Preparation and plasticizing mechanism of deep eutectic solvent/lignin plasticized chitosan films

Chitosan (CS) is a natural biopolymer from crab shells known for its biocompatibility and biodegradability; however, CS films are extremely rigid, limiting their applications. In this study, CS composite films were pre-pared based on the selective dissolution of lignin by deep eutectic solvents (DES), and the toughening effect of this DES/lignin on a CS film substrate was examined, along with its corresponding mechanism. The addition of DES/lignin effectively increased the plasticity of the CS film, giving a maximum elongation at break of 62.6 % for the plasticized film, which is 12.5 times that of the CS film. Fourier transform infrared spectroscopy and nuclear magnetic resonance analyses showed that molecules in the DES/lignin complex interacted with CS to break the hydrogen bonds between the CS molecules; simultaneously, each molecule recombined with the CS molecules via hydrogen bonding. Thus, the rigidity of the CS molecular chain was weakened to achieve a plasticized CS film, thereby demonstrating the ability of DES/regenerated lignin to improve the toughness of CS films, which pro-vides a reference for modifying plasticity and could lead to the broader utilization of CS films.

Automated summary

This study prepared chitosan (CS) composite films by selectively dissolving lignin using deep eutectic solvents (DES), and investigated the toughening effect of DES/lignin on CS film substrate and its mechanism. The addition of DES/lignin effectively improved the plasticity of CS film, resulting in a maximum elongation at break of 62.6% for the plasticized film, which was 12.5 times that of the CS film. FTIR and NMR analyses demonstrated that the molecules in the DES/lignin complex interacted with CS, breaking the hydrogen bonds between CS molecules, and then recombined with CS molecules via hydrogen bonding. This study shows the potential of DES/regenerated lignin in improving the toughness of CS films and provides insights for the modification of plasticity in CS films.