International Journal of Organic Chemistry, 2011, 1, 105-112
doi:10.4236/ijoc.2011.13016 Published Online September 2011 (http://www.SciRP.org/journal/ijoc)
Study on the Effect of Carboxyl Terminated Butadiene
Acrylonitrile (CTBN) Copolymer Concentration on the
Decomposition Kinetics Parameters of Blends of Glycidyl
Epoxy and Non-Glycidyl Epoxy Resin
Garima Tripathi, Deepak Srivastava
Department of Pl ast i c Tec hn o l ogy, Harcourt Butler Technological Institute, Kanpur, In dia
Received June 25, 2011; revised August 1, 2011; accepted August 25, 2011
Abstract
The degradation of the epoxy system was studied for the prepared six blend samples with the incorporation
of 0 wt% - 25 wt% carboxyl terminated butadiene acrylonitrile (CTBN) copolymer, on a dynamic basis using
Thermo gravimetric analysis (TGA) technique under a nitrogen atmosphere. The blends were prepared by
physical mixing and were cured with diamine. The degradation of each sample followed second-order deg-
radation kinetics, which was calculated by Coats-Redfern equation using best-fit analysis. This was further
confirmed by linear regression analysis. The validity of data was checked by t-test statistical analysis. From
this value of reaction order, activation energy (E), and pre-exponential factor (Z) were calculated. It was
found that the activation energy increased with the addition of liquid elastomer.
Keywords: Diglycidyl Ether of Bis-Phenol-A, Cycloaliphatic Epoxy Resin, Carboxyl Terminated Butadiene
Acrylonotrile (CTBN) Copolymer, Thermogravimetric Analysis (TGA), Degradation Kinetics
1. Introduction
Research in the field of thermal degradation of epoxy
systems is of great interest because this is an outstanding
problem in the application these systems in different
types of environment and for wider usage of these mate-
rials as structural adhesives, coatings and as matrices in
fiber reinforced composites [1-4]. To characterize the
durability of polymers, it is common practice to follow
some important properties with time within the tempera-
ture range of interest, until a certain preselected limit is
attained [1]. In that way reliable data are only valid for
the actual temperature under consideration and cannot be
transformed to other service temperatures.
The unsatisfactory situation could be overcome, if the
changes would not be followed via a certain property,
but by a molecular process. Reactions related to degrada-
tion also obey Arrhenius kinetics. Thus, when the kinet-
ics of thermal degradation is known, the data can be
transformed over the whole temperature range and the
temperature-dependent service lifetime can be calculated
from these data. Research in thermal degradation of ep-
oxy systems is of great interest because this is an out-
standing problem in the application these systems in dif-
ferent types of environment and for wider usage of these
materials as structural adhesives, coatings and as matri-
ces in fiber reinforced composites [2-5]. For that reason
thermogravimetry (TG) technique is widely used for
studying the degradation phenomenon of epoxy resins.
Various mathematical and experimental methods were
developed [5-7] to obtain kinetic parameters viz. order of
reaction (n), activation energy (E), pre exponential factor
(Z), master curves of degradation [2], and their average
life times[3]. Coats-Redfern [8] equation was one of
them to describe the aforesaid parameters.
The degradation behavior of diglycidyl ether of bis-
phenol-A epoxy and CTBN has been studied extensively
[9-17], but the decomposition behavior of blends of
DGEBA epoxy, cycloalipahtic epoxy and CTBN has
hardly been investigated [18]. Keeping this in view, vari-
ous blend compositions of DGEBA epoxy, cycloali-
phatic epoxy and CTBN has been prepared and eval-
uated their kinetic parameters.

G. TRIPATHI ET AL.
106
2. Experimental
2.1. Materials
The diglycidyl ether of bisphenol—A (DGEBA)—based
epoxy resin (LY 556) (epoxide equivalent weight: 192
eq/g), cycloaliphatic epoxy resin (CY 230) (epoxide
equivalent weight: 145 eq/g) and cure agent was HT 976,
(4,4’-diamino diphenyl sulphone) (DDS) were the com-
mercial product (M/s Ciba Speciality Chemicals Pvt. Ltd.,
Mumbai, INDIA). The elastomer employed was carboxyl
terminated butadiene acrylonitrile (CTBN) copolymer
(trade name Hycar 1300 × 13) and was kindly supplied
by M/s Emerald Performance Materials, LLC, Hong
Kong with molecular weight,
M
n 3500 containing
acrylonotrile content 27% and carboxyl content 32%.
2.2. Sample Preparation
Six blend samples containing 0 - 25 phr CTBN were
prepared according to the procedure similar to that
adopted in our previous publication [19] for DGEBA
epoxy and CTBN. The calculated quantity of epoxy resin
(as per formulations given in Table 1) was, firstly,
stirred at 120˚C to entrap out all air bubbles from it. To
this homogeneous mixture, the calculated quantity of
DDS was added and stirred at 130˚C ± 5˚C for half an
hour to get clear solution.
2.3. Curing of Blend Samples
The cure process of all blend samples followed four
steps: First, the epoxy resin (3:1) was degassed followed
by addition of 0 - 25 phr CTBN in the epoxy resin. To
this mixture (36 phr) DDS was added and finally, the
whole mixture degassed again. The mixture were poured
into preheated open iron mold (8” × 8”) and cured into
hot air oven at 170˚C for 1 hour and then post cured for 2
hours at 200˚C. Specimens for the entire test were cut
from this block (square sheet) of cured material.
Table 1. Composition of epoxy resin with CTBN: blends
containing DDS.
S.No. DGEBA:CAE
(3:1) (gram) CTBN (gram) Sample Code
Curea
Temp.
T (˚C)
Cureb Time
t (sec)
1 100 00 EP3100 175.94 21.8
2 95 05 EP3105 175.41 19.2
3 90 10 EP3110 165.41 17.6
4 85 15 EP3115 163.92 16.7
5 80 20 EP3120 164.00 18.0
6 75 25 EP3125 - -
aas observed by Dynamic Runs; bas observed by isothermal runs.
2.4. Characterization of the Blend Samples
2.4.1. Fourier- T ransf orm Infra-Red (FTIR)
Spectroscopy
FTIR spectroscopy has been used to monitor the extent
of cure of DGEBA/CAE/CTBN/DDS blend systems and
the reaction, which occurred when such modifiers were
used. For the infrared (IR) measurement a small portion
of the cured epoxy system was ground to a fine powder,
mixed with potassium bromide (KBr) powder and
pressed into a pellet by hand press. FTIR were recorded
by Nicollet Magna 750.
2.4.2. Cure Schedule by Differential Scanning
Calorimetry (DSC) Analysis
Cure temperature of the prepared samples was observed
by taking very little quantity of sample into shallow alu-
minium pan of DSC (TA instruments, USA; Model DSC
2920), which was sealed by an aluminium cover. This
was placed in sample cell of the instrument. The starting
temperature programmed rate and final temperature were
taken at the heating rate of 10˚C/min. Dynamic scans
were obtained which were used for assessing the cure
temperature of the sample.
2.4.3. Thermogravimetric Analysis (TGA)
The kinetic parameters for the thermal decomposition of
these blends were evaluated by thermogravimetric ana-
lyzer (TGA) recorded on TA Instrument (Model
Hi.Res.2950 TGA unit interfaced with TA instruments
Inc.Thermal Analyst 2100 (Du Pont) control unit. The
TGA cell was purged with nitrogen at 60ml/min during
degradation runs. The amount of sample taken was ap-
proximately 5 - 10 mg in a platinum sample pan. The
heating rate in each run was kept at10˚C/min and the
temperature range was ambient to 800˚C.
2.4.4. Kinetic Methods
The application of dynamic thermogravimetry (DTG)
methods holds great promise as a tool for unraveling the
mechanisms of physical and chemical processes that oc-
cur during polymer degradation. There are various me-
thods which are used to analyze the non-isothermal ki-
netics. They are as follows:
Flynn-Wall-O za wa (FWO) method [20,7]
This method was derived from the integral method.
The technique assumes that A, function of conversion
f(

), and E are independent of T, whereas A and E are
independent of the degree of conversion (

). Equation
(2) may then be integrated to give the following in loga-
rithmic form:




logloglog log

g
AE pERT  (1)

107 G. TRIPATHI ET AL.
where

g

is the integral function of conversion and
p is the integral function. With Doyle's approximation [8]
for the integral, which allows for E/RT > 20, Equation (3)
now can be simplified as



logloglog2.315 0.4567
A
ER gERT 
(2)
Coats-Redfern (CR) method [8]
The CR method is also an integral method, and it in-
volves the thermal degradation mechanism. With an as-
ymptotic approximation for resolution of Equation (2),
the following equation can be obtained:

2
ln ln







g
A
RE
ER T


T
(3)
The expressions of

g

for the different mecha-
nisms and E for the degradation mechanism can be ob-
tained from the slope of a plot of ln

2

 
g
T  versus
1000/T.
Tang (TM) method [21]
Following the Doyle’s approximation Tang’s method
comes forward. It says that, with the logarithms of both
the side taken and an approximation formula for the so-
lution of Equation (2) (Doyle’s approximation) used, the
following equation can be obtained:

1.594661
lnln 3.635041
1.001450
1.894661ln









AE
Rg
T
E
ERT


(4)
The plots of

1.894661
ln T 

versus 1/T give a group of
straight lines. E can be obtained from the slope -
1.001450 E/R of the regression line.
Kissinger-Akahira-Sunose (KAS) method [22]
This method is an integral is conversional method
similar to the FWO method.

2
lnln 




 


A
R
Eg RT T


E
(5)
The dependence of

2
ln T 

on 1/T calculated for
the same

value at different

’s can be used to cal-
culate E.
Above mentioned methods are used frequently to cal-
culate the degradation kinetics. In the present investiga-
tion we are expanding the Coats and Redfern [9] method
to calculate the different parameters.
The percent weights versus temperature curves from
TGA were used for this purpose. The data from the TGA
curve were utilized in Coats-Redfern equation as given
in Scheme 1. This equation was used to determine the
values of order of degradation reaction (n), activation
energy (E) and pre-exponential factor (Z).
A graph between X and Y was plotted using the best
fit technique and the value of n was evaluated. This value
of n was further confirmed by linear regression analysis
using computer software and the values of coefficient of
determination (R2) were taken as a measure of validity of
data. With this value of n, the activation energy (E) and
pre-exponential factor (Z) were determined from the
slope and intercept values of the X and Y plots/regres-
sion equations.
3. Results and Discussion
3.1. Fourier-Transform Infrared (FTIR)
Spectroscopic Analysis
Figure 1 showed the FTIR spectrum of blend sample,
EP3100. There was no shifting of peak positions related to
oxirane functionality of glycidyl type DGEBA epoxy
resin (912.7 and 834.5 cm–1) and non-glycidyl type
cycloaliphatic epoxy resin (757.9 cm–1) while physical
blending of both the epoxies in comparison to the peak
positions of individual epoxy systems and discussed
elsewhere [11-13].
As 10 wt% CTBN was added the blend sample (viz.
sample EP3110) (Figure 2), the peak intensity of carboxyl
group near 1724 cm–1 increased which might be due to
increase in carboxylic content of CTBN in the epoxy
matrix. The peak intensities of oxirane group of glycidyl
type epoxy resin (912.7 cm–1), non-glycidyl type epoxy
resin (757.9 cm–1) were found to be increased. This
clearly indicated that the occurrence of chemical reaction
between the epoxy groups and CTBN occurred.
The change in the peak intensity showed that there
was consumption of free functional groups of elastomer,
epoxy and amine during curing reaction. By observing
all these changes it might be said, that the main reaction
of curing was a polyaddition esterification reaction. The
complete disappearance of peaks indicated the formation
of carboxylate salt between amine catalyst and carboxyl
group which rapidly reacted with epoxy to produce ep-
oxy terminated rubber. The IR spectra (Figure 3) of
cured product clearly evidenced the process of curing
3.2 Effect of CTBN on the Cure Schedule of
Prepared Blends
Figures 4 and 5 showed the dynamic DSC trace of the
sample EP3100 and EP3110 conducted from 25˚C - 325˚C
with a heating rate of 10˚C/min.The related data for all
the prepared blends i.e. cure temperature (T) and cure
time (t) are shown in Table 1. Table 1 clearly indicated
that the cure time decreased with the incorporation

G. TRIPATHI ET AL.
108
Figure 1. IR spectra of EP3100
Figure 2. FTIR spectrum of EP3110.
Figure 3. FTIR Spectrum of Cured EP3110.
Figure 4. DSC trace of EP3100.
Figure 5. DSC trace of sample EP3110.
of CTBN in the resin matrix up to 20 wt% of CTBN. A
similar result was drawn by Wise et al. [15] that the use
of CTBN rubber modifiers induced a high reactivity of
the end groups with the epoxide ring, which would result
in shorter curing times. This behavior brought to more
perfect network structure. The increasing reaction rate of
the epoxy-modified resin may be attributed to the inter-
action between the carboxyl-terminated groups of CTBN
rubber and the epoxide rings of the monomer.
3.3 Thermogravimetric Analysis
The onset/initial temperature (IDT) (TI), maximum rate
of mass-loss (PDT) (TP) and extrapolated final decompo-
sition temperature (FDT) (TF) were noted from TG traces
and are presented in Table 2.
The relative thermal stability of the cured blend resin
was compared by determining percent char yield at
800˚C.All the blend systems containing equal weight
ratios of DGEBA epoxy and CAE (3:1) having 0 wt% -
25 wt% CTBN cured with 36 wt% DDS showed single
step degradation (decomposition) behavior (Figure 6). A
major loss of 10% to 75 % was observed in the tempera-
ture range of 300˚C - 550˚C.

109 G. TRIPATHI ET AL.
Typical TGA curves of prepared blend samples re-
vealed that the thermal degradation of the system con-
sisted of only one independent step respectively. The
experimental data obtained are listed in Table 2. Com-
parison of initial degradation temperature (IDT) (Figure
7) values showed that, with the incorporation of CTBN,
the TI increased as the weight % of CTBN increased.
This indicated that the addition of CTBN to epoxy sys-
tem could improve the thermal oxidative stability of the
resin system. This conclusion was also reached by the
Table 2. Data obtained from TG traces of prepared blends.
S.
No.
Sample
Code
TI
(˚C)
TP
(˚C)
TF
(˚C)
Mass loss
(%)
Char yield
(%)
1 EP3100 330 ± 0.5 406.9 ± 1610 ± 1 82.4 17.6
2 EP3105 331 ± 0.85 423.9 ± 0.5535 ± 1.2 75.8 24.2
3 EP3110 349 ± 0.5 426.3 ± 0.85545 ± 1 77.7 22.3
4 EP3115 350 ± 1 423.7 ± 1540 ± 1 76.1 23.4
5 EP3120 358 ± 0.85 420.8 ± 1560 ± 0.95 72.0 28.0
6 EP3125 362 ± 1 425.5 ± 1530 ± 1.5 77.3 22.7
TI—initial degradation temperature; TP—Peak derivative temperature; TS—
Stop degradation temperature.
Figure 6. TGA Trace of EP3105.
Figure 7. IDT and FDT of prepared blend samples.
previous researchers [9,15-17]. This conclusion will be
further addressed in the following activation energy re-
lated discussion.
The char yields of all the prepared samples with
CTBN were higher than that of sample EP3100 The ki-
netic parameters, viz. order of reaction (n), activation
energy of degradation (E), and pre-exponential factor (Z)
of thermal decomposition of the blends of epoxy and
CTBN cured with DDS have been evaluated by the dy-
namic thermo grams of TGA.
The fractional decomposition “α” for the respective
temperature has been calculated from TGA data by using
the integral equation of Coats-Redfern. If a graph is
plotted between X and Y (for n in the range of 0 - 2) for
all sets, the best fit values of n was found to two (Figure
8). This value of n was further confirmed by linear re-
gression analysis over the TG data in accordance with
the values of X and Y obtained from Coats-Redfern equa-
tion. The coefficient of correlation, r, for this order of
reaction was found to be 0.90, 0.91, 0.95, 0.94 and 0.95
for the prepared blends. Other statistical test [24] data
and related regression equations are given in Table 3. It
is clear from the results that values of the activation en-
ergy increased, but with an associated proportional varia-
tion in Z, (Table 4), a phenomenon common in isother-
mal kinetic treatment [25].
Higher values of activation energies of the blend sys-
tems (Figure 9) may be attributed to the presence of
polynuclearity in the resin backbone chain. Hence, for a
system to be perfectly cured, higher energy was required.
This is also clear from the higher char yield of blends.
Increasing the activation energy indicated the steric hin-
drance of the molecules of more complex structure of
blends and the cured product with polyamine. The curing
reaction itself may be a complex function of the energy
of reactive molecules as well as the relative configura-
tion of the reactant molecules reaction process may be
hindered because of the presence of polynuclear structure
in the backbone. High activation energy for the decom-
position of blends led to better thermal stability of such
Figure 8. Linear fit data plot for the prepared samples.

G. TRIPATHI ET AL.
110
Table 4. Activation energy and preexponential factors of
prepared blends.
S.
No. Sample Code Activation Energy(E) (K·Cal/mol)
Pre-exponential
Factor(Z)
(Min–1)
CalculatedPlot Calculated Plot
1 EP3100 243.02 240.91 4.04*10–6 3.9*10–6
2 EP3105 293.49 288.08 3.81*10–6 3.4*10–6
3 EP3110 305.69 291.74 3.02*10–6 2.98*10–6
4 EP3115 315.69 302.96 2.76*10–6 2.76*10–6
5 EP3120 387.97 354.98 2.70*10–6 2.02*10–6
6 EP3125 255.64 240.18 2.98*10–6 2.83*10–6
Figure 9. Half-life time ( t1/2) of prepared samples.
Table 3. Statistical test data of prepared blend samples.
No Sample Code Correlation
Coefficient(r) Standard error of Coefficient tcal (calculated) ttab (Table value)Degree of freedom Confidence level (P = 0.02) Regression Equation
1 EP3100 0.9503 0.0052 9.45 2.72 11 98% Y = 22.7918 – 20.2893X
2 EP3105 0.9451 0.0056 9.78 2.68 12 98% Y = 17.4732 – 16.5088X
3 EP3110 0.9521 0.0049 13.12 2.72 11 98% Y = 15.9089 – 15.3480X
4 EP3115 0.9053 0.0056 12.67 2.72 11 98% Y = 13.0703 – 13.3685X
5 EP3120 0.8992 0.0047 13.83 2.72 11 98% Y = 12.1967 – 12.7089X
6 EP3125 0.9414 0.0055 14.10 2.72 11 98% Y = 22.3579 – 15.9865X
blend system. This fact has been previously reported in
the literature for different systems. [26-29].
processing temperature regions and the estimated life-
time of the polymers. It supplies a simple and convenient
approach to use as an accelerated ageing process for
quality control experiments. The decomposition kinetics
at elevated temperature could be extrapolated back to the
service conditions for which the lifetime prediction is
required. Two parameters, half-life time t1/2, and lifetime
tf are used to evaluate the service lifetime of the materials.
The half-life time is defined as the value of  becomes
0.50 (Figure 10) and the lifetime of polymer to failure is
generally defined to be when the degree of decomposi-
tion reaches 0.50.
Higher values of pre-exponential factor give rise to a
faster high curing reaction [30,31] which might be due to
an increased number of collisions which ultimately lead
to a higher interaction of reactive sites.
3.4. Estimation of Half-Life Time, t1/2 and Life
Time, tf
In polymer science, thermal analysis methods have found
important applications; among them is the determination
of kinetic parameters. Thermo degradation kinetics can
be studied by thermogravimetric analysis, which is a
useful tool, because the information can be obtained
from a single thermogram. Kinetic parameters such as
activation energies and pre-exponential factors are cal-
culated using integral and differential methods reported
in the literature. With experimental procedures, informa-
tion about the kinetics of decomposition and in-use life-
time projections can be obtained. The ability to predict
the life-time is valuable, because the costs of premature
failure in actual end use can be high. TG provides a
method for accelerating the life time testing of polymers
so that short-term experiments can be used to predict
in-use life-time.
An important application of TG kinetic parameters is
to predict the highest usable temperature, the optimum
Figure 10. Comparison of Ea values of prepared blend sam-
ples.

111 G. TRIPATHI ET AL.
4. Conclusions
On the basis of preceding results and discussion the fol-
lowing conclusions may be drawn:
1) The proposed mechanism for curing reaction of the
blend of DGEBA: CAE and carboxyl terminated butadi-
ene Acrylonitrile copolymer (CTBN) in presence of 4,
4’-diamino diphenyl sulphone (DDS) was found to be
well suitable for such system, which was confirmed by
FTIR analysis.
2) The addition of CTBN liquid rubber improved the
thermal stability of the pure epoxy resin.
3) The degradation of ternary blends proceeds with
2ndorder, which was determined by best-fit and regres-
sion analysis. The obtained data were found to be highly
significant (confirmed by statistical analysis) i.e. the
change in the value of X (temperature) will change the
value of Y (activation energy) significantly.
4) The blends were found to be more thermally stable
having high activation energy as the CTBN content in
the blend was increased upto 20%.
5) Half-life, t1/2 of the prepared samples was increased
upto 15 wt% CTBN addition and decreased thereafter.
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