Prediction of colour change of thermally modified wood by near infrared spectroscopy

Colour changes of untreated and thermally modified (120 degrees C, 180 degrees C and 220 degrees C) southern pine wood are predicted by near infrared spectroscopy (NIR). Colour change information originating from thermal chemical decomposition was assessed by NIR spectroscopy while wood surface colour change values in the CIE1976 L*a*b* system were determined with a colour measurement instrument. Calibration models were built using partial least squares and corresponding cross-validation. A close relationship between colour change values and NIR spectra of thermally modified wood allowed for easy clustering. The proposed colour prediction model for thermally modified wood produced very high R-2 values (above 0.90) and was well suited to NIR spectra acquired from wood tangential surfaces, suggesting that the method can provide effective, online quality control.