Abstract
Wood is widely used throughout society for building resources and paper. To further expand wood’s use in the wood industry, we tested the bending strength properties of wood and certified its internal quality by using near-infrared spectroscopy (NIRS). In this study, the relationship between bending strength and loading direction was compared by changing the light acquisition point of wood surfaces to elucidate the anisotropy of the wood using NIRS. The two loading directions were defined by using a bending test as the radial section and the tangential section. Two light acquisition points with NIRS were also defined by a bending test as the loading position (the compression surface) and the opposite surface (the tensile surface), and a comparison was made between the prediction accuracy of the wood’s mechanical strength properties obtained via a bending test using two pieces of light acquisition data. The strength properties of the wood bending tests were the elastic modulus in bending (Eb), the bending strength (Fb) and density (DEN). Cryptomeria japonica was prepared and cut into a final size of 20 mm × 20 mm × 320 mm. Near-infrared (NIR) spectra were obtained from the compression force side and the tensile force side (calculating these averages), and a partial-least-squares regression (PLSR) was performed for the regression analysis. In the NIR measurement position, the best calibration results of the PLSR were the averaged data between the side undergoing the compression force and that undergoing the tensile force. Comparing the two loading directions, the result for the radial section was slightly superior to that of the tangential section. The radial section showed a good relationship between the spectra acquisition position and the arrangement of the wood’s structure. The estimation accuracy of bending strength properties differed depending on the location where the NIR spectra acquisition was performed.
Highlights
Near infrared spectroscopy (NIRS) is widely used for nondestructive measurement with agricultural commodities, including wood
The radial section showed a good relationship between the spectra acquisition position and the arrangement of the wood’s structure
Focusing on the two loading directions, the radial section result was slightly superior to the section result
Summary
Near infrared spectroscopy (NIRS) is widely used for nondestructive measurement with agricultural commodities, including wood. The use of wood is essential to our lives because wood was a building material, and a stock of paper Wood properties such as bending strength, compressive strength and chemical composition are important for using the right wood in the right place. It had been shown that many wood properties can be measured non-destructively using near infrared spectroscopy; and industrial applications are being attempted. Both wood mechanical properties as the bending test and chemical components like cellulose, hemicellulose and lignin are simultaneously measured by using NIRS [1,2,3,4]. NIRS measurement data for the loading position and the opposite side may affect the prediction accuracy
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