Performance comparison of dome and basket extrusion granulation

Abstract

A water dispersible granule (WG) formulation is a dry, solid formulation containing active ingredients intended to be diluted/dispersed in water prior to application. If the co-formulants are properly selected, WGs typically have desirable physical and chemical stability. In addition, storage and transport of dry formulations are inherently easier than liquid formulation types. WG formulations of agricultural products offer the added advantage of low dust and safer handling compared to wettable powders (WP).WG formulations can be prepared via several types of granulation processes, with paste extrusion being the most common in crop protection products. Granules created by paste extrusion generally offer improved resistance to attrition, and higher and more consistent bulk density compared to WP formulations. Rapid and complete dispersion in a variety of water conditions is a key performance parameters used to evaluate WG formulations.Among common paste extrusion methods, basket and dome extrusion are the two widely used techniques. Basket extrusion is thought to be less process sensitive. Historically, products originally designed to be dome extruded can often be basket extruded, but not vice versa. In this work, milled powder premixes of varying water solubility are paste extruded using these two technologies. The paste extrudates are dried using a lab scale vibratory fluidized bed. The products are compared based on measured performance quality criteria including dispersion, bulk density, suspensibility, wet sieve, and moisture sorption. Additionally, microscopic characterizations proved valuable in elucidating certain performance differences.