Properties of laminated veneer lumber (LVL) from different heat-treated types of wood
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The investigations were performed on untreated and heat-treated laminated veneer lumber (LVL). The heat treatment (185 °C or 212 °C) of the veneers (poplar (Populus spp.), pine (Pinus sylvestris L.), beech (Fagus sylvatica L.), and oak (Quercus robur L.)), all of which are used for plywood manufacturing, was conducted prior to LVL manufacturing. For gluing; one 2K-PVA, one 1K-PU and one MF were used. The aim of this study was to analyse the influence of the thermal treatment and material combinations on the physical-mechanical properties of the laminated wood. It was found that for both types of wood (untreated and heat-treated), the heat treatment, as well as the adhesive had an impact on the studied properties. In relation to the reference samples (untreated material), the swelling behaviour was reduced by 21 % throughout heat treatment at 185 °C. At 212 °C heat treatment, the swelling behaviour was reduced to 40 %. The compressive strength reduced after heat treatment at 185 °C by 20 % and about 33 % at 212 °C, and the tensile shear strength by 8 % and 17 %, respectively. The reduction in bending strength was 8 % and 18 %, the decrease of the MOE in bending strength was 7 % and 12 %, and the resistance to axial screw withdrawal decreased by 12 % and 23 %, respectively.