Polyvinyl Acetate Adhesives Research Articles

Cisalhamento na Linha de Cola de Compensados de Eucalyptus sp. e Adesivo PVA

Studies on new adhesives and resins for bonding wood and wood products are being carried out with the intention to improve their properties, taking into account a lower environmental impact. To this end, new formulations of polyvinyl acetate (PVA) adhesives have been developed, because they have no polluting harmful to health chemicals in their composition, in contrast to formaldehyde-based resins; which in turn are the most commonly used for wood panels production these days. This study tested three different formulations of PVA adhesives, with different pressing times and temperatures for the production of Eucalyptus sp. plywood, obtaining satisfactory results with respect to shear strength at the bondline, which was higher for the PVA adhesives compared to the urea-formaldehyde and phenol-formaldehyde panels found in the literature.

Starch-sugar synergy in wood adhesion science: basic studies and particleboard production

Synergic properties between starch and sugar were discovered. 100% crop-based starch and sugar formulations were studied. Classical preliminary tests such as curing temperature and gel time were measured for different starch-sucrose water suspensions. More significant information was deducted with applied tests such as plywood gluing tests and particleboard production. Wood-to-wood bonding properties were analysed applying NaOH and high temperature (180°C) as catalysts for starch gelification. Comparable strength to commercial urea-formaldehyde and polyvinyl acetate adhesives was achieved in plywood tests. Consequently, the knowledge acquired in wood bonding of flat surfaces was applied to particleboard production. These derived particleboards showed that it is possible to obtain a panel with only carbohydrates as gluing agent. Starch-sugar synergy in alkaline environment increases the internal bond (IB) of the natural panels up to 0.25 N/mm2. Possible mechanisms of synergy between these saccharides were proposed. Finally, a blended formulation with Mimosa tannin allows for achieving an internal bond of 0.40 N/mm2, which is the required value for interior grade particleboards (DIN EN 312). Starch-sugar-tannin adhesives are 100% environmentally-friendly formulations.

Effect of adhesive type on the bending moment capacity of miter frame corner joints

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.

The effect of adhesive type and bond line thickness on the strength of mortise and tenon joints

This study was carried out in order to determine the effects of adhesive type, bond line thickness and moisture content on the strength of mortise and tenon joints. The polyvinyl acetate (PVAc), urea-formaldehyde (UF) and animal adhesives were used, combined with three different bond line thicknesses. At the same time the effect of the moisture content of the wood was investigated by using wood material conditioned to 8%, 12%, 15% moisture contents. The results of the experiments showed that the strength difference between tight fitting and loose fitting joints was 28% if animal adhesive was used, 11% with UF adhesive and negligible with PVAc adhesive. The effect of the moisture content of the wood when the joints were assembled did not depend on the adhesive used. If 12% is taken as the standard moisture content, increasing it to 15% weakened joints by 15% and decreasing it to 8% strengthened them by 6%, irrespective of the adhesive. Test results indicate that strongest joints are obtained when a close tolerance is maintained between the tenon and mortise.

Shear strength of calabrian pine (Pinus brutia Ten.) bonded with polyurethane and polyvinyl acetate adhesives

AbstractIn this study, the change in shear strength on radial and tangential surfaces of Calabrian pine (Pinus brutia Ten.) wood having different roughness values as the result of sawing with a circular ripsaw, planning, and sanding, and bonded with polyurethane (PU) and polyvinyl acetate (PVAc) adhesives at the pressure levels of 3, 6, and 9 kg f/cm2 were studied. A total of 360 specimens of each, prepared with the objective of being able to determine the effect of the variables on bond performance, were subjected to the shear test in the universal test machine in accordance with the ASTM D 905–98 standard. The values obtained were analyzed statistically and the results were interpreted. The highest shear strength (11.83 N/mm2) for plane of cut was obtained on the tangential surface after sanding and applying PVAc adhesive with a pressing pressure of 9 kg f/cm2. The lowest shear strength (6.01 N/mm2) was obtained in the joinings made on the planed surfaces by using PU adhesive and a pressing pressure of 3 kg f/cm2. The highest shear strength (9.10 N/mm2) on the radial surface was obtained after sanding and applying PVAc adhesive and pressing with a pressure of 6 kg f/cm2. The lowest shear strength (3.76 N/mm2) was obtained in the specimens whose surfaces were sanded and by using PU adhesive and with a pressing pressure of 3 kg f/cm2. In general, in the radial surfaces, just like in the tangential surfaces, the specimens bonded with PVAc produced a higher shear strength compared to those glued with PU. According to these results, it is definitely necessary to sand the surfaces prior to the bonding process to have a higher shear strength. The bonding process should be made on the tangential surfaces with higher pressures. The PVAc adhesive should be preferred instead of the PU adhesive. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4856–4867, 2006

The shear strength of Calabrian pine (Pinus brutia Ten.) bonded with polyurethane and polyvinyl acetate adhesives

AbstractIn this study, the change in shear strength on radial and tangential surfaces of Calabrian Pine (Pinus brutia Ten.) wood having different roughness values as the result of sawing with a circular ripsaw, planing and sanding, and bonded with polyurethane (PU) and polyvinyl acetate (PVAc) adhesives at the pressure levels of 3, 6, and 9 kgf/cm2, was studied. Each of the 360 specimens prepared to determine the effect of the variables on bond performance were subjected to shear test in an universal test machine in accordance with the ASTM D 905–98 standards. The values obtained were analyzed statistically and the results were interpreted. The highest shear strength (11.83 N/mm2) for plane of cut was obtained on the tangential surface after sanding and applying PVAc adhesive with a pressing pressure of 9 kgf/cm2. The lowest shear strength (6.01 N/mm2) was obtained in the joinings made on the planed surfaces by using PU adhesive and a pressing pressure of 3 kgf/cm2. The highest shear strength (9.10 N/mm2) on the radial surface was obtained after sanding and applying PVAc adhesive and pressing with a pressure of 6 kgf/cm2. The lowest shear strength (3.76 N/mm2) was obtained in the specimens whose surfaces were sanded and glued with PU adhesive with a pressing pressure of 3 kgf/cm2. In general, in the radial surfaces, just like in the tangential surfaces, the specimens bonded with PVAc exhibited a higher shear strength compared with those glued with PU. According to these results, it is definitely necessary to sand the surfaces prior to the bonding process to have a higher shear strength. The bonding process should be made on the tangential surfaces with higher pressures. The PVAc adhesive should be preferred instead of the PU adhesive. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3050–3061, 2006

Shear Properties of Components Used in Stressed-Skin Panels

In this study, certain mechanical and rheological properties of structural lumber subjected to shear stresses and the long-term lateral load-slip behavior of silicone elastomeric and polyvinyl-acetate adhesives (PVA) with an isocyanide hardener were evaluated as part of a larger project designed to predict the long-term behavior of stressed-skin panels under load. Sixteen pieces of solid wood and 16 glued joints were evaluated in several test series in order to determine the desired properties. Wood modulus of rigidity was determined from the initial deformation recorded in long-term tests. The relative creep was also determined under constant environmental conditions (20°C, 65% RH). Four combinations of long-term tests on glued joints were conducted on wood-chipboard and wood-steel connections with the two adhesives. Analyses showed that the creep rate, relative creep, and joint variability were greatest for the silicone adhesive. Two mathematical models (power functions with and without exponential term...

Effects of apitong (Dipterocarpus spp.) extractives on bond strength development and curing rate of adhesives

Abstract Emulsion polymer isocyanate ( API ), polyvinyl acetate ( PVAC ) and resorcinol-formaldehyde ( RF ) adhesives were used to produce single lap shear specimens using resinous and non-resinous apitong (Dipterocarpus spp.) timbers. Tests showed that joints made with highly resinous apitong were about 40% weaker than similar joints made with non-resinous apitong. The resinous apitong was treated with different solvents to yield five different extractives which were characterized by infra-red analysis. Apitong extractives were then added to API, PVAC and RF adhesives and joints made with buna (Fagus crenata), a timber known to be low in extractives and easy to bond. Joints prepared using extractive-containing adhesives were generally weaker than those made with the unmodified adhesives. RF adhesives containing extractives cured more slowly than unmodified RF . It is thought that the acidic nature of the extractives changes the pH of the system sufficiently to affect the curing mechanism