Thermal modification of wood is a process in which, in the absence of atmospheric oxygen, wood is heated at a elevated temperature in the range of 180 °C in 240 °C, thereby changing certain properties of the wood. Main advantages of TMW (thermally modified wood) are improved resistance to decay, lower equilibrium moisture and better dimensional stability. Due to increasing demand for TMW, the need for simple and quick quality control has emerged. Spruce wood, beech wood, ash wood and poplar wood were thermally modified according to three different processes at temperatures ranging from 180 °C to 230 °C. We compared the influence of wood species, temperature and modification process on relevant wood properties. Mass loss during modification was gravimetrically determined, colour was measured using CIE L*a*b* colour scale, »envelope« and »true« density were determined, compressive strength and modulus of elasticity were measured, pH was measured, the contact angle of water droplet on surface was monitored, so was water and water vapour uptake. Mass loss is higher for samples modified at a higher temperature and so is colour change. Contact angle is higher on samples treated at a higher temperature. Short-term absorption through end surface of the sample in beech wood is lower at a higher temperature of modification; equilibrium moisture content is lower respectively. As most indicative method for determining degree of modification has proven to be DVS (dynamic sorption of water vapour).
|
