Compatibiliser activity and morphology stability during twin-screw extrusion and injection moulding of compatibilised blends

The influence of screw speed, agitator configuration, and compatibiliser, namely maleated polypropylene (mPP), during twin-screw extrusion upon the morphology, dispersion stability, and properties of polyamide-6/polypropylene (PA6/iPP) blends has been investigated. For mPP contents of 2.4 vol% and greater, the number average domain diameters measured in the extruded compound, Dn(ex), were found to decrease to a limiting value at the specific mechanical energy input, Se, around 0.07 kW h kg−1, when Se was controlled by the screw configuration and screw speed. For mixing energies greater than 0.07 kW h kg−1, the domain size was principally determined by the ratio of specific interfacial area, Sext, between the PA and iPP phases to the estimated volume fraction of in situ formed copolymer, φc; Sext/φc≈45 μm−1. The difference, ΔDn, between Dn(ex) and the average domain diameter measured in the cores of the samples after injection moulding, Dn(m), was calculated: ΔDn=|Dn(ext)−Dn(m)|. It was found that ΔDn∝Dn(ext); i.e. larger droplets in the extrudate underwent the greatest changes in dimension in the subsequent moulding process.