ALBERT

Description: In accordance with sustainable economic and social development, Europe supports the use of energy from renewable sources to decrease the use of fossil fuels. Among renewable energy sources, wood, especially production wood waste from the supply chain, represents an exploitable source in line with a circular economy development. In this context, processing of residues produced by wood companies becomes an important resource. This work deals with the possible energy recovery of glued wood wastes. Two solid biofuels were produced from glued wood wastes: pellets and briquettes. They have been produced in collaboration with a local company and analyzed according to the applicable EN ISO international standards. The results were compared with the limits imposed by the standards in order to identify their quality class and their applicability to the current market. The amount of adhesive present in the wood wastes does not negatively affect the intrinsic characteristics of the material that is suitable for the production of solid biofuels. In addition, the amount of wood waste containing cross-linked polyurethane was calculated in order not to compromise the quality of solid biofuels made therefrom.

Description: The research determined the resistance to compression and low velocity impact of wood-based sandwich panels, the face sheet made of high-density fiber board, and high pressure laminate, while its auxetic lattice core was made by 3D printing using LayWood bio-composite filament. The core's auxetic property (i.e. exhibiting negative Poisson's ratio) was observed within the planes parallel to the facings. The ability of particular types of multilayer panels to absorb the energy was also determined. Based on the analysis of the obtained test results, it was proven that the core denoted as B, with inclination angle of the cell ribs $${{varphi }_{x}=varphi }_{y}=65^circ$$ φ x = φ y = 65 ∘ , shows the highest compressive strength. It was determined that the dynamic load causes a very high overload in high-density fiber board face sheets. This results in damage to the sandwich panel surface and core structure. Cells of type B favorably minimize the differences in absorbed energy when using different face sheets and the energy value for low velocity impact. Taking into account the amount of absorbed energy, the most attractive is the panel with the D-type orthotropic core characterized by an inclination angle of the cell ribs $${varphi }_{x}= 30^circ , {varphi }_{y}=60^circ$$ φ x = 30 ∘ , φ y = 60 ∘ . The amount of energy absorbed by samples with high-density fiberboard face sheets increases significantly depending on the impactor's energy. For panels with face sheets manufactured from high-pressure laminate, the amount of energy absorbed decreases.

Description: In this paper, a new method of measuring slicing checks for flat-sliced veneers was evaluated. The method is based on image analysis of veneer cross-sections, having highlighted the slicing checks using surface staining. The segmentation of the checks consists of global thresholding followed by some morphological operations. The outputs of the algorithm are check depth ratio and check frequency. The method was tested on flat-sliced oak (Quercus robur L. and Quercus petraea (Matt). Liebl.) veneers of different thicknesses (1.5, 2.5, 3.5 and 4.5 mm). Two distinct wood qualities and two different cutting directions (lengthwise-sliced and plain-sliced veneers) were evaluated. The algorithm performance resulted in an overall accuracy of 85% enabling an accessible method for relatively fast and accurate measurements of slicing check characteristics in lamella cross-sections. Regression analysis indicated a lack of fixed bias but the presence of proportional bias with the presented method. Check measurements indicate that by varying cutting parameters, it is possible to achieve desired check characteristics independent of slicing thickness. The semi-automated slicing check detection method could benefit further research and optimisation of the slicing process parameters and pave the way towards industrial quality control of slicing checks. The intended area of application is veneer-laminated products for interior use with the focus on veneered wood flooring.

Description: Surface tension of solid wood surfaces affects the wettability and thus the adhesion of various adhesives and wood coatings. By measuring the contact angle of the wood, the surface tension can be calculated based on the Young-Dupré equation. Several publications have reported on contact angle measured with different test liquids, under different conditions. Results can only be compared if the test conditions are similar. While the roles of the drop volume, image shooting time etc., are widely recognized, the role of the wood surface moisture content (MC) is not evaluated in detail. In this study, the effect of wood moisture content on contact angle values, measured with distilled water and diiodomethane, on sanded birch (Betula pendula) surfaces was investigated, in order to find the relationship between them. With increasing MC from approximately 6% to 30%, increasing contact angle (decreasing surface tension) values were measured according to a logarithmic function. The function makes possible the calculation of contact angles that correspond to different MCs.

Description: Raw pine wood processing and especially its mechanical processing constitute a significant share among technological operations leading to obtaining a finished product. Stable implementation of machining operations, ensuring long-term repeatable processing results depends on many factors, such as quality and invariability of raw material, technical condition of technological equipment, adopted parameters of work, qualifications and experience of operators, as well as preparation and properties of the machining tools used. It seems that the greatest potential in the search for opportunities to increase the efficiency of machining operations has the modification of machining tools used in it. This paper presents the results of research work aimed at determining how the life of cutting tools used in planing operations of wet pine wood is affected by the application of chromium aluminum nitride (AlCrN) coating to planar industrial planing knives in the process of physical vapour deposition. For this purpose operational tests were carried out under production conditions in a medium-sized wood processing company. The study compares the effective working time, rounding radius, the profile along the knife (size of worn edge displacement, wear area of the cutting edge), selected texture parameters of the planar industrial planing knife rake face and visual analyses of cutting edge condition of AlCrN-coated planar knives and unmodified ones. The obtained experimental results showed the possibility of increasing the life of AlCrN-coated knives up to 154% compared to the results obtained with uncoated ones. The proposed modification of the operational features of the knives does not involve any changes in the technological process of planing, does not require any interference with the machining station nor its parameters, therefore enabling rapid and easy implementation into industrial practice.

Description: Bark characteristics are not only used in the forest-wood supply chain, for example to calculate standing volumes, but also to transform wood volumes and masses. In this study, bark thickness, bark volume and bark mass were analyzed on the basis of 150 Scots pine discs, with a mean diameter of 13 cm. The mean double bark thickness was 3.02 mm, the mean bark volume proportion was 5.6% and mean bark mass proportion was 3.3%. Bark proportions were significantly affected by the log-specific variables ‘diameter over bark’, ‘proportion of bark damage’ and ‘double bark thickness’.

Description: The high-cycle fatigue behaviour of a timber-to-timber connection with self-tapping screws is examined with the fasteners under bending due to their alignment lateral to the load direction. The cyclic tests were carried out with a sinusoidal non-reversed load ($$R=0.1$$ R = 0.1 ) with a loading frequency of 5 Hz. The examined connection is designed for the quasistatic failure mechanism with two plastic hinges per shear plane according to Johansen’s theory (European Yield Model), which is mirrored in the observed fatigue failure. Based on 30 cyclic tests on four nominal stress levels $$left( S=left{ 0.47,;0.41,;0.31,;0.20 ight} ight) $$ S = 0.47 , 0.41 , 0.31 , 0.20 in the finite-life regime the respective Wöhler-curve is obtained, showing high conformity with the test data due to a consideration of the specific density of the individual specimens. It is shown that the examined fasteners show a superior fatigue behaviour under bending compared to axial loading. A simple safe-side approach for the application of Wöhler-curves for axial loading of threaded fasteners to the present case of fastener bending is proposed, extending the field of possible applications for the results of existing and future studies of the behaviour under axial loading.

Description: Various fire-retardants (FR) for the pre-treatment of wood flour, for example, ammonium polyphosphate and different formulations based on phosphorus- and nitrogen-compounds, as well as for application during compounding were tested for their effectiveness in injection-molded and extruded composites based on high-density polyethylene and polypropylene. Small-scale tests for flammability of polymeric materials and for determination of the limiting oxygen index were used to characterize the composite materials. Differences pertaining to the applied compounding conditions, i.e., underwater granulation versus air granulation, were determined. The amount of phosphorus leached from FR during underwater granulation was analyzed. Artificial weathering trials were performed and reaction-to-fire performance and color changes of FR-composites were evaluated. Tensile strength properties of the composites and results for cold water immersion tests are also reported. An optimized formulation based on pre-treated wood flour was developed and extruded into façade profiles for the single burning item test according to DIN EN 13823. The test showed that classification C-s3, d0 according to DIN EN 13501-1 can be achieved if pre-treated wood flour is used. The use of untreated wood flour leads to a lower classification (D-s2, d0). Fire performance of extruded façade profiles can be improved by the use of pre-treated wood flour and enables new applications in the building sector.

Description: Laser engraving of photographs on wood surfaces is a challenging task. To optimize the outcome and production quality it is necessary to control every aspect of the laser engraving process. Most of the production machines and technologies overall are mainly focused on laser power control. However, with other systems and deeper knowledge of the wood characteristics it is possible to achieve even better quality. This paper deals with enlarging the number of achievable shades of burned wood and its optimization. A calibration system was developed to control colour shades of engraved wood with a combination of laser power and optic focus. With this approach it is possible to widen achievable palette of engraved shades by continuous control of chemical processes of laser and wood interaction. The production is divided into wood burning and wood carbonization by variation of laser beam focus.

Description: In search for greener building materials, geopolymer wood composites (GWC) were produced through alkali activation of fly ash, using pine and eucalypt wood particles. The study examined the influence of grinding fly ash, wood species and hot water treatment of wood particles on the physical properties and specific compressive strength of GWC before and after 200 cycles of soaking and drying. Ash-grinding affected particle size distribution, as the hot water pretreatment of the wood affected its extractives. The particle size analysis showed that grinding decreased the mean particle size of raw ash by 55% and played a major role in the composite’s properties, as lower densities and specific strength with high water absorption were recorded for GWC from raw ash than from ground ash. The ash-grinding step doubled the specific strength of the composites before the aging test. A decrease in specific strength (15–32%) was observed for all composites after the soaking and drying cycles. Hot water washing of the wood resulted in a 47% and 67% reduction in the extractive content of the pine and eucalypt particles, respectively. An improvement of 27% and 3% was noted in specific strength values respectively for GWC with treated pine and eucalypt particles. In general, lower specific strength was recorded for pine-based composites than eucalypt ones, due to the fast impregnation and high water absorption from the mixture by pine particles. It was revealed that hot water treatment of wood improves GWC properties less compared to wood species or fly ash particle size.

Description: Wood fibre insulation boards (WFIB) are typically made from softwood fibres. However, due to the rapid decrease in softwood stands in Germany, the industry will be forced to adapt to the wood market. Therefore, alternative approaches for the substitution of softwood with hardwood will be needed in the fibre industry. The objective of this paper is to address the characterisation of hardwood fibres regarding their availability for the WFIB industry. The physico-mechanical properties of WFIB are significantly determined by the length of the fibres. Longer softwood fibres usually generate higher strength properties and a lower thermal conductivity than shorter hardwood fibres. In this paper, the potential application of hardwood fibres (up to 20,500 μm long) produced in a refiner by thermo-mechanical pulping (TMP) to WFIB production was examined. The scanner-based system FibreShape was used for the automatic optical analysis of the geodesic length distribution of fibres. The analysed hardwood fibres contained significantly more dust and were shorter than respectively produced softwood fibres, limiting their applicability for WFIB production. Thus, two analytical approaches were chosen to receive longer fibres and less dust: (1) blending hardwood fibres with supporting softwood fibres (20%, 50 and 80% proportion of softwood), and (2) mathematical fractionation of hardwood fibres based on the fibre length to remove all particles smaller than 500 μm. It was concluded that the practical fractionation seems to be economically and ecologically challenging and that blending hardwood fibres with at least 50% softwood fibres offers a promising approach, which should be further studied.

Description: Panels from laminated phenol-formaldehyde resin (PF) impregnated and compressed wood (Compreg) with top veneers from European species of beech, maple and white birch were prepared, each without or coated with resin pre-impregnated overlay papers. To clarify the outdoor resistance of Compreg surfaces, long-term artificial weathering experiments were performed. Weather-related color changes, gloss retention and microscopic and surface topographical surface alterations were examined. It has been observed that the application of PF impregnated paper overlays and combinations of them with melamine formaldehyde resin (MF) treated films significantly improved the weather resistance of Compreg surfaces. The extent of UV and moisture-induced surface damages of Compreg has been shown to also be dependent on the veneer types used as surface top layer. Highest surface and color stabilization against weather was achieved providing Compreg with top veneers from maple combined with PF overlays or applying both MF and PF impregnated overlay films as surface finish.

Description: Self-tapping wood screws are important fasteners in timber construction. A characteristic of these screws is their high axial load-bearing capacity, which also depends on their withdrawal capacity. This is used for structural design and is thus an important optimization parameter for wood screws. To increase the withdrawal capacity, knowledge of the influence of the thread parameters, such as outer diameter, pitch or flank angle, is required. The influences of pitch and flank angle on the withdrawal capacity have not yet been sufficiently subjected to research and are therefore investigated in this study. A total of ten specially developed screw prototypes with pitches in the range of 3.04 mm and 5.9 mm and flank angles in the range of 35° and 45° are used. The screw prototypes are flat ribbed bars with uncoiled screw thread. The effect on the withdrawal capacity is measured using an experimental setup based on test standard EN 1382:2016. The pitch showed a significant influence (p = 0.000, f = 0.37) whereas the influence of flank angle was not significant (p = 0.283). A smaller pitch leads to a higher withdrawal capacity, irrespective of the flank angle. The experimental results are explained based on the theoretical models of bonding mechanisms and conical stress distribution. To optimize the withdrawal capacity of a ø 8 mm screw, a smaller pitch is preferable. The determined influence of the pitch can also be used to improve the accuracies of calculation models for the withdrawal capacity.

Description: The biological durability of wood is frequently determined in laboratory tests with monocultures of different decay fungi under ideal conditions for fungal growth. To avoid contamination with mould and inhibition of fungal growth, wood specimens need to be sterilized using different methods. To determine the mass loss of wood blocks during incubation, the initial total dry mass is needed but should be determined without oven-drying to avoid the loss of volatile compounds of the tested wood. In this study the effect of different sterilization techniques in combination with different methods of determining the oven-dry weight on mass loss (MLF) in agar plate wood block tests was investigated. No significant MLF differences were observed between sterilization through gamma radiation, steam, autoclaving, ethanol dipping and oven-drying. Solely, non-sterilized specimens showed reduced MLF, since the test fungus was inhibited by mould growth. Oven-drying of wood species that contain volatile and resistance-affecting compounds such as Scots pine (Pinus sylvestris) led to reduced biological durability and should either be avoided or adapted to kiln-drying temperatures usually applied in practice.