Peter Rademacher

Comparison of selected physical and mechanical properties of densified beech wood plasticized by ammonia and saturated steam

Gaseous ammonia treatment in combination with densification of wood has been known for several decades, but these days there is no industrial production of materials modified in this way; also, little has been published in this area of wood science. In this study, selected physical and mechanical properties, i.e. density profile, bending strength, hardness and moisture absorption were investigated for Lignamon (1), which was obtained from the Czech industrial production. Selected properties were also investigated using steam-densified beech (2) and native beech (3) and compared with each other. Densitometry of Lignamon showed a large variability in the density profile compared to that of only densified beech. It is affected by the degree of densification, temperature and moisture gradients, and their relationship to the glass transition of the wood cell wall. Modulus of elasticity, hardness, moisture exclusion and anti-swelling efficiency of Lignamon are enhanced compared to densified beech. The enhanced dimensional stability and lower hygroscopicity of Lignamon are probably caused by heat treatment during the process. Further investigation will be carried out with self-produced Lignamon samples.

Standard and non-standard deformation behaviour of European beech and Norway spruce during compression

Abstract The goal of the study is to investigate the non-standard deformation behaviour of wood loaded by compression parallel to the grain. This is represented as a negative increment of strain in the range of plastic deformations when the load continues to increase. The objectives of this study are to point out this problem and to provide its description based on the deformation fields that have been analysed using three approaches: a) full-field optical technique based on digital image correlation (DIC); b) “clip on” extensometer and its virtual analogy, and c) crosshead displacement method. Further, the negative strain phenomenon was studied depending on the sample length. The samples were made from the European beech (Fagus sylvatica L.) and Norway spruce (Picea abies L. Karst.). Based on the strain analysis, it can be concluded that the deformation field consists of three sub-regions exhibiting different stiffness values (three-spring model). The failure of less stiff zones near the compression plates during the “non-standard” compression behaviour causes almost zero compression deformation of the stiffer middle zone or even leads to its expansion. The three-zone heterogeneity of deformation field induces a deviation of the displacement and strain measured by the proposed approaches. This phenomenon substantially influences the resulting longitudinal Young’s modulus and, therefore, should be of concern when measuring wood in such mode.

Measured temperature and moisture profiles during thermal modification of beech (Fagus sylvatica L.) and spruce (Picea abies L. Karst.) wood

Abstract The temperature and moisture profiles during thermal modification of beech (Fagus sylvatica L.) and spruce (Picea abies L. Karst.) wood have been investigated. Specimens with dimensions of 80×80×200 mm3 were heat treated based on ThermoWood technology. Heat transfer was continuously measured by several thermocouples placed into various positions of the samples. In the course of the treatment, samples were removed from the chamber at different times, and their moisture content (MC) was measured by the so-called slicing technique. The complete data of heat and moisture movement during the heat treatment process are presented. Significant temperature gradients occur in the initial and modification stages of the process. In the latter, the chamber temperature was 200°C for 3 h, but exothermic reaction increased the sample temperatures to 240°C (beech) and 215°C (spruce). Thermodiffusion (Soret effect) at the beginning of the process was observed. Therefore, the MC under surfaces (in transverse and in longitudinal direction) was increasing ∼0.5%–3% for 5 h. The results provide a better insight into details of thermal modification of wood.

Plasticity increase of beech veneer by steaming and gaseous ammonia treatment

Ammonia treatment was used in order to change the colour of wood and also to plasticize the wood before bending or compressing. The mechanism and the process of gaseous ammonia treatment impact on wood are not very well known. The goal of this study was to quantify the effect of gaseousammonia on mechanical properties, i.e., modulus of elasticity (MOE), modulus of rupture (MOR) and deflection at maximal loading force (yFmax). When wood was treated by water and ammonia vapour together, significant changes in plasticity of wood were observed. The samples which were firstlyexposed to water vapour and then to ammonia vapour exhibit the lowest values of MOE and MOR and an enhanced flexibility of the material. The results show that ammonia treatment increases wood plasticity. This process can be used for manufacturing of bent furniture.