Service life prediction of rubber compound by accelerated ageing and mechanical properties

INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN ENGINEERING
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online), Volume 5, Issue 11, November (2014), pp. 46-60 © IAEME
AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 5, Issue 11, November (2014), pp. 46-60
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46

IJARET
© I A E M E
SERVICE LIFE PREDICTION OF RUBBER COMPOUND
BY ACCELERATED AGEING AND MECHANICAL
PROPERTIES
Chandresh Dwivedi1*, K Rajkumar1, Maninee Vibhande2, Nikhil Shinde2,
Shrutika Sankhe2
1Indian Rubber Manufactures Research Association, Thane
2Dept. of Chemical Engineering, SOJE Thane
ABSTRACT
Generally, the useful life of a rubber component is governed by its susceptibility to failure by
either mechanical or chemical deterioration. There are well established tests to address the failure
properties of elastomers – fracture mechanism toinvestigate mechanical durability and also
accelerated aging tests for chemical degradation. This paper is presented to experimentally estimate
the life span of the rubber blend comprising NR and SBR in a ratio of 3:1 at accelerated ageing
conditions. The specimens are subjected to ageing at different temperatures mainly at 900C, 1000C,
1200C and 1500C. The changes estimated at these temperatures were then understood with the help
of the concept of Arrhenius theory and were compared to the rubber sample at ordinary conditions
and the retention in physical properties was assessed.
Keywords: Service Life, Ageing, Mechanical Properties, Arrhenius Law.
INTRODUCTION
Rubber is a widely used material in many applications. Products made from rubber have a
flexible and stable three dimensional chemical structure and are able to withstand under force large
deformations. For example the material can be stretched repeatedly to at least twice its original
length and, upon immediate release of the stress, will return with force to approximately its original
length. Under load the product should not show creep or relaxation. Besides these properties the
modulus of rubber is from hundred to ten thousand times lower compared to other solid materials
like steel, plastics and ceramics. This combination of unique properties gives rubber its specific
applications like seals, shock absorbers and tires.

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976
6480(Print), ISSN 0976 – 6499(Online), Volume 5, Issue

11, November (2014), pp. 46
An elastomeric component may be said to reach the end of its life when it fails to function
properly – as in seal leakage or a loose elastomeric bushing
aspect of its behavior leads to failure of an inspection. Either way, longer more assured lives are
being expected of rubber components at the same time as other demands
and increased operating temperature.
There are many factors that lead to degradation of rubber
to degradation of rubber are, fatigue causing mechanical aspects, environmental factors, rubber
formulation and consecutive behavior.
A tire compound when subjected to mechanical loading under specific conditions is likely to
rupture after a certain period of time. The appraisal of this life span proves beneficial in
understanding the concept of life predictio
With time, we observe specific changes in the rubber sa
Aging means change in the physical p
physical properties with respect to
deleterious effect on rubber, both on crack nucleation life, and on fatigue crack growth rate.
Temperature effects occur independently of any chemical changes that may occur due to aging or
continued vulcanization[2,3]. Temperature has a large effect on the rate of these chemical processes,
which can result in additional degradation of fatigue life at elevated te
period.
THERMAL AGING
Rubber materials are sensitive to temperature and this is particularly evident at low
temperatures. This is a reversible situation as the temperature is increased well above the glass
transition temperature the material recovers its elastomeric characteristics. In a laboratory
chemical degradation can be accelerated by aging the compound at temperatures higher than the
intended service temperature. This testing involves finding degradation rate and stability of rubber
sample exposed to accelerate to thermal condition to p
time period, degradation behavior is studied to life of sample expected for long time, long
temperature explore with quantitative prediction of life of sample. There is established model that
describe the relationship between reaction rate and temperature.
47
– or when its appearance or some o
– such as: reduced space
Rubber has a tendency to degrade after a certain period of time.
[1]. The four main types of causes that leads
prediction of the rubber compound[2].
sample collectively termed as ‘Aging’.
ing properties of rubber. Thermal aging concerns with the change of
various temperature change. Elevated temperature has a
. temperatures, or over long
predict the life of rubber sample
ationship –
6-60 © IAEME
other
cy . mple ing mperatures, study
redict [3,4]. For some

48

The condition of short period of time with an elevated temperature is useful to yield
predictions of the property degradation expected in the long run with quantitative predictions of
lifetimes obtained from the use of Arrhenius relation[6,7,8] So this method assumes that the chemical
deterioration induced in the lab testing is the factor determining the service life in the field. Although
oxidation of rubber is fairly complex, thermally activated processes can be described using the
Arrhenius equation if certain conditions apply.
Assumption for Arrhenius theory
1. The rate of each chemical step involved in the oxidation process (initiation, oxygen uptake,
termination) must respond the same to changes in temperature.
2. The oxidation proceeds uniformly throughout the material.
Mathematical Representation
Arrhenius theory is originally derived from Thermodynamics. When these assumptions hold,
the rate of oxidative aging, at the use temperature T1, can be determined from the aging rate
measured in the lab at a test temperature T2 from Arrhenius equation [7,8]given by,
K = ·

Where,
K = Overall rate constant of aging process.
= pre exponential factor
= reaction rate at temperature

= reaction rate at temperature
.
Ea. = activation energy. J/mol·K or cal/mol·K
R = gas constant (8.314 J/mol·K or 1.987 cal/mol·K)
Effectiveness
Arrhenius behavior will be more effective even when the thermal degradation process is more
complicated. In this case the measured ‘Ea.’ is only an effective activation energy, but nevertheless
still useful for predictions [11]. Although fracture mechanics and Arrhenius extrapolations are both
firmly based on well understood principles, service life predictions are reliable only to the extent that
the relevant failure mechanisms are identified, all contributing factors accounted for, and the samples
used for laboratory test are representative.
Activation Energy
Activation Energy is the minimum Energy by which the colliding molecules of sample must
have in order to bring about the degradation reaction. Lower the value of activation energy, higher
will be the rate at which the degradation will proceed. Higher value of activation energy, lower will
be the rate at which deterioration proceed [8].

Graphically Determination Using Arrhenius Plot
49

If concentration dependency of rate is not known, degradation rate against Temperature data
plotted in the graph, slope will be equal to {
}. So, activation energy is determined
experimentally by carrying out reaction at several temperature. The reaction rate at any temperature
is obtained from the change in the selected property with the exposure time at that temperature[7,9].
Ln r =

!
Fig: Arrhenius Plot
Four cut samples are then exposed to different temperature 800C to 120# continuously in hot
air oven. Sample is then taken out and conditioned at room temperature. A condition of the rubber
(e.g. brittleness or hardness) is assumed that corresponds to a degree of deterioration likely to cause
product failure. The service life is then estimated as the time for the material to reach this condition
at the service temperature. This can be extrapolated to determine life to the service temperature (TS)
property[13,8,7].
Methodology
1. Before we began, the number of sets of samples required for each tests (for Tensile,
Abrasion, flexing and tearing) which were supposed to be conducted at different temperature
and time period were prepared.
2. Respective number of samples were then exposed to different temperatures (i.e. at 80oC,
90oC, 100oC, 120#) continuously in the hot air oven.
3. Then sample was taken out periodically at room temperature according to test plan.
4. The property of the rubber (e.g. brittleness or hardness) was assumed that corresponds to a
degree of degradation likely to cause product failure. The service life was then estimated as
the time for the material to reach this condition at the service temperature.
The service life can be easily changed by choosing a different property, end-point criterion or
test-piece geometry. To improve the accuracy of the prediction, more test temperatures and a greater
number of samples should be tested. Exposed samples are conditioned at room temperature and
analyzed by spectrophotometer. Spectrum will be analyzed by software to study the quantitative
changes in cracks of the sample i.e. variation in the crack length of the samples.

Temperature ranges (80, 90,110,120

There arises a question in
120# for thermal aging of given rubber sample.
11, November (2014), pp. 46
When sample is subjected to higher temperature, rate of degradation rapidly goes on
changing. So, as we have discussed earlier, it is
higher temperature.
As the temperature tends to increase it becomes more feasible
behavior in a short period of time
procrastinating as it requires more time for the sample to degrade.
Mechanical Test
2) Tensile strength test
The properties that are typically determined during a tensile test are
elongation at break, stress at a given elongation, elongation at a given stress, stress at yield, and
elongation at yield. The tensile testing is carried out by
specific extension rate to a standard tensile specimen with known dimensions (gauge length and
cross sectional area perpendicular to the load direction) till failure.
Dumbbell shaped Specimen
3) Crescent tear test:
This test also measures the force required to propagate a nick already produced in the test
piece, and the rate of propagation is not related to the jaw speed.
mm by a single stroke of the blade
4) Angle tear test:
This test is a combination of tear initiation and propagation. Stress is built up at the point of
the angle until it is sufficient to initiate a tear and then further stresses propagate this tear. However,
50
#)
our mind that why the selected temperature
sample.[8]
e easier to estimate the activation energy at
to estimate the degradation
time. But, in case of lower temperature
inating . applying longitudinal or axial load at a
Nick the test piece to a depth 0.5
blade[9]
–
6-60 © IAEME
range is from 80oC to
temperatures the process is little
tensile strength,

it is only possible to measure the overall force required to rupture the test piece, and, therefore, the
force cannot be resolved in two components producing initiation and propagation[9,12]
51
EXPERIMENATL DETAIL
Sample Requirement

In order to calculate the total quantity of the rubber material required, we need to know the
total number of specimens we want to conduct a particular test. Therefore, the following table gives
us the information regarding the number of sets that were needed for the experiment.
Condition Duration(in days)
Total set of
samples
Unaged 1
90°C 1 3 5 10 20 6
100°C 1 3 5 10 --- 5
120°C 1 3 5 10 --- 4
150°C 1 3 5 --- 3
Total Number of sets 19
Formulation:
Sample formulation is the gist of all the ingredients present in the given compound with their
quantities.
CONTENT BASIC FORMULATION (pphr)
NR(RSS 3) 75
SBR 25
Carbon Black HAF 330 60
Oil 5
ZnO (activator) 5
Stearic Acid(activator) 1
TDQ (antioxidant) 2
6PPD antoX (antioxidant) 42
Sulphur (curing agent) 2.5
CBS (accelerators) 0.7
Total content 218.2
Molding
Compression, transfer, and injection-molding techniques are used to shape the final product.
Once in the mold, the rubber compound is vulcanized at temperatures ranging from 100 to 200°C.

11, November (2014), pp. 46
The cure time and the temperature are determined beforehand with a c
oscillating disk rheometer.

The compounded sample is sent
from an oscillating disc rheometer (MDR 2000)
samples were molded by compression
CALCULATIONS AND GRAPHICAL ANALYSIS
1. Life Estimation
A. By Tensile Strength.
Tensile strength retention in % with respect to time
Time period
in Hr.
Property reten.
at 90°C
0 90.73
24 100
72 94.59
120 89.19
240 67.95
480 50.58
Graph1:
The above plot of tensile strength retention against time period can give time required for any
% retention value for the particular temperature curves shown in graph
52
curemeter, such as the
to the rheometerat 150°C with a cure time of
according to ASTM D2084
molding, as per the need.
S ensile period in hour
Property reten.
at 100°C
Property reten.
at 120°C
95.14 100
100 51.49
79.35 39.57
58.7 30.21
45.75 ¯
¯ ¯
: Tensile Strength (T.S.) Retention at 90°C
icular graph-1
–
6-60 © IAEME
uremeter, $% obtained
is 8.82min. Then the
Property reten.
at 150°C
100
35.3
9.36
¯
¯
¯

For 55% retention,

Temperature(°C)
Time(Hr.)
Arrhenius Data:
357.4 133.1 28.4
For degradation, we consider
90 100 120
first order reaction, so the term ln(k) is
and hence Arrhenius data is predicted in the following table.
Temp 1/T (in kelvin)
90 0.0028
100 0.0027
120 0.0025
150 0.0024
Graph 2
In the above plot, we obtain a
span) at ambient temperature.
At, ambient temperature i.e. T= 298
If we trace the value of temperature (x=1/T=
function f(x).
F(x) = ln (1/sec) = -18.415
Time at 298k or Life span = 99433536.1sec =
11, November (2014), pp. 46
53
Time(Hr.) ln(1/
357.4
133.1
28.4
15.46
2: Arrhenius plot for 55% retention of T.S.
linear nature and using this we can find out
298K
e 0.00335) in the graph, we get
3.2 years.
–
6-60 © IAEME
150
15.46
taken as ln(1/ t in sec)
t in sec)
-14.07
-13.08
-11.25
-10.93
the time period (life
the value of

For 60% retention,

Graph 3
3: Arrhenius plot for 60% retention of T.S.
F(x) = -18.1875
Therefore, Life span for 60% retention of T.S. =
Similarly, we have estimated the life using other testing p
B. Abrasion Index –
Graph 4
11, November (2014), pp. 46
2.78 years
54
properties by graphical
4: Abrasion property retention graph
–
6-60 © IAEME
roperties analysis

Arrhenius data:
Graph For 55% retention,

11, November (2014), pp. 46
Graph 5: Arrhenius plot for 55% retention of Abrasion Index
F(x) = -18.5726
Therefore, Life span for 55% retention of Abrasion Index =
For 60% retention
Graph 6: Arrhenius plot for 60% retention of Abrasion Index
F(x) = -18.2627
Therefore, Life span for 60% retention of Abrasion Index =
55
3.36 years
0% 2.9years
–
6-60 © IAEME

C. Angle Tear Strength-

Graph 7: Angle Tear Strength
Arrhenius data:
For 55% retention,
11, November (2014), pp. 46
Retention at 900C, 1000C, 1200C and 150
Graph 8: Arrhenius plot for 55% retention of Tear strength retention
F(x) = -17.6343
Therefore, Life span for 55% retention of Angle tear strength =
56
3years.
–
6-60 © IAEME
0C

For 60% retention of tear strength,

F(x) = -17.7215
Therefore, Life span for 60% retention of Angle tear strength =
D. Crescent Tear Strength-
Graph 10
11, November (2014), pp. 46
57
0% 2.56years.
10: Crescent Tear Strength Retention
–
6-60 © IAEME

Arrhenius data:
For 55% retention,

11, November (2014), pp. 46
Graph 11: Arrhenius plot for 55% retention of Tear strength
F(x) = -18.2939
Therefore, Life span for 55% retention of Crescent tear strength =
For 60% retention of crescent tear strength,
F(x)= -18.2757
Therefore, Life span for 60% retention of Crescent tear strength =
58
retention
3.1years.
% 2.8
–
6-60 © IAEME

59
RESULTS AND DISCUSSION

We have made a tread tire compound (NR-SBR) with 3:1 proportion of their standard range
of properties. Further, the samples were subjected to ageing at different temperatures in order to get a
retention percentage. We have selected the temperatures 900C, 1000C, 1200C and 1500C. The
selection of these temperatures weredone in order to complete this experiment of life prediction in a
short duration where current tests available in the industries require longer time. So we have taken a
maximum time period of 20days for aging at 90°C as degradation rate is slow at low temperatures
and retention falls up to 50%. A whole month was taken for successful completion of all the tests in
predefined time. This time period had been decided to get a property retention upto 50 %. From
graphs (1,4, 7, 10) we observe that at 90oC and 100°C, the retention gradually decreases with time.
Where as in case of 120°C it falls rapidly and a steep curve is obtained as compared to 900 C and
1000C and at 150°C graph of retention falls immediately. So, the Retention of these mentioned
properties decrease with increase in temperature as well as time.
Using this temperature range and then plotting time retention as well as Arrhenius graph, we
have obtained a range of values for life spans of our rubber blend for 55% and 60% retention of
property which are shown below:
Tests
Life span (in year)
for 55% retention for 60% retention
Tensile Test 3.2 2.78
Abrasion Index Test 3.36 2.9
Angle Tear Test 3 2.56
Crescent Test 3.1 2.86
We can observe that life span for 55% retention is more as compared to 60% retention for
each test. This shows that as time for ageing a sample increases the rate of degradation also
increases, which proves that our data obtained from the experiment is correct. Thus life span values
at 55% retention 3 to 3.4 year and at 60% retention 2.6 to 2.9 years respectively.
So for overall life of compound we can assume the minimum value at this specified retention i.e. for
55% retention life is 3 years. And for 60% retention life is 2.6years
CONCLUSION
NR-SBR a tread tire compound is widely used in the tire industries and NR is ubiquitous in
India. SBR is the most economical and environmental friendly rubber. Natural rubber is often used
in heavy vehicles. A blend of this rubber compound.This project helps is in studying the life
prediction techniques for life span of a compound. As we are considering the minimum value for
Life span, life of our compound 2.6years to for 55 and 3years for 60% retention which is allowable.
REFERENCE
[1] Y. S. RohanaYahya, A. R. Azura. And Z. Ahmad.(2011). Effect of curing system on
thermal degradation behaviour of NR, Journal of Physical Science, vol-22(2), 1-14.
[2] C. M. Roland. Vagaries of elastomer service life prediction, invited lecture,
polymerphysics.net.

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