Chemical changes of wood during steaming measured by IR spectroscopy

Black locust, poplar and spruce samples were steamed at 80°C and 120°C for 48 hours. IR difference spectra and the CIE Lab colour coordinates were measured for determining the chemical changes caused by the steaming. Steaming at 80°C caused only small changes in both IR spectra and colour. But steaming at 120°C produced intensive colour change and well-visible changes in IR spectra. The guaiacyl lignin in hardwoods underwent slight degradation but in spruce suffered substantial degradation during steaming at 120°C. The syringyl lignin absorbing around 1600 cm−1 did not show any changes, indicating that it is more stable to steaming than guaiacyl lignin. The absorption decrease at 1175 cm−1 indicated the cleavage of ether linkage in cellulose and hemicelluloses at both steaming temperatures.