In 2012, Wang double coated urea in a pan granulator with
k-Carrageenan-sodium alginate (kC-SA) as the inner shell and a crosslinked
k-Carrageenan graft, copolymerized with polyacrylic acid and
celite (kC-g-poly AA/celite), as the outer shell [58]. Sodium alginate is
an anionic naturalmacromolecule extracted frommarine algae. Similarly,
k-Carrageenan is an anionic polysaccharide extracted from red seaweed.
The combination of both materials enhanced the mechanical
strength of the coating layers and the hydrogel's brittleness which
then eased water super-absorption. After coating, granules with a thin
layer were dried and subjected to a duplicate coating step for better
thickness. The same procedure was repeated to enclose kC-SA coated
urea granules in a superabsorbent outer coating of (kC-g-poly AA/celite)
followed by drying at 30 °C to obtain the final product. Soil incubation
experiments revealed 39%, 72%, and 94% nitrogen release on days two,
five and twenty-five, respectively. The release mechanism was the
same as depicted by the same author in previous studies [12] and [53].
The use of SPMs to produce CRCU offers a number of advantages, the
most prominent being super-absorption of water combined with the
controlled release of urea. However, the preparation steps are complex
and required raw materials are costly. The CRCU products produced
thus far offer higher costs which present a major impediment to their
commercialization. Another aspect that prevents their commercialization
is the non-biodegradability of some coatingmaterialswhich causes
a new type of soil pollution. However, this remains a relatively new
research field and scientists are addressing these issues.
In 2012, Wang double coated urea in a pan granulator withk-Carrageenan-sodium alginate (kC-SA) as the inner shell and a crosslinkedk-Carrageenan graft, copolymerized with polyacrylic acid andcelite (kC-g-poly AA/celite), as the outer shell [58]. Sodium alginate isan anionic naturalmacromolecule extracted frommarine algae. Similarly,k-Carrageenan is an anionic polysaccharide extracted from red seaweed.The combination of both materials enhanced the mechanicalstrength of the coating layers and the hydrogel's brittleness whichthen eased water super-absorption. After coating, granules with a thinlayer were dried and subjected to a duplicate coating step for betterthickness. The same procedure was repeated to enclose kC-SA coatedurea granules in a superabsorbent outer coating of (kC-g-poly AA/celite)followed by drying at 30 °C to obtain the final product. Soil incubationexperiments revealed 39%, 72%, and 94% nitrogen release on days two,five and twenty-five, respectively. The release mechanism was thesame as depicted by the same author in previous studies [12] and [53].The use of SPMs to produce CRCU offers a number of advantages, themost prominent being super-absorption of water combined with thecontrolled release of urea. However, the preparation steps are complexand required raw materials are costly. The CRCU products producedthus far offer higher costs which present a major impediment to theircommercialization. Another aspect that prevents their commercializationis the non-biodegradability of some coatingmaterialswhich causesa new type of soil pollution. However, this remains a relatively newresearch field and scientists are addressing these issues.
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