Rheological behavior and flow instability in capillary extrusion of ultrahigh-molecular-weight polyethylene/high-density polyethylene/nano-SiO2 blends

Rheological behaviors of ultrahigh-molecular-weight polyethylene (PE)/high-density PE/SiO2 blends are investigated using parallel-plate rheometer and capillary rheometer. The molecular chain conformational change mechanism is used to explain flow instabilities during extrusion. The viewpoints are proposed: (1) critical shear rate depends on the relative strength of irreversible viscous loss and reversible elastic orientation for molecular chains in transverse velocity gradient field inside the die and (2) critical shear stress depends on the extent of molecular chain conformational change inside the die, and the ease of conformational recovery after leaving the die. Modified nano-SiO2 particles are detected a certain interfacial adhesion in PE matrix. The interfacial interaction limits viscous flow inside the die and conformational recovery after leaving the die, thus causing not only the flow instabilities to occur prematurely on shear rate and delaying sharkskin on shear stress, but also an alternate "sharkskin-melt fracture" appearance after global extrusion fracture. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47713.