Near-infrared spectroscopy in the wood-based products industry

Abstract

"Near infrared" is the designation of the electromagnetic spectrum region immediately after the visible region. According to ASTM (American Society of Testing and Materials), its wavelength is between 780 and 2500 nm. Although some experiments have been carried out in the 20's, it wasn't until the 60's that near-infrared spectroscopy started being used to its full potential. Since then, this technique has been widely used in fields as varied as pharmaceutical, food processing, agriculture, petrochemical, food processing, agriculture, forestry, cosmetic, environmental, medical and polymers. The main advantages of near infrared (NIR) spectroscopy are: it is nondestructive, may be performed on-line or off-line, samples can be in solid or liquid state, sampling preparation is minimal, analysis is fast and equipment operation simple. On the other hand, NIR spectroscopy also has its drawbacks. Due to the complexity of the signal, it is necessary to process the data in order to obtain values of interest. Chemometric methods (e.g., data-based modeling techniques) must be used to allow establishing relations between several measurements and the characteristics of the analyzed product. In the context of forestry and forest products, NIR applications have been mostly focused on analysis of chemical composition of wood, and characterization of paper and wood properties. Recently, work has been done in the context of wood based panels industry, mainly for characterization of physical and mechanical properties of the panels, and for on-line monitoring of fiber properties, such as moisture content, fiber length distribution. In addition, NIR methodologies have been developed to identify and check the conformity of laminating paper impregnated with formaldehyde-based resins. Formaldehyde-based resins are widely used in the production of wood-based panels. In this industry, NIR spectroscopy has been used for monitoring the industrial process, analyzing and check the conformity of raw materials. Moreover, NIR has been used online for continuously evaluation of raw materials content during synthesis, to provide a methodology for monitoring resin production and to ensure reproducibility of the final product. In the wood preservation industry, preliminary studies with decayed wood indicated that NIR may be useful in detecting and quantifying biodeterioration of wood.