We prepared polypropylene/organoclay nanocomposites by melt blending in a twin-screw extruder, exploring the domain of high screw speeds (up to 1 100 min(-1)). The samples were characterized at both microscale (size of agglomerates) and nanoscale (level of exfoliation). We show that, despite a satisfactory exfoliation, the polymer matrix suffered important thermomechanical degradation by chain scission. We propose a way to correct this degradation on the viscosity curves and we confirm that high screw speeds are not necessarily favorable to clay exfoliation, essentially because of the too high melt temperatures encountered during the process.