Disintegration and release kinetics of dry compacted urea composites: A formulation and process design study

Abstract

The hydrolysis of conventional urea fertilizer accounts for a 50 % loss in the field, which results in atmospheric and water stream contamination due to the volatilization of greenhouse and ozone scavenger gases, and nitrate leaching, respectively. Fertilizer granule structural design can be a potential solution to minimize the field losses. Nonetheless, quantitative analysis of urea dissolution as affected by formulation and process design remains underexplored. In this study, urea and a binder in powder form were mixed at a fixed binder-solid ratio of 5 % (w/w) and compacted at different loads using a punch-die set on a standard material testing system. The binders tested to produce the binary mixtures were hydroxypropyl methylcellulose grade E5- HPMC, high molecular weight hydroxypropyl cellulose- HPC, gluten from wheat, and a mixture of xanthan and konjac gums. The total porosity, apparent diffusion, and dynamic contact angle profiles of the compacts were measured at ambient conditions. The hydrophilicity of the formulations with gums, attributable to their lower contact angle when compared with control samples, helps explain the fast in-matrix mass transfer. Based on Weibull distribution model analysis, all the dissolution curves followed either sigmoidal or exponential shape profiles. Within the formulations evaluated in this study, the synergism between densification and higher hydration capacity of formulations with gums ensured binder mobility and gelation at the solid-liquid interface. The results indicate that gel formation reduced solvation and dissolution, resulting in a delay of nutrient release. These findings will aid in the optimization of controlled-release fertilizer formulations for field crops and help understand the effect of binder physicochemical characteristics on the microstructure of granular fertilizers.