Effects of water-soluble extractives on the moisture sorption properties of spruce wood hygrothermally treated at 120°C and different humidity levels

Sitka spruce wood specimens were heated at 120 degrees C and different relative humidity during heating (RHh) levels for 2-7 days and their equilibrium moisture contents (EMCs) were measured at 25 degrees C and 11-97% relative humidity (RH) before and after the removal of the water-soluble extractives. By heating at 80% RHh or less, a longer heating at higher RHh resulted in a greater reduction in the EMC; further, the reduction in EMC was greater at higher RH. Conversely, the EMC value of the wood specimens heated at 100% RHh demonstrated a steep increase at high RH levels, exceeding that of the unheated wood at 97% RH. An increase of this nature in EMC was not realized after the removal of the water-soluble extractives. These results indicate that the deliquescent nature of water-soluble extractives, the decomposition residue of hemicelluloses, has significant influence on the moisture sorption of wood when the wood is heated in saturated water vapour.

Automated summary

The research findings show that both the relative humidity and heating time during wood heating significantly affect the moisture content of wood, especially under high humidity conditions. The deliquescent nature of water-soluble extractives and the decomposition residue of hemicelluloses have a significant influence on the moisture sorption of wood.