Shear Strength Of Wood Joints Research Articles

Glycidyl methacrylate co-polymer emulsion-based heat and water-resistant wood adhesive

This work aims to add an epoxy-ended co-monomer to polyvinyl acetate (PVAc) emulsion adhesive-based wood adhesive to improve its resistance to heat and moisture. Here, glycidyl methacrylate (GMA), vinyl neodecanoate (VeoVa), and vinyl acetate (VAc) emulsion copolymers have been created and evaluated as wood adhesives. To prepare the emulsion-based adhesive samples, a polyvinyl alcohol (PVA) solution, aluminium chloride solution, preservatives, and a plasticizer are added. Following that, the poly(VAc–VeoVa–GMA) based adhesive sample is compared with the VAc, VeoVa, and methyl methacrylate (MMA) (poly(VAc-VeoVa-MMA)) co-polymer-based adhesive. Tensile shear strength of wood joints under dry and wet conditions was tested in compliance with EN 204-205 standard to assess the adhesives’ performance. The EN 14257 standard, which defines the shear stress of wood joints at 80 °C, was used to assess the heat resistance of the wood adhesives. Tests on the hardness of films confirmed the results of differential scanning calorimetry, which indicated that the glass transition temperature in the GMA-based adhesive was significantly higher than in the MMA-based adhesive. After 6 h of bonding, EN 204 shows that the tensile shear strength of a GMA-based adhesive increased by 15.56% in a dry environment, by 16.67% in a wet environment and 37.84% heat resistance when compared to a co-polymer-based adhesive based on MMA. The approach that was developed provides a simple and useful way of developing adhesives with enhanced heat, water, and bonding strength resistance.

The effect of silica/zeolite-A nanocomposite on the polyvinyl acetate wood adhesive

The silica/zeolite-A nanocomposite additive was loaded at different values (1 - 4% wt) into polyvinyl acetate matrix to improve its wood adhesive properties. The silica nanoparticles were prepared by calcination method using rice husk as source material. X-ray diffraction analysis, FTIR spectroscopy, and SEM techniques were used for the characterization of the nanocomposite. The thermal stability and adhesion properties of modified polyvinyl acetate were evaluated by thermogravimetric analysis (TGA) method and measuring the shear strength of wood joints respectively. According to the results, the addition of silica/zeolite-A nanocomposite into polyvinyl acetate in dry condition and elevated temperatures was led to the enhanced shear strength of wood joints. However, in wet conditions, improvement of shear strength which was obtained by the addition of silica/zeolite-A nanocomposite was lower than that of the dry condition. Additionally, the thermal stability of polyvinyl acetate was affected by silica/zeolite-A nanocomposite. Polyvinyl acetate containing silica/zeolite-A nanocomposite additive showed better stability in water with respect to the pristine polyvinyl acetate.

Cellulose nanofibrils/polyvinyl acetate nanocomposite adhesives with improved mechanical properties

Cellulose nanofibrils (CNFs) are nanoscale cellulose produced from renewable resources with strong reinforcing potential when included in a polymer matrix. In this work, the effect of the addition of CNFs on the properties of waterborne polyvinylacetate (PVA) adhesive was investigated. Adhesive formulations with different contents in CNFs from 1 to 10wt.% was prepared by simple mixing of PVA dispersion with CNFs suspension in water. The viscosity of the adhesive increased with the addition of CNFs, namely over a content of 5%. Shear strength of wood joints at dry as well as wet conditions was improved by CNFs inclusion. Adding 10% of CNF to the PVA adhesive increased the shear strength by about 2 folds compared to the neat adhesive. This strengthening effect was explained by the strong reinforcing impact brought by CNFs inclusion in the PVA matrix. The addition of CNFs also improved the water resistance of PVA adhesive and strongly enhanced the mechanical performance in wet conditions, namely over 7% of CNF content.

Impact of cold temperatures on the shear strength of Norway spruce joints glued with different adhesives

As wood construction increasingly uses engineered wood products worldwide, concerns arise about the integrity of the wood and adhesives used. Bondline strength is a crucial issue for engineered wood applications, especially in cold climates. In this study, Norway spruce (Picea abies) joints (150 mm × 20 mm × 10 mm) were bonded with seven commercially available adhesives: polyurethane (PUR), polyvinyl acetate (PVAc), emulsion-polymer-isocyanate (EPI), melamine-formaldehyde (MF), phenol-resorcinol-formaldehyde (PRF), melamine-urea-formaldehyde1 (MUF1), and melamine-urea-formaldehyde2 (MUF2). Each adhesive was tested at six temperatures: 20, −20, −30, −40, −50 and −60 °C. Generally, within the temperature test range, temperature changes significantly affected the shear strength of solid wood and wood joints. As the temperature decreased, the shear strength decreased. PUR adhesive in most cases resulted in the strongest shear strength and MUF adhesive resulted in the weakest. MF and PRF adhesives responded to temperature changes in a similar manner to that of the PUR adhesive. The shear strengths of wood joints with PVAc and EPI adhesives were more sensitive to temperature change. At low temperatures, the variability of shear strengths increased with all adhesives. Percent wood failures of joints bonded with different adhesives in most cases were not sensitive to temperature changes.

Nano-aluminum oxide as a reinforcing material for thermoplastic adhesives

Nanoparticles of aluminum oxide were used to improve bonding strength of PVA (polyvinyl acetate) in wet conditions and elevated temperatures. Shear strength of wood joints was improved by inclusion of nanoparticles to PVA in all conditions. The improvement on performance of PVA in dry state by adding nanoparticles could be measured in terms of wood failure. In wet conditions and at elevated temperature, nanoparticles significantly increased shear strength of wood joints. Thermal stability of PVA was affected by nanoparticles as well. Nanostructure studies showed that dispersing well nanoparticles in PVA is a crucial step to obtain nanocomposites with superior properties.

Improving performance of polyvinyl acetate (PVA) as a binder for wood by combination with melamine based adhesives

In this study blending PVA with MUF and MF was evaluated as an approach to enhance the performance of PVA towards water and elevated temperatures. MF and MUF were added to PVA at different proportions: 15%, 30%, 50%, 70% and 100%. Blends of PVA with MF and MUF were used as adhesives to bond wood joints. The shear strength of wood joints was measured at dry and wet states, and elevated temperatures. Thermogravimetric analysis was used to study thermal stability of PVA and its blends with MF and MUF. The structural changes caused by the inclusions were characterized by Fourier transforms infrared spectroscopy (FT-IR). The results showed that shear strength of wood joints were improved by the addition of MF and MUF to PVA in all conditions. Adding small amounts of MUF or MF (as low as 15%) enhanced the performance of wood joints towards water and elevated temperatures. The extent of improvement was sometimes so high that the strength of glue line surpassed strength of wood in wet conditions leading to wood failure rather than glue failure. MF had more effectiveness in improving shear strength of wood joints than MUF in all conditions. Thermal stability of PVA was increased by MF but the effect of MUF on thermal stability of PVA was dependent on MUF proportions and temperatures. FT-IR analyses showed that there are some chemical bonds between PVA and MF. Considering costs, effectiveness and formaldehyde emission, adding 15% MF to PVA seems the optimal proportion of MF in the PVA blends.

Effects of adding nano-clay on performance of polyvinyl acetate (PVA) as a wood adhesive

Polyvinyl acetate (PVA), a thermoplastic polymer, has poor performance at elevated temperatures and humid conditions as a wood adhesive. Two types of hydrophilic nano-clay were mixed at different loadings (1%, 2% and 4%) with PVA to improve the performance of PVA towards water and elevated temperatures. The properties of PVA-clay nanocomposites were characterized by measuring the shear strength of wood block shear-type assemblies bonded with new formulated adhesives in dry and wet, and also, at elevated temperatures. Thermal stability and structure of the PVA-clay nanocomposites were studied by thermogravimetric analysis (TGA), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that shear strength of wood joints increased in all states by adding nano-clay to PVA. Inclusion of nano-clay improved the thermal stability of PVA to different degrees depending on nano-clay loading and type. The morphological studies revealed that the fluctuations observed in thermal stability and bond strength of the nanocomposites stem from dispersion quality of nano-clay.

Hydroxymethylated resorcinol (HMR) priming agent for improved bondability of wax-treated wood

The effects of hydroxymethylated resorcinol (HMR) on the tensile shear strength of wood joints treated with montan ester wax were studied with polyvinyl acetate (PVAc) and melamine formaldehyde (MF) adhesives. Untreated specimens which were bonded with MF and PVAc had similar bond strength properties under dry conditions, but MF bonded specimens’ tensile shear strength values were higher than that of PVAc glued specimens under wet conditions. With both adhesives tested, dry tensile shear strengths of wax-treated specimens were in a comparable range to those of untreated wood, while under wet conditions the strength values of wax-treated specimens were significantly lower than those of the controls.