Quantification of Wood Thermal Treatment by Electron Paramagnetic Resonance Spectroscopy

Abstract

The process of thermally treating wood can impart desirable properties such as an aesthetically appealing color, dimensional stability, and increased resistance to moisture and fungal decay. However, potential undesirable outcomes, such as increased brittleness, may arise with extensive thermal treatment. Due to this risk, it is extremely important to quantify the extent of heat treatment on a specimen for quality control. Previously, free radical content in thermally treated wood was discovered. We therefore set out to quantify the radical content of thermally treated wood samples utilizing electron paramagnetic resonance (EPR) spectroscopy and attempted to find out if this could be correlated with the extent of heat treatment. We heat-treated samples using a pilot-scale, in-house oven kiln (an industrially relevant process), as well as in the highly controlled and quantifiable environment of a thermogravimetric analysis (TGA) analyzer. With these wood samples, we measured the free radical content using EPR to determine the correlation between radical content and other factors such as: treatment temperature, treatment atmosphere, rate of formation, treatment time, and the effects of moisture. Our main goal was to find reliable methods for quantifying the extent of heat treatment in thermally treated wood by the use of EPR spectroscopy.