MODIFICATION OF THE PROPERTIES OF NATURAL RUBBER BY COPOLYMERIZATION WITH A BIOPOLYMER FOR A CONTROLLED RELEASE OF UREA FERTILIZER - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 245

Table 1. Summary of literature review concerning encapsulation of fertiliserfertilizer
by using rubber

Condition Results References

Riyajan et al. (2012) NR grafting cassava starch, latex,

urea.

Rate of urea release, CSt content in
graft copolymer.

Creaming skim natural rubber latex,
Blending with polystyrene, gamma
radiation, Sodium alginate.

Non-spherical capsules containing a
homogeneous urea dispersion.

Tangboriboonrat et al.
(1999)

Rubber matrix type, the
concentration of sodium alginate
used as the capsule coating agent,
and the initial concentration of urea.

The lowest rate of urea released from
the capsules coated urea-
unvulcanized rubber, from which the
release was prolonged for ∼ 50 days.

Tangboriboonrat and
Sirichaiwat (1996)

Helaly et al. (1993)

Styrene butadiene rubber
ammonium nitrate.

Helaly et al. (1990)

The rate of releasing fetilizers
from capsule was controlled by the
concentration of fertilizer,
temperature of the enviroment and
pH medium. The urea release form
capsule is prolonged for two
months.

Urea-rubber matrices as slow-
release fertilizers.

Hepburn et al. (1989a)

Hepburn et al.
(1989b)

Urea fertilizer by rubber. Processing
and vulcanization procedures. Hepburn et al. (1989c)

3.3. Encapsulated FertiliserFertilizer with Natural Polymer
and Synthetic Polymer

It is well known that 40-70% of the nitrogen fertilizers applied to agriculture fields are
lost so it has been suggested that slow release nitrogen fertilizers need to be developed to try
to avoid losses. Previous workers have studied the use of natural polymers e.g., cellulose
(Riyajan, 2009), starch (Riyajan, et al., 2012), and sawdust as polymer membranes for the
encapsulation of the fertilizer. A brief literature review is summarized in Table 1. Among
them, natural rubber (NR) has been widely used as a polymer membrane for controlling the
release of fertilizer because it has good water resistance.
Tangboriboonrat and co-workers produced an encapsulated urea fertilizer using the
natural rubber latex (Tangboriboonrat and Sirichaiwat, 1996) and skim natural rubber latex
(Tangboriboonrat et al., 1999) for the controlled release of urea. They studied many factors
that affected the release rate of urea such as the type of rubber matrix, the concentration of SA
used as the capsule coating agent, and the initial concentration of urea. The maximum
efficiency of the encapsulated urea in capsules was 80%. After the capsule coating was made
using unvulcanized rubber, the lowest rate of urea released from the capsules was achieved
using coated urea-unvulcanized rubber. The completion of the urea release from the capsule
was roughly 50 days. In the case of the skimmed NR latex, the creamed skimmed latex was
blended with 15-45 phr SA and then its blend was used for encapsulation of urea fertilizer.
They reported that the non-spherical capsules contained a homogeneous urea. They used
SEM to try to explain why there was a need to use a split feeding mixing technique to