Effects of water-soluble extractives on the vibrational properties and color of hygrothermally treated spruce wood

Sitka spruce wood specimens were heated at 120-140 degrees C and different relative humidity values (RHh), and their specific dynamic Young's moduli (E/), mechanical loss tangents (tan), and CIELAB color parameters were measured at 25 degrees C and 60% relative humidity before and after the removal of water-soluble extractives. The E/ and tan values were significantly decreased and increased, respectively, with increases in mass loss by heating at 100% RHh. After the removal of water-soluble extractives, the decreased E/ was increased and the increased tan was decreased. This suggested that water-soluble sugars, i.e., depolymerization products of hemicelluloses, acted as plasticizers to decrease E/ and increase tan values of hygrothermally treated wood, particularly for wood heated in humid conditions. By heating at 60-75% RHh, the E/ was slightly increased and tan was almost unchanged. The water-soluble extractives had little effect on the color of the hygrothermally treated wood, irrespective of RHh.