International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 06
77
Producing Slow Release Urea by Coating with
Starch/Acrylic Acid in Fluid Bed Spraying
Suherman and Didi Dwi Anggoro
Abstract—The controlled release technology by coating for
increasing the efficiency of fertilizer can reduce fertilizer’s losses
and minimize environmental pollution. Starch mixed with acrylic
acid, PEG and water were used as coating solution. The coating
process of granular urea was conducted in fluid bed spray coater.
The influence of bed temperature, and concentration of starch on
properties of coated urea product was investigated. Microscopic
analysis by SEM shows the formation of a thin layer on the
surface of coated urea product that has a different morphology,
more compact, and any irregularities of the crystal. The
dissolution rate of the product decraesed with increasing
concentration of starch and decreasing bed temperature. The
percent coating of the product increased with increasing
concentration of starch and decreasing bed temperature. The
dustiness of the product increased with increasing starch
concentration and bed temperature.
Index Terms— coating, controlled release, fluid bed, spraying,
starch, urea
I. INTRODUCTION
U
rea is as nitrogenous fertilizer, widely used in agriculture
because of its high nitrogen content (45%). However,
about 20–70% of the applied urea fertilizer is lost to the
environment, causing serious pollution and increasing costs.
The losses are due to leaching, decomposition and ammonium
volatilization in soil, handling and storage [1]. The controlledrelease technology, by coating, can be utilized to increase the
efficiency of urea fertilizer. The coating of urea has been
studied by many investigators, with different techniques
(rotating drum, fluidized bed, spouted bed) and various
materials (sulfur, resin, polymers). The Tennessee Valley
Authority (TVA) first developed the continuous coating
process of urea with sulfur in rotating drums [2]. Salman [3-4]
performed the coating of urea with polyethylene. Posey and
Hester [5] developed a low-density polyethylene film for
controlled release urea. Tangboriboorant et al. [6] prepared
encapsulated urea fertilizer using rubber latex. Garcı´a et al.
[7] used pine tree Kraft lignin in formulations for coating of
urea. Abraham and Pillai [8] obtained controlled release urea
Department of Chemical Engineering, Faculty of Engineering, University
of Diponegoro, Address: Jl. Prof. Soedharto, SH., Tembalang, Semarang,
Indonesia 50239, Tel. +62 24 7460058; Fax. +62 24 76480675; email:
hermancrb@yahoo.com
This project is financially supported by Faculty of Engineering, University
of Diponegoro, Indonesia (Project No: 3203/UN7.3.3/PG/2011).
fertilizer with acrylamide copolymers. Many works have
reported the improvement of the coating quality by using
sulfur as coating agent [9-11]. Other coating agent has used
such as modified sulfur with with dicyclopentadiene (DCPD)
[12], Neem [13] and Phosphogypsum [14].
Furthermore, over the last years, there has been an
increasing interest in the use of polymers combining with
starch as coating material. Starch is one of the most abundant
polysaccharides polymer, which blended with the synthetic
polymer polyvinyl alcohol (PVA) has been studied as a
potential biodegradable polymer [15-18]. Starch is the
cheapest biopolymer and is fully biodegradable. Therefore,
this research is to study in depth the effect of the process
changes on particle formation and formulation of coating urea
by using starch. This process carried out by fluidized bed
spray coating (FBSC).
II. EXPERIMENTALS
A. Materials
The granular Urea (PT Petrokimia Gresik, Indonesia) was
sieved in sieve tray 2 mm of diameter. Starch, Acrylic Acid,
and Polyethylene Glycol (PEG)were of analytical purity.
B. Preparation of coating solution
Coating solution were produced as follow. The calculated
amounts of starch, acrylic acid, and 1 gram PEG were mixed at
various ratios (starch content is from 0 – 2 wt%) and mixture
was slowly added water of 30 mL at room temperature under
continuous stirring until homogenous. Then, thus coating
solution is ready for use.
C. Apparatus
The fluidized bed was made from a flexi glass. A spraying
nozzle of an air-atomized nozzle was centrally set above the
fluidized bed. Urea particles of 100 g in weight were put in the
fluidized bed, and the bed was fluidized at higher than their
minimum fluidization. The coating solution of 30 mL, at room
temperature and flowrate of 0.5 mL/min, under a pressure was
atomized with compressed air, and sprayed onto the urea
particles in the fluidized bed for coating. After spraying a set
quantity of coating material, the particles were taken out for
analysis.
D. Microscopic structure
Scanning Electron Microscopy (SEM) was be used to study
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International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 06
the morphology of the particles. The observed under SEM at
magnifications of 50X and 500X.
E. Dissolution rate
5 g of urea particles in a beaker containing 50 ml of double
distilled water maintained at room temperature. Magnetic
stirrer was used at constant speed. The time required for
complete dissolution of urea was noted down [14].
F. Percent coating
10 g urea granules were immersed in 100 ml water. After
vigorously shaking, the coating was liberated from the urea.
Sub-sequently, the coating was obtained after filtration and
evaporation of the water [3].
η=
Mi − Mo
x100%
M
78
Images were taken at these magnifications and analysis of
these images for changes in surface properties was done.
Several sample images was shown below for coated and
uncoated urea with different surface.
Fig. 2 shows the surface of the slices of coated urea in
magnifications 50X. These figure indicates that there are two
morphological forms, namely the existence of an outer layer
and the particles of urea itself. This difference is more clearly
visible when carried by 500X magnification (Fig. 3). The
surface of the outer layer is more soft and dense when
compared with urea. This has led to the declining value of
dissolution rate than the coated urea.
(1)
Mi = weight of filter paper and sample (gram); Mo = weight
of filter paper (gram); M = weight of sample (5 gram)
G. Dustiness
10 grams of coated urea in a bunker funnel compressed air
is passed from the bottom of the funnel with 10 Psi of
pressure. After 5 min sample is removed from the bunker
funnel and then weighed. The weight loss was calculated. The
amount of weight loss was called dust [14].
Fig. 2. Cross-sectional slices of Coated Urea in magnifications of 50X.
III. RESULTS AND DISCUSSION
A. Photos of Coated Urea Product
Fig. 1 show urea that has been coated with a starch and
acrylic acid which green color. The purpose of use color, is to
distinguish between the uncoated urea with coated urea.
Furthermore, this product was tested by microscopy analysis,
dissolution rate, dustiness, and coating efficiency.
Fig. 3. Cross-sectional slices of Coated Urea in magnifications of 500X
Fig. 1. Product urea coated with Acrylic Acid/Amylum with adding green
colour.
B. Microscopic Analysis
The aim of surface analysis of urea particle by SEM is to get
a microscopic picture of the particle surface. The existence of
the layers is expected in the coating process. Irregulaties
surfaces and shape of particles before and after coating were
observed. Several particles were selected randomly and
observed under SEM at magnifications of 50X and 500X.
C. Dissolution Rate
Fig. 4 describes the influence of polymer concentration
(starch) to the dissolution rate. The dissolution rate decreases
when the concentration of starch increases. This is illustrated
by the decrease in dissolution rate occurred from 0.00189 g /
min at no starch in coating solution, to be 0.00124 g / min at 2
% weight of starch in coating solution. Polymer serves as a
physical barrier urea release into the environment. So the more
starch the more physical barrier on the surface of the urea
which resulted in the release of the longer time and dissolution
rate (release rate) is getting smaller. The results are consistent
with Vashishtha, et al [14] i.e. the greater the concentration of
coating the dissolution rate decreases. The same phenomenon
is also found in studies conducted Choi and Meisen [19]
regarding the use of sulfur coating urea, and Ozturk [20] on
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International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 06
the coating of urea using Ethylcellulose.
79
coating solution, the greater the percent of coating. Solution
concentration is a parameter which has affect to the duration of
the operation and growth mechanisms. When the operation
takes place at high concentrations, the degree of saturation
during drying can reach a maximum. This leads to an increase
in the rate of crystallization on the surface of the particles. The
greater concentration reflect that the content of starch in
solution more and more, so the possibility of attachment of
starch on the surface of the particle the greater urea [21].
Fig. 4. The influence of weight of starch in coating solution on dissolution
rate
Fig. 5 shows that the higher the bed temperature causes the
greater the dissolution rate. This is because the larger the bed
temperature, the faster drying rate. The quickly drying will
reduce the formation of liquid bridges between particles [21].
Thus, the polymer layer formed on the surface of the particles
of urea will be less. This has resulted in declining dissolution
rate. In addition, at high bed temperatures produce many
agglomerates (clods).
Dissolution Rate (gr/min)
0,0035
0,0030
0,0025
0,0020
0,0015
0,0010
30
35
40
45
50
Bed Temperature
55
60
(oC)
Fig. 5. The influence of bed temperature on dissolution rate
Percent of Coating (%)
16
14
12
10
8
6
30
35
40
45
50
55
60
Bed Temperature (°C)
Fig. 7. The influence of weight of starch in coating solution on dissolution
rate
Fig. 7 shows that the percent of coating decreases with
increasing bed temperature. It is indicated by the percentage
decrease in the efficiency of the coating formed from 12.8% at
40 °C to 8.2% at a temperature 55 °C. Analytical studies
related to the influence of temperature on the growth
mechanism of generating two types of change in size
according to the temperature range used. For temperatures
lower than 100 °C, the particle size decreases with decreasing
temperature [21]. The decrease is due to faster drying which
will reduce the formation of liquid bridges between particles
[21]. In addition, the increase in bed temperature has a
negative effect on the efficiency of coating due to the loss of
solute due to the increase of drying [21].
E. Dustiness
D. Percent of Coating
Fig. 8. The influence of weight of starch in coating solution on dustiness
Fig. 6. The influence of weight of starch on percent of coating
Fig. 6 shows that the higher the concentration of starch in
Fig. 8 shows that the greater the concentration of starch, the
greater the resulting dustiness. This is because the greater the
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International Journal of Engineering & Technology IJET-IJENS Vol: 11 No: 06
concentration means that more particles coating. Therefore
generation dust will be more due to layers are bonded at the
surface of the urea is less strong. As with the results of
research Vashishtha [14] which displays that the dust that
coated urea coating with 5% concentration solution fewer than
in the dust at 15%.
Fig. 9 shows that the higher the bed temperature, the more
dustiness. This is because, with the higher temperature of the
drying, the dry layer formed. These results are consistent with
research Vashishtha [14]. At a temperature of 35 °C only 0.03
grams of dust generated, whereas at 55 °C produced 0.07
grams of dust.
0,8
[5]
[6]
[7]
[8]
[9]
[10]
0,7
[11]
Dustiness (%)
0,6
0,5
[12]
0,4
0,3
[13]
0,2
0,1
0
30
35
40
45
50
55
60
[14]
Bed Temperature (oC)
[15]
Fig. 9. The influence of bed temperature on dustiness
IV. CONCLUSION
[16]
Controlled Release Urea has been successfully produced by
coating urea with starch using a fluid bed spray coater. Anaysis
spectroscopy using the SEM showed the formation of a thin
layer on the surface of coated urea product that has a different
morphology, more compact, and any irregularities of the
crystal. Dissolution rate of coated urea products will lower
with lower of bed temperature FBSC, and vice versa
dissolution rate of coated urea products will be lower with the
higher concentration of starch. Percent coating of coated urea
products will lower with the higher the bed temperature FBSC,
and vice versa percent coating coated urea will be higher with
the higher concentration of starch. Dustiness of coated urea
products will be higher with the higher temperature FBSC bed,
and or the concentration of starch.
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112506-7474 IJET-IJENS @ December 2011 IJENS
Dr.-Ing. Suherman. Born in Cirebon, Indonesia, August
4, 1976. He graduated Dr.-Ing. in the field drying of
polymer from Otto-von-Guericke University, Magdeburg,
Germany on 2007. His research interest in drying area.
Now, he is a lecturer in Department of Chemical
Engineering, University of Diponegoro, Semarang. Email:
hermancrb@yahoo.com.
Didi Dwi Anggoro, PhD. Born in Jakarta, Indonesia,
November 14, 1967. He graduated PhD. from University
Technology of Malaysia on 2003. His research interest
in chemical process. Now, he is a lecturer in Department
of Chemical Engineering, University of Diponegoro,
Semarang. Email: anggoro_phd@yahoo.com.
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