NIR Spectroscopy Monitors Wood

A team from the Competence Centre for Wood Composites and Wood Chemistry in Linz and from the University of Natural Resources and Applied Life Sciences Vienna, both in Austria, and from Technical University of Munich, has shown that near-infrared spectroscopy may be useful for process control of wood acetylation. This process reduces mechanical and chemical differences between species, making wood a more predictable material for building and engineering.

Partial least-squares regression modelling leads to very good correlation between predicted and measured weight percentage gain (WPG) for a wide range of wood species in milled wood samples (a) and milled acetylated veneer samples (b). Reprinted with permission of Analytical Chemistry.

The researchers applied both Fourier transform infrared spectroscopy (FTIR) and NIR spectroscopy to milled wood particles, shavings and veneers, and they used various species and mixtures to simulate input material variation for industrial processing. A Bruker spectrometer with fibre probe and germanium diode detector was used for NIR spectroscopy. A DLATGS (deuterated L-alanine-doped triglycine sulphate) detector allowed the same instrument to measure FTIR-KBr spectra. A Pike Technologies attenuated total reflection (ATR) device and a Bruker spectrometer recorded the FTIR-ATR spectra. The researchers used second-derivative preprocessing and multivariate analysis to extract data from the overlapping NIR bands. The data correlated with weight percentage gain, showing that the technique has potential for use in on-line process control.

They conclude that FTIR is a good laboratory method because band heights correlate well with acetyl group content.

(Analytical Chemistry, 15 Feb. 2008, pp. 1272-1279)