Industrial & Engineering Chemistry Research, Vol.41, No.22, 5436-5446, 2002
Process intensification in particle technology: Intensive granulation of powders by thermomechanically induced melt fracture
Process intensification in particle technology is illustrated by a novel continuous agglomeration and microencapsulation (granulation) technique based on the thermomechanically induced melt fracture. This intensive structuring method is based on the nonisothermal flow-induced phase inversion phenomenon in which the continuous phase of the fluid (poly(ethylene glycol) melt) undergoes fractional solidification, thus essentially increasing the volume fraction of the solid phase during passage between two disks. The polymer melt containing the filler particles (calcium carbonate) is fed centrally (using an extruder) into the gap between two disks, one of which is stationary (stator) while the other rotates (rotor) at a constant angular velocity. These disks have several sets of cavities formed in such a way that the upper and lower cavities never match during rotation and that they can achieve mixing as well as pumping. The rotor and stator are kept at different temperatures so as to allow the cooling of the melt as it is displaced outward in the radial direction, thus causing solidification while undergoing deformation. As the filled polymer melt travels between the heated stator and cooler rotor cavities, locally crystallized filled polymer particles are created (nucleation) which are subsequently re-dispersed into the polymer binder as a solid dispersed phase. This causes the fluid to (crumble) fracture and form granulated particles, the size of which approaches the clearance between the disks, and the size distribution narrows as the granulated particles move outward in the radial direction. The technique produces granulated particles with a narrow size distribution in which the concentration of the filler is constant (size independent), therefore giving a product which cannot be produced by any known granulation process.