Influence of citric acid on the properties of glycerol-plasticized dry starch (DTPS) and DTPS/poly(lactic acid) blends

In the presence of citric acid (CA), one-step extrusion processing is used to prepare poly(lactic acid)/thermoplastic dry starch (PLA/DTPS) blends (50/50, %, w/w) in a single-screw extruder. The rheological study proves that CA decreases the viscosity of both DTPS and of DTPS/PLA blends. The low viscosity increases the dispersion and decreases the interfacial tension between DTPS and PLA, as shown by scanning electron microscopy (SEM). In the presence of CA, the tensile strength of DTPS/PLA reaches 41 MPa-similar to that of pure PLA-because of improved dispersion and compatibility. At the same time, CA increases not only the degradation of starch, but also the interaction between DTPS and PLA, as detected by Fourier transform infrared (FTIR) spectroscopy. The blend containing CA has a higher thermal stability. The water absorption of DTPS and DTPS/PLA blends is also studied.