An apparatus and method for continuously reducing the viscosity of molten moldable polymeric material uses shear vibration under extensional flow to cause shear thinning and/or disentanglement. One or more station treatment cavities (3) are defined by a gap composed of two closely separated surfaces (6, 7) in relative motion with each other at given speed and/or submitted to relative oscillations, with given frequency and amplitude to produce a shear deformation on the molten material and a controlled variation of the gap dimension. The surfaces have a contour profile of ribs and/or bumps and/or grooves (5, 12) over which the molten moldable material can flow and/or can be dragged and/or is being pushed through and/or pumped through. The treatment cavities have an inlet (30) through which the molten moldable material can pass into, and an outlet (31) through which it can exit each treatment cavity. |