A tunable controlled-release urea fertilizer coated with a biodegradable polyurethane-nanoclay composite layer
AbstractTo minimize a loss of urea to the environment and also control a release activity, a tunable and controlled-release urea fertilizer (TCRF) was created. Composite coating layers of the TCRF were synthesized using a composite of nanoclay (B27), and a linseed oil-modified polyurethane resin (BURNOCK® UL65). The concentration of B27 nanoclay was varied from 0, 3, 5 and 10 wt% and called TCRF, TCRF-3, TCRF-5 and TCRF-10, respectively. Firstly, nanocomposite free-standing films (NFs) with 0, 0.5, 1, 3, 5 and 10 wt% of B27 were synthesized and tested to demonstrate the mechanical properties of the coating layer. When the B27 clay content increased, the Young’s modulus and yield strength were increased. On the other hand, the elongation at break was decreased. NFs were also characterized by XRD and TEM, which showed a partial exfoliated nanocomposite character. The water contact angle measurement showed that all NFs had hydrophobicity properties (87°–90° contact angle). Moreover, the microorganism degradability test showed that the NFs degraded at 37?±?2°C and 58?±?2°C in manure, a common agriculture media. The study on coated urea fertilizers found that the thickness of all TCRFs layers is around 52–54 ?m. The nitrogen release profiles of the TCRF at 60°C in water as a predictive analytic model were investigated using an elemental analyzer that is a pathway analysis method to understand the release profiles of the TCRFs. All release profiles fitted well with the sigmoidal model, which was suitable for a common plant growth. The profiles gave diffusion coefficients (D) in the range of 49–69 ?m2 h?1 and presented an inverse trend to the yield strength of the NFs. The investigation demonstrated that B27 played an important role in tuning the strength of the coating layers that affected the urea release to the plants and the environment.