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Thermal modification of wood changes its chemical, physical, and structural properties, which may affect adhesive bondline quality and bonding performance. This research compared the effect of thermal modification on the adhesive bonding performance of poplar (Liriodendron tulipifera) wood. Samples were prepared from thermally modified and unmodified yellow poplar using one-component polyurethane (PUR) and polyvinyl acetate (PVA), as they are adhesives used in wood products. Microscopic properties of the bondlines were investigated to understand shear performance and durability. Adhesive line thickness, penetration, shear strength, and moisture durability were measured, and failure modes were recorded. Thermal modification negatively affected the wood and adhesive interaction by reducing penetration (31.2% in PUR and 29% in PVA), therefore creating a thicker adhesive line (70% in PUR and 2% in PVA) and consequently causing a significant reduction in the shear strength of both adhesive types (27% in PUR and 36% in PVA) compared with non-modified specimens. The PUR adhesive had higher shear strength than PVA by 2.7% in non-modified and 14% in thermally modified wood. [ABSTRACT FROM AUTHOR]

Particleboards, which are widely used in various fields, are commonly coated with solid and liquid surface coating materials to achieve better physical, mechanical, and aesthetic results. This study produced lowdensity particleboards from waste wood bark using different adhesive mixtures and densities. These particleboards were then coated with three types of varnish: water-based (Aq), polyurethane-based (Pu), and oil/wax-based (Ow). The color, gloss, and surface roughness values of the coated boards were determined to investigate the effect of varnish type, total adhesive usage, and density on these properties. In the board groups produced with the same glue ratio and density, the roughness values obtained with Ow varnish application were mostly higher compared to Aq and Pu. In the Ow varnish type, the roughness (Rmax) decreased linearly with increasing total adhesive amount in particleboards produced at low density (320 kg/m³). The highest color change (ΔE*) values for all variations were obtained in the Ow varnish type, while the highest gloss values were achieved at 85° and in the B2 (4%-420 kg/m³) board group. It was concluded that higher density should be preferred for smoother and glossier surfaces, which are important in terms of surface properties and aesthetics. Overall, these findings highlight the preference for higher density to achieve smoother and glossier surfaces in areas where surface properties and aesthetics are significant. [ABSTRACT FROM AUTHOR]

This article reviews publications with the goal of understanding the role of hydrophobic copolymers added to size-press starch as a means to make paper products more resistant to penetration by aqueous fluids. The underlying technology is considered, including background related to starch, size-press equipment, and various hydrophobic copolymers and latex products that have been evaluated. The resulting hydrophobization of the paper has been reported to depend not only on the dosage of the hydrophobic additive, but also on its molecular mass and ionic form. The mechanism appears to rely on an ability of starch to serve as a temporary host for hydrophobic compounds in aqueous solution. It has been proposed that hydrophobic copolymers added with size press starch tend to migrate to the air interface during drying of the starch film, thus allowing the low-energy functional groups, such as styrene or alkyl chains, to face outwards. Further research is needed to address various mechanistic questions. There may be opportunities to further raise the performance of this type of technology as practiced within paper production factories. [ABSTRACT FROM AUTHOR]

Novel lignin-based polyurethane (LPU) and LPU-nanosilica composite films were prepared using in situ polymerization. The effects of various nanosilica contents on the structure and properties of the LPU matrix films were investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), dynamic thermomechanical analysis (DMA), tensile test, and contact angle measurements. The results showed that hydrogen bonding and cross-linking occurred between the -N-H and -C=O functional groups in the LPUnanosilica films. Morphological and surface energy analyses showed uniform dispersion of amine modified silica nanoparticles in the LPU matrix at low concentrations. The incorporation of silica nanoparticles considerably improved the thermal stability and mechanical properties of the LPU films because of the introduction of silicon-oxygen bond between the LPU matrix and nanosilica. Overall, the introduction of small amounts of silica nanoparticles could improve the properties of the renewable LPU films, which are useful in the development of biomaterials. [ABSTRACT FROM AUTHOR]

Fillers can greatly affect the properties of adhesives, and this research aimed at enhancing the performance of adhesives by using different concentrations of fillers. This paper describes the influence of using recycled polyurethane particles (powder of particle size from 10 µm to 50 µm) as a filler on some properties of polyurethane adhesives for the gluing of wood. Two kinds of one-component, moisture-curing polyurethane adhesives were used. The observed properties were the contact angle between the wood and adhesive droplet, and the strength of bonded joints (shear strength). From the results, it was concluded that the contact angle increased with an increase in filler (in the entire observed range from 0% to 15% filler). The content of filler also affected the strength of bonded joints and their thermal stability. The strength of bonded joints decreased with an increase in filler content when samples were conditioned in cold water. However, the strength of bonded joints increased with an increase in filler content when samples were boiled in water. [ABSTRACT FROM AUTHOR]

Effects of cold liquids on the cured film of selected coatings, the thickness of the final film coating on the resulting surface resistance, and different wood species on the resistance of the coating were investigated. It was demonstrated that different liquids affected the degradation of the cured film coating. The most aggressive liquid used was nail polish remover, followed by ethanol 40%, bleach, vinegar, and mouthwash. The least aggressive was dishwashing liquid. There was no evidence of a difference in the quality of the cured film coating applied on softwood and hardwood. The thickness of the coating had no statistically significant effect on the quality of the film. The liquids used for the tests are commonly used in households. [ABSTRACT FROM AUTHOR]

A bio-based polyurethane and a thermosetting acrylic were tested in conjunction with nano-fibrillated cellulose and conventional kraft fiber to evaluate their use as a bio-derived, biodegradable packaging foam. Foams were evaluated for their density, water uptake, and compressive creep behavior. Bio-based urethane had a mean density of 68 kg/m3, mean water uptake of 4% in 24 h, and exceeded the 10% limit on compressive strain when tested at 71 °C and 22 °C, but remained below the limit when tested at -54 °C. The thermosetting acrylic had a mean density of 128 kg/m3, mean water uptake of 337% in 24 h, and showed less than 10% compressive creep at all three temperature conditions. The bio-derived urethane was able to incorporate 4% cellulose by mass, and the thermosetting acrylic was able to incorporate 48% cellulose by mass. In a 12-week test of biodegradation under fungal attack by Gloeophyllum trabeum and Rhodonia placenta, the urethane foam had < 3% mass loss and the acrylic foam had < 1% mass loss. The acrylic foams showed potential for durable packaging, particularly if they could be combined with a surface sealant that could be ruptured at the end of service life to promote degradation of the foam. [ABSTRACT FROM AUTHOR]

Glued-in rods have successfully been used for connections or reinforcement of timber structures due to their high strength and stiffness. However, their performance is potentially sensitive to temperature. This paper deals with an experimental investigation of the connections and adhesives in elevated temperatures. First, dynamic mechanical analysis (DMA) tests were performed to characterize an epoxy (EPX) and a polyurethane (PUR) adhesive. The evolution of the stiffness and the glass transition temperature, Tg, were measured in the range of 30 °C to 120 °C. Then, a total of 66 specimens with glued-in rods and the same adhesives were tested under a static tensile load at 20 °C, 40 °C, 50 °C, 60 °C, and 70 °C. In both types of tests, the EPX outperformed PUR due to its higher stiffness at temperatures of up to 40 °C; however, it showed a more rapid degradation of the stiffness and strength than the PUR at higher temperatures. No direct correlation was established between the Tg and the performance of the connections. The test results suggest that timber structures with glued-in rods may be vulnerable in service at temperatures above 40 °C. [ABSTRACT FROM AUTHOR]

Lignosulfonate and lignosulfonate hydrolyzed under alkaline conditions were used as the polyol components in polyurethane foam formulations. Although the treatment increased hydroxyl group abundance, it did not improve the applicability of hydrolyzed lignosulfonate in polyurethane foam. Thus, the use of original lignosulfonate yielded foams of thermal stability and mechanical properties comparable to other types of biobased foams (Young's moduli 0.95 to 4.42 MPa, 50% weight loss, and temperature ca. 500 °C). Lignosulfonates can be a renewable polyol component for the formulation of rigid, semi-rigid, and flexible foams. [ABSTRACT FROM AUTHOR]

An experimental method was developed in this investigation to evaluate the shear strength of adhesive bonds in solid wood materials. The new method was tested against the standard test methods described in ASTM D-905, EN 205, and EN 302-1. Specimens were constructed of Oriental Beech (Fagus orientalis L.) and bonded with three different wood adhesives. Using the proposed method in the study, unintentional errors in cutting and testing processes of the shear specimens were decreased, which led to a decrease in the variability of the results. The worst stability was observed in the data obtained when the EN 205 and ASTM D-905 standard methods were used. [ABSTRACT FROM AUTHOR]

In this study, the optical and mechanical properties of polyurethane were improved by modified nanocrystalline cellulose (NCC). The surface of NCC was modified by 3-glycidoxypropyltrimethoxysilane (GPTMS) and 3-methacryloxy-propyltrimethoxysilane (MPS) to overcome the lack of compatibility with polyurethane. Polyurethane with modified NCC was characterized by wetting property, X-ray powder diffraction, and thermogravimetric analysis. The pencil hardness, specular gloss, and abrasion resistance of modified polyurethane were determined using the methods of Chinese National Standards GB/T 6739-2006, GB/T 9754-2007, and GB/T 1768-2006. The wetting property of NCC modified by GPTMS increased by 25.9%, and modification from MPS resulted in a 22.5% decrease of the contact angle. MPS-modified NCC affected the crystal structure and thermal stability of polyurethane more significantly than NCC modified by GPTMS. The pencil hardness of polyurethane was enhanced with 1.5% modified NCC. The specular gloss and abrasion resistance of modified polyurethane increased by 253.1% (1.0% NCC modified by GPTMS) and 59.4% (1.5% NCC modified by GPTMS), respectively. MPS-modified NCC led to the inconspicuous improvements. [ABSTRACT FROM AUTHOR]

Two hyperbranched polyglycerols (HBPGs) and one oligoglycerol containing bisphenol A in the core of the molecule were synthesized from glycerol carbonate and applied as polyols in 2-component polyurethane adhesive systems. It was shown that mechanical performance of the joints made in solid wood depended on the hydroxyl functionality of the polyglycerol as well as on the type of the isocyanate used as a cross-linker. The shear strengths of the best-performing joints exceeded that of the substrate. Eventually, it was proved that hyperbranched polyglycerols might be convenient glycerol-derived raw materials for polyurethane adhesives. [ABSTRACT FROM AUTHOR]

Bio-based polyurethane (PU) spray foam insulation was prepared with soy polyol. The effects of adding wood fiber and water on the thermal and mechanical properties of the insulations were studied. The decomposition temperature (Td) of the foams increased with fiber reinforcement due to a higher degree of crosslinking. Alternatively, different fiber length contributed to different crosslinking. In addition, the neat foams, which didn't contain wood fibers, had exceptional thermal stability with the increase of the amount of H2O by forming more stable polyurea adducts. In addition, PU spray foam blown with a larger content of H2O had higher compressive strength by forming a stiffer phase. Still, PU spray foam reinforced with fiber also had superior compressive strength due to the fiber framing into the foam struts. The effect of the fiber length on the compressive strength was evaluated. The degree of complex networks was influenced by the fiber length. However, the tensile strength was weakened with the addition of wood fiber. [ABSTRACT FROM AUTHOR]

Environmentally friendly polyurethane (PU) spray foam insulation was prepared by substituting petrochemical polyol with soy-based polyol. The effects of adding wood fiber and water on the cell morphologies were studied. Cell size increased with the presence of wood fiber, but it decreased with an increase of water (H2O). Still, shorter fiber decreased in foam density but increased in cell size and open cell content. [ABSTRACT FROM AUTHOR]

The bending moment capacity was studied under the diagonal tensile and compression loadings of miter corner joints with dovetail fitting in frames made with medium density fiberboard (MDF). The influence of the type of adhesive in the joints with dovetail fitting on bending moment capacity under diagonal tensile and compression loading were considered, and the joints without adhesive were compared. A total of 80 each miter frame corner joint specimens with dovetail fitting were made. Polyvinyl acetate (PVAc), polyurethane (PU), and cyanoacrylate (CA) adhesives were used, and 20 specimens were prepared without adhesive (WA) with dovetail fitting. MDF was used as a frame material, as in normal practice. The specimens were subjected to diagonal tensile and compression loadings in accordance with ASTM-D 143-94. The data were analyzed statistically. The highest bending moment capacity under diagonal tensile loading (46.09 Nm) was obtained in the specimens bonded with CA adhesive and the highest bending moment capacity under diagonal compression loading (72.04 Nm) was obtained in the specimens glued with PVAc adhesive. Other than this, since there is no difference between these and the unbonded joints, the PU adhesive was not effective in increasing the bending moment capacity under diagonal tensile loading, and the PU and CA adhesives were not effective in increasing the bending moment capacity under diagonal compression loadings. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the effect of heat treatment on the shear strength of tali (Erythrophleum ivorense) and iroko (Chlorophora excelsa) woods, bonded with some structural adhesives. Shear strength of untreated and heat-treated woods bonded with phenol-formaldehyde (PF), melamine-urea-formaldehyde (MUF), melamine-formaldehyde (MF), and polyurethane (PUR) adhesives was studied. An industrial heat treatment method (ThermoWood) was used. The timbers were thermally modified for 2 hours at 180 °C. Laminated samples having two sample sets were prepared from untreated and heat-treated wood for the shear strength test. The results of the tests showed that the heat treatment affected shear strength of laminated wood negatively. Although there was a considerable difference in adhesive bond shear strength between untreated and treated wood, both wood species bonded with the adhesives fulfilled the required value for shear strength of the adhesive bonds. PF, MUF, MF, and PUR adhesives performed in a rather similar way for both wood species. [ABSTRACT FROM AUTHOR]