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Acoustic and Mechanical Properties Wood Drying Wood Science Journal article

Impact of drying parameter, tissue type, and lumber orientation on the collapse shrinkage of Macassar ebony wood

Jingyuan Zhang, Jing Li, Bingquan Wang, Shixue Ren, Jian-feng Zhan

19 May 2025 · Drying Technology

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Abstract

Strengthening the fundamental understanding of drying-related collapse phenomena and improving methods to regulate collapse-type deformations are critical for enhancing the industrial utilization of collapse-prone hardwood lumber. This study aimed to investigate wood-moisture desorption and drying-triggered collapse deformation in green Macassar ebony wood under isothermal conditions. Twelve isothermal drying (desorption) tests were conducted under a factorial design of four temperatures (40°C, 60°C, 80°C, and 90°C) and three relative humidity (RH) levels (50%, 70%, and 90%), with tests terminating once the target moisture content (MC) was achieved. Specimens were sourced from twelve distinct locations within a large cross-sectional square timber, encompassing both sapwood and heartwood, as well as back-sawn and mixed-sawn lumber. Evaluated parameters included collapse depth (CD), collapse factor (CF), and volumetric shrinkage rate (VS). The test results demonstrated that under specified RH conditions, stepwise increases in drying temperature (from 40°C to 90°C) progressively elevated key parameters – CD, CF, and VS in the studied specimens, indicating a statistically significant impact on collapse-related deformations (p < 0.001 for all parameters). Under isothermal conditions, stepwise decreases in RH also led to increases in CD, CF, and VS for most specimens, though these effects were largely nonsignificant for collapse deformation (p = 0.77, p = 0.83, and p = 0.01, respectively). Furthermore, heartwood specimens (e.g., A4–A9) exhibited significantly higher collapse values than sapwood specimens, highlighting the pronounced influence of tissue type (heartwood vs. sapwood) on collapse-related deformation (p < 0.001). Finally, stepwise differences in volumetric shrinkage (ΔVS) curves revealed abnormal shrinkage at MC above the fiber saturation point (FSP), confirming the occurrence of collapse-type shrinkage beyond the hygroscopic range and its dependence on drying parameters.

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