THE DEVELOPMENT OF LAMINAR MORPHOLOGY DURING EXTRUSION OF POLYMER BLENDS

Studies of the microstructure and permeability of extruded ribbons of polypropylene (PP)/ethylene vinyl alcohol copolymer (EVOH) and polyeth ylene (PE)/polyamide-6 (PA-6) blends have shown that it is possible to control the flow-inducedd morphology to generate discontinuous overla pping platelets of EVOH or PA-6 dispersed phase in a PP or HDPE matrix phase. The effects of the following factors on morphology development and blend properties were considered: blending sequence, melt tempera ture, composition, compatibilizer level, die design, screw type, and c ooling conditions. The impact properties and interfacial adhesion of l aminar blends of PP and EVOH were improved without diminishing the bar rier properties. The oxygen and toluene permeability of extruded sampl es with EVOH content of 25 vol% resembled values obtained with multila yer systems. Processing conditions had a major influence on the morpho logy of blends of high density polyethylene and polyamide-6 (HDPE/PA-6 ), and, under special processing conditions, laminar morphology was ob tained in this system. The toluene permeability of extruded ribbons of HDPE/PA-6 blends was in the range obtained with multilayer systems.