 is the lowest with 2.3 g/10 min. Composites with the smallest particles showed the least water uptake.

During the manufacture of veneers cracks and other damages occur. These damages impair and reduce the veneer cross-section. By means of microscopic investigations cracks and damages in veneer cross-sections were documented and measured. These investigations were conducted with industrially sliced 0.3, 0.6 and 1.2 mm thick veneers. The results determine the residual cross-sections in dependence of veneer thickness which can be used for numerical calculations.

Wood veneer/biopolyethylene (bio-PE) biocomposite materials were produced by using poly(N-vinylformamide-co-vinylamine) (PVFA-co-PVAm) copolymers as a phase-mediating reagent. In a preliminary step, PVFA-co-PVAm was adsorbed onto the wood veneer component from aqueous solution. In its adsorbed form, it served as an adhesion promoter and improved the compatibility between both the highly polar wood veneer and weakly polar bio-PE surface. Structural parameters and their effect on the adsorption process, such as the degree of hydrolysis (DH) of poly(N-vinylformamide) (PVFA) (30, 50, and > 90%), the molecular weight of PVFA-co-PVAm (Mw 10,000, 45,000, or 340,000 g/mol), and the pH value (4, 7, and 11) influenced the resulting wetting behavior of the PVFA-co-PVAm-modified wood veneer surface. Thus, the hydrophobizing effect of the PVFA-co-PVAm was clearly detectable because the contact angle with water was considerably increased up to 116° by adsorption of PVFA-co-PVAm 9095 at pH 11. The adsorbed amount of PVFA-co-PVAm was determined by energy-dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS). The PVFA-co-PVAm-coated wood veneers were consolidated with bio-PE in a hot press process. The modified composite materials showed remarkably improved Young’s moduli (552 MPa) and tensile strengths (4.5 MPa) compared to former composite materials produced without PVFA-co-PVAm modification.

Large string instruments, such as cellos and double basses, are manufactured, bought and played all over the world. Thereby they are exposed to different climate conditions. This paper describes shape alterations using the example of a double bass stored at different climatic conditions. By means of an optical measurement these shape alterations were recorded and represented. The results clearly show spots with strong and without deformations. Thus, weak points of the construction are localised and improvements can be established for the construction of string instruments.

Milling is one of the most important cutting procedures in the wood industry. It allows shaping of workpiece surfaces with a high chip-removal rate. This is possible because of a fast rotary cutting motion, the possibility to place many cutting edges on the tool circumference and a fast linear feeding motion. Due to these different kinds of motions the resulting effective motion follows a prolonged cycloid which forms periodic waves on the workpiece surface. These surface patterns, called cuttermarks, may be visible on the machined surface after cutting and mainly influence the workpiece quality. Further surface machining steps are required to meet the demanded standards of surface quality. This is why researchers have been looking for possibilities to lower or avoid these cuttermarks. Beside the description and the analyses of the geometry of cuttermarks, magnitudes of disturbance, mechanical and mechatronic approaches and alternative procedures will be introduced and discussed. Especially mechat...

The possibility of the use of thermally modified European beech (Fagus sylvatica L.) in necks of electric bass guitars for the substitution of Hard maple (Acer saccharum) has been studied. The heat treatments were performed at relatively mild treatment temperatures of 140 and 160 °C for 12 h. The acoustic properties were determined by means of experimental modal analysis (EMA) and the mechanical properties by means of static and impact bending tests. The results show that both the acoustic and mechanical, static properties of beech improve significantly owing to thermal modification, being similar or better compared to Hard maple. The impact bending strengths decrease owing to thermal modification. Additional tests on complete necks of electric bass guitars by means of EMA and plucking tests on total instruments show that thermally treated beech at mild temperatures can substitute Hard maple for the use as neck material in electric bass guitars.

This paper deals with the determination of the capillary pore-size distribution (CPSD) and equilibrium moisture content (EMC) of untreated and thermally modified (TM) Norway spruce [Picea abies (L.) Karst.] by means of the pressure plate technique (PPT). Desorption experiments were conducted at very high values of relative humidity (RH) in the range between 99.2% and 100%. The thermal modification of spruce results in an alteration of the CPSD, owing to the formation of intercellular cracks in the middle lamella, as a result of cell-wall compression. The desorption curves for both untreated and TM spruce show an extremely upward bend at 99.97% RH. This step reflects an EMC of 38.1% for untreated spruce and 33.8% for TM spruce. None of the samples shrunk during the PPT measurements. Following desorption experiments at 97.4% RH, all samples shrunk. This step reflects an EMC of 27.9% for untreated spruce and 21.7% for TM spruce.

Short-rotation coppices have potential to be the future source of raw materials for many applications in the wood and paper industries. It is important to establish methods and products to handle their waste biomass. In this paper, the properties of bast fibers extracted from the bark of willow trees (Salix spp.) were evaluated for potential future use in the production of natural fiber-polymer composites. The anatomy of the fibers was investigated through optical and electron microscopy. The thermogravimetric analysis of these fibers showed that the major mass loss occurs at 257 °C. The density of the fibers was measured with a gas pycnometer (1.19 ± 0.2 g/cm3). The chemical analysis showed that willow bark fibers have a composition similar to willow wood. As an indicator of mechanical properties, single willow bast fibers were characterized by tensile tests. The results revealed values for tensile strength (307.6 ± 130.1 MPa) and Young’s modulus (16.9 ± 8.4 GPa) that are comparable to some commonly used natural fibers. The overall results showed that willow bast fibers have the required mechanical properties as well as thermal stability for application in reinforcement of polymers.

One of the visual modification of wood is the formation of dark zone lines (ZLs) via interaction of fungi. The result is called spalted wood, which has hitherto been produced mainly in small batches. The main goal of the present study is to further develop techniques for rapid formation of ZLs in hardwoods. Various white rot and brown rot fungi were tested to this purpose. Initially, interactions of 148 combinations of 17 basidiomycetes in malt extract agar were evaluated and their antagonistic interactions were characterised in order to identify fungal pairs capable of rapidly forming high-quality ZLs. Six types of interactions were observed, among others; antibiosis and inhibition in contact, which differ in terms of variables including mycelial overgrowth and zone line formation. Furthermore, 23 pairs of ZL forming fungi on malt extract agar were identified. Then the interactions of five selected pairs of fungi grown on the hardwood species Acer pseudoplatanus L., Betula pendula Roth. and Populus nigra L. were examined to assess their utility for controlled mycological wood modification, also in terms of a possible substrate dependency of their interactions. The results indicate that Lentinus tigrinus fungus is one of the best and quickest producer of ZLs in mycological wood modification.

This paper deals with the determination of the pore-size distribution of untreated and thermally modified twin samples of Norway spruce (Picea abies (L.) Karst.) and sycamore maple (Acer pseudoplatanus L.) by means of mercury intrusion porosimetry. The investigations considered oven-dried and at 22 °C and 95 % relative humidity-conditioned samples. A special sample holder and a novel method for evacuation were developed for the measurements. This was necessary both to ensure that samples were positioned at a defined distance and the conditioned samples did not dry in an uncontrolled manner. The results clearly show that the climatic state influences the results. Thermal modification greatly alters the pore-size distribution of spruce. This can be largely attributed to the formation of intercellular spaces in the middle lamella as a result of cell-wall compression due to thermal modification. The alteration of the pore structure of maple due to thermal modification is not as pronounced as that of spruce.