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

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.