Viscosity decrease by interfacial slippage between immiscible polymers

Abstract

The rheological behavior under pressure‐driven shear flow was studied using binary blends with a sea‐island structure. The addition of a low‐viscosity dispersion having a high interfacial tension with the continuous phase greatly reduces the shear viscosity, for example, the addition of atactic polystyrene (PS) with a low viscosity to isotactic polypropylene (PP) and the addition of PP with a low viscosity to PS. The interfacial slippage occurs because of the poor adhesive strength with the enlarged interfacial area and is responsible for the viscosity decrease. When the dispersion has a similar viscosity to the continuous phase, the viscosity decrease is barely detected. This is because the deformation of dispersed droplets is restricted, which creates a small interfacial area. The interfacial tension between the continuous and dispersed phases plays a crucial role on the shear viscosity. In the case of PP, the addition of linear low‐density polyethylene with a relatively low interfacial tension to PP has almost no impact on the shear viscosity. This is despite the polyethylene having a low viscosity.

Improvement in Processability for Injection Molding of Bisphenol-A Polycarbonate by Addition of Low-Density Polyethylene

“…In the skin region, i.e., high shear rate region, LDPE droplets were deformed greatly to the flow direction. As a result, a large interfacial area was provided, which pronounced the interfacial slippage between PC and LDPE, as revealed in previous studies [ 8 , 9 , 16 ]. In contrast, spherical LDPE droplets were observed in the core.…”

“…When the interfacial tension is not so high, this leads to a thick interfacial thickness, and shear viscosity of the blend does not decrease greatly. Such a phenomenon was confirmed for the blends of polypropylene (PP) as a continuous phase and ethylene-α-olefin copolymer as dispersion [ 16 ].…”

“…Due to the high interfacial tension between the PC and PS [ 10 ], the interfacial thickness decreases, and interfacial slippage takes place during flow [ 11 , 12 , 13 , 14 , 15 ]. This is the origin of viscosity drop [ 9 , 16 ]. When the interfacial tension is not so high, this leads to a thick interfacial thickness, and shear viscosity of the blend does not decrease greatly.…”

Anomalous Postprocessing Dimensional Change of Injection-Molded Products Composed of Poly(lactic acid) and Poly(vinyl alcohol)

“…It was found that the addition of PVAL decreased the shear viscosity greatly. When an immiscible polymer having low viscosity is dispersed, the apparent shear viscosity decreased greatly due to the slippage at the enlarged interfacial area. − Interfacial slippage occurs for most immiscible polymer pairs because the interfacial thickness is not thick enough to have good adhesion in general. − Considering the interfacial tension between PLA and PVAL (1.64 mN/m), the viscosity decrease at the present system was also attributed to the interfacial slippage.…”

Non-Stick Length of Polymer–Polymer Interfaces under Small-Amplitude Oscillatory Shear Measurement

“…Issues of interest regarding the interface rheology of polymeric flows include the drag friction of a droplet [ 1 , 2 ], the coalescence kinetics of droplets in immiscible blends and emulsions [ 3 ], the viscosity reduction in polymer blends [ 4 , 5 ] and emulsions [ 6 ] by interfacial slip, multilayer melt flow in coextrusion processing [ 7 ], adhesion properties in relation to the effect of melt rheological processing [ 8 ], and the interface formation in multi-material 3D printing [ 9 ]. Understanding these phenomena requires the characterization of not only the bulk rheology of the components but also of the interface rheology.…”