Enhancing the structure and properties of starch/epoxidized soybean oil-based bioplastics via ionic crosslinking

The work investigated the effects of Al 3+ crosslinking concentration and pH on the structure and properties of bioplastics from oxidized starch and epoxidized soybean oil (ESO) systematically. FTIR suggested that Al 3+ treatment altered the intermolecular interaction in the oxidized starch/ESO-based bioplastics by hampering the hydrogen bond interaction within starch molecules. Elemental analysis and XRD results revealed that Al 3+ contents of starch increased significantly when starch was modified by higher Al 3+ concentration. Al 3+ modification improved the thermal stability of starch and bioplastics, attributed to the strong interaction between Al 3+ and starch. Moreover, the incorporation of Al 3+ caused a reinforcing effect on the oxidized starch/ESO-based bioplastics, resulting in the significant increase of tensile strength and reduction of elongation at break. The Al 3+ -crosslinked bioplastics showed higher opacity and hydrophobicity due to stronger interactions in the bioplastics. Comparatively, Al 3+ crosslinking under acid condition provided better transparency to the bioplastics, while the neutral pH crosslinking contributed to higher Al 3+ content and thermal stability, and lower moisture content and solubility to the bioplastics. Accordingly, low Al 3+ concentration led to higher mechanical and water resistance properties in the neutral condition. The study demonstrated the potential of Al 3+ to regulate the physicochemical properties of oxidized starch/ESO-based bioplastics.