Molecular association of adsorbed water with lignocellulosic materials examined by micro-FTIR spectroscopy

For lignocellulosic materials, water adsorption is extremely important for its product performance. For gaining a deeper understanding of moisture adsorption mechanisms, the molecular interactions between adsorbed water and a typical lignocellulosic material (i.e., wood) were studied using in-situ microscopic Fourier transform infrared (micro-FTIR) spectroscopy and a specially designed sample cell. The spectral shifts of 1733 cm−1, 1604 cm−1 and 1236 cm−1 and different spectra between the moist and dry spectra indicated that carbonyl CO and CO groups preferred to combine with water molecules to form hydrogen bonds. From component band analysis of the spectral range of 2900-3700 cm−1, three peaks at 3178 cm−1, 3514 cm−1 and 3602 cm−1 were identified and assigned to strongly, moderately and weakly hydrogen-bonded water molecules, respectively. According to the variation trend of these hydrogen-bonded water molecules, three sections were divided for the adsorption process. Furthermore, the molecular structure of water absorbed by hydrophilic groups of wood in each section was demonstrated.