Chemical analysis and cellulose crystallinity of thermally modified Eucalyptus nitens wood from open and closed reactor systems using FTIR and X-ray crystallography

Currently there is a growing market for high quality solid wood products in Chile made from Eucalyptus nitens. Thermal modifications have been used to obtain such products out of fast growing species. The chemical and crystallinity changes in the modified wood were investigated using diffuse reflectance FTIR spectroscopy and crystalline analysis by X-ray diffraction to analyze the difference between thermal modifications processes using pressure under wet conditions (closed system) and processes without pressure under drier conditions (open system). In general, the FTIR spectra showed differences in the degradation of the hemicelluloses in the peaks of the C=O linkages, but almost no differences in the peaks that identify the lignin structure of the wood, as it was difficult to separate the different chemical reactions due to the depolymerization of lignin only observing the bands. The degree of crystallinity showed a tendency to increase at high pressure in the closed system modifications and at temperatures above 200 °C in the open system modifications, but no significant differences at low modification pressure and temperatures. Nonetheless, there were differences in FTIR spectra and cellulose crystallinity when directly comparing modifications with the same corrected mass loss under different conditions.