Release kinetic model of nitrogen released encapsulated in starch-alginate controlled released urea: Diffusion and its decay release
Siew Wei Phang, Lee Tin Sin, Soo‐Tueen Bee, Tiam‐Ting Tee
Abstract
Controlled released urea (CRU) encapsulated in starch-alginate (St-Alg) cross-linked with calcium chloride was investigated as a supplement of N-nutrient for the use in agriculture nursery. The urea concentration was determined with ultraviolet/visible light absorption spectrophotometer (UV/VIS). The urea release data was fitted and compared with 3 empirical exponential equations models to support the interpretation and comprehension of the release mechanisms. The release kinetic for St-Alg CRU beads was found to have good Ritger-Peppas model fitting at R2 value more than 0.99, which suggested that the release behaviour of urea in St-Alg matrix consists of three stages: i. an extremely low diffusion exponential (n) value, indicating an initial rapid release of urea attributed to the high surface’s porosity of St-Alg beads, that allowing an instantaneous water penetration into the matrix that dissolved and release the soluble content, which can be observed in the ; ii. a period of linear release when the solution reaches an equilibrium while the total volume of the polymer matrix remains almost constant; and iii. an extremely high n value (>0.86) indicating the rapid “decaying release” of urea caused by the decaying of the hydrophilic polymer matrix.