An Evaluation of the Use of Near Infrared (NIR) Spectroscopy to Identify Water and Oil-borne Preservatives

In this research we experimented with a new and rapid way of analyzing wood. Near Infrared (NIR) spectroscopy together with multivariate analysis is becoming a widely used technique in the field of forest products especially for property determination and is already firmly established in the pulp and paper industry. This method is ideal for the chemical analysis of wood, and therefore preservative-treated wood. Several commercially treated deckboards were obtained for this study: CCA/Hem-Fir; CCA/Eastern Hemlock; ACZA/Douglas Fir and ACQA-Hem-Fir. They were milled and scanned with a NIR spectrometer. Visually, the NIR spectra appear very similar, however when incorporated into the multivariate software; differences start to emerge. This software applies multivariate statistical techniques to the spectra, identifying chemical changes in the wood that are caused by preservatives. The samples separated out according to treatment and were easily distinguishable. Additionally, the technique was able to determine the preservative retention levels present. Two oil-based preservatives were also studied: Copper Napthenate and Oxine Copper. Again these samples separated and clustered according to their treatments. Furthermore with the Copper Napthenate samples, there was a clear graduation in solution strength. This technique is rapid, non-destructive, portable and relatively low cost. It appears to have the potential for identifying both inorganic preservatives (those that contain copper, chromium or arsenic) and organic (carbon based) preservatives. The results clearly demonstrate that this technique has potential for use in a variety of recycling and sorting applications.