Agriculture Reference
In-Depth Information
Chapter 10
M
ODIFICATION OF THE
P
ROPERTIES OF
N
ATURAL
R
UBBER BY
C
OPOLYMERIZATION
WITH
A
B
IOPOLYMER FOR
A
C
ONTROLLED
R
ELEASE OF
U
REA
F
ERTILIZER
Sa-Ad Riyajan
*
Department of Materials Science and Technology, Faculty of Science,
Prince of Songkla University, Hat Yai, Songkhala, Thailand
A
BSTRACT
One of the problems associated with the use of fertilizers in conventional agriculture
is the loss of fertilizer through volatilization and leaching by rain, which can cause
serious environmental problems away from the original site of application. Thus, one
solution to this problem would be to encapsulate fertilizers using biopolymer membranes
to control the diffusion of water and the release of the water-soluble active fertilizer. The
objective of this chapter is to develop a new product for the controlled release of a urea
fertilizer, using a modified natural rubber (NR) with another biopolymer, and to
demonstrate its performance in water and soil for an agriculture field. The approaches for
preparing the capsules and the release of the urea fertilizer from the capsule are
discussed. Factors e.g., the modification methods for NR, the NR content, the numbers of
NR layers, the ratio between the NR and biopolymer on the optimum release rate of urea
from the capsules obtained from the coating were subsequently investigated. The
properties of NR were improved by chemical modification, e.g., crosslinking, grafting
and epoxidation reactions of NR. In parallel, the NR was blended with other polymers,
e.g., poly(vinyl alcohol) (PVA), polyacryamide, starch (St) or sodium alginate (SA) and
cellulose fiber to increase its agricultural usefulness. The rate of the fertilizer release from
the capsule decreased with an increase of the NR coating layer and the NR concentration
in polymer membrane and polymer blend ratios. The rate of the swelling ratio for these
samples was responsible for the release of fertilizer from the capsule in an aqueous phase.
When the capsules were coated with modified NR latex, it was found that the release rate
of urea was significantly decreased and the duration of release was prolonged for roughly
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