Engineering Electrospun Nanostructured Coatings on Macroscopic Particles

Electrospinning is widely used in industrial applications to produce coatings with different structures and improved physicochemical properties such as mechanical strength, corrosion resistance, and permeability. Electrospinning is commonly used for coating planar surfaces as opposed to coating nonplanar surfaces, such as macroscopic spheroidal substrates, which remains challenging. Herein, we engineered electrospun coatings on macroscopic particles (i.e., urea granules, steel balls, glass beads, natural zeolite) using biocompatible polymers (i.e., biodegradable beeswax and polycaprolactone). The morphology of the coatings was tuned to afford different architectures including beads, a mixture of beads and fibers, and fibers by changing the instrument operating and solution conditions. Urea granules were chosen as a model substrate to assess the release properties and potential application of the coatings as controlled-release fertilizers. The mechanical properties, hydrophobicity, water vapor permeability, and urea release rate of the coatings were studied. Notably, compared to traditionally prepared spray coatings, the engineered electrospun coatings displayed highly uniform coating coverage to the entirety of the particle surface, a lower water vapor permeability of 0.08 × 10^-7 g m h^-1 m^-2 Pa^-1 (versus 0.13 × 10^-7 g m h^-1 m^-2 Pa^-1, corresponding to a reduction of 38%) and a prolonged release of urea from 12 to 26 days.