International Journal of Adhesion and Adhesives, 2024
The paper deals with the behaviour of glued joints of wooden sections exposed to long and short t... more The paper deals with the behaviour of glued joints of wooden sections exposed to long and short term elevated temperatures. If the adhesive is not sufficiently temperature resistant, the glued joint may lose adhesion, which could result in a change in behaviour of the glued element cross-section when exposed to fire. Moreover, detailed knowledge of the behaviour of bonded joints under such long and short term thermal exposures will enable us to make informed decisions about the need for major structural intervention in structures post exposure. Three types of adhesives: phenol-resorcinol-formaldehyde (PRF), polyurethane (PUR) and emulsion polyisocyanate (EPI), commonly used in load bearing wooden structures, were chosen for the experimental work. Thermal analysis showed that the PRF and PUR were not sufficiently cured, especially the PRF. Calorimetric analysis showed the point at which thermal degradation of all three adhesives began, at 135 • C for EPI and at about 160 • C for PRF and PUR. Spruce lap joints, with a cross section of 40 × 48 mm, bonded using these adhesives were exposed to temperatures of 140 and 170 • C. To properly distinguish the effect of thermal exposure duration on the lap joints, different thermal durations were used: 20, 40, 60 and 80 min, plus 3 h and 1 day. The thermal resistance at each of the elevated temperatures was investigated through measurement of the reduction in tensile shear strength. At an elevated temperature of 140 • C there was no significant strength reduction in all of the tested adhesives, it was only a longer duration (1 day) that produced a reduction in the tensile shear strength properties (31.0% for PRF, 16.2% for PUR and 34.1% for EPI). A temperature of 170 • C produced a greater decrease in strength, a significant drop (more than 15%) was found for PRF and EPI after an exposure of 40 min; for PUR after 60 min. Moreover, the longer duration exposures to a temperature of 170 • C resulted in a total loss in strength for PUR and a half loss of strength for EPI; for both these isocyanates adhesives this was confirmed by the total loss of wood failure criterium. On the contrary, a strength reduction of 50.0% and a sufficient wood failure criterium for a 1day temperature exposure at 170 • C was found for PRF.
This experiment compared commercially available moisture meters (three capacitive metersand one r... more This experiment compared commercially available moisture meters (three capacitive metersand one resistance meter) and tested their predictive ability at different moisture conditions on selected beech (Fagus sylvatica) and spruce (Picea abies (L.) Karst.) wood samples. The measurements were carried out on the samples at specified moisture intervals ranging from 5% to 30% moisture content (MC). The resistance meter showed a close correlation to gravimetric MC values; the influence of the measuring direction for MC below 17% was found when higher MCs in the transverse direction for both species were archieved. The difference was 4.6 times higher for softwood and 1.6 times higher for hardwood. Differences between radial and tangential transverse measuring were not observed. The close correlation coefficient of MC measurements was also found for capacitive methods. The effect of the direction was found for all the tested meters when higher MC values in the longitudinal measurements were...
Asia-Pacific Conference on FRP in Structures, 2007
The principle of reinforcing and strengthening timber elements can be considered to be a specific... more The principle of reinforcing and strengthening timber elements can be considered to be a specific application. In the area of reinforcement, factors related to anisotropic timber properties must be taken into consideration. The authors of this article focus on evaluating the increased load bearing capacity of timber elements using FRP materials. Various marginal conditions, which have an impact on the value of strengthening, have been assessed in the experiments. These conditions included the type of fabric, its thickness, and the type of timber material. (solid and glued laminated timber, glulam). Furthermore, the types and causes of individual failures of both beams and FRP materials were analysed. The elasticity and flexibility characteristics of materials strengthened by such methods were determined. The relationships achieved were compared with a numerical model using a finite element method in the ANSYS program. However, the resultant values are not the only important consider...
The highest resistance to the action of wood-decay fungi was achieved for boards bonded with ceme... more The highest resistance to the action of wood-decay fungi was achieved for boards bonded with cementitious binder, for which the mass loss (ML) was passive for the tested fungi at both 3.8% for Coniophora puteana and 3.6% for Pleurotus ostreatus due to the carbonation process. By contrast, the lowest bioresistance was shown for particleboard. The achieved ML values were related to the changes of the internal structure, which were proven by the vertical density profile parameters and the surface area parameter. The effects of the ML and delamination process by immersion in water on the internal bond strength were determined individually to distinguish both synergistic
parameters. The results showed the effect of long-term water immersion on the loss of internal bond strength, especially for wood particle board.
International Journal of Adhesion and Adhesives, 2021
Lap joints were prepared by gluing spruce plates with three types of adhesives (phenol-resorcinol... more Lap joints were prepared by gluing spruce plates with three types of adhesives (phenol-resorcinol-formaldehyde, PRF; one-component polyurethane, PUR; and epoxy, EP). The joints were exposed to 140 °C and 170 °C for 24 h (20, 40, 60, 80, 180 and 1140 min) and then loaded in four-point bending to verify the behavior of glued lap joints in building structures exposed to fire in its initial stage and stressed in transverse direction. The lap joint strength was compared to that of spruce specimens exposed to the same conditions and of the same stressed area. The failure mode of lap joints was evaluated visually; the failure mode was caused by exceeding the transverse load capacity of bulk wood. The strength of spruce fell by 40% after exposure to both temperatures for 20 min and next decrease began after 80-min exposure at 170 °C as a result of the beginning of hemicellulose decomposition. Only PUR improved the spruce strength at 20 °C (by 30%) and at both temperatures except that after exposure to 170 °C for long time (3 and 24 h). The PUR-spruce lap joints revealed very good fire resistance for the initial fire exposure (80 min at 140 °C and 40 min at 170 °C). The strength of both PRF and EP lap joints was the same as that of spruce at 20 °C but PRF improved the spruce strength at 140 °C after 20-min exposure (by 45%) and at 170 °C, where PRF lap joints bore the load irrespective of wood degradation. The EP lap joints revealed the worse thermal resistance due to the rubber state of incompletely post-cured and degraded EP. To evaluate an adhesive structure and its prospective change after thermal exposure and to evaluate the influence of an adhesive thickness, the adhesives were cured in a form of bulk and thin films and tested by Thermogravimetry (TGA), Differential Scanning Calorimetry, Fourier Transformed Infrared Spectroscopy (FTIR) and evolved gas analysis (EVA) using TGA-FTIR. Curing and post-curing process was shown to be thickness dependent only in case of EP. Low-molecular components detected during adhesives heating were products of PUR and PRF post-curing and of unreacted hardnener decomposition in case of EP. All adhesives were degraded after thermal exposure to both elevated temperatures.
The work deals with the modification of the properties of epoxy adhesive. The modification consis... more The work deals with the modification of the properties of epoxy adhesive. The modification consists of reinforcing this adhesive with cellulose fibres. In the field of wood glued elements, the current research focuses on the possibility of increasing the ductile behaviour of the epoxy adhesive, which would significantly increase the ability of the adhesive to transfer the stresses induced by the volumetric changes of the wood adherend. For this purpose, the adhesive was modified with fibres having a reinforcing character, which may include cellulose fibres. Due to the epoxy resin’s non-polar nature and the cellulose fibre's hydrophilic nature, which inhibits the fibre's homogeneous dispersion, the fibres have been modified with silanes. This paper describes the effect of adhesive modification by determination of tensile and shear strength at different amounts of filling and different types of silane pre-treatment of cellulose fibres. The optimum filling amount can be conside...
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...
The aim of the experiment was to determine the durability of wood based board materials against w... more The aim of the experiment was to determine the durability of wood based board materials against wood-rot fungi (Serpula lacrymans) effect. The particle boards, oriented strands boards and plywood as the testing materials were chosen. The spruce solid wood as the reference testing material was selected due to the fact that is most common timber species in the Central European region. The testing samples were exposed to wood-rot fungi and in the individual time periods the weight loss (declaring the deterioration process) and mechanical properties (static bending strength and tensile strength perpendicular to the plane of the board) was investigated. It was found that the deterioration of board materials in a very small weight decreases (up to 1.0%) leads to a significant decrease of their strength properties.
This article describes the evaluation of the durability of joints composed of wood adherends with... more This article describes the evaluation of the durability of joints composed of wood adherends with a bonded layer of fibre-reinforced polymer (FRP) fabric. Carbon and glass fibres in an epoxy matrix were studied. The main purpose of FRP usage with timber in the construction industry is generally to improve the stiffness/strength of reinforced members without any influence on their service-life or any environmental impact. From the perspective of the timber reinforcement process, optimal dimensional stability during moisture changes in wood should be one of the most important criteria for such joints. Therefore, FRP/wood joints were evaluated with regard to the influence of real external environmental conditions on the bondline over a period of 40 months. During exposure to these conditions, specimen failures and defects were continuously visually evaluated. The decisive factor in this evaluation was bond integrity, verified by the tensile shear strength of the FRP/wood joint. After the experimental study, it was noted that the first 20 months have a significant effect on bondline failure occurrences, which involve decreases in tensile shear strength. In the next 20 months, the FRP/wood bondlines resist other severe hygrothermal stresses without significant strength decreases. An additional observed parameter was the percentage of wood failure in the bonded area of single lap joints, which characterises the mode of failure of the bonded joint. To determine the influence of ageing on adhesive due to ultraviolet radiation and varying temperature, infrared absorption spectroscopy analysis was performed to reveal changes in the macromolecular structure of the epoxy adhesive. Findings showed that UV radiation had a significant influence on the degradation of the adhesive structure.
The contribution deals with the durability of modified wood-polymer composite samples intended to... more The contribution deals with the durability of modified wood-polymer composite samples intended to alternate solid wood non-bearing structures (fences, sidings). The modification was made to the polymer matrix, which is partly consisting of commercially available regranulate. Four types of composite with varying amount of regranulate admixture are exposed to adverse ambience simulating the external conditions through moisture, freeze and high temperature action. The aim of the research is to determine the influence of regranulate share on the visual and mechanical characteristic of the material, which would be decisive in the process of specific tile production.
The paper deals with the evaluation of epoxy adhesive modification by silane coupling agent used ... more The paper deals with the evaluation of epoxy adhesive modification by silane coupling agent used for gluing process of spruce wood. Moreover, the usage of primer containing the silane coupling agent was performed to find out, whether better compatibility between spruce wood and epoxy adhesive at the interface bondline can ensure sufficient resistance to delamination process. As the main criterion, tensile shear strength properties of glued specimens in different thermal and moisture exposures were carried out.
International Journal of Adhesion and Adhesives, 2024
The paper deals with the behaviour of glued joints of wooden sections exposed to long and short t... more The paper deals with the behaviour of glued joints of wooden sections exposed to long and short term elevated temperatures. If the adhesive is not sufficiently temperature resistant, the glued joint may lose adhesion, which could result in a change in behaviour of the glued element cross-section when exposed to fire. Moreover, detailed knowledge of the behaviour of bonded joints under such long and short term thermal exposures will enable us to make informed decisions about the need for major structural intervention in structures post exposure. Three types of adhesives: phenol-resorcinol-formaldehyde (PRF), polyurethane (PUR) and emulsion polyisocyanate (EPI), commonly used in load bearing wooden structures, were chosen for the experimental work. Thermal analysis showed that the PRF and PUR were not sufficiently cured, especially the PRF. Calorimetric analysis showed the point at which thermal degradation of all three adhesives began, at 135 • C for EPI and at about 160 • C for PRF and PUR. Spruce lap joints, with a cross section of 40 × 48 mm, bonded using these adhesives were exposed to temperatures of 140 and 170 • C. To properly distinguish the effect of thermal exposure duration on the lap joints, different thermal durations were used: 20, 40, 60 and 80 min, plus 3 h and 1 day. The thermal resistance at each of the elevated temperatures was investigated through measurement of the reduction in tensile shear strength. At an elevated temperature of 140 • C there was no significant strength reduction in all of the tested adhesives, it was only a longer duration (1 day) that produced a reduction in the tensile shear strength properties (31.0% for PRF, 16.2% for PUR and 34.1% for EPI). A temperature of 170 • C produced a greater decrease in strength, a significant drop (more than 15%) was found for PRF and EPI after an exposure of 40 min; for PUR after 60 min. Moreover, the longer duration exposures to a temperature of 170 • C resulted in a total loss in strength for PUR and a half loss of strength for EPI; for both these isocyanates adhesives this was confirmed by the total loss of wood failure criterium. On the contrary, a strength reduction of 50.0% and a sufficient wood failure criterium for a 1day temperature exposure at 170 • C was found for PRF.
This experiment compared commercially available moisture meters (three capacitive metersand one r... more This experiment compared commercially available moisture meters (three capacitive metersand one resistance meter) and tested their predictive ability at different moisture conditions on selected beech (Fagus sylvatica) and spruce (Picea abies (L.) Karst.) wood samples. The measurements were carried out on the samples at specified moisture intervals ranging from 5% to 30% moisture content (MC). The resistance meter showed a close correlation to gravimetric MC values; the influence of the measuring direction for MC below 17% was found when higher MCs in the transverse direction for both species were archieved. The difference was 4.6 times higher for softwood and 1.6 times higher for hardwood. Differences between radial and tangential transverse measuring were not observed. The close correlation coefficient of MC measurements was also found for capacitive methods. The effect of the direction was found for all the tested meters when higher MC values in the longitudinal measurements were...
Asia-Pacific Conference on FRP in Structures, 2007
The principle of reinforcing and strengthening timber elements can be considered to be a specific... more The principle of reinforcing and strengthening timber elements can be considered to be a specific application. In the area of reinforcement, factors related to anisotropic timber properties must be taken into consideration. The authors of this article focus on evaluating the increased load bearing capacity of timber elements using FRP materials. Various marginal conditions, which have an impact on the value of strengthening, have been assessed in the experiments. These conditions included the type of fabric, its thickness, and the type of timber material. (solid and glued laminated timber, glulam). Furthermore, the types and causes of individual failures of both beams and FRP materials were analysed. The elasticity and flexibility characteristics of materials strengthened by such methods were determined. The relationships achieved were compared with a numerical model using a finite element method in the ANSYS program. However, the resultant values are not the only important consider...
The highest resistance to the action of wood-decay fungi was achieved for boards bonded with ceme... more The highest resistance to the action of wood-decay fungi was achieved for boards bonded with cementitious binder, for which the mass loss (ML) was passive for the tested fungi at both 3.8% for Coniophora puteana and 3.6% for Pleurotus ostreatus due to the carbonation process. By contrast, the lowest bioresistance was shown for particleboard. The achieved ML values were related to the changes of the internal structure, which were proven by the vertical density profile parameters and the surface area parameter. The effects of the ML and delamination process by immersion in water on the internal bond strength were determined individually to distinguish both synergistic
parameters. The results showed the effect of long-term water immersion on the loss of internal bond strength, especially for wood particle board.
International Journal of Adhesion and Adhesives, 2021
Lap joints were prepared by gluing spruce plates with three types of adhesives (phenol-resorcinol... more Lap joints were prepared by gluing spruce plates with three types of adhesives (phenol-resorcinol-formaldehyde, PRF; one-component polyurethane, PUR; and epoxy, EP). The joints were exposed to 140 °C and 170 °C for 24 h (20, 40, 60, 80, 180 and 1140 min) and then loaded in four-point bending to verify the behavior of glued lap joints in building structures exposed to fire in its initial stage and stressed in transverse direction. The lap joint strength was compared to that of spruce specimens exposed to the same conditions and of the same stressed area. The failure mode of lap joints was evaluated visually; the failure mode was caused by exceeding the transverse load capacity of bulk wood. The strength of spruce fell by 40% after exposure to both temperatures for 20 min and next decrease began after 80-min exposure at 170 °C as a result of the beginning of hemicellulose decomposition. Only PUR improved the spruce strength at 20 °C (by 30%) and at both temperatures except that after exposure to 170 °C for long time (3 and 24 h). The PUR-spruce lap joints revealed very good fire resistance for the initial fire exposure (80 min at 140 °C and 40 min at 170 °C). The strength of both PRF and EP lap joints was the same as that of spruce at 20 °C but PRF improved the spruce strength at 140 °C after 20-min exposure (by 45%) and at 170 °C, where PRF lap joints bore the load irrespective of wood degradation. The EP lap joints revealed the worse thermal resistance due to the rubber state of incompletely post-cured and degraded EP. To evaluate an adhesive structure and its prospective change after thermal exposure and to evaluate the influence of an adhesive thickness, the adhesives were cured in a form of bulk and thin films and tested by Thermogravimetry (TGA), Differential Scanning Calorimetry, Fourier Transformed Infrared Spectroscopy (FTIR) and evolved gas analysis (EVA) using TGA-FTIR. Curing and post-curing process was shown to be thickness dependent only in case of EP. Low-molecular components detected during adhesives heating were products of PUR and PRF post-curing and of unreacted hardnener decomposition in case of EP. All adhesives were degraded after thermal exposure to both elevated temperatures.
The work deals with the modification of the properties of epoxy adhesive. The modification consis... more The work deals with the modification of the properties of epoxy adhesive. The modification consists of reinforcing this adhesive with cellulose fibres. In the field of wood glued elements, the current research focuses on the possibility of increasing the ductile behaviour of the epoxy adhesive, which would significantly increase the ability of the adhesive to transfer the stresses induced by the volumetric changes of the wood adherend. For this purpose, the adhesive was modified with fibres having a reinforcing character, which may include cellulose fibres. Due to the epoxy resin’s non-polar nature and the cellulose fibre's hydrophilic nature, which inhibits the fibre's homogeneous dispersion, the fibres have been modified with silanes. This paper describes the effect of adhesive modification by determination of tensile and shear strength at different amounts of filling and different types of silane pre-treatment of cellulose fibres. The optimum filling amount can be conside...
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...
The aim of the experiment was to determine the durability of wood based board materials against w... more The aim of the experiment was to determine the durability of wood based board materials against wood-rot fungi (Serpula lacrymans) effect. The particle boards, oriented strands boards and plywood as the testing materials were chosen. The spruce solid wood as the reference testing material was selected due to the fact that is most common timber species in the Central European region. The testing samples were exposed to wood-rot fungi and in the individual time periods the weight loss (declaring the deterioration process) and mechanical properties (static bending strength and tensile strength perpendicular to the plane of the board) was investigated. It was found that the deterioration of board materials in a very small weight decreases (up to 1.0%) leads to a significant decrease of their strength properties.
This article describes the evaluation of the durability of joints composed of wood adherends with... more This article describes the evaluation of the durability of joints composed of wood adherends with a bonded layer of fibre-reinforced polymer (FRP) fabric. Carbon and glass fibres in an epoxy matrix were studied. The main purpose of FRP usage with timber in the construction industry is generally to improve the stiffness/strength of reinforced members without any influence on their service-life or any environmental impact. From the perspective of the timber reinforcement process, optimal dimensional stability during moisture changes in wood should be one of the most important criteria for such joints. Therefore, FRP/wood joints were evaluated with regard to the influence of real external environmental conditions on the bondline over a period of 40 months. During exposure to these conditions, specimen failures and defects were continuously visually evaluated. The decisive factor in this evaluation was bond integrity, verified by the tensile shear strength of the FRP/wood joint. After the experimental study, it was noted that the first 20 months have a significant effect on bondline failure occurrences, which involve decreases in tensile shear strength. In the next 20 months, the FRP/wood bondlines resist other severe hygrothermal stresses without significant strength decreases. An additional observed parameter was the percentage of wood failure in the bonded area of single lap joints, which characterises the mode of failure of the bonded joint. To determine the influence of ageing on adhesive due to ultraviolet radiation and varying temperature, infrared absorption spectroscopy analysis was performed to reveal changes in the macromolecular structure of the epoxy adhesive. Findings showed that UV radiation had a significant influence on the degradation of the adhesive structure.
The contribution deals with the durability of modified wood-polymer composite samples intended to... more The contribution deals with the durability of modified wood-polymer composite samples intended to alternate solid wood non-bearing structures (fences, sidings). The modification was made to the polymer matrix, which is partly consisting of commercially available regranulate. Four types of composite with varying amount of regranulate admixture are exposed to adverse ambience simulating the external conditions through moisture, freeze and high temperature action. The aim of the research is to determine the influence of regranulate share on the visual and mechanical characteristic of the material, which would be decisive in the process of specific tile production.
The paper deals with the evaluation of epoxy adhesive modification by silane coupling agent used ... more The paper deals with the evaluation of epoxy adhesive modification by silane coupling agent used for gluing process of spruce wood. Moreover, the usage of primer containing the silane coupling agent was performed to find out, whether better compatibility between spruce wood and epoxy adhesive at the interface bondline can ensure sufficient resistance to delamination process. As the main criterion, tensile shear strength properties of glued specimens in different thermal and moisture exposures were carried out.
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Papers by Jan Vanerek
parameters. The results showed the effect of long-term water immersion on the loss of internal bond strength, especially for wood particle board.
parameters. The results showed the effect of long-term water immersion on the loss of internal bond strength, especially for wood particle board.