In 2005, Ito [64] prepared dual coated urea granules with an inner
layer of poorly soluble isobutylidendiurea (IBDU) and the outer layer
of starch with wax powder in a high shear granulator mixer using a
simple blending technique. Through HPLC, he found that the nutrient
release rate can be modified by adjusting both the fraction of dispersed
particles and the thickness of both inner and outer coatings.With only
one coating (in the absence of an outer coating), that shell was subject
to a diffusion release mechanism. The dual layer, on the other hand,
followed a sigmoidal pattern of controlled release. The sigmoidal release
pattern, as necessitated by some applications, refers to an initial slowerrelease quantity followed by consistent increases. The proposed release
mechanism followed a dual path. First off, the core nutrient shrunk in
size after dissolution in water. Secondly, the concentration of the core
nutrient solution kept decreasing until the concentration equilibrated
within the reservoir. The release rate from a single layer preparation
had soluble particles with a faster diffusion release pattern attributed
to the formation of microchannels through which active nutrients
immediately flowed. However, the dual layer product caused a sigmoidal
release because of the hindrance offered by the outer, more impermeable
layer.
In 2005, Ito [64] prepared dual coated urea granules with an innerlayer of poorly soluble isobutylidendiurea (IBDU) and the outer layerof starch with wax powder in a high shear granulator mixer using asimple blending technique. Through HPLC, he found that the nutrientrelease rate can be modified by adjusting both the fraction of dispersedparticles and the thickness of both inner and outer coatings.With onlyone coating (in the absence of an outer coating), that shell was subjectto a diffusion release mechanism. The dual layer, on the other hand,followed a sigmoidal pattern of controlled release. The sigmoidal releasepattern, as necessitated by some applications, refers to an initial slowerrelease quantity followed by consistent increases. The proposed releasemechanism followed a dual path. First off, the core nutrient shrunk insize after dissolution in water. Secondly, the concentration of the corenutrient solution kept decreasing until the concentration equilibratedwithin the reservoir. The release rate from a single layer preparationhad soluble particles with a faster diffusion release pattern attributedto the formation of microchannels through which active nutrientsimmediately flowed. However, the dual layer product caused a sigmoidalrelease because of the hindrance offered by the outer, more impermeablelayer.
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