Thermoplastic Starch/Ternary Deep Eutectic Solvent/Lignin Materials: Study of Physicochemical Properties and Fire Behavior

The goal of the work was to prepare thermoplastic starch (TPS), for the first time plasticized with ternary deep eutectic solvents (DESs) based on urea/resorcinol/choline chloride (URCC) in a 2:1:1 molar ratio and enriched with lignin as an environmentally friendly functional alternative for agricultural plastics. Potato starch was effectively modified with DES via twin-screw extrusion in the presence of lignin up to 10 pph (L10) without significant loss of elasticity (tensile strength 7.4 MPa, elongation at break 65%) and good thermocompressing properties (dynamic mechanical thermal analysis (DMTA) results) of highly amorphous materials (X-ray diffractometry (XRD) results) physically modified with DES (Fourier transform infrared (FTIR) results). The URCC mixture acted both as the plasticizer and as dissolving media for lignin, facilitating mutual processing. Moreover, cone calorimetry analysis of TPS materials revealed that they exhibited better fire-retardant properties than polymers commercially used as agricultural plastics (PE, PP, and PLA). Obtained results indicate that TPS/DES and TPS/DES+L materials can be used as, e.g., biodegradable, safe, and functional mulches that do not have to be removed from the cultivating fields.