Agriculture Reference
In-Depth Information
Factors such as modification methods for NR, the absolute NR content, number of NR layers,
and the ratio between NR and the biopolymer on the release rate of urea from capsules
obtained from coating were subsequently investigated. The properties of NR were improved
by chemical modification, e.g., crosslinking, grafting and epoxidation reaction. In parallel,
NR was blended with other polymers such as PVA, St or SA, and cellulose fiber to increase
its agricultural use. There are at least two methods for the preparation of encapsulated
fertilizer, e.g., a solution-casting method and a precipitation technique. The rate of fertilizer
release from the capsule decreased with an increase of the NR coating layers and the NR
concentration in polymer membrane and polymer blend ratios. The swelling ratio for this
sample corresponded to the fertilizer release rate from the capsule in an aqueous phase. When
the capsules were coated with the modified NR latex, it was found that the release rate of the
urea was significantly decreased and the duration of release was prolonged for roughly 30 h
in an aqueous medium. In addition the urea in the swollen polymer blend with a low amount
of NR can diffuse rapidly and can be released quickly. A graft copolymer between NR and a
biopolymer for coating, the capsule matrix of the bead becomes denser resulting in a decrease
in the rate of diffusion of urea through the swollen beads due to chemical interactions
between the NR and the biopolymer through the grafting interaction. The rate of urea release
from the capsule coated with unvulcanized NR was higher than that of a coating with
unvulcanized NR due to a special ability to wet the urea during the production of the beads
and a poor dispersion of urea in the vulcanized NR matrix. Hence, urea is easily diffused from
the bead in the water medium. In addition, the modified rubber could be effectively applied
for encapsulation of the urea fertilizer. The resulting polymer membrane of the capsule was
degraded in natural soil. Two nonhomologous enzymes involved in this process and the
respective genes were recently identified in species of the genera Streptomyces and
Xanthomonas . The enzyme from the microorganisms first destroys the chemical structure of
the modified NR to produce short polymer chains. The main advantages of the value-added
NR products and a biopolymer are that they are more environmentally friendly with a low
cost.
A CKNOWLEDGMENTS
The author is grateful for the fundamental research grant from Price of Songkla
University (SCI 540032S) and The Thailand Research Fund/the Commission on Higher
Education (MRG5380190) that supported this work.
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Arenskötter, M., Bröker, D. & Steinbüchel, A. (2004). Biology of the metabolically diverse
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