Crosslinking of chitosan films processed by compression molding.

An alternative approach towards more sustainable chitosan films, through their manufacture by thermo-compression molding, was explore in this work. This strategy permitted the reduction of production times and avoided the use of organic solvents since biopolymer and acid were mixed in their solid form. Furthermore, the acid used as a crosslinker was citric acid, a natural policarboxylic acid, which promoted the reaction with chitosan, as shown by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). This crosslinking reaction led to the formation of homogeneous structures, as observed by scanning electron microscopy (SEM), indicating a good compatibility among all the components of the mixture and enhancing the mechanical properties of the resulting films. In particular, an increase of 80% for tensile strength and an increase of 3000% for elongation at break were observed for the crosslinked films. In addition to the homogeneous surface of citric acid-incorporated films, all the films showed hydrophobic character and the addition of citric acid led to a more amorphous structure. In sum, citric acid-incorporated chitosan films manufactured by compression molding were found to show potential for food and pharmaceutical applications.