Investigating sapwood and heartwood density changes of short rotation teak wood after chemical and thermal modification using X-ray computed tomography

Abstract Differences in characteristics between sapwood and heartwood of short-rotation teak are a significant obstacle to valorize mixed boards containing both types of wood. Chemical and thermal modifications are attractive methods to improve the quality of short rotation teak wood allowing homogenization of both sapwood and heartwood properties like decay resistance, dimensional stability and color. However, no data are available on the difference in density between sapwood and heartwood of short-rotation teak, as well as on the effect of such treatments to achieve homogeneity. Density profiling is important to assess the homogenization of the modification process of chemically and thermally modified wood. The objective of this study was to determine the effect of chemical and thermal modification on the density profile of sapwood and heartwood of short rotation teak from pith to the bark using X-ray computed tomography (XCT). The chemical and thermal modifications applied were furfurylation (FA), thermal modification at 150 and 220 °C, and a combination of glycerol-maleic anhydride (GMA) impregnation and thermal modification at 150 and 220 °C. XCT was used to investigate the density variation of short rotation teak wood before and after chemical and thermal modification. A registration process using Avizo software was applied to overcome the deformation effects due to chemical and thermal modification treatments. The results show that the vessel diameter increased after FA treatment due to polymer-induced swelling, while it decreased after GMA220 treatment due to vessel collapse caused by thermal effects. FA treatment increased the density of short rotation teak wood, and the density profile changes were rather uniform. There was a decrease in density due to thermal and GMA treatments, with a significant difference in density changes between sapwood and heartwood. The density profile allowed to observe the homogeneity of sapwood and heartwood density according to the applied treatment. Chemical and thermal modification showed weak effect on the homogenization of the density profile between sapwood and heartwood.