A near infrared spectroscopic study of the structural modifications of lime (Tilia cordata Mill.) wood during hydro-thermal treatment.

The modifications and/or degradation of lime (Tillia cordata) wood components during wood heat treatment under low temperature at about 140°C and 10% percentage of relative humidity were evaluated. The aim of this study was to obtain results by simple NIR coupled with second derivative, principal component analysis and two dimensional correlation spectroscopy in order to better understand how these techniques are able to evaluate structural differences resulted under hydro-thermal treatment of the wood over a period of 504h. The NIR spectra of treated samples were compared with the reference one. Due to the broad bands in the NIR spectra, the assignment and modifications occurring during treatment is difficult, therefore the second derivative principal component analysis were applied. Principal component analysis by first two components was able to differentiate the samples series, PC1 being considered as the time axis, and PC2 as the axis representing the structural modification of wood components. 2D NIR correlation spectroscopy was able to estimate the sequential order of the groups variations under the hydro-thermal treatment time as external perturbation, indicating as first moment changes the OH and CO groups from carbohydrates and lignin, followed by CarH, CH and CH2 groups from lignin, cellulose and hemicelluloses.