Thermal and morphological characteristics of polypropylene/smectic polyester blends

Several blends of isotactic polypropylene, iPP, and the liquid crystalline polymer poly(triethylene glycol p,p′-bibenzoate), PTEB, have been prepared with different compositions, and analyzed by scanning electron microscopy, polarizing optical microscopy, infrared spectroscopy, X-ray diffraction with synchrotron radiation, and thermal methods (thermogravimetric analysis and differential scanning calorimetry). The results show a good adhesion matrix-dispersed phase when a maleic anhydride-grafted PP is used as compatibilizer, MA-g-PP. The calorimetric and synchrotron experiments indicate higher crystallization temperatures for the iPP component in the blends when compared with those of pure iPP. The higher crystallization temperature seems to be associated with a crystallinity increase. Optical microscopy results point out the nucleating effects of both PTEB and MA-g-PP on the iPP spherulites. The synchrotron experiments reveal that, on cooling from the isotropic melt, a SmA mesophase is formed first from the PTEB component, followed by its transformation into a tilted SmC mesophase. The isotropic-SmA transition is clearly affected in the blends with higher contents in iPP.