Alteration of Bending Properties of Wood Due to Ammonia Treatment and Additional Densification

Abstract

This paper deals with comparative studies of bending behavior of untreated and modified European beech (Fagus sylvatica L.), European oak (Quercus spp.) and black locust (Robinia pseudoacacia L.). The modification of the woods included both ammonia treatment and ammonia treatment in combination with mechanical densification. For each ammonia treatment, pure gaseous ammonia was used. The investigations were conducted by means of three-point bending tests. The bulk density increases significantly due to ammonia treatment and, furthermore, due to additional mechanical densification. The modulus of rupture is not affected by ammonia treatment. Additional mechanical densification, however, leads to a strong increase in the strength and stiffness. The deflection behavior changes in such a way that the ammonia treatment leads to an increase in deflection, and the additional mechanical densification further reinforces this trend.

11th Hardwood Conference Proceedings

“…The phenomenon of densifying wood with ammonia lies in the fact, that ammonia leads to a so called self-densification without the need of additional mechanical forces. This behaviour is already known and has been described in literature (Bariska, 1975;Hackenberg, 2018;Hackenberg et al, 2021;Pollisco et al, 1971). However, the relationship between self-densification and the applied process intensity remains open.…”

Selected Properties of Densified Hornbeam and Paulownia Wood Plasticised in Ammonia Solution

“…A significant increase in the analysed mechanical parameters proves that ammonia is a suitable plasticiser. Its good plasticising properties have been described many times [ 17 , 19 , 21 ]. However, the biggest problem of mechanically densified wood is the post-deformation recovery associated with the discharge of the elastic energy previously accumulated and partially preserved in the drying process.…”

“…Due to the washing out of soluble substances and the deep penetration of ammonia and water particles into the cell membrane structure, an additional capillary system appears, and the inner surface of the wood is increased. Microfibrils gain greater freedom of movement from each other, manifested externally in the advanced plasticisation of the wood tissue [ 17 , 18 , 19 , 20 , 21 ].…”

10th Hardwood Conference Proceedings

“…One fixation method is, for example, thermal treatment in the state of densification (Sandberg and Navi 2007). An alternative method to achieve higher strength values and to perform plasticization and fixation in one process is gaseous ammonia treatment (Hackenberg et al 2021, Schuerch 1963. More generally, this process has already been applied industrially under certain parameters (Stojčev 1979).…”