Study of the collapse and recovery of Eucalyptus urophydis during conventional kiln drying
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ORIGINAL ARTICLE
Study of the collapse and recovery of Eucalyptus urophydis during conventional kiln drying Lin Yang1,2,3 · Honghai Liu1 Received: 12 May 2020 / Accepted: 9 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The collapse of Eucalyptus urophydis wood during conventional kiln drying prevents the widespread use of its wood products. This research aims to explore its collapse and recovery characteristics, as well as the effect of continuous and cyclic drying. The collapse was measured by total shrinkage, and cell deformation was observed at three critical points using scanning electron microscopy. The collapse and recovery were investigated by integrating the shrinkage curves and observing the cell micro-deformation. The results showed that the continuous drying rate was faster than that of cyclic drying, especially when the moisture content was below the fiber saturation point. Compared with relative humidity, the temperature had a greater effect on the tangential absolute dry shrinkage. Although cyclic drying decreased collapse, its effect was apparent only at low temperatures and was weak at high temperatures. The collapse recovery time was affected by temperature, and recovery occurred quickly at high temperatures, and the moisture content range was longer. In contrast to continuous drying, the high relative humidity period during cyclic drying led to earlier collapse recovery. The degree and trends of microscopic collapse were consistent with the macroscopic scanning measurements.
1 Introduction With the gradual reduction in natural forest resources, plantation wood with high density and strength has become increasingly used in wood products in China (Guo et al. 2009; Xu 2011), particularly Eucalyptus wood (Yang et al. 2011). Severe deformation occurs due to collapse during conventional kiln drying and is a major obstacle preventing the widespread use of these materials (Ananias et al. 2013; Blakemore and Northway 2009). Wood shrinks below the fiber saturation point (FSP) due to moisture loss. Wood deformation above the FSP is small (Babiak and Kúdela 1995; Kelsey 1956), and below the FSP, it is typically referred to as normal shrinkage. During drying, * Honghai Liu seaman‑[email protected] 1
College of Furnishings and Industrial Design, Nanjing Forestry University, Nanjing 210037, China
2
Key Laboratory of Bio-based Material Science and Technology (Northeast Forestry University), Ministry of Education, Harbin 150040, China
3
Co‑Innovation Center of Efficient Processing and Utilization of Forest Resources, Nanjing Forestry University, Nanjing 210037, China
radial and tangential shrinkage are usually relatively large, which leads to the overall shrinkage of wood (Almeida et al. 2009); however, for collapse-prone woods, such as some eucalyptus species, special deformation (collapse) occurs during drying, and the total shrinkage also includes collapse. Above the FSP, collapse is equivalent to the total shrinkage, but below the FSP, the total shrinkage is the
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