Efficient mixing of polymer blends of extreme viscosity ratio: Elimination of phase inversion via solid-state shear pulverization

A novel, continuous process, solid-state shear pulverization (S³P), efficiently mixes blends with different component viscosities. Melt mixing immiscible polymers or like polymers of different molecular weight often requires long processing times. With a batch, intensive melt mixer, a polyethylene (PE)/polystyrene (PS) blend with a viscosity ratio (low to high) of 0.019 required up to 35 min to undergo phase inversion. Phase inversion is associated with a morphological change in which the majority component, the high-viscosity material in these blends, transforms from the dispersed to the matrix phase, and may be quantified by a change from low to high mixing torque. In contrast, such blends subjected to short-residence-time (approx. 3 min) S³P yielded a morphology with a PS matrix and a PE dispersed phase with phase diameters ≤ 1 μm. Thus, S³P directly produces matrix and dispersed phases like those obtained after phase inversion during a melt-mixing process. This assertion is supported by the similarity in the near-plateaus in torque obtained in the melt mixer at short times with the pulverized blend and at long times with the non-pulverized blend. The utility of S³P to overcome problems associated with melt mixing like polymers of extreme viscosity ratio is also shown.