AIAA 2010-6515
46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit
25 - 28 July 2010, Nashville, TN
Thermal decomposition characteristics of the Ethylene
Oxide-Tetrahydrofuran Copolyether binder
Y. L. Sun1, H. C. Dang1, B. Z. Zhu1 , Shufen Li2
1. School of Metallurgy & Resources, Anhui University of Technology, Maanshan, Anhui
243002, China
2. Department of Chemical Physics, University of Science & Technology of China,
Hefei Anhui 230026, China
ABSTRACT
Thermal gravimetric analysis (TG),
differential thermal analysis (DTA), and
in-situ Fourier Transform Infra-Red
spectrometer (FTIR) experiments were
used
to
investigate
the
thermal
decomposition characteristics of PET
binder. The results of TG-DTA show that
PET binder takes place only one step
weight loss at a heating rate of 5oC/min.
While the heating rate rises (≥10oC/min),
PET binder takes place two-step weight
loss. The first step is an exothermic
reaction, and the second step is the
endothermic reaction. Moreover the start
and termination decomposition temperature
and peak temperature of PET all shift to the
higher temperatures with the increase of
heating rate. In-situ FTIR results show that
the first step weight loss of PET is the
depolymerization reaction and the second
step is mainly the decomposition reaction
of -CH2-and C-O-C.
1. INTRODUCTION
Aluminum/water propellant is a new
type of “green” high-energy density
propellant, and has a very good application
prospect in the high-speed underwater
propulsion system. It is considered to be
the ideal propellant for the ultra-high-speed,
long range underwater weapon. Currently,
however,
aluminum/water
propellant
encounters a "bottleneck" problem which
the reaction activity is lower, and the
reaction start-up is more difficult. The
emergence of nano-aluminum powder
provides the necessary conditions for the
application of aluminum/water propulsion
system. However, nano-aluminum powder
used in aluminum/water propulsion system
possesses some disadvantages which can be
summarized as follows [1]: (1) When
nano-aluminum powder is exposed to the
air, it can be easily oxidized, which is very
bad for the burning. (2) Nano-aluminum
powder which the surface is not processed
is very easy to react with water, so
nano-aluminum powder/water mixture can
not be stored. (3) Nano-aluminum powder
easily agglomerates, and this reduces the
combustion efficiency of propulsion
systems. In order to solve the above
problems, the surface process of
nano-aluminum powder is necessary.
Ethylene
Oxide-Tetrahydrofuran
Copolyether (PET) is an important "soft
segment" raw material in polyurethane (PU)
industry [2], and is also an important binder
for rocket propellant [3]. PET skeleton
contains quite flexible ether bond, so it has
very good liquidity. Moreover, narrow
Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
molecular weight distribution is helpful to
obtain
homogeneous
composite
cross-linked network. Especially that, PET
is a liquid at room temperature, and the
above-mentioned problem could be solved
by PET coating nano-aluminum powder in
the aluminum/water propulsion system.
The decomposition characteristics of
components in propellant will directly
affect the combustion characteristics of the
whole system. The correlation still exists
between the thermal decomposition
characteristics of the components and
combustion characteristics of the whole
system under certain conditions. If
nano-aluminum powder is coated by PET,
the thermal decomposition characteristics
of PET need to be understood for the most
effective use of it. So the present work
mainly focuses on obtaining information on
the decomposition characteristics of PET
binder. It is hoped that this work would be
useful in providing a clearer understanding
of high performance propellant studies.
2. EXPERIMENTS
2.1. Raw material
PET (the average functionality of 2.0).
2.2. Thermal decomposition experiments
TG-DTA experiments were carried out
with Shimadzu DTG-60H TG-DTA
instruments at a heating rate of 5oC /min,
10oC /min, 15oC /min (at atmosphere =
flowing N2 gas at a rate of 20ml/min). The
sample weights are 6~7mg and the sample
pans are alundum.
Spectra were recorded using KBr pellets in
the 4000~400cm–1 region with a resolution
of 2cm–1. In order to make the temperature
steady, the heating rate is 2oC/min for the
temperature-controlled FTIR experiments.
The heating profile is linear and the
atmosphere is N2 gas. The samples were
dissolved by dichloromethane and then
were prepared in KBr pellets. The samples
were heated by a heater and the
thermocouple contacts the samples. The
FTIR analysises were performed on the
solid residues of the samples during the
thermal decomposition.
3. RESULTS AND DISCUSSION
3.1Thermal Characterization of PET
The typical TG/DTG curves for PET
decomposition at the heating rate of 10oC
/min are given in Fig. 1, illustrating the
decomposition characterization. PET shows
two steps of mass loss. The first step
demonstrates a mass loss of 88% in the
temperature region of ~170–292oC. The
second step covers a temperature region
from ~ 292 to ~407oC and the percentage of
the mass loss is 9%. As can be seen from
the DTG curve, the maximum mass loss
rate of PET occurs at 273oC.
DrTGA(mg/s)
TG/%
100
0.000
80
-0.002
60
-0.004
40
-0.006
20
-0.008
273oC
0
2.3. In-situ FTIR experiments
In-situ FTIR measurements of PET
binder were performed with a Nicolet
Magna 750 FTIR spectrometer in the
temperature range of 25 to 470oC [4].
0
100
200
300
-0.010
400
500
Temperature/o C
Fig. 1 TG/DTG curves of PET
Fig. 2 shows the DTA curve of PET at
the heating rate of 10oC /min. It can be
seen from Fig. 2 that there is an exothermic
peak in temperature range of 172oC~292oC.
As can be seen from the above TG curve,
that mass loss of PET mainly occurs in this
temperature range. This indicates the first
step of PET decomposition is exothermal
reaction. There is an endothermic peak in
the temperature range of 292oC~303oC,
indicating that the second step of PET
decomposition is endothermal reaction.
the heating rate of 10oC /min, respectively.
The initial temperature and the final
temperature
of
the
second
step
o
decomposition of PET are 333 C and 415oC
at the heat rate of 15oC /min, respectively.
So it can be seen that with the increase of
heating rate, the initial and final
temperature of PET decomposition shifts to
the higher temperature.
Fig. 3 TG curves of PET at different
heating rates
Fig. 2 DTA curve of PET
3.2 Influence of Heating Rate on
Thermal Decomposition Characteristics
of PET
The TG curves of PET at different
heating rates (Fig. 3) show that PET shows
a step of mass loss at the heating rate of
5oC /min. The step covers a temperature
region from ~169 to~257oC and involves a
mass loss of ~94%. With the increase of
heating rate, PET changes from a one-step
mass loss into a two-step mass loss. As is
mentioned above, PET shows two steps of
mass loss at the heating rate of 10oC /min.
When the heating rate increases to 15oC
/min, the initial temperature and the final
temperature of the first step decomposition
of PET increase to 183oC and 333oC, which
increase by 11oC and 41oC compared with
The initial and final temperatures of PET
decomposition increases with the increase
of heating rate. This is because achieving
the same temperature; the higher heating
rate experiences a shorter reaction time, so
the degree of reaction decreases with the
heating rates increasing. At the same time,
heating rate could influence the heat
transfer and temperature gradient of
measuring point and sample, the outer layer
sample and the internal sample. These result
in a more serious thermal hysteresis, so TG
curves shift to higher temperature at higher
heating rates.
Fig. 4 shows the DTA curves of PET under
different heating rates. It can be seen that
PET only exhibits an exothermic peak at the
heating rate of 5oC /min. However, the
DTA curve of PET changes largely when
the heating rate increases to 10oC /min and
15oC /min. The decomposition of PET
exhibits an exothermic peak and an
endothermic peak, which correspond to the
results of TG. Moreover, with the increase
of heating rate, the peak temperature and
the main reaction temperature range all
increase. Heating rate could influence the
pyrolysis of the sample from the positive
and negative aspects. When the heating rate
increases, the sample particles which reach
the temperature of pyrolysis have a short
reaction time (in the same temperature
region). This is advantageous to the
thermal decomposition. But the sample
experiences shorter reaction time, and the
extent of reaction will decrease. At the
same time, the temperature difference of
particles between inside and outside
becomes larger, so this will lead to serious
thermal hysteresis. Moreover, pyrolysis
products of the outer particles have no time
to diffuse. This will influence pyrolysis of
the inner particles. The superimposition of
positive and negative aspects causes the
curves to shift to the higher temperature.
So with the increasing heating rate, peak
temperature and the main reaction
temperature range will increase.
Fig. 4 DTA curves of PET at different
heating rates
According to measurement results of the
DTA, the heat release of the first step
reaction of PET is 3.05kJ/g, 1.025kJ/g and
724.065J/g when the heating rate is 5oC
/min, 10oC /min and 15oC /min, respectively.
The heat absorptions of the second step
reaction are 56.25 J/g and 99.21 J/g,
respectively. So it can be seen that with the
increase of heating rate, the exothermic
quantity reduces and endothermic quantity
increases.
3.3 In-situ FTIR of PET
Fig 5 shows the in-situ FTIR of PET at
different temperatures. At 25°C, the two
adsorption peaks at 2951cm-1 and 2871cm-1
appear due to -CH2- asymmetric stretching
vibrations and symmetric stretching
vibrations, respectively. The adsorption
peak at 1113cm-1 is attributed to stretching
vibration of C-O-C. The bands at
1454~1211cm-1 are attributed to various
vibrations of CH2 groups in PET polymer.
It can be seen from Fig 5 that the intensity
of the spectra of PET changes little in the
wave number range 1454~1211cm-1 at
25~170°C and these implies that the groups
do not decompose in this wave number
range. The intensity of the adsorption peaks
notably changes at 170~255°C. The
intensities of the adsorption peaks at
2951cm-1,
2871cm-1,
2871cm-1
and
1113cm-1 remarkably decrease. The
absorption peak intensity in the range of
1454cm-1~1211cm-1
is
very
weak.
Increasing the temperature to 295°C, the
absorption peak at 1454cm-1~1211cm-1
completely disappears. This shows that
these groups have absolutely decomposed
in the wave number range 1454cm-1
~1211cm-1. According to the above result of
TG, the first step of PET decomposition
takes place in this temperature region. This
illustrates the depolymerization reaction
occurs at the first step of PET
decomposition. With the temperature
further increasing, the intensity of
absorption peak of the remaining groups
continues to decrease. Heating to 450°C,
the absorption peak completely disappears.
It can be seen from Fig. 5 that the second
step of PET decomposition mainly occurs
the decomposition of -CH2- and C-O-C
groups. So it can be concluded that the
depolymerization reaction of PET mainly
occurs at the heating rate of 5oC /min, i. e.,
the depolymerization reaction of PET
mainly occurs at a slow heating rate. When
the heating rate increases, PET takes place
depolymerization
reaction
and
decomposition reaction.
Fig. 5 the in-situ FTIR curves of PET at
different temperatures
4. CONCLUSION
The results of TG-DTA and in-Situ FTIR
experiments show that with the slowly
heating up, depolymerization reaction of
PET occurred. When the heating rate is
relatively higher, PET takes place two-step
decomposition. The first step is the
depolymerization of PET with an
exothermic process; while the second step
is the decomposition reaction of -CH2- and
C-O-C in PET with an endothermic process.
In addition, with the increase of heating rate,
the start and termination temperature of
PET decomposition and peak temperature
all shift to higher temperatures.
ACKNOWLEDGMENT
The authors greatly appreciate the
financial support provided by the National
Natural Science Foundation of China (No.
50806001.) and Education Department
Foundation
of
Anhui
Province
(KJ2008B184).
REFERENCES
[1] M. S. Zou, R. J. Yang, X. Y. Xiao, et al..
Advances
in
Aluminum/Water
Propellant,
Chinese Journal of
Energetic Materials, Vol. 15, No. 4,
2007, pp421-424.
[2] F. T. Cheng, Y. Q. Duo, S. G. Luo, et al..
Effect of Molecular Weight of
Polyethylene Glycol on the Properties
and
Morphology
of
EO/THF
Copolyether TPU, Polymeric Materials
Science & engineering, Vol. 17, No. 3,
2001, pp54-61.
[3] W. Xu, X. J. Wang, X. X. Liu, et al..
Research progress in energetic binders,
Journal of Rocket Propulsion, Vol. 33,
No. 3, 2007, pp44-67.
[4] Z. Jiang, K. J. Yuan, S. F. Li, et al..
Study of FTIR Spectra and Thermal
Analysis of Polyurethane, Vol. 26, No. 4,
2006, pp624-628.