Recently, a renewed interest in non-harmful, environmentally friendly adhesives has ensued among the industry professionals, both environmental and healthcare scientists. In this study, organic rich lake sediments (sapropel) from two lakes located in Latgale Region of Latvia were used as a glue to investigate the potential use of such adhesive for manufacture of composite materials from wood. Sapropel is a valuable resource with multiple areas of application, e.g., agriculture, balneology. Available amount of sapropel in Latvia is estimated at up to 2 billion m**3. Prior the tests, characterization of sapropel samples was done. Properties of the obtained composite material samples from wood and sapropel, as well as the mechanical properties were investigated. Tests involved the assessment of static bending strength and shear strength tests, durability according to their operating performance (D1-D4), as well as dried natural peat tensile strength perpendicular to the grain direction were determined and compared to the literature data; and the opportunities to use new composite materials in accordance with to the standards were discussed. The results of the study revealed an insight into possibilities to develop products of higher added value from sapropel as adhesive in combination with various resources. Results indicated that the samples made from Lake Pilvelis sapropel gain to better results of bending strength determination (parallel bending - 88.7 MPa). The aim of this study was to explore options to produce veneer using two kinds of sapropel as a glue and to determine the optimal properties according to the standards, as well as to characterize properties of the obtained composite material.

Lodgepole pine (Pinus contorta) samples from three different provenances in Canada were investigated. All trees were the same age and had been grown in Latvia in similar conditions. Lodgepole pine of Summit Lake provenance had higher wood density (503 kg m-3) and a higher late wood content (46%) in comparison to Fort Nelson and Pink Mountain provenances. Investigation of chemical composition of wood indicated Summit Lake provenance wood as superior in cellulose content (49.7%), but no differences in lignin and extractives content were found between samples. Kraft pulp yield of Summit Lake samples (48%) was the highest, but the handsheet strength properties were relatively higher for pulp from Pink Mountain provenance pine wood.

Invention of light weight panel with a trade mark of Dendrolight is one of the most distinguished wood industry innovations of the last decade. At present three layers cellular wood panels have wide non structural application. The aim of the research is to evaluate the bending properties of three layer cellular wood panels for structural application. There were 8 specimens manufactured with thickness 136 or 152 mm, width 300 mm and length 2,500 mm of each of the six horizontal load bearing panel structural models. Scots pine (Pinus sylvestris L.) cellular wood and solid pine wood ribs were used as internal layer of the structural panels. Cellular wood core was placed in horizontal or vertical direction. Scots pine solid wood panels and birch plywood were used as top layer material. Applied glue was polivinilacetate Cascol 3353. The most common stress type in structural subflooring panels is bending; therefore, the influence of the cellular material orientation, ribs and top layer material on the sandwich type structural panel bending strength (MOR) and stiffness (MOE) were evaluated according to LVS EN 408:2011. Extra parameters like moisture content and apparent density were determined. Cellular wood in vertical direction can be used as raw material for structural panel production. Panels with solid timber external layers, with ribs and with vertical orientation of the cellular material showed the highest MOR (35.2 N mmE-2) and MOE (11,500 N mmE-2) values. The influence of the solid wood ribs on the bending properties is directly dependent on external layer material.

The Duration of Load (DOL) effect is the combined influence of the mechanical loading history and climatic history on the strength of materials. DOL effect is one of the most important characteristics of wood and wood-based materials. The material degradation or damage induces strength reductions. Creep is one of the most important effects of DOL. Creep is a phenomenon that negatively affects functional compliance, behaviour and strength of timber structures in extended years of exploitation. The creep phenomenon is affected by surrounding temperature, relative humidity, timber moisture content and other factors. The study aimed to establish a correct factor system for accurate prediction of long-term deformations of timber structures that is corresponding to environmental conditions and timber properties in the region of Latvia. The experimental research was made in Jelgava, Latvia, and represents timber beam four-point long-term loading in bending with variable cross section height-span length ratio under uncontrolled climatic conditions. There were 12 timber beams with two different span lengths – 1.32 m and 1.50 m used. The timber beam cross section dimensions: height – 60 mm, width – 30 mm. The timber beams were not dried and the moisture content at the start of the experiment varied from 19% to 33%. The applied load values – 0.40 kN and 0.31 kN. Moisture content fluctuations and negative air temperature accelerated creep development and intensity. Prediction of final long-term deformations should rate not only the type of timber material and service class but the strength class, too.

No simple method has yet been found for satisfactory wood bio-resistance improvement regarding material performance in its end-use. An attempt to obtain material with proper strength and bio-durability by combined wood thermal modification and impregnation with a biocide is being researched. To select the most appropriate treatment conditions for the combined process, changes in wood physical and mechanical properties depending on the treatment temperature were investigated in the present study. For the investigation, in Latvia the most widespread wood – softwood pine (Pinus sylvestris L.) and hardwood birch (Betula spp.) was used. Changes of wood mechanical and physical properties due to thermal modification were investigated and effect of treatment temperature and relative humidity on wood characteristics evaluated. It was found that, due to different degree of changes, no identical treatment conditions suit for birch and pine wood. Birch wood is considerably more sensitive to temperature and acceptable strength was maintained only for birch wood treated at 150 °C and for pine wood treated at 160 °C. Nevertheless at higher environmental humidity equilibrium moisture content and consequently radial and tangential swelling increased for all studied wood types, substantially smaller changes due to elevated humidity were detected for modified wood.

In this study, antifungal properties of an organoclay additive were investigated. Two types of organoclay (red and white) were tested in Petri dishes to determine their toxicity against the brown rot fungus Coniophora puteana and the white rot fungus Trametes versicolor. Red organoclay was more efficient than the white one and, depending on the fungus, inhibited or stopped the fungal growth. Red organoclay was chosen as an additive to produce a new type of plywood product. Biological durability of this plywood product was determined according to the methods: NF B 51-295 (bending strength test) and LVS ENV 12038:2002 (mass loss test). The loss in bending strength exceeded 81% and 65% after exposure to brown and white rot fungi, respectively. The mass loss of the plywood product after the decay test was higher than 3%, which defined the material as not fully resistant against decay fungi. According to CEN/TS 15083-1:2005, the plywood product corresponded to the durability class 3 (moderately durable) to 5 (not durable) depending on the fungus.

Birch plywood has proved itself to be one of the most rational ways of wood processing. Growing demand of high performance birch plywood products requires a complex numerical analysis based on Finite Element Method (FEM), instead of using simple analytical assumptions, which prevent optimization of plywood construction (lay-up). In the research samples of birch plywood of several thicknesses, both sanded and non-sanded, with fibre direction of external veneer both in the longitudinal and transverse directions were tested. An extensometer and optical strain gauge were used for strain measurement. The FEM analysis, using commercial software SolidWorks Simulation Premium (SW), versus experimental bending and tension testing according to LVS EN 789 was carried out in this paper. The analysis of results indicates that there is a high correlation between the results of the experiments and the FEM. Particularly for in tension loaded specimens one can be tested up to the maximum ply strength (100 MPa); meanwhile, in bending up to 71MPa – the average stress in load bearing ply at the proportionality limit. Due to software restrictions, shear stresses cannot be evaluated. Future studies are considered to investigate terms for designing plywood with dynamic properties of strength and stiffness to be taken into account.

The manufacturers of wood-based panels are interested to get easy and cheap method for determination of characteristic values of panels. The correlation between European standards EN 789 and EN 310 tests results can be used as an alternative procedure for determination of characteristic values of bending properties. The correlations between two results of bending properties determined by testing methods of European standards EN 789 and EN 310 are studied in this paper. The ratio of EN 789 test results divided with EN 310 test results (ratio of EN 789/EN 310), depending on panel thickness and glue type, was examined. Samples from 846 panels of birch (Betula sp.) plywood with thickness ranging from 6.5 to 30 mm and two glue types - phenol formaldehyde and melamine urea formaldehyde resin - were used for verification of the correlations. The results show that the panel thickness influences the ratio of EN 789/EN 310 and the highest ratio were found between 12 and 15 mm panels. When the panel thickness is increased or decreased, the ratio of EN 789/EN 310 decreases significantly. The regression equations for each thickness of plywood are presented. The difference between plywood glued with phenol formaldehyde and melamine urea formaldehyde resin glues was not found.

The article discusses investigations in a flat rectangular contact area of two elastic solids (brake friction lining and disc) using a theoretical method. The solids are in free as well as in forced movement. The investigations have resulted in correlations describing deformation and stiffness parameters of solid flat joint in different loads: transference of the centre of cross section delta0 the angle of turning phi of one solid in relation to the other (as a result of friction lining deformation), and tension sigmax in any cross section of the contact area. The results of the investigations make it possible to analyze the stiffness of the contact of solids, test the strength of the contact areas, optimize the contact are of solids, and prognosticate even wear out of friction lining.

The manufacture and export of pallets is one of the largest sectors of the wood industry. For the manufacturing of pallets mainly softwood - spruce (Picea abies L. Karst.) and pine (Pinus sylvestris L.) wood - materials are used. The price of those materials is increasing. It could be better for the production of pallets if the manufacturers could use hardwood - alder (Alnus incana L. Moench) and aspen (Populus tremula L.) wood materials. The reasons for that could be that these materials are not so expensive and that softwood materials could be used more in the wood industry where it is more necessary. But at that point more information about the physical and mechanical properties of hardwood materials needed. Basing on the previous research on quality and mechanical properties of softwood and hardwood and on the present research work the practical and theoretical values of deflection and strength of pallets have been assessed. The research enables us to optimize the preparation for pallet production. The aim of the research is to find out the strength of the pallets without destroying.