7 SERVICE LIFE PREDICTION OF RUBBER COMPOUND BY ... LIFE PREDICTI… · SERVICE LIFE PREDICTION OF...

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

46

SERVICE LIFE PREDICTION OF RUBBER COMPOUND

BY ACCELERATED AGEING AND MECHANICAL

PROPERTIES

Chandresh Dwivedi1*

, K Rajkumar1, Maninee Vibhande

2, Nikhil Shinde

2,

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, 100

0C,

1200C and 150

0C. 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.

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International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976

6480(Print), ISSN 0976 – 6499(Online), Volume 5, Issue

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.


6499(Online), Volume 5, Issue 11, November (2014), pp. 46

47


as in seal leakage or a loose elastomeric bushing – or when its appearance or some o


being expected of rubber components at the same time as other demands – such as: reduced space

and increased operating temperature. Rubber has a tendency to degrade after a certain period of time.

There are many factors that lead to degradation of rubber[1]

. The four main types of causes that leads


and consecutive behavior.



understanding the concept of life prediction of the rubber compound[2]

.

With time, we observe specific changes in the rubber sample collectively termed as ‘Aging’.

ing means change in the physical properties of rubber. Thermal aging concerns with the change of

physical properties with respect to various temperature change. Elevated temperature has a




which can result in additional degradation of fatigue life at elevated temperatures, or over long

sensitive to temperature and this is particularly evident at low


transition temperature the material recovers its elastomeric characteristics. In a laboratory



sample exposed to accelerate to thermal condition to predict the life of rubber sample



ationship between reaction rate and temperature.


6-60 © IAEME


or when its appearance or some other


such as: reduced space

cy to degrade after a certain period of time.

. The four main types of causes that leads




mple collectively termed as ‘Aging’.

ing concerns with the change of

various temperature change. Elevated temperature has a




mperatures, or over long

sensitive to temperature and this is particularly evident at low


transition temperature the material recovers its elastomeric characteristics. In a laboratory study



redict the life of rubber sample[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 = ��·��

= �� exp �− �� 1

�− 1

��

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]

.



49

Graphically Determination Using Arrhenius Plot

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 = − ��

�� + ln "�

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, 100

oC, 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.

� 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

Temperature ranges (80, 90,110,120℃℃℃℃) in our mind that why the selected temperature

for thermal aging of given rubber sample.[8]

subjected to higher temperature, rate of degradation rapidly goes on

e have discussed earlier, it is easier to estimate the activation energy at

As the temperature tends to increase it becomes more feasible to estimate the degradation

period of time. But, in case of lower temperature

inating as it requires more time for the sample to degrade.

The properties that are typically determined during a tensile test are

at a given elongation, elongation at a given stress, stress at yield, and

. The tensile testing is carried out by applying longitudinal or axial load at a


cross sectional area perpendicular to the load direction) till failure.

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. Nick the test piece to a depth 0.5

mm by a single stroke of the blade[9]




6-60 © IAEME

our mind that why the selected temperature range is from 80oC to

subjected to higher temperature, rate of degradation rapidly goes on

easier to estimate the activation energy at

to estimate the degradation

lower temperatures the process is little

The properties that are typically determined during a tensile test are tensile strength,

at a given elongation, elongation at a given stress, stress at yield, and

longitudinal or axial load at a


This test also measures the force required to propagate a nick already produced in the test

Nick the test piece to a depth 0.5





51

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]

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.



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

The cure time and the temperature are determined beforehand with a curemeter, such as the

The compounded sample is sent to the rheometerat 150°C with a cure time of

rheometer (MDR 2000) according to ASTM D2084

compression molding, as per the need.

S AND GRAPHICAL ANALYSIS

ensile strength retention in % with respect to time period in hour

Property reten. 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 temperature curves shown in graph-1


6-60 © IAEME

uremeter, such as the

with a cure time of $%� obtained

ASTM D2084 is 8.82min. Then the

Property reten.

at 150°C

100

35.3

9.36

¯

¯

¯




For 55% retention,

Temperature(°C)

Time(Hr.)

Arrhenius Data:

For degradation, we consider

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 =



53

90 100 120

357.4 133.1 28.4

For degradation, we consider first order reaction, so the term ln(k) is

predicted in the following table.

1/T (in kelvin) Time(Hr.) ln(1/

0.0028 357.4

0.0027 133.1

0.0025 28.4

0.0024 15.46

Graph 2: Arrhenius plot for 55% retention of T.S.

the above plot, we obtain a linear nature and using this we can find out

At, ambient temperature i.e. T= 298K

e trace the value of temperature (x=1/T=0.00335) in the graph, we get

99433536.1sec = 3.2 years.


6-60 © IAEME

150

15.46

is taken as ln(1/ t in sec)

ln(1/ t in sec)

-14.07

-13.08

-11.25

-10.93

we can find out the time period (life

0.00335) in the graph, we get the value of



For 60% retention,

Graph 3

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



54

Graph 3: Arrhenius plot for 60% retention of T.S.

Therefore, Life span for 60% retention of T.S. = 2.78 years

estimated the life using other testing properties by graphical

Graph 4: Abrasion property retention graph


6-60 © IAEME

roperties by graphical analysis



Arrhenius data:

Graph For 55% retention,

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

Arrhenius plot for 55% retention of Abrasion Index

Therefore, Life span for 55% retention of Abrasion Index = 3.36 years


0% retention of Abrasion Index = 2.9years


6-60 © IAEME





C. Angle Tear Strength-

Graph 7: Angle Tear Strength

Arrhenius data:

For 55% retention,

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

Angle Tear Strength Retention at 900C, 100

0C, 120

0C and 150

Arrhenius plot for 55% retention of Tear strength retention

Therefore, Life span for 55% retention of Angle tear strength = 3years.


6-60 © IAEME

C and 150

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



57

0% retention of tear strength,


Therefore, Life span for 60% retention of Angle tear strength = 2.56years.

Graph 10: Crescent Tear Strength Retention


6-60 © IAEME




Arrhenius data:

For 55% retention,

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


Therefore, Life span for 55% retention of Crescent tear strength = 3.1years.

For 60% retention of crescent tear strength,


% retention of Crescent tear strength = 2.8


6-60 © IAEME

retention




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, 100

0C, 120

0C and 150

0C. 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.



60

[3] G. K. Kannan, L. V. Gaikwad, L. Nirmala, and N. C. Kumar, (2010). Thermal Aging

Studies of Bromyl Rubber used in NBC personal protection equipment, Journal of Scientific

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[4] P. H. Mott, C. M. Roland.(2009). Aging of Natural Rubber in air and seawater, Navel

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[5] V. A. Coveney, (2013). Service life Prediction- Process and Challenge, Woodhead

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[6] Maria D. Ellul. Mechanical Fatigue, Advanced Elastomer System.

[7] UdayKarmarkar, (2007). Shelf Life Prediction of medical gloves, Akron Rubber

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[8] A. S. Maxwell, W. R. Broughton, G Dean and G. D. Sims, (2005). Review of Accelerated

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[9] ASTM D624, (2001). Std. test method for Tear strength of conventional vulcanized Rubber

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[10] ASTM D412, (2013). Standard Test Methods for Vulcanized Rubber and Thermoplastic

Elastomers—Tension (ASTM, USA).

[11] W. V. Mars, (2004). Factor affecting the Fatigue Life of Rubber (a literature survey),

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[12] G. J. Lake and A. G. Thmas, in A. D. Roert, Ed, Natural Rubber Science and Technology,

Oxfor University press, Oxford, 1988, pp.731-772.

[13] Laidler, K.J., Principles of Chemistry, Harcourt, Brace & World, New York, 1966.

[14] Moore, W.J., Physical Chemistry, Prentice-Hall, 1962.

[15] Moeller, T., Inorganic Chemistry, John Wiley, 1982.

[16] K. Rajkumar, P. Thavamani, Chandresh Dwivedi and Pankajregar, “An Eco-Friendly

Rubber-Textile Composites for Construction of Rubber Dam to use in Watersheds

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[17] Salih Abbas Al- Juothry, “The Influence Surface Area and Sturcture of Particles Carbon

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