Composites made from annual plants, such as winter rapeseed, can be used as an alternative to wood-based composites because of their ecological character, low price, as well as physical and ...mechanical properties. The goal of this study was to prepare such boards and evaluate their properties. Unmodified material and chemically and hydrothermally modified rapeseed particles glued by powder polyester glue were used. The characteristics measured were the internal bonding, swelling and moisture uptake over time, and surface soundness. The results showed that modification of the raw material influenced the properties of the resulting composites. The highest swelling values were exhibited by the boards with particles that were alkaline-modified. Boards made from hydrothermally modified particles achieved the highest strengths compared with the commercially produced boards. The alkaline modification of the particles resulted in a stronger adhesive bond between the particle and adhesive. During the internal bonding test, the boards made from the alkaline-modified particles exhibited cohesive failures in the particles. Therefore, the modification of the particles increased the mechanical properties of the boards, but the physical properties deteriorated.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Changes in the air permeability and density profiles of 12-mm-thick oriented strand board (OSB) specimens were evaluated in relation to changes in their moisture content. The test methodology ...consisted of the simulation of real conditions that may occur during construction. Using a water bath, the OSB moisture content was increased from 10% to 17%, and the consequent changes in the air permeability and vertical density profile (VDP) were analyzed. The air permeability and VDP were then reanalyzed after acclimatization of the OSB to a balanced moisture content at 60% relative air humidity and 11.4 °C. After wetting the boards with an initial moisture content of 10% for 2 h and naturally re-drying them in laboratory conditions, an average increase of 11.7% in air permeability was observed. The increase in air permeability was 5.6% with a pressure difference of 50 Pa. After redrying, the boards showed a 1.1% lower average density and 14.5% lower maximum density in the surface layers. From the results, it followed that even the short-term effects of water and the related increase in moisture content of the OSB had a negative impact on the air permeability and VDP.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Lignin is produced worldwide in pulp mills and is currently mainly used for energy recovery. Because of its chemical properties, one possible utilisation is the production of lignin-based materials. ...Currently, developed lignin-based adhesives are based mainly on lignosulfonate instead of kraft lignin since lignosulfonate is more reactive than kraft lignin. However, worldwide substantially more kraft lignin is produced. The presented research deals with the development of resin chemically modified with kraft lignin up to 40% (w/w) content of kraft lignin. The synthesis of adhesives is described, and developed adhesives are characterised. Namely, viscosity, mechanical properties of resins and results of differential scanning calorimetry are presented. Furthermore, the developed kraft-lignin-based adhesives were used for the production of particleboards. Pre-pressing in a cold press followed by hot pressing in a laboratory press was used for the production of particleboards. The physical (thickness swelling, moisture uptake, vertical density profile), as well as mechanical (internal bonding, modulus of rupture, modulus of elasticity in three-point bending) properties of particleboards, were evaluated. The results clearly show that kraft lignin can be used for the production of lignin-based adhesives for the production of particleboards
Using crop residues for the production of composite materials is increasingly substantiated due to the increasing lack of quality wood pulp in the wood processing industry. Crop residues of winter ...rapeseed, the stems of which are produced in the amount of 42 million tons each year in the European Union and have not yet been exploited for products with high added value, are a potentially interesting raw material for the manufacture of composite materials. If materials based on annual plants are to fully replace the use of materials based on wood, glass, metal or plastic, it is necessary to know their characteristics. In the wood processing industry most of the attention is focused on physical properties, which have an immediate effect on the mechanical properties. Knowledge of the effect of the interaction of several factors (feedstock, technological parameters) on characteristics describing the elastic properties of the material is this article's contribution. Knowledge of the interaction of these factors gives the manufacturer instructions for modifying the input parameters with the aim of producing a material with specific mechanical properties appropriate for the intended use.The article deals with the mechanical properties of composite materials manufactured from winter rapeseed crop residues subjected to bending. The results of the research describe the effect of surface modification (chemical or hydrothermal) of particles on the bending characteristics measured within the elastic region: bending modulus of elasticity „MOE“, elastic potential „EP“, stress at the limit of proportionality „LOP“. Thanks to the acquired knowledge, we can specifically modify the properties of composite material for the intended use in the future.
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•Different rapeseed particle modification was used in order to enhance bonding of particles and adhesive in particleboards.•Pretreatment of rapeseed particles affected bending properties of particleboards produced from these materials.•The highest bending characteristics in the elastic area reached boards produced from hydrothermal treated particles.
The main aim of this work was the development of a novel adhesive based on lignin and beeswax suitable for the production of biocomposite materials from beech and spruce wood particles. Adhesive ...synthesis was based on natural and non-toxic products without any formaldehyde or other petroleum-based products (two adhesive variants were derived from beech and spruce kraft lignin filled with rapeseed straw powder; beeswax was used as a hydrophobizing agent). The thermal degradation properties and thermal stability of the prepared adhesives were evaluated using TGA and DSC. The prepared adhesives were used to produce particleboards. Consequently, the physical and mechanical properties of composites were evaluated in detail, as well as the character of bond rupture. The IR spectra (FTIR) of adhesives and particleboards were recorded in order to characterize the adhesives and composites from the chemical point of view. Particleboards produced from spruce particles achieved higher mechanical properties (IB, MOR, and MOE) than particleboards produced from beech particles. While the effect of the type of adhesive on mechanical properties was not observed, the adhesive used did affect physical properties; thickness swelling of boards was lower when using a beech-derived adhesive. Except for tensile shear strength and MOE, the developed adhesive did not reach values of reference UF adhesive. Based on the results it can be stated that the prepared adhesive can only be applied for internal purposes due to its ability to be hydrolyzed.
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•Adhesives derived from black liquor were used for composite manufacturing.•Residual sodium hydroxide degraded rapeseed straw powder used as a filler.•Adhesive from beech lignin provided better thickness swelling of boards.•Particleboards from spruce particles reached better mechanical properties.
Timber suffers from various biological damages. Recent efforts aim on nature-friendly sustainable technologies of wood protection to replace classical synthetic agents having usually negative impact ...on many non-target organisms including man. This research investigated the biocidal effectiveness of lavender oil (LO) in protecting the Norway spruce (Picea abies) wood against the termites Reticulitermes flavipes and the brown-rot fungus Rhodonia placenta. Following, selected physical characteristics of spruce wood treated with LO were evaluated: colour changes, roughness, surface wetting with water and surface free energy (SFE). Experiments showed that LO increased the resistance of spruce wood to termites nearly to the level of its treatment with commercial biocide based on trivalent boron and quaternary ammonium salt. The additional hydrophobic treatment of wood ensured its full termite-resistance even after artificial weathering in Xenotest and leaching in water according to EN 84, respectively. It shows a high potential of LO to protect wood against termites. Adversely, the effectiveness of 5% LO against rot was not sufficient. The colour of the oil-treated wood was preserved, its roughness increased slightly, and wetting and SFE led to a positive change, improving the adhesion of potentially applied coatings or adhesives for exterior exposures.
In this study, high-pressure laminates (HPL) impregnated with phenol-formaldehyde (PF) resins enriched with kraft lignin were developed. Pulverised kraft lignin was added to the commercial PF resin ...in the amounts of 1% and 5% (solid to solid). Laminates were manufactured using pressure impregnation of the resins into the papers and using hot pressing of HPL in a laboratory press. Laminates with a lignin content of 1% (L-LPF-1) showed the highest bending strength (72.42 MPa) and Brinell hardness (9.41); they also exhibited the best moisture uptake (9.61) and thickness swelling after immersion in water (3.32%). Except for impact bending, laminates with a lignin content of 5% (L-LPF-5) had worse properties. However, the differences between the variants are mostly not statistically significant and are comparable with the results of commercial PF resin. Scanning electron microscopy confirmed the homogenous structure of produced laminates and the occurrence of cohesive failures in ruptured L-LPF-1 laminates, whereas in ruptured L-LPF-5 laminates adhesive failures were also observed. Based on the conducted research it can be said that the utilisation of kraft lignin as an additive to PF resin (in the amount of 1%) has a positive effect on the produced HPL.
The bendability of a material can be classified as both a positive and negative characteristic. The classification depends on the intended use of the given material. In the case of materials intended ...for bending (solid wood), this property is positive; whereas in the case of building materials this property may have a negative effect on the stability and durability of the finished structure. Depending on the use of the material, different characteristics of bendability can be used to describe it. The important characteristics include the force and deflection at the limit of proportionality and at the modulus of rupture. Because the bendability also depends on the material thickness, this characteristic is most often expressed as the ratio of the material thickness to the smallest achievable bent radius. Therefore, an analysis of the minimum curve radius and coefficient of bendability was performed. The bending characteristics were measured for composite materials, which were made of crushed rapeseed stalk and bonded with powder polyester adhesive. The stalks were subjected to different modifications (R, H2O, and NaOH). The results of this work indicated that rapeseed is a prospective raw material for the production of composite materials with specific properties.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Advancing climate change is affecting the health and vitality of forests in many parts of the world. Europe is currently facing spruce bark beetle outbreaks, which are most often caused by wind ...disturbances, hot summers, or lack of rainfall and are having a massive economic impact on the forestry sector. The aim of this research article was to summarize current scientific knowledge about the structure and physical and mechanical properties of wood from bark beetle-attacked trees. Spruce stands are attacked by a number of beetles, of which Ips typographus is the most common and widespread in Central Europe. When attacking a tree, bark beetles introduce ophiostomatoid fungi into the tree, which then have a greater effect on the properties of the wood than the beetles themselves. Fungal hyphae grow through the lumina of wood cells and spread between individual cells through pits. Both white rot and brown rot fungi are associated with enzymatic degradation of lignin or holocellulose, which is subsequently reflected in the change of the physical and mechanical properties of wood. Wood-decay fungi that colonize wood after infestation of a tree with bark beetles can cause significant changes in the structure and properties of the wood, and these changes are predominantly negative, in the form of reducing modulus of rupture, modulus of elasticity, discolouration, or, over time, weight loss. In certain specific examples, a reduction in energy consumption for the production of wood particles from beetle-attacked trees, or an increase in surface free energy due to wood infestation by staining fungi in order to achieve better adhesion of paints or glues, can be evaluated positively.
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