This work deals with the evaluation of Laminated Veneer Lumber (LVL) made from rotary cut beech (Fagus sylvatica L.) veneers, which were treated with low molecular weight alkaline phenolic resins with the aim of cell wall modification. Beech-LVL, and derived products from it, are already used and accepted for structural purposes, e.g. fabrication halls and multi-storey buildings, though they benefit from its higher mechanical properties compared to softwoods. On the other hand, susceptibility to biological decay and possibility of dimensional changes limit the applicability to dry climate conditions. Therefore, it is the aim of the BMBF funded research project DauerBuche, belonging to the BioEconomyform Cluster e.V., to achieve durability against fungal decay, increase of weathering performance and dimensional stability. As modification of the cell wall is the best way to provide dimensional stability and durability to protect wood and wood products against these corrupting influences, a modification on basis of phenol formaldehyde was chosen. This seemed to be more attractive than other chemical treatments or thermal treatment, because earlier work showed a sufficient preservation of the mechanical properties, which is crucial for building applications. The dimensional stability was evaluated in a 4h-boiling test with a subsequent drying and evaluation for delamination. Volumetric swelling was found to be reduced by 57% at moderate Weight-Percent-Gain (WPG) for undensified boards. The durability of the LVL against white rot fungus Trametes versicolor has been tested for 16 weeks according to the standard ENV 12038. This test offered that the mass loss was decreased to less than 1% by the PF-treatment. The mechanical properties modulus of rupture (MOR), modulus of elasticity (MOE) and impact bending strength have been assessed. It came out that for the undensified products the MOR could be preserved and MOE was significantly increased. The modification also enabled densification which resulted in further increase of MOR and MOE. Due to the loss of flexibility the absorbed energy at the impact bending test was considerably lower. Over all it was concluded that the WPG could be much lower than it was found in former studies for this type of modification. Especially for products that are wished to have high strength values and a resistance against fungal decay, but do not have to have the highest dimensional stability, 15% WPG was sufficient. The possibility of reducing the product volume for a building project because of its elevated mechanical strength qualifies the additional costs for the modification.
Keywords: beech, durability, dimensional stability, laminated veneer lumber, phenolic resin
Authors
Bicke S.
Wood Biology and Wood Products, Burckhardt Institute, Goerg-August-University Göttingen, Göttingen, Germany
Biziks V.
Wood Biology and Wood Products, Burckhardt Institute, Goerg-August-University Göttingen, Göttingen, Germany
Militz H.
Wood Biology and Wood Products, Burckhardt Institute, Goerg-August-University Göttingen, Göttingen, Germany
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