Perpendicular Mechano-Sorptive Strains during Moisture Desorption from Eucalyptus nitens Specimens

Abstract

aThe purpose of this paper was to determine the mechano-sorptive strains produced during desorption of moisture from Eucalyptus nitens specimens, from a perspective of modeling wood drying stresses. Eucalyptus nitens samples were tested in the radial and tangential directions. The mechano-sorptive strain was measured by cantilever bending during desorption. The runs were performed in a conditioning chamber at constant low temperature and variable equilibrium moisture content. Four load levels were considered for testing. The results showed that the mechano-sorptive strain during desorption of moisture was proportional to applied stress and reached the maximum value in the tangential direction. Also, the mechano-sorption coefficient depended on wood orientation and reached the maximum value of 5.46 × 10 -2 in the tangential direction. Bio-Bio, Av. Collao 1202, 4081112, Concepción, Chile; *Corresponding author: nattperez@gmail.com Keywords INTRODUCTIONChile has approximately 0.74 million hectares of Eucalyptus plantations available for industrial processing, and approximately 30% contain Eucalyptus nitens (INFOR 2015). E. nitens plantations are mainly distributed in the VIII and X regions, and they are the fastest growing species in Chile. E. nitens plantations grow as fast as 77 m 3 /ha/year (INFOR 1989), and they are well adapted to the cold winter conditions in Southern Chile (INFOR 2004).The volume of wood from E. nitens available in Chile for commercial use is estimated to reach 7 million m 3 per year in 2040 (INFOR 2015). This abundance is an incentive for processing this species into solid wood products for domestic and international markets. Unfortunately, the development of commercial solid products from this species is currently limited by the sawlog performance due to longitudinal growthstrains (Valencia et al. 2011) and drying difficulties due to their propensity of surface and internal checking, collapse, and higher transversal shrinkage (Ananías et al. 2009(Ananías et al. , 2014Sepúlveda et al. 2016). A more comprehensive understanding of the drying properties of E. nitens is essential for the successful processing of this species in commercial solid wood products.E. nitens is highly prone to internal checking (Leandro et al. 2008;Rebolledo et al. 2013). E. nitens of lower density tends to be associated with higher internal intra-ring PEER-REVIEWED ARTICLE bioresources.com Pérez et al. (2016). "Mechano-sorptive strain," BioResources 11(4), 8277-8284. 8278checking. The drying of E. nitens solid wood is also limited by collapse propensity (Ananías et al. 2009(Ananías et al. , 2014Sepúlveda et al. 2016). During the initial stages of drying, the surface layers shrink and exert compressive stresses on the core-wood, inducing drying stresses. These behaviors change with moisture content and temperature variations during drying. The drying stresses cause permanent and transitory deformations on the wood, i.e., warping and internal checking. For E. nitens, Pérez et al. (2013) observed that drying stres...

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