Browsing by Author "Proller, Marco"

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    Investigating the potential of strength grading green Eucalyptus grandis lumber using multi-sensor technology
    (North Carolina State University, 2017-11) Nocetti, Michela; Proller, Marco; Brunetti, Michele; Dowse, George P.; Wessels, C. Brand
    The exploitation of Eucalyptus grandis lumber as structural material may take advantage of the finger-joint and edge-gluing of the boards while they are still wet, so as to reduce the natural susceptibility of the species to warp and split during drying. But the strength grading needed for structural uses, usually performed on dried lumber, should be done before any gluing process, then already in wet condition. Thus, detection and assessment of selected properties of the wet lumber were evaluated. Eucalyptus grandis boards were measured by a multi-sensor machine soon after sawing, then dried and measured again. Destructive bending tests were then performed to determine the mechanical properties of the lumber and several predictive models were compared. The determination on non-destructive parameters by the machine was as effective on fresh as on dry lumber. The dynamic modulus of elasticity was the best single predictor of mechanical properties. In contrast, the know parameter did not show a correlation between strength and stiffness robust enough to justify the efforts to measure it. Wet grading proved to be as effective as dry grading. Therefore, the study suggests that measuring only dynamic modulus of elasticity on fresh lumber is the best approach for the mechanical grading in Eucalyptus grandis.
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    An investigation into the edge gluing of green Eucalyptus grandis lumber using a one-component polyurethane adhesive
    (Stellenbosch : Stellenbosch University, 2017-03) Proller, Marco; Wessels, Brand; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: South Africa is a timber-scarce country with a relatively small portion of only about 1% of its total land area being used for commercial forestry. Due to an increasing demand for timber but restrictions regarding the expansion of plantation area, the country is expected to experience a shortage of softwood supply for saw logs in the near future. The predominant hardwood species Eucalyptus grandis is, despite good strength and stiffness properties, at present for the most part used for wood chip or pulp and paper production. This is mainly owing to growth stresses, splitting, and the low dimensional stability of the wood, which therefore could not comply with the requirements of the South African national standard for sawn eucalyptus timber (SANS 1707-1 2010). As wood defects often develop or aggravate during the drying stage, the edge-bonding of Eucalyptus grandis lumber in its wet state was considered to possibly inhibit this behaviour. This study consisted of two experiments. In the first experiment shear tests were used to determine the influence of various material and processing variables on the bonding quality of green Eucalyptus grandis wood with a moisture-curing one-component polyurethane adhesive. The experimental design for this investigation comprised 16 groups with different combinations of parameters for wood density, moisture content, adhesive spread rate and pressure. Ten samples per group were tested for shear strength. The penetration behaviour of the one-component polyurethane adhesive into the wood structure was additionally investigated on samples with extreme results, employing a micro CT scanner. All tested samples clearly exceeded the minimum shear strength for cross-laminated timber products according to EN 16351 (2015). Better results were generally obtained for samples with an increased moisture content of roughly 60% compared to specimens with a lower moisture content around fibre saturation point, which could be linked to an enhanced adhesive penetration. In the second experiment the potential of edge gluing green Eucalyptus grandis boards before kiln drying in order to inhibit the development of certain wood defects was investigated. Edge-glued panels were produced from wet material above fibre saturation point and kiln-dried together with non-edgebonded control boards from the same material source. After drying, the panels were sawn apart into single boards, graded regarding the development of check, split, bow, cup and twist and compared to the results obtained for the control boards. The ability of stress-relief grooves in boards to reduce the development of defects was also investigated. The results showed that the edge gluing of green Eucalyptus grandis lumber before kiln drying could not decrease the number of board rejections according to the SANS 1707-1 (2010) requirements for sawn eucalyptus timber. Cup could be significantly decreased, while twist was only reduced for boards without pith. Stress-relief grooves did not have a significant influence on the development of any of the investigated defects but caused severe deformation and damage in some of the boards. Further investigations should be carried out on mass timber products such as cross-laminated timber, where green edge-glued and kiln-dried Eucalyptus grandis panels could be used as a component.