Process Intensification in Particle Technology: Intensive Agglomeration and Micro-encapsulation of Powders by Non-Isothermal Flow Induced Phase Inversion Process
G. Akay and L. Tong
This paper deals with the dynamics of an intensified granulation process for the agglomeration or micro-encapsulation of fine particles. The process is based on non-isothermal flow induced phase inversion phenomenon which is encountered in multi-phase systems. Poly(ethylene) glycol is used as a binder and calcium carbonate particles are used as the active material (filler) to obtain multi-nucleus type of micro-capsules. The binder and filler are melt mixed in an extruder and fed into a novel granulator. The granulator consists of a rotor block sandwiched between two stators in the form of circular disks. The stators and rotor block with upper and lower rotor surface have cavities which are used to pump and mix the melt and convey the granules once they are formed. There is a temperature gradient applied between the upper stator and upper rotor which allows the solidification of the binder while it is mixed and conveyed radially outwards. During this process, granule nuclei are formed which eventually leads to thermo-mechanically induced melt fracture and the formation of granules. The granule size distribution as a function of position indicates that small particles tend to have longer residence time and hence it appears that the granule particle size increases and the particle size distribution narrows as the granules are transported radially outwards. This particle segregation was investigated by using granules with a bimodal size distribution. The granulator yields a very narrow size distribution in which the filler concentration is independent of granule size range. Granule mean size is dictated by the clearance of the gap between the rotor and stator.