Analysis of the Phase Structure of Partially Miscible PP/PE Blends via Rheometry
Sprache des Vortragstitels:
Annual European Rheology Conference 2013
Sprache des Tagungstitel:
Oscillatory shear rheometry is a powerful tool for the detection of phase separation in molten polymers and thus for the investigation of the solubility of each component in a mixture. This is due to additional long-time relaxation processes, which are caused by the deformation of the interface between different phases and which, compared to monophasic melts, are reflected in a significant increase of the dynamic moduli at low frequencies. The sample preparation for such measurements typically involves one or several crystallization steps, which in turn induce phase separation in the sample. Neither will this phase separation be balanced out by diffusion in the melt, nor is the rheometer suitable to be used as a compounder. Consequently, the results of such an investigation might be somewhat distorted. It seems therefore desirable to avoid any crystallization between the compounding and the rheological characterization of a blend. For that purpose, an experimental set-up was designed in such a way that after compounding, the molten blends are directly injected into the measuring cell of a rheometer, where the dynamic moduli are determined. On the assumption of complete miscibility, the relaxation time spectrum of each blend is calculated from the combined molar mass distributions of the components. This hypothetical spectrum is then compared to the spectrum obtained from the measured moduli. The difference between both spectra is related to the properties of the interface. Additional information about the phase structure is gained from further evaluation of the rheological data using the model of Gramespacher and Meissner. However, a modification to this model is introduced to describe the behaviour of the investigated blends more accurately.