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Figure 33. Possible mechanism of the release of urea from the encapsulated urea fertiliserfertilizer with
NR-g-CPAM in a water medium.
Figure 34. Effect of vulcanizsation of NR latex on the % cumulative loss of urea fertiliserfertilizer in
from beads stirred in water medium.
3.8. Effect of Unprevulcanizsed or Prevulcanizsed NR
This part describes the effect of crosslinking the NR with sulfur to form vulcanized
rubber on the cumulative release (%) of urea from the beads compared to an unvulcanized
sample and the results are provided in Figure 34. It is obvious that there was a high rate of
urea released from the two samples within 9 h. The rate of urea released from the capsule,
coated with unvulcanized NR, was higher than those coated with unprevulcanized NR. One
explanation for these results was that the unvulcanized NR showed a special ability to wet the
urea during the production of the bead. This phenomenon resulted from a poor dispersion of
urea in the vulcanized NR matrix and hence it more easily diffused from the bead in the water
medium. These results are in agreement with a previous work (Tangboriboonrat and
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