Dynamic imine crosslinking for waterproof starch plastic with tunable mechanical properties.

Starch-based plastics offer a potential solution to environmental pollution and can reduce the dependence on petroleum-based plastics. However, effectively preparing starch-based plastics with moisture resistance and high strength remains challenging. Herein, dialdehyde starch (DAS) with different degrees of oxidation was first synthesised. The molecular weight and crystallinity of DAS decreased depending on the aldehyde content, as determined through scanning electron microscopy, X-ray diffraction and molecular weight analyses. Subsequently, a sustainable starch plastic (DAS-DA) was prepared via the dynamic imine crosslinking of DAS with diamines. The influence of the degree of oxidation of DAS on the structure and properties of DAS-DA was systematically investigated. No linear relationship was observed between the tensile strength of DAS-DA and the aldehyde content of DAS. When the aldehyde content was 41.1 %, the resulting DAS41-DA exhibited optimal mechanical strength (27.8 MPa), exceeding that of most reported starch-based plastics. In addition, owing to the presence of imine crosslinking networks, DAS41-DA exhibited excellent water and solvent resistance (>60 days), good thermal stability (456 °C-462 °C) and excellent reprocessability and biodegradability. These findings provide a theoretical basis for the preparation of high-performance bioplastics from aldehyde-containing polysaccharides.