Bulletin of the Transilvania University of Brasov. Series II: Forestry • Wood Industry • Agricultural Food Engineering

Effect of Process Conditions on Waterborne Wood Coating Performance Applied by Dipping

2023-12-20T12:07:23+00:00

Bio-based commercial coating systems are still not widely used to protect wooden elements and constructions used outdoors. In some cases, this is due to insufficient information about the technology and conditions of the film formation process. The present research aims to determine the influence of the process conditions on the properties of a coating applied by dipping on spruce, beech, and beech plywood surfaces. A waterborne one component bio-based varnish system was used. The study researched the following parameters: the amount of varnish applied, varnish penetration into the wood, and roughness of the surfaces after coating and drying. The variables investigated were the dipping orientation to the grain direction in the wood specimens, the wood surface treatment before coating, and the dipping time. Polynomial regression models were derived. It was established that with a single dip for 5 seconds, surfaces with a good appearance were obtained, but the varnish amount exceeded the norms recommended by the manufacturer several times. When axially dipping spruce and beech specimens, the varnish amount was the least when the surfaces were sanded with P150 grit-sized sandpaper. For the plywood specimens, the treatment had no effect. In tangential dipping, the characteristics of the wood species determined the varnish amount and the roughness parameter values. The sanding process had a more significant influence than the sandpaper grit size. The penetration was affected by the wood species characteristics, the wood surface treatment before coating, and the dipping time. In axial dipping, the penetration was times greater than in tangential dipping.

Performance of Wood Dowels and Same Size Metallic Connectors Used for Furniture Joints

2023-12-20T12:15:47+00:00

For a circular and sustainable economy, the reuse of wood furniture parts has gathered increasing importance. Disassemblable joints and purposefully developed elements may support this reuse. Despite the relatively high number of structural connectors, newly developed fittings have appeared on the market, combining the advantages of the previous ones or introducing new solutions, like the Domino dowels and connectors developed to make strong hidden joints. In furniture manufacturing, both panel and frame elements are joined for load-bearing, semi-load-bearing, or non-load-bearing connections. Metallic Domino connectors have recently been developed and recommended by the manufacturer only as connecting elements, and not as supporting elements of furniture constructions. In daily practice, the general consideration exists that these metallic connectors are strong enough to perform well as load-bearing elements. The main goal of this research was to examine the strength of corner (L) and T joints made with upper wood dowels and metallic connectors, to compare their performance. For the experiments, same-sized wood dowels and metallic connectors were used. The tension and compression test results indicate that the type of joint (corner versus T) is a stronger influencing factor of performance than the type of jointing element (wood dowel vs. metallic connector). Domino dowels are manufactured in different sizes. Further research will focus on finding the wood dowel equivalent to a given metallic connector of different sizes.

The Challenge of Strength Grading UK Hardwoods

2023-12-20T12:27:38+00:00

Recent research in Europe is bringing a wider range of wood species to the construction market as structural timber and glue laminated products. This option would also open markets for currently underused UK species, foremost hardwoods, but testing efforts when developing strength grading assignments for any minor UK species are prohibitive, as the resource is small and scattered. Grading approaches that require less material for destructive testing could be employed to open routes to market for structural hardwood products. In addition, the European hardwood research has revealed some gaps and uncertainties in grading standards. In particular, data are lacking to support adjustment equations for size, moisture content, and testing arrangement for hardwoods. This paper outlines a new PhD project that will focus on these problems and aims to develop an easier route for strength grading hardwoods.

Comparative Research Regarding the Hydrophilic Extractives Content in Turkey Oak and Sessile Oak Wood and Their Related Staining Susceptibility by Reaction with Iron

2023-12-20T12:34:44+00:00

The paper presents the experimental results concerning the amount of extractable substances and the color changes determined by the reaction of the tannins contained in wood with iron. Tests were performed comparatively with sapwood and heartwood samples of two Quercus species, namely Turkey oak (Quercus cerris L.) and sessile oak (Quercus petraea (Matt.) Liebl.). The findings show that Turkey oak sapwood has an unexpectedly high amount of extractable substances, higher than the heartwood of the same species. This result was obtained with three extraction methods (cold water, hot water, and NaOH 1% solution). The FTIR investigation of the extracts impregnated on quantitative filter paper seems to confirm these results. Visual assessment and color measurements after applying FeCl₃ highlight that both oak species are prone to staining in contact with iron due to their tannin content. The values of the total color difference between the state and after the reaction with FeCl₃, lower fer for Turkey oak compared to sessile oak, correlate with a lower extractive content of this wood species.

A Simulation Study of the Heat Balance of Concrete Pits During Boiling of Non-Frozen Logs

2023-12-20T12:47:44+00:00

This paper presents an approach for computing the heat balance of boiling pits during the plasticizing of non-frozen logs intended for the production of peeled veneer. With the help of our non-stationary model, the heating times of beech logs with a diameter of 0.4 m, an initial temperature of 10°C, and a moisture content of 0.6 kg∙kg^-1 were determined at water temperatures in the pit equal to 70, 80, and 90°C. Using the determined logs’ boiling durations and the mentioned approach, the change in the total energy required to carry out the entire boiling process and that required for each of the individual components of the heat balance was calculated. Computer simulations were conducted for a concrete pit with overall dimensions of 8.0 × 2.6 x 2.5 m, a working volume of 20 m³, and a degree of filling with logs equal to 45, 60, and 75%. It was found that the increase in the water temperature from 70 to 90°C causes an increase in the total specific energy, as well as in the energy for the heating of the logs themselves, the construction, and the water of the pit. At the same time, the energy required to cover the heat losses of the pit decreases and the energy for heating the metal heater/radiator itself does not change. A decrease in the degree of filling of the pit with logs from 75 to 45% causes an increase in both the total energy and all its components except the energy for heating the logs, which remains unchanged.

Effect of Variable Growth Conditions on Selected Anatomical Properties of Hungarian Turkey Oak Wood

2023-12-20T13:08:14+00:00

Quercus cerris (Turkey oak) has been categorized as a drought-tolerant species because it can survive with rainfall below 400 mm/year, and it usually develops deep and penetrating taproots. This characteristic suggests that Turkey oak is a survival candidate species for the future environment with the predicted climate scenarios in Hungary. Potentially, Turkey oak could support a sustainable supply of timber to the Hungarian wood industry in the future, as the aesthetic value is similar to that of noble oaks. The objectives of the study are to determine 1; the selected micro-level wood properties (wood tissue characteristics) and 2; the selected macrolevel wood properties (tree-ring width, sapwood-heartwood ratio) for Turkey oak from two different sites. The heartwood portion for all trees constituted 67-82% of the cross-diameter. The growth-ring width decreased from pith to bark. The annual rings in the sapwood had a width value range of 1000 to 1600 μm; in heartwood 1600 to 2500 μm; in juvenile wood 2400 to 3300 μm. Soil quality and stand composition had a significant effect on growth-ring width. Fibre length ranged from 800.03 to 1305.59 m, whereas fibre-wall thickness varied between 11.73 and 18.51 μm, with soil quality and species composition having a highly significant influence. The earlywood parts of the growth rings had a vessel diameter range of 274.62-401.54 μm, whereas the latewood portion ranged from 46.50 to 190.08 μm. Overall, stand composition was a major source of variation in the properties studied.

Simulation-Based Performance Analysis of Impregnated Wood with Phase Change Material for Energy Efficient Timber Structures

2023-12-20T13:56:28+00:00

Organic phase change materials (PCMs) offer a promising approach to improving the energy efficiency and sustainability of buildings. Impregnating wood with PCMs presents the opportunity for its application in building construction to reduce energy consumption for heating and cooling of indoor spaces. In this study, the process of solid wood impregnation with PCMs was conducted, along with the characterisation of their thermal properties. To define an optimal melting point and quantity to be incorporated into test cubes exposed outdoors for long term in Kuchl (Austria), a digital model was used to simulate beech and spruce that were impregnated with PCMs featuring two differing melting points. The results show that incorporating PCM into walls and floor can potentially reduce summer overheating by up to 48%. This effect is achieved using a building design that includes wood impregnated with PCM with a lower melting point of around 21°C. However, the building design and use of the employed PCMs do not reduce energy consumption for heating during winter. The results show that the performance is strongly dependent on the melting point of the PCM and its quantity in the building. These findings contribute to improving the design of the experimental test cube with impregnated wood and highlight the challenges.

Influence of Density on the Withdrawal Staple Strength from Hemp Shive Panels

2023-12-20T14:41:31+00:00

Particleboards are the main material used in the production of furniture and furnishings. The shortage of wood raw material and the everincreasing amount of particleboards produced suggest a search for alternative raw material sources for this panel type. On the other hand, significant quantities of agro-industrial lignocellulosic residues are available worldwide. Such a type of residue is hemp shives. Basic joints in furniture frames are stapled joints, as it should be said that density is the main characteristic of particleboards, and their other properties strongly correlate with it. The present research studies the influence of the density of panels from hemp shives on their staple withdrawal resistance. For this purpose, panels from hemp shives with melamine-formaldehyde (MF) resin as an adhesive and densities from 600 kg.m^-3 to 900 kg.m^-3 were produced in laboratory conditions. The density of the panels varied with a step of 100 kg.m-3. As a result of the research, it was found that the staple withdrawal resistance of hemp shives particleboards from the edge and side of the panels increases almost twice with the increase of their density. It was also found that, unlike industrial particleboards, edge staple withdrawal resistance is higher in hemp shive panels than side staple withdrawal resistance. Laboratory-produced panels from hemp shives have a higher staple withdrawal resistance at similar densities than industrial particleboards. However, this is at the expense of using expensive MF resin and the significantly extended press factor. The main novelty of the research is the establishment of the effect of the density of hemp shive particleboards on their staple withdrawal resistance, as well as the demonstration of the possibility of producing panels from an alternative lignocellulosic raw material with a better staple withdrawal resistance than that of industrial particleboards manufactured from wood raw material.

Effects of Cutting Parameters and Grain Direction on Surface Quality of Three Wood Species Obtained by CNC Milling

2023-12-20T17:24:31+00:00

Computer Numerical Control (CNC) machines are increasingly popular in the production of furniture and wood products, because they combine high processing quality with short production time. The effective use of CNC machines depends on the processing parameters, which also affects the quality of the processed surface. The aim of this study was to determine the effect of feed rate, cutting direction, and grain direction on the surface roughness of various types of wood. Three European wood species (oak, beech, fir) were cut with a spindle speed of 16,000 rpm and two different feed rates (5,000 and 10,000 mm/min) using end mill tools on the CNC machine. The milling was performed in two cutting directions (radial and tangential) and two grain orientations (0° and 90°). An analysis of variance (ANOVA) was performed to evaluate the impact of the cutting parameters. The surface roughness measurements were taken, and two surface roughness parameters (Ra and Rz) were measured to determine the surface quality of the wood. According to the results of this study, the lowest surface roughness values, milling with the same processing parameters, occurred for oak wood, while the highest values occurred for fir.

The Lifespans of Products Made with MDF

2023-12-20T17:45:08+00:00

The Horizon Europe funded EcoReFibre project (www.ecorefibre.eu) is concerned with recycling fibreboards and, in particular, Medium Density Fibreboard. This paper covers our research on determining the typical lifespans of products containing fibreboard. Knowing the lifespan of a product is important as it is the main determining factor that influences the age when it becomes waste. This paper proposes that the average age at which a product containing MDF becomes waste is between 10.7 and 12.1 years.

Influence of Properties of Building Materials in Wooden Sandwich Constructions on Overall Fire Resistance

2023-12-20T17:54:29+00:00

By choosing suitable individual building materials for a sandwich structure, we can ensure an increase in the fire resistance of the entire structure. The influence of the properties of individual building materials on the overall fire resistance in sandwich constructions has not been well researched. It is for this reason that we focus our contribution on the influence of the properties of building materials in wooden sandwich structures on overall fire resistance. In the wooden sandwich constructions we created, we worked with reference constructions composed of thermal insulation with different surface treatments and with constructions that have the same thermal insulation, but we added 40 mm thick mineral wool to them. Subsequently, we tested the structures according to the EN 1365-1 standard [4]. After processing the obtained results, we came to conclusions about the effect of mineral wool and its combination with suitable thermal insulation on overall fire resistance.

Evaluation of CNC Routed Surface Quality of Beech (Fagus sylvatica L.) with Different Milling Angles as Function of Grain Orientation

2023-12-20T18:03:24+00:00

The paper presents an experimental investigation of the quality of CNC routed surfaces with a V-Grooving router bit (90°) on various milling angles as a function of wood grain direction on beech (Fagus sylvatica L.) wood. The quality of the machined surface was first visually assessed for the presence of raised fibre and other processing defects on the routed circles with a diameter of 180 mm using feed speeds of 3 m/min and 6 m/min respectively, and spindle speeds of 12,000, 15,000, and 18,000 rpm. The quality of the processed surfaces on the circle indicated the most unfavourable CNC routing regime accompanied by the conclusions regarding the most unfavourable angles related to the grain. Further research considered the assessment of the surface quality on straight CNC routing with angles of 0, 15, 30, 45, 60, 75, and 90° related to the wood grain direction at feed speeds of 3 and 6 m/min and spindle speed of 15,000 rpm. In this case, the characterisation of the wood surface quality was made by measuring the roughness parameters. The highest values of the roughness parameters, showing the presence of the fibres detached from the surface, were recorded for the cutting angle of 60, followed closely by 75°, then 45°, and 90° at a feed speed of 3 m/min. No significant difference was found between the Rk of the cutting angles from 0° to 45°, but it increased significantly for 60, 75, and 90°, showing frequent deeper anatomical voids on the surface.

Investigations of Surface-Treated Wood by a Micro-Indentation Approach: A Short Review and a Case Study

2023-12-20T18:13:58+00:00

Over the past 50 years, instrumented indentation, in which an indenter tip probes the specimen surface with a regulated force and displacement to characterize its mechanical properties, has evolved. With the development of atomic force microscopy, instrumented nanoindentation has been extensively applied, and instrumented indentation in the micro range (micro-indentation) has been somewhat overshadowed by nanoindentation. However, micro-indentation remains an extremely useful technique that has the potential to investigate various properties of surface treated wood. In the first, overview-type part of the paper, instrumented micro-indentation is described and some examples of its possible applications in the field of wood science and technology are presented. To illustrate the importance of this experimental technique, some results of micro-indentation experiments carried out in our wood surface treatment laboratory are shown in the second part of the paper. The objects of the tests were untreated Scots pine wood and Scots pine wood with surface deposits of SiO₂ or ZnO. The differences between the mechanical properties of early and latewood could be clearly distinguished by the micro indentation technique. On the other hand, the influence of ZnO and SiO₂ particles on mechanical properties as a function of indentation depth could not be detected by this technique.

Properties of Hemp Shive Panels with Different Resin Content

2023-12-20T18:26:51+00:00

Wood-based panels are one of the leading materials for frame structures of furniture. The worldwide shortage of wood raw materials necessitates searching for alternative sources to produce panels. Hemp shives are a representative of precisely this type of raw material. They are characterised by low bulk density and high fibre strength. For this study, four types of one-layered panels from hemp shives were fabricated in laboratory conditions, with a resin content of 8, 10, 12, and 14%, respectively. Accordingly, their main physical and mechanical properties were determined and compared to those of particleboards from raw wood material. It was found that the obtained panels from hemp shives have very good mechanical properties, and their high edge screw withdrawal resistance is very promising in terms of applicability for furniture constructions. As a direct result of these findings, the resin content is not recommended to be above 10%.

An Experimental Method to Evaluate the Contribution of Wood Substrate and Coating Film to the Light Induced Colour Changes of Wood Surfaces

2023-12-20T18:36:17+00:00

The paper presents an original laboratory method developed to determine and compare the light-induced colour changes of uncoated and coated wood surfaces, while also allowing the highlighting and evaluation of the individual contributions of the substrate and coating film to the global effect. Two types of wood test samples: V1 (uncoated) and V2 (coated) and coating films on 1mm thick clear glass slides were employed. The behaviour of the wood substrate under the coating film was simulated on uncoated substrate covered with a coated glass slide. European maple (Acer pseudoplatanus L.) and two types of transparent water-based varnishes with 2k formulations were used. The samples were exposed for up to 72 hours to artificial UV-VIS light in accelerated tests simulating natural light passing through window glass. Colour changes were measured in the CIELab system, as well as the chemical changes of the wood substrate and the coating films by FTIR analysis. Exposure of uncoated maple wood resulted in a total colour difference (E) of 10.83 units and this was only slightly reduced by coating (9.29-9.81 units). Exposure through the glass slide reduced the colour changes of the uncoated and coated wood surfaces by 37-43%. Colour changes of 5.79-6.85 units were measured on the wood substrate exposed under coated glass slides, whilst the colour changes of the coating films on glass slides were only 0.64-1.0 units, which indicates a maximum contribution of the wood substrate to the light-induced colour changes of the coated surfaces. FTIR investigation confirmed this finding.

Variation in Moisture Content and Density Whitin and Among Freshly Felled Sclerocarya birrea and Anogeissus leiocarpus

2023-12-20T18:49:26+00:00

This papaer studiess the variations in moisture content within and among tree species of Sclerocarya birrea and Anogeissus leiocarpus, as well as the green density of a cubic meter of freshly felled wood from this species. The trees included in this research grew in Western Kordofan State, Sudan. Following their felling, tiny square samples of varying sizes (n=10) were gathered and weighed from each vertical position within the bole length (10, 50, and 90%). The results show that the average MC and the green density of the freshly felled wood were 109.97% and 686 kg/m3 for S. birrea, while the values of A. leiocarpus were 35.55% and 980 kg/m3, respectively. Furthermore, the findings of the analysis of variance revealed that the MC [%] varied significantly only between the tree species. Conversely, there was no significant difference in MC [%] within the vertical positions of the bole length for either species.