Blending of immiscible polymers in a mixing zone of a twin screw extruder - Effects of compatibilization

The dependence of the morphology development of physical as well as of reac tive compatibilized polypropylene/polyamide 6 (PP/PA6) blends in a mixing z one of a co-rotating twin screw extruder on blend composition and screw rot ational speed was investigated. A special process analytical set-up based o n a co-rotating twin screw extruder was used, which allowed melt sampling f rom different positions along the operating extruder in time periods less t han 10 seconds. It has been shown that the disperse particle sizes in physi cal blends depend crucially on the blend composition because of the increas ing influence of coalescence with an increasing concentration of the disper se phase. Furthermore, the morphology of physical PP/PAG blends depends str ongly on their rheological properties. In contrast, the influence of the sc rew rotational speed on the morphology is minor. The resulting particle siz e in a mixing zone is achieved already after a short screw length. The part icle size of compatibilized blends is significantly smaller than in physica l blends because of the better conditions for drop break-up and the suppres sion of coalescence effects. Due to this, compatibilization has a stronger influence on the blend morphology than a variation of process or rheologica l conditions with physical blends. Furthermore, the compatibilization leads to a concurrent crystallization of the PA6 phase with the PP phase.