Wet granulation: Effect of surface tension, polymer concentration and particle morphology on particle agglomeration and granule strength

The main goal of this research was to determine the effect of binder characteristics (surface tension and polymer concentration), initial particle morphology (size, surface roughness and shape), and operating conditions (binder addition rate) on particle agglomeration and granule strength following the wet granulation process. The amperage curve was used to determine the parameters of particle agglomeration (phase time, phase volume and phase adhesion) and the mechanism of particle agglomeration through an indirect measurement of the adhesion force which develops during the wet agglomeration process. The granule strength was determined by a confined compression test, and the granule strength curve was used to analyze the particle agglomeration in conjunction with the amperage curve. Both the amperage curve and granule strength analysis indicated the involvement of capillary phenomena in particle agglomeration throughout the wet massing process. Surface tension was found to affect particle agglomeration and granule strength by affecting both the liquid requirement and the particle distance of the agglomerates. Different degrees of polymer concentration were all found to produce similar particle agglomeration in the wet massing stage, but had a significant effect on granule strength in the dried stage. Particle size showed a significant effect on particle agglomeration in the wetting and bridge formation stage and also on granule strength in dried stage. The increase of granule strength depends on particle size. Particle surface roughness showed a significant effect on particle agglomeration and granule strength and dominated the differences in the chemical nature, particle size and shape of the powders. Surface roughness needed to be smoothed out to increase the available particle-particle contact area before particle-liquid-particle interactions. Granule strength varied inversely with particle surface roughness. Particle shape showed different particle-particle interactions induced by capillary phenomena depending on the particle's geometric parameters. An asymmetrically-shaped particle with a smooth surface starts orderly packing earlier than an asymmetrically-shaped powder with a rough surface.