Investigation of Partial Miscibility of PP/PE Blends using the Relaxation Time Spectrum
Sprache des Vortragstitels:
Advances in Polymer Science and Technology (APST) 3
Sprache des Tagungstitel:
Oscillatory shear rheometry is a powerful tool for the detection of phase separation in polymer melts. This is due to additional relaxation processes following the deformation of the interface between the matrix and the inclusions.
Crystallization, as it usually happens during the sample preparation, can lead to distorted results as it induces phase separation which then might prevail during the measurement. A sample preparation method which avoids crystallization is presented.
Blends of PP and PE of various viscosities were prepared in a HAAKE Minilab II micro-compounder. After compounding, the molten blends were transported directly into the measuring cell of a rheometer (Anton Paar MCR 501). Afterwards, the dynamic moduli were measured.
Assuming total miscibility, the relaxation time spectrum of a blend can be calculated from the combined molar mass distributions of its components. On the other hand, the spectrum of a real blend can be obtained from the measured dynamic moduli. The difference between these spectra is related to the properties of the interface between the phases.
Results and Discussion
Results show a discrepancy between conventionally prepared compression molded samples and those prepared without crystallization, the extent of which varies with changes in the content of the minor phase and in the viscosity ratio of the components. Partial solubility is detected, which is more pronounced for PP in PE than vice versa. The model of Gramespacher and Meissner gives information about the respective volume fractions of the components and the ratio of interfacial tension to particle size, but it is refined in order to allow for a more accurate description of the behavior of the blends.