Morphologies and properties of thermo-molded biodegradable plastics based on glycerol-plasticized wheat gluten

The aim of the present work was to study the influences of aldehydes and l-cysteine on the morphology and the properties of thermo-molded biodegradable plastics based on glycerol-plasticized wheat gluten. The aldehydes and l-cysteine in 10% aqueous solution were incorporated with gluten and glycerol by mixing at room temperature and the resultant mixtures were thermo-molded at 100 °C for 12 min.Morphology, moisture absorption, dynamic mechanical properties, tensile properties (tensile strength and elongation at break), and thermal degradation behavior of the plastics produced were evaluated in relation to the crosslinking type. Experimental results showed that the morphology, the glass transition of gluten and the tensile properties were closely linked to the type of the crosslinking reaction that led to the formation of a protein network. Crosslinking through disulfide bonding led to a high degree of phase separation and a high glass transition temperature of the gluten-rich phase while aldehyde-induced crosslinking restricted the phase separation in a low degree and lowered the glass transition temperature of the gluten-rich phase. Aldehyde-induced crosslinking improved tensile strength whereas lowered elongation at break and Young's modulus in comparison with crosslinking via disulfide bonding in the crosslinker-free and the l-cysteine-containing plastics.