Influence of processing conditions on the evolution of morphology in PVDF/PS and PP/PS polymer blends: Examining the processing-phase inversion mechanism

摘要

Understanding morphological changes in polymer blends in the initial melting region of an extruder is crucial for optimizing the polymer mixing process. In blends with a large difference in their softening temperatures, a processing-phase inversion transition occurs when a larger volume-fraction of the higher melting component is present. The morphological changes in 80/20 PVDF/PS blends were examined (where PVDF forms the major phase) in an internal mixer under different processing conditions, such as preset temperature program, fill volume and rotor speed. We studied the torque behavior, energy consumption during mixing and phase inversion point for both 80/20 PVDF/PS and 80/20 PP/PS blends. PP needed 2.4 times higher mechanical energy to be deformed and to achieve a similar phase inverted state, compared to PVDF. To examine the effect of the minor phase properties, two 80/20 PVDF/minor ph.ase systems were examined: (i) a low-melting viscous EVA (ethylene vinyl acetate copolymer), and (ii) a low viscosity PCL (polycaprolactone). Using a range of techniques, such as torque monitoring, optical microscopy, SEM etc., it is established that the nature of the minor phase (amorphous vs. semicrystalline), minor phase melt viscosity and the exact processing parameters influence the point at which the phase inversion occurs.