Chitosan spray-dried microcapsule and microsphere as fertilizer host for swellable - controlled release materials

A fertilizer delivery system based on chitosan (Ch) or chitosan/montmorillonite clay (Ch/MMt) was developed by spray drying technique using 2-fluid (2FN) and 3-fluid (3FN) nozzles. 2FN provided solid microspheres and 3FN formed microcapsules structures. Morphology is dependent upon formulation and the type of nozzle used. As higher the number of the components (polymer, clay and sodium tripolyphosphate (TPP)) in the microparticles more collapsed and non-shaped spheres are generated. Different structures provided distinct nutrient releasing profiles. Higher swelling values (similar to 500%) and slower fertilizer releasing process (under 70% in the firsts measurements) are observed for microcapsules. This phenomenon occurs due to entrapped nutrient by an extra chitosan outer layer. The swelling-controlled release mechanism was observed for both microcapsules and microspheres instead of diffusion-controlled. Swelling characteristic was confirmed in soil medium since after water irrigation higher fertilizer releases were observed.