Mechanical, morphological, thermal, and fire-retardant properties of sustainable chitosan-lignin based bioplastics

Lignin can function as a fire retardant for biocomposites because of its excellent thermal stability. This work evaluated the impact of integrating technical lignin into chitosan-based bioplastics to enhance their mechanical and thermal properties. The solvent-casting technique was employed for the preparation of chitosan-lignin bioplastics. The incorporation of lignin improved the antioxidant properties and mechanical strength of the bioplastic, and it functions as a UV-blocking agent, as evidenced by UV-shielding studies, which indicates a reduction in the transmittance of the chitosan-lignin bioplastic by approximately four fold. The incorporation of lignin washed 3× with HCl into the chitosan-based bioplastic increased the tensile strength of the material by 36.41 % and the elastic modulus by 56.04 %. The antioxidant activity of the chitosan-lignin-based bioplastic ranged from 75.80 % to 80.38 %, whereas that of neat chitosan was only 25.02 %. Thermal analysis revealed that incorporating lignin as an additive in a chitosan-based bioplastic improved the thermal stability and flame retardancy of the bioplastic. This is indicated by a higher limiting oxygen index (LOI) value ranging from 42 to 48 % for the chitosan-lignin bioplastics than for the control bioplastic (27 %), which has a UL-94 rating in the V-0 range. These findings support the fact that the antioxidant, strength, and fire-retardant performance of chitosan-based bioplastics could be enhanced by the addition of lignin.