The effect of a progressive grated extrusion mixing head on the melt blending of polymers

Blending of polymers using single screw extrusion is not generally effective using conventional, square pitch screw geometries without mixing elements. In many cases, the degree of dispersion required for a good polymer blend is difficult to achieve using a single screw.; In this study a novel mixing head was designed in an attempt to improve mixing for a series of polymer blends. The progressive grating action of the mixing head is designed to improve particle distribution and dispersion when blending a polymer matrix. During extrusion the polymer melt is forced through a primary set of grating teeth and then sequentially forced through a smaller set of teeth before being forced through the breaker plate and die. Various blending levels of polypropylene/high impact polystyrene were evaluated by producing an extruded sheet with a general purpose head, a Maddock mixing head and a progressive grating mixing head. The sheet produced by the three mixing heads was then tested and evaluated for drop dart impact and tensile properties. An incompatible blend was selected so that the effect of mixing could be more readily observed. Atomic force microscopy was also conducted on samples to investigate the morphology of the blend.; The grated mixing head did slightly improve the ductility of the sheet when compared to other types mixing heads, but a weak interphase of the polymers still existed. The atomic force microscopy results show that the grated mixing head did in fact improve the distributive and dispersive mixing quality of the melt.