Pavlo Bekhta - Academia.edu (original) (raw)
Papers by Pavlo Bekhta
Forests
Wood remains one of the most attractive building materials [...]
Polymers
The ongoing transition from a linear to a circular, low-carbon bioeconomy is crucial for reducing... more The ongoing transition from a linear to a circular, low-carbon bioeconomy is crucial for reducing the consumption of global natural resources, minimizing waste generation, reducing carbon emissions, and creating more sustainable growth and jobs, the prerequisites necessary to achieve climate neutrality targets and stop biodiversity loss [...]
Forests
Ukrainian companies mainly use birch in the manufacture of plywood, but species, such as black al... more Ukrainian companies mainly use birch in the manufacture of plywood, but species, such as black alder, are not yet widely used in the manufacture of plywood due to their poorer properties. It is well known that thermal compression is often used to improve the properties of solid wood. Good lay-up schemes of veneer can maximize the advantages and minimize the disadvantages of these wood species, and generally improve the utility value of the plywood. This research aimed to develop plywood panels with two wood species and two types of veneer treatments in order to evaluate the influences of different lay-up schemes on the properties of the plywood. Five-layer plywood panels were formed with 16 different lay-up schemes using birch (Betula verrucosa Ehrh.) (B) and black alder (Alnus glutinosa L.) (A) veneers, which were non-densified (N) and thermally densified (D). The different lay-up schemes were used to identify opportunities to improve the mechanical and physical properties of the p...
Polymers
Traditional wood-based composites are bonded with synthetic formaldehyde-based adhesives [...]
Materials
The aim of this study was to improve the properties of lightweight particleboards by their veneer... more The aim of this study was to improve the properties of lightweight particleboards by their veneering. The industrially produced wood particles, rotary-cut birch veneer, expanded polystyrene (EPS) granules and urea-formaldehyde (UF) resin were used to manufacture non-veneered and veneered boards in laboratory conditions. The boards were manufactured with different densities of 350, 450 and 550 kg/m3 and with various levels of EPS content 4, 7 and 10%. Boards without EPS granules as the reference were also manufactured. Bending strength (MOR), modulus of elasticity in bending (MOE), internal bond (IB) strength, thickness swelling (TS) and water absorption (WA) of lightweight particleboards were determined. This study confirmed that veneering of lightweight particleboards by birch veneer improved mechanical properties significantly. The MOR and MOE of veneered boards throughout the whole density range of 350–550 kg/m3 meet the requirements of the CEN/TS 16368 for lightweight particlebo...
Annals of Warsaw University of Life Sciences - SGGW. Forestry and Wood Technology, 2014
Polymers
The volume of deadwood increases annually because of changes in environmental, climatic, and hydr... more The volume of deadwood increases annually because of changes in environmental, climatic, and hydrological conditions. On the other hand, during the last decade, manufacturers of wood-based boards have been facing an acute problem of a shortage of conventional raw materials. The purpose of this study was to evaluate the possibility of using wood particles from deadwood in the production of particleboards. Three-layer particleboards with different content of deadwood particles (0%, 25%, 50%, 75%, 100%) were produced. Conventional urea-formaldehyde (UF) resin was used for gluing the particles. The physical and mechanical properties of the boards, as well as the formaldehyde content in the boards, were determined. In addition, the effect of adding melamine-urea-formaldehyde (MUF) resin to UF adhesive on the properties of the boards was investigated. Replacing conventional sound wood particles with deadwood particles leads to deterioration of the physical and mechanical properties of the...
Materials
In this work, to better understand the bonding process of plastic plywood panels, the effects of ... more In this work, to better understand the bonding process of plastic plywood panels, the effects of recycled low-density polyethylene (rLDPE) film of three thicknesses (50, 100, and 150 µm) and veneers of four various wood species (beech, birch, hornbeam, and poplar) on the properties of panels were studied. The obtained properties were also compared with the properties of plywood panels bonded by virgin low-density polyethylene (LDPE) film. The results showed that properties of plywood samples bonded with rLDPE and virgin LDPE films differ insignificantly. Samples bonded with rLDPE film demonstrated satisfactory physical and mechanical properties. It was also established that the best mechanical properties of plywood are provided by beech veneer and the lowest by poplar veneer. However, poplar plywood had the best water absorption and swelling thickness, and the bonding strength at the level of birch and hornbeam plywood. The properties of rLDPE-bonded plywood improved with increasing...
Forests
Surface roughness is an important factor during the processes of wood gluing and finishing. This ... more Surface roughness is an important factor during the processes of wood gluing and finishing. This study proposed a new approach for the preparation of wood veneer surfaces before varnishing through the use of thermal compression instead of sanding. The quality of the pre-treated surface was examined using surface roughness measurements. In the experiment, a wood veneer of black alder and birch, before varnishing, was subjected to sanding with a sandpaper of 180 grit size, and thermal compression at temperatures of 180 and 210 °C. Three different types of commercially manufactured varnishes (water-based (WB), polyurethane (PUR) and UV-cured (UV)) were applied to the prepared veneer surfaces with various numbers of varnish layers. Seven roughness parameters such as Ra, Rz, Rq, Rp, Rv, Rsk, and Rku were determined for the sanded and thermally densified unvarnished and varnished surfaces. The profile surface was recorded with a portable surface roughness tester along and across the wood ...
Coatings
The objective of this study was to investigate the gloss of different types of commercially manuf... more The objective of this study was to investigate the gloss of different types of commercially manufactured varnish systems, including water-based (WB), polyurethane (PUR) and UV-cured (UV), applied on veneered MDF panels with sanded and thermally densified alder and birch wood veneers. The varnishes were applied at various numbers of layers on veneered panels. The gloss was measured at three angles of incident light: 20°, 60° and 85°. Statistical analysis showed that the type of varnish, the number of layers, the pre-treatment process, the wood species and direction of wood fibers significantly affect gloss of the coatings of veneered MDF panels. The type of varnish had a dominant effect on gloss. The highest gloss values were measured for the UV-varnished surface, and the lowest for WB- and PUR-varnished surfaces. Gloss was enhanced with an increase in the number of layers. Birch veneer provided higher gloss values compared to alder veneer. The gloss values measured along the wood fi...
Annals of Warsaw Agricultural University. Forestry and Wood Technology, 2003
European Journal of Wood and Wood Products, 2020
The plywood consumption in various applications is increasing, especially in construction. In ser... more The plywood consumption in various applications is increasing, especially in construction. In service, plywood can be exposed to a range of outdoor conditions, sometimes at elevated temperatures. This requires an understanding of the structural behavior and knowledge of the effects of the elevated temperatures on the properties of plywood. Therefore, the objective of this research was to study the effect of exposure time on physical and mechanical properties of plywood at elevated temperatures. The plywood samples were tested after exposure to nine different temperatures (50 °C, 75 °C, 100 °C, 125 °C, 150 °C, 175 °C, 200 °C, 225 °C and 250 °C) and ten exposure time levels (0.5, 1, 1.5, 2, 2.5, 3, 6, 8, 10 and 12 h) at each temperature. Additionally, a set of control samples was tested at room temperature. The findings of this study indicated that exposure of plywood panels to elevated temperature caused significant degradation of their bending and bonding strengths, whereas the hydrophobicity of the panels improved. Three stages of plywood degradation could be distinguished. Below 175 °C, there is a slow decline in strength; the decisive change already occurs at 175 °C; but as temperature increases beyond 175 °C, a rapid decrease in strength is observed. Plywood samples lost 98.1% of their initial strength after 1.5 h of exposure at 250 °C, and lost 98.5% after 6 h of exposure at a temperature of 225 °C. Statistical regression-based models were also developed and evaluated for predicting the strength loss of plywood panels as a function of weight loss. As the weight losses of panels increased, the losses in bending and bonding strength increased too. The decrease in bending and bonding strength only becomes significant when the weight loss exceeds 5%. When the weight losses increased above 15%, plywood samples almost lost their strength.
Effects of short-term thermomechanical densification on the structure and properties of wood veneers
Polymers
Oil palm plantations have expanded rapidly in Southeast Asia, particularly in Indonesia and Malay... more Oil palm plantations have expanded rapidly in Southeast Asia, particularly in Indonesia and Malaysia. A lot of products, including food and other edible products, oleo-chemicals, cosmetics, personal and household care, pharmaceutical products, and biodiesels are derived from palm oil, thus making them one of the most economically important plants. After 25–30 years of age, the palms are felled and replaced due to declining oil production. Oil palm trunks (OPT) are considered significant waste products. The trunks remain on the plantation site for nutrient recycling or burning. This increases insect and fungi populations causing environmental problems for the new palm generation or air pollution due to the fire. Up till now, OPT has received less attention in research studies. Therefore, this review summarizes the utilization of OPT into products made of oil palm fibers mainly derived from OPT and its application as the substitution of wood panel products. Some research works have be...
Forests
The aim of this pioneering study was to compare and evaluate two different pre-treatment processe... more The aim of this pioneering study was to compare and evaluate two different pre-treatment processes of wooden surfaces prior to varnishing by sanding or thermal compression in terms of the impact on the color characteristics of the varnished surface. In the experiment, a wood veneer of black alder and birch before varnishing was subjected to sanding with a sandpaper of 180 grit size, or thermal compression at temperatures of 180 and 210 °C. Three different kinds of commercially manufactured transparent varnish (water-based (WB) varnish, polyurethane (PUR) varnish and UV-cured (UV) varnish) were applied to the prepared veneer surfaces. The samples prepared in this way were also subjected to an artificial aging process in indoor conditions by ultraviolet light and infrared irradiation (UVL + IR). The colors of the surfaces in the CIE L*a*b* system were measured and color differences (ΔL*, Δa*, Δb* and ΔE) were determined for sanded and thermally densified, unvarnished and varnished, as...
Наукові праці Лісівничої академії наук України, Dec 26, 2019
Construction and Building Materials
Abstract In this study the effect of veneer densification on the temperature change inside the pl... more Abstract In this study the effect of veneer densification on the temperature change inside the plywood during the hot pressing step was analyzed. In addition, the shear strength of the plywood was determined. Rotary-cut birch veneer and phenol-formaldehyde resin were used to make the plywood samples. The multi-layers plywood structures made of densified and non-densified veneers with and without adhesive were investigated. Plywood products of 3, 5, 7, 9 and 11-layers were manufactured under laboratory conditions. It was found that the multi-layers plywood made of densified veneers was heated faster when compared to the plywood made of non-densified veneers. This will reduce the pressing time of plywood made of densified veneer by 2–29% depending on the number of veneer layers. The shear strength values of the plywood made of densified veneers were found two times higher than the normalized value of 1.0 MPa, meeting the EN 314-1 standard requirements. Findings of this work are useful for industrial applications to optimize the plywood production.
Polymers
This study examined the effects of selected types of thermoplastics on the physical and mechanica... more This study examined the effects of selected types of thermoplastics on the physical and mechanical properties of polymer-triticale boards. The investigated thermoplastics differed in their type (polypropylene (PP), polyethylene (PE), polystyrene (PS)), form (granulate, agglomerate) and origin (native, recycled). The resulting five-ply boards contained layers made from different materials (straw or pine wood) and featured different moisture contents (2%, 25%, and 7% for the face, middle, and core layers, respectively). Thermoplastics were added only to two external layers, where they substituted 30% of straw particles. This study demonstrated that, irrespective of their type, thermoplastics added to the face layers most favorably reduced the hydrophobic properties of the boards, i.e., thickness, swelling, and V100, by nearly 20%. The bending strength and modulus of elasticity were about 10% lower in the experimental boards than in the reference ones, but still within the limits set o...
Polymers
Thermoplastic films exhibit good potential to be used as adhesives for the production of veneer-b... more Thermoplastic films exhibit good potential to be used as adhesives for the production of veneer-based composites. This work presents the first effort to develop and evaluate composites based on alder veneers and high-density polyethylene (HDPE) film. The effects of hot-pressing temperature (140, 160, and 180 °C), hot-pressing pressure (0.8, 1.2, and 1.6 MPa), hot-pressing time (1, 2, 3, and 5 min), and type of adhesives on the physical and mechanical properties of alder plywood panels were investigated. The effects of these variables on the core-layer temperature during the hot pressing of multiplywood panels using various adhesives were also studied. Three types of adhesives were used: urea–formaldehyde (UF), phenol–formaldehyde (PF), and HDPE film. UF and PF adhesives were used for the comparison. The findings of this work indicate that formaldehyde-free HDPE film adhesive gave values of mechanical properties of alder plywood panels that are comparable to those obtained with tradi...
Forests
Wood remains one of the most attractive building materials [...]
Polymers
The ongoing transition from a linear to a circular, low-carbon bioeconomy is crucial for reducing... more The ongoing transition from a linear to a circular, low-carbon bioeconomy is crucial for reducing the consumption of global natural resources, minimizing waste generation, reducing carbon emissions, and creating more sustainable growth and jobs, the prerequisites necessary to achieve climate neutrality targets and stop biodiversity loss [...]
Forests
Ukrainian companies mainly use birch in the manufacture of plywood, but species, such as black al... more Ukrainian companies mainly use birch in the manufacture of plywood, but species, such as black alder, are not yet widely used in the manufacture of plywood due to their poorer properties. It is well known that thermal compression is often used to improve the properties of solid wood. Good lay-up schemes of veneer can maximize the advantages and minimize the disadvantages of these wood species, and generally improve the utility value of the plywood. This research aimed to develop plywood panels with two wood species and two types of veneer treatments in order to evaluate the influences of different lay-up schemes on the properties of the plywood. Five-layer plywood panels were formed with 16 different lay-up schemes using birch (Betula verrucosa Ehrh.) (B) and black alder (Alnus glutinosa L.) (A) veneers, which were non-densified (N) and thermally densified (D). The different lay-up schemes were used to identify opportunities to improve the mechanical and physical properties of the p...
Polymers
Traditional wood-based composites are bonded with synthetic formaldehyde-based adhesives [...]
Materials
The aim of this study was to improve the properties of lightweight particleboards by their veneer... more The aim of this study was to improve the properties of lightweight particleboards by their veneering. The industrially produced wood particles, rotary-cut birch veneer, expanded polystyrene (EPS) granules and urea-formaldehyde (UF) resin were used to manufacture non-veneered and veneered boards in laboratory conditions. The boards were manufactured with different densities of 350, 450 and 550 kg/m3 and with various levels of EPS content 4, 7 and 10%. Boards without EPS granules as the reference were also manufactured. Bending strength (MOR), modulus of elasticity in bending (MOE), internal bond (IB) strength, thickness swelling (TS) and water absorption (WA) of lightweight particleboards were determined. This study confirmed that veneering of lightweight particleboards by birch veneer improved mechanical properties significantly. The MOR and MOE of veneered boards throughout the whole density range of 350–550 kg/m3 meet the requirements of the CEN/TS 16368 for lightweight particlebo...
Annals of Warsaw University of Life Sciences - SGGW. Forestry and Wood Technology, 2014
Polymers
The volume of deadwood increases annually because of changes in environmental, climatic, and hydr... more The volume of deadwood increases annually because of changes in environmental, climatic, and hydrological conditions. On the other hand, during the last decade, manufacturers of wood-based boards have been facing an acute problem of a shortage of conventional raw materials. The purpose of this study was to evaluate the possibility of using wood particles from deadwood in the production of particleboards. Three-layer particleboards with different content of deadwood particles (0%, 25%, 50%, 75%, 100%) were produced. Conventional urea-formaldehyde (UF) resin was used for gluing the particles. The physical and mechanical properties of the boards, as well as the formaldehyde content in the boards, were determined. In addition, the effect of adding melamine-urea-formaldehyde (MUF) resin to UF adhesive on the properties of the boards was investigated. Replacing conventional sound wood particles with deadwood particles leads to deterioration of the physical and mechanical properties of the...
Materials
In this work, to better understand the bonding process of plastic plywood panels, the effects of ... more In this work, to better understand the bonding process of plastic plywood panels, the effects of recycled low-density polyethylene (rLDPE) film of three thicknesses (50, 100, and 150 µm) and veneers of four various wood species (beech, birch, hornbeam, and poplar) on the properties of panels were studied. The obtained properties were also compared with the properties of plywood panels bonded by virgin low-density polyethylene (LDPE) film. The results showed that properties of plywood samples bonded with rLDPE and virgin LDPE films differ insignificantly. Samples bonded with rLDPE film demonstrated satisfactory physical and mechanical properties. It was also established that the best mechanical properties of plywood are provided by beech veneer and the lowest by poplar veneer. However, poplar plywood had the best water absorption and swelling thickness, and the bonding strength at the level of birch and hornbeam plywood. The properties of rLDPE-bonded plywood improved with increasing...
Forests
Surface roughness is an important factor during the processes of wood gluing and finishing. This ... more Surface roughness is an important factor during the processes of wood gluing and finishing. This study proposed a new approach for the preparation of wood veneer surfaces before varnishing through the use of thermal compression instead of sanding. The quality of the pre-treated surface was examined using surface roughness measurements. In the experiment, a wood veneer of black alder and birch, before varnishing, was subjected to sanding with a sandpaper of 180 grit size, and thermal compression at temperatures of 180 and 210 °C. Three different types of commercially manufactured varnishes (water-based (WB), polyurethane (PUR) and UV-cured (UV)) were applied to the prepared veneer surfaces with various numbers of varnish layers. Seven roughness parameters such as Ra, Rz, Rq, Rp, Rv, Rsk, and Rku were determined for the sanded and thermally densified unvarnished and varnished surfaces. The profile surface was recorded with a portable surface roughness tester along and across the wood ...
Coatings
The objective of this study was to investigate the gloss of different types of commercially manuf... more The objective of this study was to investigate the gloss of different types of commercially manufactured varnish systems, including water-based (WB), polyurethane (PUR) and UV-cured (UV), applied on veneered MDF panels with sanded and thermally densified alder and birch wood veneers. The varnishes were applied at various numbers of layers on veneered panels. The gloss was measured at three angles of incident light: 20°, 60° and 85°. Statistical analysis showed that the type of varnish, the number of layers, the pre-treatment process, the wood species and direction of wood fibers significantly affect gloss of the coatings of veneered MDF panels. The type of varnish had a dominant effect on gloss. The highest gloss values were measured for the UV-varnished surface, and the lowest for WB- and PUR-varnished surfaces. Gloss was enhanced with an increase in the number of layers. Birch veneer provided higher gloss values compared to alder veneer. The gloss values measured along the wood fi...
Annals of Warsaw Agricultural University. Forestry and Wood Technology, 2003
European Journal of Wood and Wood Products, 2020
The plywood consumption in various applications is increasing, especially in construction. In ser... more The plywood consumption in various applications is increasing, especially in construction. In service, plywood can be exposed to a range of outdoor conditions, sometimes at elevated temperatures. This requires an understanding of the structural behavior and knowledge of the effects of the elevated temperatures on the properties of plywood. Therefore, the objective of this research was to study the effect of exposure time on physical and mechanical properties of plywood at elevated temperatures. The plywood samples were tested after exposure to nine different temperatures (50 °C, 75 °C, 100 °C, 125 °C, 150 °C, 175 °C, 200 °C, 225 °C and 250 °C) and ten exposure time levels (0.5, 1, 1.5, 2, 2.5, 3, 6, 8, 10 and 12 h) at each temperature. Additionally, a set of control samples was tested at room temperature. The findings of this study indicated that exposure of plywood panels to elevated temperature caused significant degradation of their bending and bonding strengths, whereas the hydrophobicity of the panels improved. Three stages of plywood degradation could be distinguished. Below 175 °C, there is a slow decline in strength; the decisive change already occurs at 175 °C; but as temperature increases beyond 175 °C, a rapid decrease in strength is observed. Plywood samples lost 98.1% of their initial strength after 1.5 h of exposure at 250 °C, and lost 98.5% after 6 h of exposure at a temperature of 225 °C. Statistical regression-based models were also developed and evaluated for predicting the strength loss of plywood panels as a function of weight loss. As the weight losses of panels increased, the losses in bending and bonding strength increased too. The decrease in bending and bonding strength only becomes significant when the weight loss exceeds 5%. When the weight losses increased above 15%, plywood samples almost lost their strength.
Effects of short-term thermomechanical densification on the structure and properties of wood veneers
Polymers
Oil palm plantations have expanded rapidly in Southeast Asia, particularly in Indonesia and Malay... more Oil palm plantations have expanded rapidly in Southeast Asia, particularly in Indonesia and Malaysia. A lot of products, including food and other edible products, oleo-chemicals, cosmetics, personal and household care, pharmaceutical products, and biodiesels are derived from palm oil, thus making them one of the most economically important plants. After 25–30 years of age, the palms are felled and replaced due to declining oil production. Oil palm trunks (OPT) are considered significant waste products. The trunks remain on the plantation site for nutrient recycling or burning. This increases insect and fungi populations causing environmental problems for the new palm generation or air pollution due to the fire. Up till now, OPT has received less attention in research studies. Therefore, this review summarizes the utilization of OPT into products made of oil palm fibers mainly derived from OPT and its application as the substitution of wood panel products. Some research works have be...
Forests
The aim of this pioneering study was to compare and evaluate two different pre-treatment processe... more The aim of this pioneering study was to compare and evaluate two different pre-treatment processes of wooden surfaces prior to varnishing by sanding or thermal compression in terms of the impact on the color characteristics of the varnished surface. In the experiment, a wood veneer of black alder and birch before varnishing was subjected to sanding with a sandpaper of 180 grit size, or thermal compression at temperatures of 180 and 210 °C. Three different kinds of commercially manufactured transparent varnish (water-based (WB) varnish, polyurethane (PUR) varnish and UV-cured (UV) varnish) were applied to the prepared veneer surfaces. The samples prepared in this way were also subjected to an artificial aging process in indoor conditions by ultraviolet light and infrared irradiation (UVL + IR). The colors of the surfaces in the CIE L*a*b* system were measured and color differences (ΔL*, Δa*, Δb* and ΔE) were determined for sanded and thermally densified, unvarnished and varnished, as...
Наукові праці Лісівничої академії наук України, Dec 26, 2019
Construction and Building Materials
Abstract In this study the effect of veneer densification on the temperature change inside the pl... more Abstract In this study the effect of veneer densification on the temperature change inside the plywood during the hot pressing step was analyzed. In addition, the shear strength of the plywood was determined. Rotary-cut birch veneer and phenol-formaldehyde resin were used to make the plywood samples. The multi-layers plywood structures made of densified and non-densified veneers with and without adhesive were investigated. Plywood products of 3, 5, 7, 9 and 11-layers were manufactured under laboratory conditions. It was found that the multi-layers plywood made of densified veneers was heated faster when compared to the plywood made of non-densified veneers. This will reduce the pressing time of plywood made of densified veneer by 2–29% depending on the number of veneer layers. The shear strength values of the plywood made of densified veneers were found two times higher than the normalized value of 1.0 MPa, meeting the EN 314-1 standard requirements. Findings of this work are useful for industrial applications to optimize the plywood production.
Polymers
This study examined the effects of selected types of thermoplastics on the physical and mechanica... more This study examined the effects of selected types of thermoplastics on the physical and mechanical properties of polymer-triticale boards. The investigated thermoplastics differed in their type (polypropylene (PP), polyethylene (PE), polystyrene (PS)), form (granulate, agglomerate) and origin (native, recycled). The resulting five-ply boards contained layers made from different materials (straw or pine wood) and featured different moisture contents (2%, 25%, and 7% for the face, middle, and core layers, respectively). Thermoplastics were added only to two external layers, where they substituted 30% of straw particles. This study demonstrated that, irrespective of their type, thermoplastics added to the face layers most favorably reduced the hydrophobic properties of the boards, i.e., thickness, swelling, and V100, by nearly 20%. The bending strength and modulus of elasticity were about 10% lower in the experimental boards than in the reference ones, but still within the limits set o...
Polymers
Thermoplastic films exhibit good potential to be used as adhesives for the production of veneer-b... more Thermoplastic films exhibit good potential to be used as adhesives for the production of veneer-based composites. This work presents the first effort to develop and evaluate composites based on alder veneers and high-density polyethylene (HDPE) film. The effects of hot-pressing temperature (140, 160, and 180 °C), hot-pressing pressure (0.8, 1.2, and 1.6 MPa), hot-pressing time (1, 2, 3, and 5 min), and type of adhesives on the physical and mechanical properties of alder plywood panels were investigated. The effects of these variables on the core-layer temperature during the hot pressing of multiplywood panels using various adhesives were also studied. Three types of adhesives were used: urea–formaldehyde (UF), phenol–formaldehyde (PF), and HDPE film. UF and PF adhesives were used for the comparison. The findings of this work indicate that formaldehyde-free HDPE film adhesive gave values of mechanical properties of alder plywood panels that are comparable to those obtained with tradi...