Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy was used to examine the impact of hydrogen bonding on the reactive amine and hydroxyl groups of chitosan. Measurements were performed on powder and film samples hydrated under different conditions. To resolve the individual OH and NH bands that overlap in the region between 3000 and 3800 cm(-1), the spectra were deconvoluted using a Gaussian curve fitting method. By analyzing the changes recorded for each Gaussian component along the dehydration process of the films at different pH values, a band assignment was proposed. This assignment was then used to analyze the ATR-FTIR spectra of the chitosan/montmorillonite composites. The changes induced by the presence of the clay were ascribed to particular mechanisms of interaction that involve the active sites of the clay and the amino or hydroxyl groups of chitosan. The comparison between the FTIR and the XRD data, evidenced that these mechanisms are intimately controlled by the type of nanostructures that are formed depending on the clay content. (C) 2016 Elsevier Ltd. All rights reserved.