Rheological properties of thermoplastic starch studied by multipass rheometer

The rheological properties of thermoplastic starch (TPS) melt were investigated using the new multipass rheometer (MPR). This rheometer consists of two servo-hydraulically driven pistons and a fully closed barrel, enabling pressurisation of sample and preventing moisture loss during the process. The starch samples (with different plasticiser contents, 70–110%, and at different glycerol/water ratio, 1:4, 2:3, and 3:2) were first well transformed into TPS in MPR and then tested at different temperatures (90, 110 and 130 °C). The TPS behaved as a shear-thinning material, and the power-law model was used to describe its rheological behaviour. The combination of glycerol and water had the greatest influence on the power-law index n while temperature had little influence. By mastercurve study, it was shown that the higher the glycerol/water ratio, the stronger the shear-thinning behaviour was. This was explained by interaction between starch and plasticiser and different structural characteristics at different conditions.