Coefficient of Thermal Expansion of Rubberwood (Hevea Brasiliensis) in Convective Drying Process

Abstract

Rubberwood drying is an energy-intensive process where drying defects are the main problems faced by the wood industry. The main objective of this study is to evaluate the coefficient of thermal expansion (CTE) of rubberwood to have a better understanding of the effect of temperature over the distortions of rubberwood during drying. Rubberwood samples were first dried at three different hot air temperatures and the mechanical properties of dried rubberwood samples were tested in the preliminary experiment to determine the suitable temperature condition for further evaluation of the CTEs of rubberwood samples. The CTEs of rubberwood in tangential and radial directions were evaluated through strain gages at three different moisture content (MC) levels: above 60%, at 12% and almost 0% (dry state). Based on the findings of this work, the CTEs of rubberwood in the tangential direction were found to have higher values than that of radial direction. The rubberwood samples had the highest CTEs values at 12% MC in both directions. Also, no significant differences were found between the experimental and expected CTE values of rubberwood as a function of specific gravity in the dry state.

Study of Thermal Expansion and Compression Strength of Three Wood Species From Plantations

“…The longitudinal direction showed the lowest dimensional change. These trends are similar to those reported by several authors (Kubler et al, 1973;Glass and Zelinka, 2010;Zhao et al, 2016;Kaung and Thanate, 2020) where, the thermal expansion of wood in the radial and the tangential direction is higher than that in the longitudinal one. This is mainly attribued to the cellulose in the wood cell wall (Zhao et al, 2016).…”

“…The CTE is recognised as a fundamental parameter in mechanical and structural design applications of materials (Zeisig et al, 2002). Thermal change of wood is an important factor in the wood drying process since temperature variations cause water to flow in the wood, and consequently hygroscopic deformations occur (Goli et al, 2019;Kaung and Thanate, 2020). For example, musical instruments are very sensitive objects, where even minimal deformations can damage its varnishes (Goli et al, 2019).…”

“…The CTE of wood depends on species, moisture content (MC), specific gravity, temperature levels and anatomical directions (Miki et al, 2014). The CTEs of wood rise with higher MCs than those in dry condition; they have a linear relation with density (Goli et al, 2019, Kaung andThanate, 2020). Thermal expansion of wood is mostly positive in all directions.…”

“…Thermal expansion of wood is mostly positive in all directions. Nevertheless, wood has different CTE values in its radial, tangential and longitudinal directions (Kaung and Thanate, 2020). The CTE value in longitudinal direction is very small, ranging from 5-10 times less than that of transverse direction, and therefore, it is not often considered (Glass and Zelinka, 2010), while that in the radial direction is slightly less than that in the tangential direction (Zhao et al, 2016).…”

“…The ability of wood to withstand a load depends on several factors, including the type, direction and duration of loading, the presence or absence of defects (knots and splits), the MC and temperature (Kaung and Thanate, 2020).…”