Lignin is a cheap and natural macromolecular compound that is
abundantly available as awastematerial frompulp and paper industries
[65]. Moreover, lignin is renewable, biodegradable, amorphous, and a
relatively hydrophobic bio-polymer compared to other polymers [66].
Perez [65] prepared a lignin based controlled release urea formulation
by mixing urea and lignin in a glass reactor immersed in a thermostatic
silicon oil bath. The mixture was heated and the resultant urea-lignin
matrix was cooled to give a glass like structure that was later milled in
a crusher to obtain the desired size range of controlled release particles.
This study also included urea coating with ethyl cellulose in aWurster
fluidized bed. Ethyl cellulose predominantly possesses high physical
and chemical stabilities with good film forming properties and is
relatively less toxic. A 5% ethanol solution of ethyl cellulosewas sprayed
onto a fluidized bed of urea granules at 60 °C followed by air drying in
the same chamber at 70 °C. Different runs were made to produce
different coating thicknesses for the analysis. Both the lignin based
controlled release urea particles and the ethyl cellulose coated granules
were subjected towater leaching experiments to evaluate release rates.
The patterns produced very slowreleases in the early stage followed by
a constant release leading to a period of decaying release. The coating's
thickness, as reported by many others, had an inverse effect in terms of
controlled release. The comparative study revealed that ethyl cellulose
coated granules were better than the lignin based slow release urea
formulation because of its coating uniformity which retarded water
diffusion through the coating layer.