Growth mechanisms in melt agglomeration in high shear mixers

This paper presents a review of factors affecting the agglomerate formation and growth mechanisms in melt agglomeration in high shear mixers. The aggl omerate formation occurs either by distribution or immersion or by a combin ation of both mechanisms. Distribution is promoted by a low binder viscosit y, by a high impeller speed, and by a small binder particle size. Effects o f the liquid saturation of the agglomerates, impeller speed, particle prope rties, binder viscosity, and electrostatic charging on the subsequent agglo merate growth are discussed, and experimental results are presented. The ag glomerate growth becomes controlled by the balance between the agglomerate strength and the shearing forces. If the agglomerate strength is sufficient ly high to resist the shearing forces of the rotating impeller, the dominan t agglomerate growth mechanism will be coalescence. The shearing forces wil l give rise to breakage if the agglomerate strength is too low, and then ag glomerate growth will occur by a simultaneous buildup and breakdown of aggl omerates, possibly combined with growth by layering of fragments upon large r agglomerates. Provided that the liquid saturation is sufficiently high, a higher agglomerate strength is primarily caused by a higher binder viscosi ty, a smaller particle size, an irregular particle shape, and by densificat ion of the agglomerates. (C) 2001 Elsevier Science B.V. All rights reserved .