Swelling strain assessment of fiber and parenchyma tissues in the tropical hardwood Ormosia coccinea
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Swelling strain assessment of fiber and parenchyma tissues in the tropical hardwood Ormosia coccinea Rosilei A. Garcia1,2 · Jedi Rosero‑Alvarado1 · Roger E. Hernández1 Received: 26 February 2020 / Accepted: 15 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The full-field swelling strains (in-plane) and displacements (out-of-plane) of a tropical hardwood [huayruro (Ormosia coccinea (Aubl.) Jacks.] were measured at a tissue level by three-dimensional digital image correlation (3D-DIC) technique. Swelling strains in tangential (Ɛxx) and radial (Ɛyy) directions and displacements in longitudinal direction (Z-axis) were measured on the cross section of wood samples from the dried condition under P 2O5 to moisture adsorption condition under three steps of relative humidity (RH) (55%, 75%, and 90% RH) and at a constant temperature of 20 °C. Global swelling coefficients (α) were also calculated and compared with 3D-DIC strains. Ɛxx, Ɛyy, and Z-axis displacement data were separately extracted from fiber- and banded parenchyma-dominated zones. The density variation between tissues was determined by X-ray densitometry. Huayruro wood had a homogeneous Ɛxx, while a different Ɛyy was observed between fiber- and banded parenchyma-dominated zones at all RH conditions. The density of the fiber tissue was more than twice as high as that of the axial parenchyma tissue. Moreover, an opposite behavior was found between tissues in longitudinal directions (Z-axis displacement), showing that parenchyma tissue swells, while fiber tissue shrinks after moisture adsorption regardless of RH level. The fiber shrinkage in the longitudinal direction intensified with moisture adsorption increasing, while parenchyma swelled at the same proportion. Results revealed a complex interaction between fiber- and banded parenchyma-dominated tissues at the three principal directions of wood after moisture adsorption. The dimensional changes at a tissue scale appear to be governed by the stiffer cell component and will depend not only on stiffness/density values but also on the proportion of each tissue composing wood.
* Rosilei A. Garcia [email protected] 1
Département des sciences du bois et de la forêt, Centre de recherche sur les matériaux renouvelables, Université Laval, Pavillon Gene‑H‑Kruger, Quebec, Canada
2
Departamento de Produtos Florestais, Universidade Federal Rural do Rio de Janeiro, Seropédica, Rio de Janeiro, Brazil
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Wood Science and Technology
Introduction Hardwoods have greater variability and a more complex and specialized structure than softwoods. Their anatomical features and cellular proportion and arrangement have a significant impact on the wood properties and suitability for several applications. The fibers are the most abundant cells of many hardwoods and are generally thick-walled and positively related to the wood density (Zieminska et al. 2013). The axial parenchyma is thin-walled, abundant in hardwood species besides exhibiting different patterns that
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