Abstract
The use of glued finger joint in green wood, directly from the sawing process, would open the possibility to obtain glued timber from small-sized wood, achieving an efficient use of the original raw material. The gluing of finger-jointed green wood, with moisture content above the fibre saturation point, may improve the efficiency and the manufacturing process of glulam or joinery. This may be especially beneficial for a hardwood such as Eucalyptus globulus L., which is a globally important forest resource, but is a challenging wood to dry. This article presents a study on the possibility to develop finger joints with wood in green state. To compare them, conventional finger joints on dry wood and solid boards without end joints were also manufactured. Cold-setting and fast-curing commercial one-component polyurethane adhesive systems were used. Finger-jointed samples were tested to determine mean and characteristic values (5th percentile) of density, bending strength and modulus of elasticity, and the results were analysed and discussed. Green-glued joints showed no statistically significant differences compared to the solid boards and improved strength properties with respect to dry-glued joints.
Highlights
Blue gum, Eucalyptus globulus, is an important plantation tree species worldwide, especially in Mediterranean climates of Europe, in South America and in its native region of Australia (Kirkpatrick, 1975)
The individual, mean and characteristic (5th percentile) values of bending strength (N/mm2), global modulus of elasticity (N/mm2) and density (Kg/m3) were determined and compared between the green glued finger joints, dry glued finger joints and the samples without finger joints. All these properties were determined with a moisture content (MC) close to
The different gluing pressure of the green and dry finger joints was not considered in this discussion, since this was adjusted to minimize the risk of indentation in the green finger assembly
Summary
Eucalyptus globulus, is an important plantation tree species worldwide, especially in Mediterranean climates of Europe, in South America and in its native region of Australia (Kirkpatrick, 1975). In the use of green gluing with finger-jointing for structural timber products, there are several important conditioning parameters, such as the previous classification of wood in green state, the density of the wood in dry state and the dry process once the wood is glued to reduce the MC, as well as the adequate performance of the adhesives and the process In this sense, Troughton and Chow (1979, 1980) successfully developed and tested finger joints from unseasoned rough western red cedar and spruce, with 30–100% MC, using commercial phenol-resorcinol glues. The comparison of the characteristic values allowed determining whether the results are satisfactory with the grade classes for structural solid wood This will show whether the use of an unconventional gluing system using green wood can add value and improve the efficiency of small log material from a species with high industrial potential
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