Development and characterization of deep eutectic solvent-assisted biochar-modified chitosan films for sustainable packaging solutions

Abstract

Growing environmental concerns about petroleum-based plastics have accelerated the development of biodegradable, sustainable packaging alternatives. Chitosan, a naturally occurring biopolymer obtained from chitin, has gained considerable research interest because of its biodegradable nature, ability to form films, and inherent antimicrobial characteristics. However, its practical application is limited by brittleness, high moisture sensitivity, and moderate mechanical strength. To address these limitations, this study investigates a dual modification strategy involving biochar reinforcement and deep eutectic solvent (DES) plasticization to develop high-performance chitosan-based composite films. In the first phase of the study, biochar-modified chitosan films were developed with varying biochar content. The incorporation of biochar significantly enhanced the stiffness and thermal stability of the films, as indicated by increased Young’s modulus and improved thermal degradation resistance. Tensile strength improved at lower biochar loadings due to effective stress transfer, whereas elongation at break decreased with increasing biochar content, reflecting reduced flexibility. Dynamic mechanical analysis further confirmed the reinforcing effect of biochar, evidenced by an increased storage modulus and reduced molecular mobility. In the second phase, deep eutectic solvents were incorporated into the optimized biochar–chitosan system to improve flexibility and interfacial compatibility. The addition of DES reduced stiffness and tensile strength, accompanied by an increase in elongation at break, indicating enhanced ductility. Viscoelastic analysis revealed a decrease in storage modulus and an increase in damping, confirming the plasticizing effect of DES. Overall, the results demonstrate that biochar and deep eutectic solvents play complementary roles in modifying chitosan films. Biochar enhances mechanical strength and thermal stability, while DES improves flexibility and processability. The combined system enables the development of biodegradable composite films with tunable and balanced properties, highlighting their potential for sustainable packaging applications.