Effects of Water on the Properties of Thermoplastic Starch Poly(lactic acid) Blend Containing Citric Acid

In order to improve the compatibility between hydrophilic starch granules and hydrophobic poly(lactic acid) (PLA), glycerol was used as plasticizer and citric acid (CA) was used as the additive to enhance the dispersion and the interfacial affinity in thermoplastic starch (TPS)/PLA blend. Water had been recognized as positive component for the properties of TPS, but it also could deteriorate the properties of PLA. So the influence of water on the properties of TPS/PLA blends was investigated through scanning electron microscopy (SEM), rheological thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR), Dynamic mechanical thermal analysis (DMTA) and tensile testing. In the presence of water and CA, the plasticization of starch in TPS/PLA blends could be improved dramatically. At the same time, a homogeneous TPS/PLA blends could be detected by SEM. But high CA and water content decreased the thermal stability of TPS/PLA blend as shown in TGA. In addition, FT-IR spectroscopy proved that CA and water could improve the interaction between TPS and PLA. The tensile testing showed that the maximum tensile strength of TPS/PLA blends could increase to 42 MPa higher than that of pure PLA. DMTA were also studied in this paper.