VOLUME 59, ISSUE 6/2018

To achieve a more prominent integration of native hardwoods into construction as load-bearing elements it is necessary to evaluate their suitability on a technological and an economical basis. This paper provides information on the strength grading characteristics of six European hardwood species. Market available dried sawn wood assortments were selected as research material. Lamellas with a cross section of 100 x 30 mm² and lengths up to three meters were strength graded visually according to DIN 4074-5 (2008). Additionally, dynamic modulus of elasticity (MOEdyn) and density were determined. Out of the investigated collectives, the collectives of the species ash, maple and European oak showed the best lamella qualities. Many big knots, that led to downgrading characterized the beech and lime collectives. In lime, inbark was also abundant, which makes it less suitable for an application in construction. The influence of pith on mechanical properties is to be investigated, since in the maple, birch and ash collectives, pith was the main downgrading criterion. Ash exhibits the highest MOEdyn values, but also the highest value variation. The highest densities were measured in the beech and oak collectives. At present, the market does not provide dried sawn wood assortments suitable as hardwood structural timber. Suitable assortments might come from round wood, which is at present consumed for energy production or from commercializing co-products from high quality products.

In the production of wood-fibre insulation materials softwood species like fir and pine are used exclusively. Fibre length and the bright colour can be referred to as main reasons therefor. Considering the advancing change of forest composition the search for alternative raw materials suitable as substitute is of great importance. An alternative can be flakes of leather which are generated as by-product during the skiving (adjusting the thickness) of leather. As a part of a research project (founding by the German BMWi) the use of leather skiving flakes in the production of wood-fibre insulation boards was investigated. Insulation boards were produced under partial substitution of softwood-fibres by chromium-free leather flakes. Flakes were homogenised in a turbulent flow mill before introducing them into the insulation board production. Physical and emission properties of the boards were determined. A substitution degree of up to 20 % of wood-fibre by leather flakes led to significantly lower emission values for VOC in general and for acetic acid and furfural in particular. In tests at industrial scale the results could be confirmed for a substitution degree of 20 %. It can be deducted that leather skiving flakes can be used as an alternative raw material for partial substitution of softwood-fibres in wood-fibre insulation board.

The effectivity of urea as a formaldehyde scavenger was determined on an E1 resin, glued wood particles as well as particleboards and fibreboards. Firstly, the effectivity was determined on an amino resin classified as E1. Afterwards wood particles were glued by pure and modified resins (classified as E1 and CARB as reference). The urea addition was adjusted by the theoretical molar ratio of urea and formaldehyde covering the area between E1 and CARB resins. Form the emission measurements on wood particles the effectivity of solid and solved urea can be concluded as nearly equally. Finally, particleboards and fibreboards were processed using modified E1 resin as well as a CARB reference. In the case of particleboards a clear tendency of decreasing formaldehyde release with increasing urea addition can be determined. The fibreboards were processed using urea and resin as mixture as well as separately. The highest efficiency was determined if urea solution was added separately independent on the order of add-on.

This article presents results of the investigations on the application of wood-based materials for additive manufacturing processes and explains the specific requirements of fused filament fabrication (FFF) and vacuum casting processes. It was observed that products made of wood filled filaments have tactile and optical properties similar to wood. Printing particular core structures with this method, which can perform as loadcarrying elements, in the designing of the products, lead to a reduction of material consumption and product weight. According to the findings of this research, in the small series production with vacuum casting, it is possible to substitute polyurethane up to 30 % with lignin. Both processes offer the possibility for the fabrication of single parts and small series production without complex tools (injection moulding). However, the application of wood flour and lignin leads to a decrease in several mechanical properties.

Based on the invention "myco-wood" by Walter Luthardt, European beech (Fagus sylvatica L.) was mycologically modified, and investigated for the suitability as alternative material for wood-cased pencils. European beech was incubated with the white rot pathogen Trametes versicolor and then impregnated with a beeswax emulsion. With suitable test methods, the material produced was examined in comparison with two conventional wood species for pencil manufacturing, incense cedar (Calocedrus decurrens Florin) and Gmelina (Gmelina arborea Roxb.). A test facility was developed to determine the sharpening properties. The mycological treatment caused a loss of bulk density. In addition, there was a decrease in the mechanical properties. The mechanical properties could not or only slightly increased by the impregnation. The sharpening properties were positively influenced both by the mycological degradation and by the impregnation.

The paper analyzes the connection of the individual layers of wood-cardboard sandwich elements by means of a shear test as well as their material properties in three-point and four-point bending tests. The aim of the analyzes is to classify the range of properties for potential fields of application in bearing structures of mechanical engineering.

Densified cellulose materials are new high performance and lightweight materials, which are produced in a two-step process. In a first step, wood is delignified, which results in a porous, hierarchical cellulose scaffold. Then, the cellulose scaffold is densified in order to increase the fibre volume content. By that, an increase of strength and stiffness by a factor of three compared to wood is obtained. The hierarchical structure and fibre orientation are retained during this two-step process, which results in the high mechanical performance in longitudinal direction. Another advantage of the cellulose material is the shapability in wet state, with fibres adapting perfectly to the shape. Upon drying, the shape is locked. These advantages, combined with the recyclability, make densified cellulose materials a promising candidate for new sustainable materials, for example for the automotive industry or in aviation.