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Thermal and Fire Retardant Behaviour of Polyurea
Arunkumar.T*
Research Scholar, Department of Mechanical Engineering
Sathyabama University,
Chennai, India
arunmailinbox@gmail.com
S.Ramachandran, Sebastian P.J, C Vipin Raj
Department of Mechanical Engineering
Sathyabama University
Chennai, India
Abstract— Thermal stability and flammability are one of the
most important properties which determine the resistance of
coating towards fire. This paper deals with the Thermal analysis
of Polyurea coating for various applications such as hydraulic
tank coating, pipelines etc. Our experimental work involves
coating polyurea on mild steel by using mechanical purge spray
gun at high pressure. It is then peeled off to get polyurea layer
which is tested for determining the fire resistance, thermal
stability, Coefficient of Linear Thermal Expansion.
Keywords— Thermal Stability, Flammability, Polyurea, Coefficient
of Linear Expansion.
I. INTRODUCTION
In every industrial or commercial application polyurea are
being used widely [1]. Polyurea contains aromatic structures
melt near their decomposition temperatures and are soluble in
some organic solvents which is used for the preparation of
varnishes and coatings[2].Polyurea were initially prepared
commercial and is used in many practical applications of
fibers, adhesives and foams[3-4]. A Polyurea coating is
formed by the reaction between an isocyanate component and
an amine-terminated resin. The isocyanate components can be
of monomer, a polymer or a blend [5]. The mechanism of fire
retardance depends on the types of additives that are physically
or chemically incorporated into the resin system [6]. It has very
high-strength and low weight characteristics. Polyurea has
relatively high flammability compared to other coatings which
can be used in the application of Military field where there can
be a situation of sudden explosions [7-10]. Here, Polyurea is
coated on mild steel base using a mechanical spray gun. The
spray gun implements impingement-mixing technology to
combine the chemicals inside the gun. If the reacted materials
are not delivered from the gun right after the trigger is released,
the material will get solidified inside the gun making the
chemicals non-usable. In order to prevent the problem of
hardening, Mechanical purge spray gun is used. A valve rod is
kept inside the mixing container of the gun. When the gun is
triggered, the valve rod opens up the two chemical ports to mix
and spray. Once the two materials combine together inside the
gun to mix, they will react at the same time and comes out of
the spray gun. The flammability behavior of polymers is based
on several factors such as burning rates, ignition
characteristics, product distribution [11] . In this study various
Parameters like fire resistance, thermal stability, Coefficient of
Linear Thermal Expansion are taken into consideration for
analysing the thermal behavior of Polyurea towards fire.
II. EXPERIMENTAL METHODOLOGY
The polyurea specimens were prepared from polyurea sheets.
The polyurea sheets were prepared by spraying polyurea over a
mild steel plate using a mechanical purge spray gun at 2500 psi
and the cast sheets were allowed to cure at room temperature,
the test specimens were die-cut from the cast sheets to the
required dimensions.
The thermal expansion experiment was done to study the
coefficient of linear thermal expansion of polyurea on a glass
substrate to find its increase in length on a work piece due to
temperature change as per the ASTM D696. The equipment to
measure the CLTE is Fused –Quartz-Tube Dilatometer shown
in Fig 1. The weight of the inner silica tube plus the measuring
device reaction shall not exert a stress of more than 70 KPa on
the specimen so that the specimen is not distorted. The inner
and outer tube is having a clearance of 1mm. The temperature
range is between 30°C and 90°C. The sample preparation for
CLTE was done by moulding or casting operation or
machining under minimum strain. The cross section of the test
specimen is in rectangular and fits easily into the measurement
system of the dilatometer without excessive play on the one
hand or friction on the other.
The length can be measured with the scale or calliper of the
conditioned specimen at room temperature to the nearest 25
µm. The new length of the specimen can be measured by
mounting the specimen in a dilatometer. The dilatometer is
installed at +30°C controlled environment. The temperature of
the bath should be maintained in the range from +30°C to
+32°C until the temperature of the specimen along the length is
constant by no further movement indicated by over a time
period of 5 to 10 min.
Record the reading of measuring device and note the actual
temperature. Without disturbing the dilatometer, change to
+90°C bath. The temperature of the bath should be maintained
in the range from +88 to +90°C until the temperature of the
specimen reaches that of the bath as denoted by no further
changes in the measuring device reading over a period of 5 to
10 min. Alternate two baths at proper temperature is kept and
while transferring the bath in the apparatus a care should be
taken not to disturb the apparatus .Test will be conducted over
a short period of time in order to avoid changes in physical
properties. The final length of the workpiece is measured at
room temperature. The test is repeated until there is any change
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 11 (2015)
© Research India Publications ::: http://www.ripublication.com
10159
in length per degree of temperature difference due to heating
degree with the change in length per degree.
Fig.1: Image of the dilatometer
Fig.2: Chamber used for thermal stability
The thermal stability experiment is used to observe the change
in the dimension of the work piece and this composite is
exposed to an extreme weather conditions. The equipment used
for this test is Envirotonics C 1500 shown in Fig 2.The
machine is capable of satisfying both the extreme hot as well
as cold conditions. The dimensions of the specimen for the test
are as per ASTM standard D476. The preliminary readings of
the work piece such as length, breadth and thickness is noted.
The work piece is kept in the thermal chamber at 850 oC, 85%
Rh and the second work piece is kept at 100oC, 10%Rh. The
initial dimension of the specimen is measured at room
temperature to the nearest 25 µm with scale or calliper. The
specimen should be kept inside the chamber for four days.
The length, breadth and width can be measured after
removing the specimen from the chamber.
The equipment for the flammability test is horizontal burning
type and the dimension is accordance to ASTM D
635.Equipment consists of a Bunsen burner, a sample holding
stand and a stopwatch. Three samples of polyurea are tested to
get an accurate result. The stand holds the specimen and the
Bunsen burners flame is used to ignite the specimen for
flammability. The stopwatch is used to get the time taken for
the specimen to burn off completely. The specimen was
marked into three columns, the column from the right side is
the area where the flame is passed to cover 100mm distance
and the time is noted using stop watch. The flame should be
extinguished at the centre of the specimen when it passes the
first 25mm .The dimension for the sample given as per ASTM
is 127×12.7×2 mm shown in Fig 3. In the first case the
specimen will be called self- extinguishing. The second case
shows the specimens are non-flammable substance. In the final
case, the specimen’s flammability would be calculated and it is
a flammable substance. The sample is exposed to flame for 10
seconds using Bunsen burner. In the final test it is mainly
concerned about the flammability test done on polyurea and
mild steel composite to infer the difference in the two tests and
to observe and conclude the beneficial presence of mild steel as
a substrate to polyurea coating.
Fig.3: Flammability sample piece before flammability test
III. RESULTS AND DISCUSSION
A. A.Coefficient of linear thermal expansion (CLTE)
The thermal expansion is calculated over the temperature
range of 30°C to 90°C which is given by the equation
α = (L2-L1)/[ Lo (T2-T1) ] = ΔL/Lo ΔT
Where,
α = average coefficient of linear thermal expansion per
degree Celsius,
ΔL = change in length of test specimen due to heating or
to cooling(L2-L1),
Lo = specimen length at room temperature
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 11 (2015)
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Δ T = temperature differences (T2-T1) °C, over which the
change in the length of the specimen is measured.
The values for heating and for cooling shall be averaged to
give the value to be reported. If thick metal plates are used,
appropriate correction should be needed to get the desirable
values for their thermal expansions.
Measurement of the length of polyurea sample before the test
at 30°C = 12.601mm.
Measurement of the length of polyurea sample after the test at
90°C = 12.606mm.
α= (ΔL/Lo)ΔT
α = {(12.606 – 12.601)/12.601} x (60 – 30)
α = (0.005/12.601) x 30
α = 0.0119°C-1
B. Thermal stability
After removing the work piece from the chamber we can
observe that it has got less change in dimension when it is
exposed to weather conditions and thickness for the both cases
is comparatively higher than the other values. The result for
thermal stability is shown in table 1.
TABLE1: TABULATION OF THE RESULTS OF THERMAL STABILITY
No. of
observations
made
First Condition
85oC, 85%Rh
Second Condition
10oC, 10%Rh
Duration
4 days
4 days
Change in length
0.23%
-1.48%
Change in width
1.13%
-1.16%
Change in
Thickness
1.88%
-7.44%
C. Flammability test
The test was to find out the flammability of polyurea by
testing on a 3 separate work pieces and is tabulated as shown
in table 2. From the test results we can say that the polyurea is
a flammable substance. Average flammability for the 3
separate work piece is 35.4 mm. The burned specimen of
individual polyurea is shown in Fig 4.The time taken by
Polyurea to burn within 75mm length is determined as 130
seconds. As the specimen is coated with mild steel as base
shown in Fig 5, did not propagate its flammability property
and this clearly states that it is a self-extinguishing composite
and strongly crosses out the flammable characteristics of
polyurea making it more reliable to use it.
TABLE.2: FLAMMABILITY TEST RESULTS
Specimen
Elapsed time
t (seconds)
Burned length
l (mm)
Burning rate
(mm/min)
Sample I
130
75
34.2
Sample II
127
75
35.4
Sample III
122
75
36.6
Fig.4: Flammable property of only polyurea coat after flammability test
Fig. 5: Flammable property of polyurea+ Mild Steel (127x12.7x2 mm)
IV. CONCLUSIONS
From our results and observations we found that polyurea as
an individual material is flammable and if it is coated with
addition to the mild steel flammable property can be
compromised.
The coefficient of linear thermal expansion is found out to be
0.0119oC-1. We also found out that the polyurea material has
very less change in dimension as it was exposed to extreme
weather conditions, but the thickness in both cases of hot and
cold climates changes considerably higher than the other
values.
The results show that polyurea must be used with more
reference to its thickness, as it shows variant change when
exposed to extreme climates for prolonged periods.
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 11 (2015)
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REFERENCES
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 10, Number 11 (2015)
© Research India Publications ::: http://www.ripublication.com
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