Influence of Citric Acid on the Properties of Glycerol-Plasticised Cornstarch Extrusion Blends

Abstract

Melt extrusion was used to prepare glycerol-plasticised dry thermoplastic starch (DTPS) in a single-screw extruder. Glycerol combined with water-plasticised starch (TPS) was studied as a standard. Citric acid (CA) was used to accelerate the plasticization of DTPS. Scanning electron microscopy revealed that residual granules existed in DTPS and the plasticisation of DTPS could be enhanced by CA. Rheological studies proved that CA decreases the shear viscosity and improves the fluidity of TPS and DTPS. It was also proved by Fourier transform infrared spectroscopy that starch and glycerol could form strong hydrogen bonds in the presence of CA. With increasing CA content, the rigid and fragile DTPS materials became more flexible, with a high tensile strength. Dynamic mechanical thermal analysis proved that CA could decrease the glass transition temperature of TPS and increase the interaction between glycerol and starch. Finally, the water absorption of DTPS and TPS were also measured.