Agriculture Reference
In-Depth Information
3.1. Method
The NR-g-St/urea mixture films were prepared by a solution-casting method. The graft
copolymer was an NR-g-St latex 25 mL (solid 5.0 g) and urea (2.0 g). The mixture was stirred
for 0.5 h at room temperature and then cast on a glass plate. In order to compare with the
natural St matrix, the St/urea film was made by the following method: the starch 5 g and 25
mL of distilled water were placed in a glass beaker and stirred mechanically for 20-30 min to
form a dispersion. The beaker was maintained in a thermostated oil bath at about 90
o
C for
20-30 min while being stirred to gelatinize the starch. Then, the urea particles were
thoroughly mixed with the gelatinized St paste with a glass rod. Finally the mixture was
poured onto a glass plate (Chen, 2008) to form the film.
3.2. Preparation of Capsules by the Precipitation Technique
The urea granules were dissolved in concentrated NR latex which were then blended with
the SA solution. Then the mixture was precipitated in a 90% aqueous solution of acetic acid
using a dropper. The capsules that formed were quickly immersed in the distilled water in
order to leach out acetic acid and then dried. The urea beads formed are shown in Figure 23
and are spherical in shape. The amount of urea released from the NR-g-St or starch matrix
were measured at 191 nm by UV-Vis spectrophotometer (UV-1601, Shimadzu). About 1 g of
capsule sample, weighed exactly, was extracted in distilled water to form a homogeneous
solution. The total urea in the solution was extracted for 72 h with distilled H
2
O and its mass
was determined spectrophotometrically. At definite intervals of time, the conical flasks were
shaken well and a 10-mL aliquots were taken for the analysis of urea using UV (Shimadzu
UV-1601) at 191 nm. The experiments were performed in triplicate in order to minimize the
error of variation. The cumulative release of urea from the capsule beads was estimated.
Figure 23. Photograph of fertiliserfertilizer beads obtained from natural rubber latex blended with the
SA solution.
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