A comparative experimental study of blending polyethylene and polystyrene in a modular self wiping co-rotating and intermeshing counter-rotating twin screw extruder is described with similar modular screw configurations. Comparisons are mane using different screw configurations possessing different numbers and placement of kneading disc blocks. Generally the intermeshing counter-rotating mode melts and mixes more rapidly than the co-rotating mode. The phase morphology in each machine seems to similarly from mixtures of pellets to polyethylene lamellae surrounding polystyrene pellets to a co-continuous morphology. Kneading disc blocks greatly enhance the rate of melting and mixing and are most effective when placed near the feed port rather than near the die. At 160 degrees C, where the polystyrene has a much higher viscosity a co-continuous morphology develops. At 260 degrees C where the polystyrene has a lower viscosity first a co-continuous and then a disperse phase morphology evolves.