In situ compatibilization of thermoplastic starch/polylactic acid blends using citric acid

In this study, in situ compatibilized thermoplastic starch (TPS)/polylactic acid (PLA) blends were obtained using citric acid (CA) as promoter of compatibilization. The TPS (60 wt%)/PLA (40 wt%) blends were prepared using 1 wt% of p-toluenesulfonic acid (p-TSA) as catalyst. The proportions of CA were 0, 5, 10, and 15 wt%. The effect of the CA content on the structural, thermal, rheological, morphological, mechanical, and biodegradation properties of the blends was evaluated. Using infrared analysis (IR), a reduction of stretching vibration of OH bonds with increasing CA content was observed. The formation of an in situ compatibilizing was evidenced by IR and scanning electronic microscopy (SEM) analysis. The glass transition temperature (T_g) and the crystallinity of the TPS/PLA decreased with decreasing CA content. Rheological analysis showed a transition from elastic to viscous behavior in the TPS/PLA blends prepared with CA. The presence of CA improved the miscibility and water resistance of the TPS/PLA blends and it increased with the CA content. However, the biodegradability (18.72–25.9%) and the mechanical properties (tensile modulus: 254–423 MPa and tensile strength: 9.18–13.31 MPa) followed an opposite behavior. CA acted as crosslinking and plasticizing agent, and promoter of formation of a TPS–CA–PLA structure.

Graphical abstract