Effect of Coating Thickness on Release Characteristics of Controlled Release Urea Produced in Fluidized Bed Using Waterborne Starch Biopolymer as Coating Material

Loss of granular urea through leaching, ammonia volatilization and denitrification can be overcome by the application of controlled release urea. Sulfur and organic polymers have been used as controlled-release coating materials but they have limitations of high cost, process complexity and environmental issues. Waterborne starch biopolymer modified with polyvinyl alcohol is a cheap, biodegradable and environmentally friendly coating material and is used for the production of controlled release urea in a fluidized bed. The effect of coating thickness is investigated on release time and diffusion coefficient of urea release in distilled water. Release time increases with increase in coating thickness. The diffusion coefficient of nutrient release decreases with increase in coating thickness. However, coating imperfections and porous coating in some cases produced the opposite results both for release time and diffusion coefficient. It is concluded that a significant coating thickness in addition to good uniformity of thickness and film integrity can produce promising controlled release characteristics.