Chemical characterisation and durability assessment of torrefied radiata pine (Pinus radiata) wood chips

Abstract Wood chips from New Zealand grown radiata pine were torrefied at 220, 260, and 300 °C with the aim of understanding the fundamentals behind the enhanced durability against major decay fungi. Chemical analysis methods, including high-resolution synchrotron-based X-ray diffraction, were used to ascertain the mode of chemical changes in wood after various torrefaction levels. Compositional analysis showed that the carbohydrates and lignin in 220 °C samples remained at about the same levels as in the control, with a noticeable drop in the relative ratio of carbohydrates levels and an increase in lignin levels at 260 °C, and a steep drop in carbohydrates and a sharp increase in lignin concentrations at 300 °C. Hemicelluloses were the most severely affected carbohydrate component, particularly with 300 °C treatment. Analysis with FTIR showed similar spectra for control and 220 °C treated chips, a broad shoulder around 1610 cm −1 at 260 °C, and several changes at 300 °C involving carbonyl at 1705 cm −1 and c c and c–c absorptions. Synchrotron-based X-ray diffraction showed a slight contraction of peak d (200) for torrefied samples, which is related to increasing hydrophobic cellulose crystallinity. The information obtained suggests that the durability enhancement achieved against Oligoporus placenta and Trametes versicolor at 260 °C can be attributed mainly to depletion of hemicelluloses, and complete resistance at 300 °C is likely to be related to changes in all cell wall components, particularly hemicelluloses and lignin.