Wood and gluing characteristics of Scots pine and silver birch depending on cambial age

With increasing competition for wood resources, the importance of using small-diameter timber, which consists predominantly of juvenile wood (JW), is growing. The manufacturing of glued products is one way to make rational use of small-diameter wood assortments. However, the properties of JW differ considerably from those of mature wood (MW) and can affect product performance. Radial profile analyses of anatomical structural elements were performed, and based on the fibre length results, the cambial ages of 17 years for silver birch (B. pendula Roth.) and 23 years for Scots pine (P. sylvestris L.) were determined to distinguish between JW and MW. The results showed that the JW of both species had a lower density and higher transverse swelling anisotropy. Lamellae of JW and MW were glued into beams using two one-component polyurethane adhesives and different assembly regimes. The glued beams were then used to prepare samples for delamination tests, performed according to the EN 302-2 standard method for Type I adhesive. Higher resistance to delamination was observed for the JW of both wood species, implying an advantage of laminated products from JW regarding bond-line stability under varying moisture conditions. For pine JW, shorter open assembly times resulted in significantly less delamination.