Melting behavior in blends of isotactic polypropylene and a liquid crystalline polymer

The influence of low contents of a liquid crystalline polymer on the crystallization and melting behavior of isotactic polypropylene (iPP) was investigated using electron and optical microscopy, differential scanning calorimetry, and X-ray diffraction. In pure iPP, the alpha modification was found, whereas for iPP/Vectra blends at Vectra concentration <5%, both alpha and beta forms were observed. The amount of beta phase varied from 0.23 to 0.16. Optical microscopy showed that Vectra was able to nucleate both alpha and beta forms. Non-isothermal crystallization produces a material with a strong tendency for recrystallization of the alpha and beta forms (alphaalpha' and betabeta' recrystallization) leading to double endotherms for both crystalline forms in DSC thermograms. Melting thermograms after isothermal crystallization at low temperatures showed a similar behavior. At values of T-c > 119 degreesC for the a form and T-c > 125 degreesC for the beta form, only one melting endotherm was observed because enough perfect crystals, not susceptible to recrystallization, were obtained. (C) 2004 Wiley Periodicals, Inc.