Effect of elongational rheology on plasticization and properties of thermoplastic starch prepared by biaxial eccentric rotor extruder

Large amounts of plasticizers were added into natural starch for thermoplastic to make it processable due to the high crystallinity and large amount of intermolecular hydrogen bonds of starch. However, the traditional screw extruders based on shear deformation cannot disperse the plasticizer evenly and plasticize the starch well, which affects the comprehensive mechanical properties. In this paper, a self-developed biaxial eccentric rotor extruder (BERE) based on elongational rheology was introduced to prepare thermoplastic starch (TPS) sheets with glycerol as plasticizer at different speeds. The TPS sheets extruded by BERE all have excellent mechanical properties and optical transparency. Scanning electron microscopy, Fourier transformation infrared spectroscopy, X-ray diffraction, dynamic rheometer and universal mechanical tester were used to reveal the morphology, type and strength of hydrogen bonds, crystal structure, dynamic rheological and mechanical properties of TPS to research the effect of elongational rheology on its plasticization and properties. The results showed that the elongational rheology produced during processing process of BERE could obviously promote the dispersion of glycerol in starch and improve the melt-plasticizing effect of TPS, and the comprehensive mechanical properties of the TPS prepared by BERE is excellent with the elongation at break of 226.1%.