Bonding performance of mixed species cross laminated timber from poplar (Populus nigra L.) and maple (Acer platanoides L.) glued with melamine and PUR adhesive

The study assesses the suitability of lower grade fast-growing poplar lumber in manufacturing Cross Laminated Timber (CLT) panels and its compatibility as a core layer in mixed-species CLT panels. Three-layered CLT panels were prepared from poplar and mixed-species maple-poplar lumber using one-component polyurethane (1C-PUR) and melamine adhesive (ME). Reference samples were prepared from spruce for comparison. 1C-PUR adhesive performed very well in delamination test for both single and mixed-species CLT. ME adhesive showed good performance in single species CLT, however, in mixed species CLT, only half of the samples tested could meet the delamination test requirement. The shear strength of mixed species CLT (10.7–10.9 N/mm2) was significantly higher than that obtained with single species CLTs (4.8–5.4 N/mm2). Both 1C-PUR and ME bonded CLT samples of poplar as well as mixed species exhibited higher shear strength properties than spruce wood CLT. Melamine-bonded CLT panels exhibited relatively better shear strength than 1C-PUR bonded CLT. The failure of joints during shear test was predominantly due to wood failure. The excellent bonding quality with 1C-PUR confirms the suitability of poplar wood for both single species as well as mixed species CLT.