Improved viscoelastic, thermal, and mechanical properties of in situ microfibrillar polypropylene/polyamide 6,6 composites via direct extrusion using a triple-screw extruder

Abstract

In this work, a triangle arrayed triple-screw extruder (TTSE) was used to prepare in situ polypropylene/polyamide 6,6 (PP/PA66) microfibrillar composites (MFCs) by direct extrusion at a processing temperature between the melting points of the two phases. The dispersed phase, PA66 particles, deformed, merged and was stretched into fibrils under the alternating shearing and extensional flow field in the TTSE. The fibrillar morphology was controlled through adjusting the PA66 content and processing parameters (temperature and screw speed). Dynamic oscillatory shear rheological properties and extensional viscosity of PP/PA66 microfibrils with different aspect ratio were studied. The obtained results showed that the storage modulus and complex viscosity of PP/PA66 MFCs were improved with increasing fibrillar aspect ratio. Meanwhile, the loss tangent tan δ value decreased and the radius of the Cole–Cole plot circle increased with an increase in fibrillar aspect ratio. The PP/PA66 MFCs exhibited a pseudo-solid or gel-like behavior. The gel point concentration, which was determined by the Winter–Chambon criterion, decreased with the increasing fibrillar aspect ratio due to the increased interfacial area and enhanced entangled network structure. Additionally, high-aspect-ratio PA66 fibrils have dramatically improved PP's melting temperature, crystallization kinetics, and mechanical properties.