Correlation of Near-Infrared Spectroscopy Measurements with the Properties of Treated Wood

Near-infrared (NIR) spectroscopy was used to predict the longitudinal tensile modulus, the longitudinal tensile strength, and the creosote content of wood from an out-of-service southern pine utility pole. Tensile samples were cut from the pole in the radial direction and near-infrared spectra were obtained before testing. Coefficients of determination $r^2$ , of 0.80–0.86 were obtained between the NIR spectra predicted modulus and measured modulus. Coefficients of determination for strength were lower, 0.58–0.63. After tensile testing, the specimens were ground in a mill and spectra were obtained from the homogeneous ground samples. There was a slight decrease in the coefficients of determination using the ground samples, 0.76–0.82 for the modulus and 0.46–0.57 for the strength. Creosote content was difficult to predict with the NIR spectra of the whole sample, but coefficients of determination $>0.9$ were obtained with the ground samples. There was little difference in the results for spectra collected over the $350\text{–}\mathrm{2,500}\mathrm{nm}$ range and those obtained with just looking at the $950\text{–}\mathrm{1,850}\mathrm{nm}$ range. This suggests that it will be feasible to predict the mechanical properties of treated timber using lightweight, relatively inexpensive, portable instruments rather than larger, more expensive systems that cover the entire NIR range.