Considering the swellability and biodegradability of konjac flour,
Yong [40] prepared a controlled release urea fertilizer and studied its
effect on various process parameters. A pallet of urea was initially heat
molded to cake and then soaked in coating material. The coating
consisted of compound polyether added to water, silicon oil and a
catalyst that was fluffed uniformly under heat for 10 min. Heating and
whisking continued with a further addition of toluene diisocyanate
and konjac flour until the solution turned white. This was then spread
on the caked urea. The coated urea was oven dried at 60–80 °C, the
setting temperature of the coating material. To study controlled release
behavior, sodium hyposulfite titration experiments were used. Coated
samples were buried in soil in beakers at constant temperature with
an additional 500 ml of water. During the first 8 weeks, only a 20%
release was observed which then rose to 70–80%. This is because the
konjac flour initially absorbed water and swelled, which, in turn,
inhibited urea release by narrowing exhaust channels. Later, the
gelation of konjac flour occurred followed by microbial attack which
disintegrated the material and assured rapid urea release. Soil burial
tests at 70–90 °C proved that the coating material was biodegradable.
In another study, 5% acetone solution of ethyl cellulose and cellulose
acetate phthalate at 30 °C were used to coat urea beads in a Wurster
fluidized bed unit at temperatures ranging from 32 to 51 °C [67]. Soil
incubation tests were done in a soil filled flask mounted on an orbital
shaker kept rotating at 120 rpm. Released ureawas analyzed by conductivity
which indicated the release rate for coating with ethyl cellulose
was higher than that of cellulose acetate phthalate. However, both
coating materials were analogous in terms of the release mechanism.
The three stage release rate was initially high, followed by a fairly
constant release preceding a prolonged decline.
Considering the swellability and biodegradability of konjac flour,Yong [40] prepared a controlled release urea fertilizer and studied itseffect on various process parameters. A pallet of urea was initially heatmolded to cake and then soaked in coating material. The coatingconsisted of compound polyether added to water, silicon oil and acatalyst that was fluffed uniformly under heat for 10 min. Heating andwhisking continued with a further addition of toluene diisocyanateand konjac flour until the solution turned white. This was then spreadon the caked urea. The coated urea was oven dried at 60–80 °C, thesetting temperature of the coating material. To study controlled releasebehavior, sodium hyposulfite titration experiments were used. Coatedsamples were buried in soil in beakers at constant temperature withan additional 500 ml of water. During the first 8 weeks, only a 20%release was observed which then rose to 70–80%. This is because thekonjac flour initially absorbed water and swelled, which, in turn,inhibited urea release by narrowing exhaust channels. Later, thegelation of konjac flour occurred followed by microbial attack whichdisintegrated the material and assured rapid urea release. Soil burialtests at 70–90 °C proved that the coating material was biodegradable.In another study, 5% acetone solution of ethyl cellulose and celluloseacetate phthalate at 30 °C were used to coat urea beads in a Wursterfluidized bed unit at temperatures ranging from 32 to 51 °C [67]. Soilincubation tests were done in a soil filled flask mounted on an orbitalshaker kept rotating at 120 rpm. Released ureawas analyzed by conductivitywhich indicated the release rate for coating with ethyl cellulosewas higher than that of cellulose acetate phthalate. However, bothcoating materials were analogous in terms of the release mechanism.The three stage release rate was initially high, followed by a fairlyconstant release preceding a prolonged decline.
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