Fabrication and release behavior of nitrapyrin Microcapsules: Using modified melamine-formaldehyde resin as shell material

Preparation and release mechanism of nitrapyrin microcapsules. Nitrapyrin dissolved in an organic solvent forms small oil droplets under the action of the surfactant Tween80. Under certain temperature conditions, pre-polymers were formed by the reaction of melamine and formaldehyde and gradually coated the surface of the small oil droplets. As the pH gradually decreased, nitrapyrin microcapsules were formed during the curing process. SEM and TEM revealed that the nitrapyrin microcapsules had a solid spherical-shell structure with micropores on the surface, a uniform shell thickness, and good dispersion. • The nitrapyrin was encapsulated by the modified melamine formaldehyde resin. • The nitrapyrin microcapsules contained solid spherical, shell-like structures. • The nitrapyrin release conformed to a double-release kinetic model in meadow black soil. As a commonly used nitrification inhibitor, nitrapyrin can significantly improve the utilization of nitrogen in soils. However, the effectiveness of the traditional dosage form of nitrapyrin is reduced by soil adsorption. In this study, nitrapyrin was encapsulated into a melamine-formaldehyde resin microcapsule with good dispersion and release behavior using an in situ polymerization method. The nitrapyrin microcapsules were characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and particle-size analysis. The results indicated that the microcapsules had a spherical-shell structure, a uniform morphology with nanoscale micropores on the surface, and a decent nitrapyrin loading content (67.19%). Tests revealed that the release behavior of the nitrapyrin microcapsules was outstanding and conformed to the double-release kinetic model. These results of this study indicate that the nitrapyrin microcapsules can be applied as nitrification inhibitors with beneficial environmental effects and high efficacy.