JAHRGANG 61, AUSGABE 2/2020

At the latest with the “Green Deal” of the EU Commission and the official science year “Bio-economy” in Germany, it has become clear that this is not a modern buzzword, but that a comprehensive reorganisation of our economy and life is approaching. The wood using and processing industry is in a good starting position due to the renewable raw material, but is far from being on the home stretch. In particular, the responsible processing of renewable raw materials into high-quality products that can be used over a multiple life cycle is not yet in focus. Whether in the construction sector, furniture production or the packaging industry – the possibilities of the recycling economy are not the focus of attention today, but primarily cost-optimised production, supplemented by the argument that the products are biodegradable. This is where the circular bio-economy must start. The paper deals with the necessity of the cascading use of wood and its valuable processing.

Compared to conventional solvent extraction methods, supercritical fluid extraction (SFE) with CO2 represents a gentle, highly efficient and environmentally friendly technique. Its application is not only for analytical purposes but also of particular interest for industrial process development regarding the extraction of natural substances. With the intention of contributing to a better understanding of SFE and its tremendous potential, in the present paper a short explanation of its physical fundamentals is given. Furthermore, examples illustrating the application of SFE for an efficient extraction of wood, bark or other plant materials and for supercritical wood impregnation are discussed.

The implementation of natural silvicultural concepts leads to an increasing amount of hardwood in the forests of Germany. This creates new potential for the material use of hardwood. Therefore, the possibility of using small diameter beechwood in cross laminated timber elements was investigated. Part 2 of the publication shows the results of the visual sorting of the sawn timber. 8.91 m³ of boards could be produced from 18.23 solid cubic meters round timber, which was equivalent to a yield of 48.9 %. 34.3 % of the boards could be assigned to the strength classes LS 10 and LS 13. Deformation of the boards and the presence of the pith turned out to be the most relevant quality-reducing features, while branches played a minor role. The roundwood qualities that were used and the specific quality characteristics were previously described in part 1.

Any form of wood coloration caused by fungi is called spalting. As one of its effects the pigment melanin is stored in the wood as a zone line. The aim of this investigation was to control the formation of this zone line in such a way that the fungus in the veneer creates desired contours or lettering. For this purpose, laboratory-scale cultivation was carried out using various methods with the zone line inducing fungi Trametes hirsuta and Lentinus tigrinus. By using specially developed inoculation techniques, the desired contours could be created or “written” by the fungi.

In the course of a cooperation project between the Institut für Holztechnik Dresden (IHD) and the Technische Universität Dresden (Institute for Natural Materials Technology, Chair of Wood Technology and Fibre Materials Technology, Paper Technology Group) and the companies Gotic GmbH and GKM Siebtechnik GmbH, investigations were carried out on the dry pulping of hitherto scarcely used waste paper assortments and on the use of the recovered fibres in the production of MDF. The aim was the development of white MDF with low formaldehyde emission, which will offer an alternative for architects, planners and interior designers in the field of indoor applications.

Lightweight construction and resource conservation are key challenges of the 21st century. Hybrid composites with natural fibres (e. g. flax, kenaf) are state of the art and are mainly used in automotive trim components. Hybrid composites unite the advantages of injection moulding and compression moulding. The combination of these processes makes it possible to achieve functionalisation with a high degree of inherent rigidity. Wood fibres offer distinct advantages over other natural fibres, but the suitability for hybrid composites has not yet been extensively investigated. The project “NFRipp” at the Technische Hochschule Rosenheim analyses the procedural and material characteristics of hybrid composites reinforced with wood fibres. For this purpose, nonwovens were laid with wood fibres and PP fibres (polypropylene). In further process steps stiffening ribs, made of directly compounded wood fibres and PP, are injected onto the nonwovens. In summary wood fibres show great potential for technical light weight constructions. The production of nonwovens via the air-lay technology and the further processing to hybrid composites could be carried out successfully.

Hot melt adhesives are a small but essential component of modern packaging. An intense debate about the sustainability of packaging has not left adhesives untouched. Often processors cannot correctly assess the influence hot melt adhesives have on sustainability aspects. Confusion exists in particular about the difference between “bio-based” and “biodegradable” and what they mean in detail. Clarification is also necessary with regard to the recycling of packaging. The overwhelming part of adhesive bonds in paper and cardboard packaging are already considered recyclable in accordance with European regulations. In terms of micro plastic emissions, packaging hot melts are also rather negligible. The biggest potential to improve sustainability is provided by hot melt adhesives that prevent the waste of materials, go easy on resources and extend the lifespan of machines.

The use of materials based on renewable raw materials is of increasing interest for numerous applications in lightweight construction. In this context, wood veneers show a particularly high potential for lightweight constructions, since they combine high density related mechanical properties with excellent optical and haptic properties. In addition, novel processes are used to create wood veneers with complex-shaped geometries. The range of applications for such structures is accordingly diverse. However, deficits can be identified in the load-oriented design and dimensioning, so that the enormous material potential has not yet been fully exploited. In this contribution, comprehensive mechanical-mechanical investigations for selected types of wood and composite configurations are performed and discussed.