The characteristics of shrinkage development in Eucalyptus urophylla  ×  E. grandis wood that are induced by moisture migration

The drying of eucalyptus wood involves coupled shrinkage and collapse driven by capillary tension and drying stress. This study investigated shrinkage in Eucalyptus urophylla × E. grandis using 2-mm and 5-mm fiber-direction specimens dried at 45, 65, and 85 °C, to elucidate the interactive effects of temperature and thickness on moisture migration and shrinkage. Two-way ANOVA showed that both temperature and thickness significantly influenced drying rates ( p < 0.001), with a significant interaction ( p < 0.001). The drying rate of 2-mm specimens was 2.9–6.6 times higher than that of 5-mm specimens at the same temperature. The 2-mm specimens dried at 45 °C exhibited the smallest internal moisture content (MC) gradient (8.5 %), resulting in minimal drying stress. Greater collapse occurred in 5-mm specimens at higher temperatures. Below the fiber saturation point (FSP), shrinkage and MC showed a strong linear relationship ( R 2 > 0.98). However, the apparent FSP estimated by regression increased with temperature (from 23.2 % to 32.1 %), reflecting the confounding effects of collapse and drying history. Among all conditions, the 2-mm specimens at 45 °C exhibited the smallest MC gradient and least evidence of collapse, suggesting that their shrinkage behavior most closely approximated free shrinkage conditions among the tested treatments.