(553f) Product Design Methodology to Overcome Segregation

Segregation is a mechanistic driven phenomenon.  Materials may segregate during processing and handling as fine particle sift through the matrix of coarse particles.  Air currents can carry finer particles to different parts of the process equipment.  Differences in particle scale friction can cause a range of velocities as material slides down a pile.  Each of these mechanisms provides a means of separating particles of different size, shape, and surface characteristics.  Ideally the segregation problem solution is to design a material insensitive to segregation effects.  However, a bulk solid mixture is always a discreet system where particle scale properties control the ability of this mixture to remain well blended.    Each mechanism reveals a distinct segregation pattern.  If one can understand all the separation tendencies that occur with a particular mixture based on particle scale properties, then one can modify those properties to minimize the separation tendency.  This paper presents a methodology of relating the segregation intensity of a multi-component mixture to particle scale properties such as particle size distribution, particle surface friction, and particle density.  The sample material studied is a typical drug mixture containing five key components.  The repose angle, particle scale friction, particle size, and particle density were measured for the key components in the mixture.  The segregation profiles and intensities were also measured using a spectral technique.  Models were developed to describe sifting segregation, angle of repose segregation, and air entrainment segregation.  These models were used with the segregation measurements and particle scale measurements to predict the expected segregation profile of all key components.   Finally, a methodology was implemented to minimize segregation of the mixture by modifying key particle scale properties to change the type and magnitude of segregation.  The model was used to guide the product design process.  In some instances the methodology provided a means of eliminating segregation due to a particular mechanism.  In some instances the methodology was used to optimize counteracting segregation mechanisms to create an overall segregation pattern that is more mixed.