Effects of thermal modification of oak wood upon selected properties of coating systems

Abstract

Heat treatment processes are usually used in low valued softwoods however there has been an increased use to change the natural colour of more valuable hardwoods without chemicals to be use indoors mainly for parquet floors. In this study, wood samples from oak (Quercus petreae L.) wood were heat treated (ThermoWood method) at 190oC for 2 hours and 212oC for 1 to 2 hours. Untreated and heat treated wood surfaces were coated by two different processes with an UV varnishing system according to manufacturer recommendations. The objective of this study was to investigate some surface properties like adhesion, glossiness, pendulum hardness and color (L*, a*, b*, ΔE, ΔL*, Δa* and Δb*). With heat treatment Lightness decreases and its magnitude is higher for higher temperatures and treating times being lower for double coated wood. There was a slight increase followed by a decrease in redness (lower a*) and a clear decrease in the yellow tone (b*). Total color variation increased with the intensity of the treatment and glossiness decreased (more for single coated wood). The adhesion strength and surface hardness decreased with the heat treatment for both single and double coated wood.