Bonding performance of wood of fast-growing tree species eucalyptus (Eucalyptus grandis) and radiata pine (Pinus radiata D.Don) with polyvinyl acetate and emulsion polymer isocyanate adhesives
¹Forest and Wood Products Research and Development Institute, Dobeles iela 41, LV-3001 Jelgava, Latvia
²‘Kokpārstrāde 98’ Ltd., ‘Dižkoki’, Allažu pagasts, Siguldas novads, LV-2154, Latvia
Fast-growing imported plantation tree species have become an available wood resource for Europe’s wood industry in the last decades. This sustainable alternative may reduce the gap between the increasing demand for and decreasing supply of the local tree species. The aim of the study was to evaluate the performance of eucalyptus (Eucalyptus grandis) and radiata pine (Pinus radiata D.Don) wood in face-bonding with polyvinyl acetate (PVAc) and emulsion polymer isocyanate (EPI) adhesive for the production of non-structural semi-finished glued laminated timber members for window manufacturing. Test specimen preparation and testing were performed according to European standards. Tensile shear strength and wood failure percentages were determined as bonding performance indicators for 3 adhesives and 3 selected bonding parameters (pressure, pressing time and adhesive spread) in 27 variations after boiling the specimens in water. According to the results, the bonding variables influence the glue-line tensile shear strength and wood failure percentages. Bonding pressure and pressing time were evaluated as the most significant factors influencing shear strength of bonded joints. For all bonding variations the average level of shear strength from 3.45 to 5.23 MPa were reached for PVAc adhesive and from 3.78 to 9.65 MPa for EPI adhesives. Both EPI adhesives provide higher performance compared to PVAc adhesive. In the case of bonding fast-growing tree species, the highest shear strength values were achieved using the lowest pressure of 0.8 MPa, adhesive spread from 150 to 180 g m-2 and longest pressing time of 40 min. Based on the general evaluation of the results, it can be stated that the wood of eucalyptus and radiata pine bonded with both EPI adhesives presents great potential for non-structural semi-finished glued laminated timber member production, especially for the use in humid conditions.