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The swelling pressure as a function of the anatomical cutting direction of European beech [Fagus sylvatica L.] and Norway spruce [Picea abies (L.) Karst.] was determined at 20 °C between 25 and 85 % relative humidity (RH). The RH was increased in steps of 20 %. The uniaxial tests were carried out on test specimens with a small cross-section. As a result, it was found that beech produces almost twice as high swelling pressures as spruce during impeded swelling. The maximum swelling pressures are reached more quickly with spruce. For both types of wood, significantly higher swelling pressures were measured in the respective tangential cutting direction than in the radial cutting direction.

This study aimed to investigate the suitability of the interlaminar shear (ILS) testing method for veneer-based composites. The ILS testing method is an established method for composite materials as a qualitative evaluation of the adhesion within the composite. The applicability of this method to veneer based composites enables a simple qualitative statement on the adhesion of the individual layers. The ILS method complements existing wood-based material tests that focus on bonding, using significantly smaller material dimensions.

Abstract To obtain special wood properties for various technical applications, fungi with their broad spectrum of activity can make a contribution. The foundations for today's mycological wood modifications were laid by researchers who wanted to increase the yield of edible mushrooms. They noticed the changed properties of the wooden substrate by the progressive wood degradation. Controlled use of fungi and an eye for the technical benefits of mycologically degraded wood revolutionized the fundaments of wood modification, primarily biological. In this context, the so-called Myko-Holz (myco-wood) plays a unique role and influences the current research for pencil wood, tone wood or even spalting.

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.

Abstract The replacement of potentially hazardous synthetic dyes with natural dyes and pigments are of great interest for a sustainable economy. In order to obtain cost‐efficient, environmentally friendly and competitive products, improvements in the cultivation and extraction of pigment‐producing organisms and in dyeing processes are necessary. In our study, we were able to scale up the production of xylindein by Chlorociboria aeruginascens from 3 to 70 L bioreactor cultivations. We have identified important bioprocess parameters like low shear stress (150 rpm, tip speed

There is a need of substitution woods for the use in musical instruments because of the limited availability of some commonly used tropical tonewoods. Before substitutions can be found, it is necessary to know about the required properties. Hence, in this paper acoustical, mechanical and physical properties of four common tropical hardwoods (Indian rosewood, ziricote, African blackwood and ebony) were determined because there are less literature values for some properties available, e.g. internal friction, hardness or swelling behaviour. The acoustic properties were determined by means of experimental modal analysis, the mechanical properties by means of static bending tests and tests of the Brinell hardness. For the swelling behaviour the volume swelling and also the differential swelling coefficients were determined. With the results it is possible to look for new ‘tonewoods’ or to specifically modified woods, e.g. thermally treated wood, to substitute tropical wood species. Keywords: Classical guitars, Acoustic properties, Mechanical properties, Tropical woods, Modal analysis

Previous studies have shown favourable properties for papaya bast fibres, with a Young's modulus of up to 10 GPa and a tensile strength of up to 100 MPa. Because the fibres remain as residues on papaya plantations across the tropics in large quantities, their use in the making of green composites would seem to be worthy of consideration. This study aims to show that such composites can have very suitable mechanical properties, comparable to or even better than the common wood plastic composites (WPCs), and as such, represent a promising raw material for composites and a low-cost alternative to wood.

Biopolymer-based flame retardants (FR) are a promising approach to ensure adequate protection against fire while minimizing health and environmental risks. Only a few, however, are suitable for industrial purposes because of their poor flame retardancy, complex synthesis pathway, expensive cleaning procedures, and inappropriate application properties. In the present work, wheat starch was modified using a common phosphate/urea reaction system and tested as flame retardant additive for wood fibers. The results indicate that starch derivatives from phosphate/urea systems can reach fire protection efficiencies similar to those of commercial flame retardants currently used in the wood fiber industry. The functionalization leads to the incorporation of fire protective phosphates (up to 38 wt.%) and nitrogen groups (up to 8.3 wt.%). The lowest levels of burning in fire tests were measured with soluble additives at a phosphate content of 3.5 wt.%. Smoldering effects could be significantly reduced compared to unmodified wood fibers. The industrial processing of a starch-based flame retardant on wood insulating materials exhibits the fundamental applicability of flame retardants. These results demonstrate that starch modified from phosphate/urea-systems is a serious alternative to traditional flame retardants.

The soft rot fungus Chlorociboria aeruginascens produces a blue−green pigment xylindein, which is of considerable interest for various applications such as in the veneer industry or in organic semiconductors. To understand the fungal growth as well as pigment production of C. aeruginascens, several studies were performed, the results of which are presented here. These studies investigated various growth conditions such as temperature, pH value, oxygen level and light intensity. It was observed that the formation of xylindein by C. aeruginascens decoupled from growth. In the primary metabolismus, the uncolored biomass is formed. Pigment production took place within the secondary metabolism, while biomass growth as well as pigment production depended on various growth conditions. It was also found that certain conditions encourage the switch in metabolism, leading to pigment production.

The blue-green pigment xylindein, produced by the soft rot fungus Chlorociboria aeruginascens, is of considerable interest for various applications such as the veneer industry or organic semiconductors. The studies presented were performed in order to understand the fungal growth as well as the pigment production of C. aeruginascens. Therefore, various nutrient compositions were investigated. As a result, observations of the formation of xylindein through C. aeruginascens decoupling from growth were made. In the primary metabolism the uncolored biomass is formed. Various carbohydrates were determined as nutrients for the fungus and as a nitrogen source it was observed that the fungus prefers the complex organic nitrogen source, that being yeast extract. Furthermore, it was discovered that the ratio between carbohydrate and nitrogen sources encourages the switch of the metabolism and therewith the production of the blue-green pigment xylindein.

Compression tests were conducted with veneers in the thickness direction. Thereby differences between the stress-strain curves of veneers and other known stress-strain curves were observed. Based on microscopic studies during the compression, it was possible to describe the deformation behaviour of the veneer, and deviations from known, typical stress-strain curves were substantiated and explained. It was found that a considerable part of the strain occurs by straightening the veneer at a relatively low stress level due to the waved form of veneer sheets and specimens. A distinctive stress plateau has not been established.

AbstractThe pore size distribution in wood affects sorption and transport of moisture. In the present paper, the pore structure of spruce and maple was examined in untreated and thermally modified samples. The relative humidities of the specimens were 33%, 43%, 53%, and 76%. Tests were carried out by helium pycnometry and mercury intrusion porosimetry. The results clearly show that thermal treatments change the apparent density, pore structure, and pore size distribution. Measurements by the mercury intrusion porosimetry indicated that the influence of various environmental conditions (humidity, temperature) on the porosity and pore size distribution is small. [ABSTRACT FROM AUTHOR]

Abstract  Bending and tensile tests were carried out on veneer of beech (Fagus sylvatica L.) and European oak (Quercus robur L./Quercus petraea Liebl.) with a thickness between 0.35 mm and 0.5 mm. The tests were done on veneer in two test series, one parallel to the fibre and the other one perpendicular to the fibre. Mechanical properties and bending radiuses were measured and evaluated. It could be concluded that the bending properties of the veneers not only depend on the bending stiffness but also the mechanical strength and structure of the material. During the tests it could be shown that the 3-point bending test procedure is not a suitable method for determining the bending modulus of rupture. [ABSTRACT FROM AUTHOR]

Due to their chemical structure, conventional flame retardants are often toxic, barely biodegradable and consequently neither healthy nor environmentally friendly. Their use is therefore increasingly limited by regulations. For this reason, research on innovative flame retardants based on sustainable materials is the main focus of this work. Wheat starch, wheat protein, xylan and tannin were modified with phosphate salts in molten urea. The functionalization leads to the incorporation of phosphates (up to 48 wt.%) and nitrogen (up to 22 wt.%). The derivatives were applied on wood fibers and tested as flame retardants. The results indicate that these modified biopolymers can provide the same flame-retardant performances as commercial compounds currently used in the wood fiber industry. Besides, the flame retardancy smoldering effects may also be reduced compared to unmodified wood fibers depending on the used biopolymer. These results show that different biopolymers modified in phosphate/urea systems are a serious alternative to conventional flame retardants.

Abstract  The modulus of elasticity of weakly thermally modified as well as native twin samples of spruce was determined at different air humidity levels. Within the range of 0 and 93% of relative humidity a higher modulus of elasticity could be proven for thermally modified samples than for native comparison samples. The functional interrelation between modulus of elasticity and wood moisture admitted for native woods could be confirmed for modified twin samples. [ABSTRACT FROM AUTHOR]

Bamboo is a very interesting bioresource for use as a building material because of its properties of strength in combination with low density. However, its susceptibility to fungi and insects is problematic for its usage. Thermal modification is used in Vietnam to improve the durability and dimensional stability of bamboo. The thermal modification causes many changes related to the physical properties of bamboo, e.g., mass, color, and equilibrium moisture content (EMC). All these changes are dependent on the modification conditions (modification temperature and duration). The mass loss (ML), the color difference (E*ab), and the reduction of EMC (EMC) were due to the thermal modification increase with higher temperature and/or longer duration. Therefore the temperature had greater influence than the modification duration. The changes were slight at 130 °C (ML: 0,3…0,6 %; E*ab: 3…5; EMC: 0,5…0,8 % ), moderate at 180 °C (ML: 1,5…4 %; E*ab: 21…37; EMC: 3,6…4,4 %), but very strong at 220 °C (ML: 14…16 %; E*ab: 46…51; EMC: 5,6…5,7%). There are close correlations between the changes mentioned above.

Abstract  The milling process of Arboform was analysed by cutting force measurements and compared with experiments on MDF and chipboard. Under similar and practice-specific conditions, the specific cutting forces of Arboform were slightly higher than the ones of MDF and chipboard but below the values for HDF taken from literature. [ABSTRACT FROM AUTHOR]