Efficient fabrication of chitin-based films with high UV-blocking and fluorescence via Hantzsch reaction

As the second most abundant polysaccharide on earth, chitin-based films are promising packaging and biomedical materials. However, the lack of special function (especially UV-blocking properties and fluorescence) usually restricts their further and high-value applications. Herein, high UV-blocking and fluorescence chitin-based films were fabricated via surface modification using acetoacetation and the Hantzsch reaction. The structure and properties of the films were characterized by NMR, FTIR, fluorescence spectrum, and tensile tests. The results showed that the benzene ring and 1,4-dihydropyridine ring (DHP) were successfully grafted on the films in the mild process. Besides, the degree of substitution of DHP (DS_DHP) increased with the reaction time, temperature, and substrate concentration. Moreover, the modification followed a first-order reaction at 20 °C with a rate constant of 2.1 × 10^-4. When the DS_DHP was over 0.029, the films exhibited 100 % UV shielding. The fluorescence spectrum demonstrated that the films had excellent solvent and temperature resistance. In addition, the films exhibited excellent mechanical strength with tensile strength up to 85.2 MPa. This work provides a facile and environmentally friendly strategy to fabricate a functional chitin-based film with potential applications in UV protection, medical packaging, and fluorescent materials.