Sirvi Autor "Iejavs, J." järgi
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Kirje 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(Estonian University of Life Sciences, 2022) Iejavs, J.; Šķēle, K.; Grants, E.; Uzuls, A.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.Kirje Effect of environmental temperature on bending strength of the finger jointed aspen lumber(2018) Iejavs, J.; Spulle, U.; Jakovlevs, V.; Buksans, E.; Zelmenis, A.Glued sauna wall boards are used as non-load-bearing structures. These products are subject to aggressive microclimate impact and very often for the gluing in length and width thermoplastic polyvinyl acetate adhesives (PVAC) are used. In the performed research sauna wall boards made of common aspen (Populus tremula L.) with mean wood moisture content 8% were used. For the gluing in length with finger joint PVAC glue of D4 (LVS EN 204) group was used. The aim of the research is identifying the impact of the environmental temperature on the strength of finger jointed aspen timber in 4 point static bending (in compliance with standard LVS EN 408). As a result of the study it was established, that after holding the finger jointed testing pieces visible in flat wise for 3 hours at the temperature of 100°C , the mean bending strength decreased by 56% or 31.7 MPa in comparison to that held in the standard atmosphere. In case of the aspen timber with finger joints visible in edge wise held for 3 hours at the temperature of 100°C , the bending strength decreased by 60% or 29.3 MPa in comparison to the testing pieces of the same type held in the standard atmosphere.Kirje Some physical and mechanical properties of wood of Fast-growing tree species eucalyptus (Eucalyptus grandis) and radiata pine (Pinus radiata D.Don)(2021) Iejavs, J.; Podnieks, M.; Uzuls, A.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 determine and compare basic physical and mechanical properties of eucalyptus (Eucalyptus grandis) wood from Uruguay and radiata pine (Pinus radiata D.Don) wood from New Zealand as an alternative for Scots pine (Pinus sylvestris L.) from Latvia, to produce non– structural semi–finished glued laminated timber members for the manufacturing of windows. Such properties as density, swelling, bending strength, bending modulus of elasticity, compression strength and resistance to impact were determined according to ISO 13061 series standards test methods for small clear wood specimens. As the result of this study it was established that there is not significant difference between the majority of radiata pine and Scots pine properties, with the exception of resistance to impact and radial swelling where radiata pine shows significantly higher values. Not surprisingly all the properties of deciduous eucalyptus wood were significantly higher compared to both coniferous tree species. Higher swelling and density properties of eucalyptus compared to radiata pine and Scots pine should be taken into consideration for the design and production of wooden window elements.Kirje Swelling pressure and form stability of cellular wood material(2018) Spulle, U.; Buksans, E.; Iejavs, J.; Rozins, R.Cellular Wood Material (hereinafter CWM) middle layer of the Dendrolight® has been developed in the beginning of this century as a wood material for minimization of internal stresses, because of the material structure and reduced swelling and shrinking impact to products in end use application. Some research has been conducted on the physical mechanical and physical chemical properties of CWM, while dimensional stability has not been well researched. The goal of this research is to perform an assessment of the CWM shrinkage and swelling impact on dimensional characteristics of the CWM multilayer composite materials. CWM swelling pressure in length, width, and height of the material were determined and compared to the relevant indicators of pine solid wood. The form stability or the impact of combination of the CWM with some facing materials wood particle board, medium density fibre board (hereinafter MDF), oriented strand board (hereinafter OSB), pine solid wood, gypsum plaster board used in wood products was investigated. The hypothesis that swelling pressure of CWM must be lower than that of pine solid wood was proved, it is 2.3 times lower in the radial direction and 3.9 times lower in tangential direction compared to pine solid wood. The CWM samples, manufactured for determining the form stability in wetting conditions deflected in the height direction by 4%, thus creating deflections also in the seams between separate lamellas of the CWM. Swelling pressure of the CWM is several times smaller than that of solid wood and can be further limited by creating complex wood and non-wood composite material panels using gluing technique.