Abstract: An apparatus for, and method of, mixing a molten composition are provided. The apparatus comprises a rotor with flow restrictors supported on its surface and supported within a bore of a casing. The mixer generates at least 100 modulating events as the molten composition flows over the flow restrictors to form a modulated composition.

Abstract: A continuous process for incorporating a thermally sensitive additive into a polymer melt of virgin polymer at a temperature at least 10° C. below a temperature at which the virgin polymer is typically processed. The virgin polymer is first processed in an apparatus which extensively shear-thins the polymer until its normally entangled molecules are substantially disentangled. This is preferably done in a TekFlow® processor. The additive is then added to the resulting modified melt which is then processed in a high-shear apparatus, e.g. a co-rotating, twin-screw extruder, but more preferably in a second TekFlow® processor. This novel process allows making concentrates having a level of additive which could not be made to date and yet have the additive substantially uniformly dispersed.