Browsing by Author "Favis, Jesse"

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    Investigating a new green edge laminating process for CLT manufacturing from twist-prone SA pine sawn timber
    (Stellenbosch : Stellenbosch University, 2023-03) Favis, Jesse; Wessels, Brand C.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: There is potential for fast-grown, low quality raw material to produce high-value cross laminated timber (CLT). South African Pine plantations are harvested in shorter-age rotations to increase productivity, which results in greater proportions of corewood in the timber. Corewood tends to have a lower density and highly variable physical properties, leading to severe deformation after the timber is dried. Twist is the drying defect that causes the most rejection of dried wood for structural applications in South Africa. It is increasingly necessary for the sawmill industry to recognise the importance of conversion efficiency as it increases profits, reduces waste and extends the supply of standing timber. Twist in sawn timber can have a large effect on the conversion efficiency of logs, affecting both the volume and value recovery. The processor can manage twist in two ways: first, by predicting twist propensity in sawn timber from specific log resources, and second, by devising strategies to reduce the twist in the sawn timber from these resources. This study investigated both the prediction of twist and the use of an alternative processing method to reduce twist. In the first sub-study, the relationship between grain angle (spiral grain) and twist deformation of fast-grown South African Pine was evaluated. The highly significant p value (2.77 x 10⁻¹⁵) association identified between grain angle and twist had a relatively low coefficient of determination (R² = 0.28). Grain angle alone could not predict this deformation; other influential properties, including variation in density, microfibril angle and curvature of growth rings should be investigated further, to be able to model twist in seasoned boards accurately. In the second study, timber boards for CLT panel layers were green-edge bonded with a one-component polyurethane adhesive (1C-PUR), before seasoning, to reduce twist deformation. The potential of this manufacturing process to improve the conversion efficiency of low-quality South African Pine wood into CLT was investigated. The new manufacturing process reduced twist by 60.1% and increased volume recovery by 7% compared with the conventional manufacturing method of manufacturing. The perfectly flat panel layers would require less pressure to be made into CLT, which would ultimately reduce the cost of the mass timber material.