Urea-Based Eutectic Mixtures as Green Plasticizers for Starch, Other Polysaccharides and Proteins

Urea (U), known as carbamide, is a cheap, ubiquitously available diamide widely used in the chemical industry. In the last two decades, this polar compound has become a component of novel green media: deep eutectic solvents (DESs), used, for example, as catalysts, solvents, modifiers, and plasticizers. Due to their physicochemical properties, they can replace molecular ionic liquids as a cheaper, more environmentally friendly alternative. Urea can be both a donor and an acceptor of hydrogen bonds, thus giving a wide range of possibilities for novel media design. Formation of H-bonding in eutectic mixtures has a lot of advantages compared to pure urea or conventional media, especially as a modifier for biopolymers. U-based DESs can be used as functional plasticizers for many abundant biopolymers like polysaccharides (especially starch, but also cellulose derivatives, agar, agarose, alginate, and chitosan) and proteins (e.g., gelatin), leading to the formation of their thermoplastic derivatives that could substitute some oil-based plastics in the future on an industrial scale.