Pan-milling mixing - a novel approach to forming polymer blends and controlling their morphology

A novel technique (pan-milling mixing) was developed to control the morphology and thus enhance the mechanical properties of polypropylenelpolyamide 6 (PP/PA6) systems. Through pan-milling at ambient temperature, PP/PA6 pellets of particle size 2-4mm can be effectively pulverized to well-mixed micrometre fine powders in the solid state. During pan-milling of mixtures of PP and PA6, the polymer molecules undergo chain scission and form copolymers that compatibilize the two polymers in situ. By press moulding the finely mixed PP/PA6 powder obtained at a temperature between the melting points of PA6 and PP (for example 200 degreesC), a blend can be obtained in which the PA6 powder, retained throughout the process in the solid state, is well dispersed in the PP matrix. The mechanical properties of the system are much better than that of PP/PA6 blends prepared by common twin screw extrusion mixing and injection moulding. Tensile strengths of the fine PA6 particle filled PP/PA6 (70/30) blend is 29.3 MPa, which is 6.1 MPa higher than that of a conventionally prepared PP/PA6 blend. The Izod notched impact strength of a fine PA6 particle-filled PP/PA6 (70/30) blend is 6.34kJ m(-2), which is 1.72 kJ m(-2) higher than that of a conventionally prepared PP/PA6 blend. Morphological analysis shows that the domain size of PA6 in the system is much smaller than that of the PP/PA6 blend, and can be controlled by the processing conditions such as temperature. (C) 2001 Society of Chemical Industry.