The demand for engineered wood products (EWPs) continues to rise internationally. However, for some important Australian commercial timbers such as plantation grown southern pine and native forest sourced spotted gum, a major impediment to achieving commercially viable EWP production is difficulties experienced in gluing – particularly for sawn laminate based EWPs such as glulam. Wettability and permeability have a major influence on wood adhesion. This study investigated the efficacy of different surface machining preparations on the wettability and permeability of southern pine and spotted gum. For both species, planing resulted in poor wettability, whereas face milling and sanding treatments post-planing improved wettability. Wettability increased in southern pine earlywood compared to latewood; and wettability decreased for both species with increased time post-surface machining. Planing resulted in the highest permeability for southern pine but the lowest permeability for spotted gum. Face milling resulted in higher permeability compared to sanding treatments.
Darwin stringybark (Eucalyptus tetrodonta) is one of Northern Australia’s most important commercial forest resources. The wood exhibits desirable wood properties including high strength, natural durability, and visual appeal. The production of engineered wood products (EWPs) such as glulam from this resource represents a significant commercial opportunity for the timber industry in northern Australia. However, a major challenge to overcome is the achievement of satisfactory glue bond performance. This study evaluated the effects of different surface machining preparations, adhesive types, and curing temperatures on the bonding characteristics of Darwin stringybark. The pre-gluing surface machining method significantly influenced the timber wettability, roughness, permeability and tensile shear strength of adhesive bonds. Planing resulted in the lowest wettability, roughness, and permeability, while bonded planed samples produced the poorest tensile shear strength. Alternative surface machining methods including face milling and sanding post-planing were shown to significantly improve the timber wettability, roughness, and permeability, and also to increase the tensile shear strength of bonded samples. The resorcinol formaldehyde adhesive resulted in slightly improved tensile shear strength in most cases compared to the polyurethane adhesive. There was no significant improvement in tensile shear strength with the use of elevated temperature curing.
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