VOLUME 63, ISSUE 3/2022

In addition to the radical reduction of CO2 emissions in the building industry, resource efficiency must be promoted significantly. On the one hand, this requires the use of the building components in biological and technical cycles and, on the other hand, the avoidance of material waste. Especially in timber construction, it must be ensured that the material use of used building components must come before the energetic substitution of fossil energy sources and that hardwood in particular is used on a large scale. In this article, research results on the use of “inferior” beech wood from the inside of the trunk for hybrid, I-profiled beams for large-span hall structures are presented.

Machining processes have always been one of the most frequently used methods for cutting wood and wood-based materials and shaping such workpieces. The process-related accumulation of chips and dust (particles) still causes massive problems with regard to their orderly and complete collection by extraction bonnets or chip collection systems. A basis for effective collection solutions is knowledge of the real conditions on the tool in the machine and in the direct emission environment with regard to chip emission, chip flight behaviour and collision and flow conditions. In order to get closer to these basics, ways and possibilities of simulating the conditions as close as possible to reality were sought using the example of the grooving sawing process in a climb cutting mode on chipboard. As a result, a new approach was found which, in a combination of CFD and DEM, enables predictions to be made on chip ejection and chip flight, taking into account the tool flow, the workpiece and the near field of the cutting process. Further focal points of investigation are presented, which continue the research work on the topic.

The subject of this study was the investigation of the fixation behaviour of mechanically densified spruce wood (Picea abies (L.) Karst.) specimens previously plasticized with gaseous ammonia. The modification included both dry and conditioned specimens in combination with different pressure levels of the ammonia gas. Mechanical compression was performed in the radial direction of the wood samples. Finally, the specimens were subjected to swelling in water to achieve maximum recovery. The fixation behaviour was evaluated and investigated on the basis of three parameters: the direct elastic springback after removal from the densification device, the elastic springback after drying, and the recovery of set after swelling in water. As expected, the reference series of dry and conditioned specimens showed very high springback and recovery of set values. The ammonia treatment resulted in a strong reduction of the springback and even caused negative springback values at high-pressure levels. Recovery of set is reduced to 21 % at high ammonia pressure level, and normally air-conditioned storage prior to ammonia treatment leads to lower recovery of set values.

Vacuum press drying is a new type of fibre processing to form complex three dimensional shaped fibre mouldings. Fibre moulding is a general term used primarily for paper-like natural fibre materials. In addition to fibre casting, stable moulded fibre parts are also produced (tensile strength = 40-100 MPa; Young's modulus = 5 GPa). This strengthened fibre moulding requires special fibre preparation and structural densification. Wet fibre sheets are layered onto multi-curved surfaces, pressed under vacuum, and dried. The attractiveness of the material lies not only in its stability but also in its biogenic origin (cellulose) and good reusability. To investigate the new process and assess its application potential, it is useful to investigate the most influencing variables. A preliminary investigation revealed the basis weight (wall thickness) and drying temperature to be the most influential process variables. The present study varies both in three stages and help to calculate the drying time using a linear approach. The results of this study are significant for future investigations of the potential application fields of moulded fibre parts.

Due to the increasing demand of environmentally friendly wood panels worldwide, wood panels producers and researchers are looking for green adhesive (renewable adhesive systems) as an alternative for synthetic adhesives from fossil sources. This interest in these bio-based adhesives has arisen to reduce the health effects relating to product emissions of volatile organic chemicals, most notably formaldehyde. One possible source of bio-based material for the development of green adhesives is from rapeseed press cake protein. The objective of this study was to investigate the feasibility of manufacturing particleboard bonded by an adhesive system based on rapeseed protein isolate (90 %) complying with the European standard EN 312 (2010). In this study, spruce wood residues were used to produce three-layered particleboard bonded by an adhesive system based on rapeseed protein isolate (90 %). The particleboard was produced with a target density of 650 kg/m³ and the mechanical and physical properties were analyzed and in addition, the formaldehyde release of the particleboards were characterized as well. The results point out that it is possible to manufacture three-layered particleboard bonded by an adhesive system based on rapeseed protein isolate (90 %) complied with the specifications of European standard EN 312 (2010) and fulfilled the requirement for interior fitments (including furniture) for use in dry conditions (Type P2). Furthermore, the formaldehyde release (24 h) of particleboards achieve the requirements of European standard EN 312 (2010) for particleboards emission class E1 and can be considered as ultra-low formaldehyde release particleboard.

As reported in the first part of this publication, the efficiency of convective drying is limited by the thermal conductivity of the cement-bonded particleboards (CBPB). Therefore, this type of drying results in low drying speed and high energy costs. The second part deals with the investigation of microwave (MW) radiation to accelerate the drying speed. However, MW drying has a crucial disadvantage, such as convective drying; drying focusses on one part of the board – the core, respectively the surface of the board. The combination of both drying methods aimed at further accelerating the drying process and reducing internal stress. With the drying of CBPB combining hot air and MW, the target moisture can be achieved within clearly shorter time as compared to the sole use of only one technology. Since no differences in the mechanical and physical properties between the new and the established drying technology were observed, it is possible to dry CBPB by keeping the quality standards with clearly higher drying rate.