Morphology and rheological properties of blends of chemically modified thermoplastic starch and polycaprolactone

Polycaprolactone (PCL) was blended in a twin‐screw extruder with chemically modified thermoplastic starch (CMPS) to provide biobased and biodegradable resin composition. Reacting starch with maleic anhydride (MA) in the presence of a plasticizer and a free radical initiator provided the CMPS. The starch modification improved interfacial adhesion and processability in blending with other thermoplastic polyesters. The rheological, mechanical, thermal, and morphological properties of the blends were examined. Differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) studies revealed that the PCL/CMPS blends are thermodynamically immiscible. However, they formed compatible blends due to the reaction of the carboxyl groups on starch backbone with hydroxyl groups of the PCL chain ends. The tensile strength and elongation decreased with increasing CMPS content, whereas the modulus increased. Dynamic viscoelastic measurements showed that the flow behavior of PCL was that of Newtonian fluid within the tested frequencies, whereas the CMPS exhibited strong shear thinning characteristics. The flow behavior of the blends varied with the CMPS content. The complex viscosity, storage, and loss moduli of the blends containing more than 40% of CMPS were higher than those of pure CMPS and PCL. In addition, the properties of CMPS to those of chemically unmodified thermoplastic starch (TPS) were compared. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers