Formation of dispersed phase in incompatible polymer blends: Interfacial and rheological effects

TLDR

Interfacial tension between polymer phases is governed by polarity differences and can be tuned over orders of magnitude with suitable dispersants. The study examined dispersed phase formation in incompatible polymer blends during melt extrusion with a co‑rotating twin‑screw extruder, using nylon/polyester matrices and ethylene‑propylene rubber dispersed phases. A master curve relating shear rate, particle diameter, interfacial tension, and viscosity ratio was derived, showing that drop size scales with interfacial tension and the 0.84 power of the viscosity ratio, with smaller drops occurring at lower interfacial tension and viscosity ratios nearer unity.

Abstract

Abstract The formation of dispersed phase in blends of incompatible polymers during melt extrusion with a co‐rotating twin screw extruder was studied, using nylon and polyester as the matrix and ethylene‐propylene rubbers as the dispersed phase. A master curve is obtained, i.e., G η m α/γ = 4 p ±0.84 , where G is the shear rate, γ the particle diameter, η the interfacial tension, η m the matrix viscosity, η d the dispersed‐drop viscosity, and p = η d /η m . The plus (+) sign applies for p > 1, and the minus (−) sign for p < 1. Thus, the dispersed‐drop size is directly proportional to the interfacial tension and the ±0.84 power of viscosity ratio. The dispersed drops are the smaller, when the interfacial tension is the lower and the viscosity ratio is the closer to unity. The interfacial tension is largely controlled by the polarities of the two phases, and can be varied over several orders of magnitude by using appropriate dispersants.