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

Colour changes of untreated and thermally modified (120°C, 180°C and 220°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 R2 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.