EVALUATION OF DENSITY AND STRENGTH OF NORWAY SPRUCE WOOD BY NEAR-INFRARED REFLECTANCE SPECTROSCOPY

The non-destructive evaluation of wood properties by Near Infrared Reflectance Spectroscopy (NIR) has been assessed. The surfaces of specimens of clear wood (Picea abies) were NIR-scanned, and the results compared to such properties as moisture content, density, compression strength and chemical and biological degradation. In addition, the NIR-scans of clear wood specimens were compared to the bending strength of the structural timber from which it had been cut. The NIR dependency of surface roughness was investigated and found to be of minor importance. NIR calibrations for moisture content (MC < 30%), density, compression strength and chemical degradation proved that the NIR technique is an excellent non-destructive method (r(2) greater than or equal to 0.9; independent test set). Even biological degradation was determined with a most promising accuracy (r(2) = 0.75; independent test set). For the prediction of the bending strength of timber NIR proved less efficient. However, NIR still contributed to timber strength prediction at the same level as annual ring width, the parameter which is presently visually assessed by timber graders. It is concluded that the NIR method is very versatile in the non-destructive evaluation of wood. The results merit further investigations in order to develop proper models and instrumentation for commercial use.