Miscibility, crystallization, and mechanical properties of poly(3-hydroxybutyrate) and poly(propylene carbonate) biodegradable blends

Nine blends of poly(3-hydroxybutyrate) (PHB) and poly(propylene carbonate) (PPC), biodegradable polyester, and pure sample films were prepared with the ratio of PHB/PPC ranging from 90/10 to 10/90 by codissolving these two polyesters in chloroform and casting the mixture. The miscibility, crystallization, melting behavior, morphology, and mechanical properties of the blends have been studied by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), wide angle X-ray diffraction (WAXD), polarizing optical microscopy (POM), and scanning electron micrograph (SEM). The results indicated that PHB showed complete miscibility with PPC for PHB/PPC 30/70, 20/80, and 10/90, as evidenced by the only one composition-dependent glass transitions (T-g) of blends, and the T(g)s close to the values calculated using the Fox equation. However, PHB showed immiscibility with PPC for the other six blends, as shown by the existence of almost unchanged T-g of PHB at about 2 degrees C. According to the DSC analysis, the crystallization of PHB was suppressed by blending with abundant PPC. This result is consistent with results obtained from X-ray and POM results. Some interaction between the two macromolecules was confirmed by using FTIR analysis. SEM graphs showed that the blends containing PHB <= 30 wt% tend to form a more compact structure, and no obvious phase separation was found. The brittleness of PHB was improved apparently by blending with PPC. (C) 2008 Wiley Periodicals, Inc.