Compatibility characterization of poly(lactic acid)/poly(propylene carbonate) blends

The compatibility of poly(lactic acid) (PLA)/poly(propylene carbonate) (PPC) blends was investigated with Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile testing. The PLA/PPC blends were prepared over the whole composition range. FTIR spectroscopy revealed that there were several specific interactions between the chains of PLA and PPC: the interaction between C-H and O=C- and C=O center dot center dot center dot O=C or C=O center dot center dot center dot O-C dipole-dipole interactions. Moreover, PLA and PPC were compatible. DSC indicated that PLA and PPC were partially miscible but compatible to some extent because of the similar chemical natures of the blend components. TGA showed that the compatibility of PLA and PPC enhanced the thermal stability of PPC in the blends. As calculated by the Horowitz-Metzger equation, the activation energy for decomposition (E-t) of PPC in PLA/PPC (70/30) was 200.6 kJ/mol, whereas E-t of pure PPC was only 56.0 kJ/mol. A study of the mechanical properties versus the composition and the strain versus the stress illustrated that there was good compatibility between PLA and PPC, and the phase inversion of the PLA/PPC system occurred between 70 and 60 wt % PLA in the PLA/PPC blends. The Pukanszky model gave credit to very strong interfacial adhesion between PLA and PPC. (c) 2005 Wiley Periodicals, Inc.