Polymer and particle separation during extrusion

Polymer de-mixing can occur during extrusion when two components of a blend have different viscosities: the lower viscosity Component tends to migrate to the region of higher shear rate. Also, particles in a blend can preferentially partition into one blend component or can migrate in the polymer melt due to velocity profile effects. This paper shows our initial experimental assessment of the idea of attempting to exploit these phenomena to advantage in the melt sorting of plastics and the formation of novel, useful morphologies. Demixing within extruders and after passing thorough a "segregation tube attachment (L/D= 175)" at the extruder exit were examined using nylon/polyethylene blends and glass beads as particles. Microscopy utilizing staining techniques, differential scanning calorimetry and Fourier Transform Infrared spectrometry were used to determine the separations and morphologies obtained. It was found that, as expected, the higher viscosity polymer component did migrate towards the low shear rate regions. Radial bands of nylon in polyethylene were obtained. Also, glass beads could be made to partition into the nylon phase. Layered shell morpologies with maximum separations of approximately 7% in the segregation tube and 28% in the 1.5" extruder were obtained.