Processing and properties of thermoplastic starch and its blends with sodium alginate

Viscosity measurements were carried out on corn starch (CS) and CS-sodium a lginate (SA) suspensions at low levels of SA [1 to 10% (w/w)], as a functio n of temperature. The addition of SA caused the granular CS gelatinization process to occur at a lower onset temperature. CS and CS-SA mixtures were e xtruded in single- and twin-screw extruders, with 15% glycerol and differen t water contents. Processing of plasticized CS-SA mixtures required lower t emperatures, which is consistent with the viscosity results. Homogeneous an d flexible extrudates were obtained by processing in a twin-screw extruder. Samples in the composition range between 0 and 10% (w/w) SA were examined using tensile tests as a function of water content. Mechanical properties w ere dependent on the water content and on the SA composition. A significant increase in the Young's modulus value was observed for the blend containin g 1% SA. Dynamic mechanical analysis was carried out for CS and CS-SA blend s. Two transitions were detected in the temperature range -80 to 150 degree sC. Scanning electron microscopy was used to examine the morphology of the extruded samples. The surfaces of the films were homogeneous, which demonst rated that the CS granules in all samples were characteristically destructu red under the conditions used in processing. (C) 2001 John Wiley & Sons, In c.