Effect of mixer type on exfoliation of polypropylene nanocomposites

Abstract

Polypropylene/organoclay nanocomposites have been prepared by melt blending in five different mixers: an internal mixer, two lab-scale, co-rotating vertical twinscrew mixers, a 30 mm co-rotating twin-screw extruder, and a multilayer extrusion system. The effectiveness of these mixers toward the dispersion of the clay into the polymer matrix was evaluated by TEM, X-ray diffraction, and melt rheology. Mechanical properties and coefficients of linear thermal expansion (CLTE) were also evaluated for these blends. The vertical twin-screw mixer at lower shear rate appears to provide the best mixing in terms of dispersion efficiency and modulus improvement. The combination of shear rate and residence time in the mixer is discussed in order to rationalize our results.