Bond Strength–Disbonding Behavior and Dimensional Stability of Walnut and Poplar Impregnated with Some Chemicals and Bonded with PVAc,VTKA and Urea Formaldehyde

The aim of this study, is to describe the effects of adhesives (PVAc-Desmodur VTKA and Urea formaldehyde) on wooden materials (walnut and poplar) cut tangentially and radially impregnated with Protim Solignum, CCA and Celcure AC 500 and exposed to: humid–water–heat resistance; heating; and cooling tests. All these tests show a decreased in bonding strength. The conclusion is that poplar wood cut tangentially and impregnated with CCA, bonded with D-VTKA adhesive can be used as a material in damp conditions where good bond strength is required.     

Effects of wood-surface roughness,adhesive viscosity and processing pressure on adhesion strength of protein adhesive

The objective of this research was to study the effects of wood-surface roughness, adhesive viscosity and processing pressure on adhesion strength between soybean protein adhesive and wood, and to seek the relative importance of the individual factors in determining adhesion strength. Processing pressure was found to be the most important factor in determining adhesion strength. An optimum pressure, which was about 4.55 MPa in this research, is needed for development of a strong bond. A higher pressure resulted in reduced adhesion strength, possibly due to damage to the wood surface; a lower pressure also resulted in decreased adhesion strength because of the lack of bond formation. Adhesive viscosity had greater effect on adhesion strength than surface roughness. Contact angle, which was found to be mainly determined by adhesive viscosity and surface roughness, was a major factor controlling adhesive penetration. A smaller contact angle, resulting from lower viscosity and rougher surface, produced deeper penetration, while a larger contact angle, resulting from higher viscosity and smoother surface, produced shallower penetration. An optimum penetration is needed to enhance adhesion strength by developing a three-dimensional interactive zone at the interface. Too deep or too much penetration would result in 'dry-out' at the interface; less penetration would limit the formation of the three-dimensional zone at the interface. Both cases resulted in reduced adhesion strength. Contact angles ranging from 35 to 47° provided the optimum penetration needed for good adhesion. The results of this research could be used as reference to determine optimum process parameters in plywood manufacturing when an aqueous based adhesive is used.     

Adhesive Characteristics of Epoxy/Dendritic Hyperbranched Polymer Blends

Adhesive characteristics of blends of a room-temperature-curing epoxy and a dendritic hyperbranched polymer (HBP) were investigated. Significant improvements in both lap shear and T-peel strengths were observed as a result of blending of HBP. Dynamic mechanical analysis of the cured blend formulations indicates a two-phase microstructure. The improvement in adhesive bond strength is achieved without significant sacrifice in glass-transition temperature of the cured epoxy network. The results were explained in terms of phase morphology analyzed by scanning electron microscopy. Cavitation and shear yielding are believed to be responsible for improvement in toughness and adhesive bond strength.     

Optimal design of an adhesively-bonded corner joint with single support based on the free vibration analysis

This study investigates the three-dimensional free vibration behaviour of an adhesively-bonded corner joint with single support. The modulus of elasticity, Poisson's ratio and density of adhesive were found to have negligible effects on the first 10 natural frequencies and mode shapes of the corner joint. The effects of the geometrical parameters, such as support length, plate thickness, adhesive thickness and joint length, on the natural frequencies, mode shapes and modal strain energies of the adhesive joint were also investigated using both the finite element method and the back-propagation artificial neural network (ANN) method. The free vibration and stress analyses were carried out for the corner joints with various random geometrical parameters so that a suitable ANN model could be trained successfully. The support length, plate thickness and joint length all played important roles in the natural frequencies, mode shapes and modal strain energies of the corner joint, whereas the adhesive thickness for the range of adhesive thickness studied had only a minor effect. The Genetic Algorithm was also combined with the present ANN models in order to determine the optimum geometrical dimensions which satisfied the maximum natural frequency and minimum modal strain energy conditions for each natural frequency and mode shape of the adhesively-bonded corner joint.