http://www.iaeme.com/IJMET/index.asp 679 [email protected]
International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 10, October 2018, pp. 679–686, Article ID: IJMET_09_10_070
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=9&IType=10
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication Scopus Indexed
THERMAL AGING INFLUENCE ON
MECHANICAL PROPERTIES AND FATIGUE
BEHAVIOR OF ACRYLONITRILE BUTADIENE
STYRENE THERMOPLASTIC POLYMER
NANOCLAY COMPOSITES
Pydi Hari Prasadarao
Research Scholar, Acharya Nagarjuna University, Guntur-522510, India
H. Ravisankar
Professor, GITAM deemed to be University, Visakhapatnam-530045, India
V.Chittaranjan Das
Professor, RVR&JC College of Engineering, Guntur-522019, India
ABSTRACT
Acrylonitrile butadiene styrene (ABS) is an engineering thermoplastic used
extensively in industrial applications due to their better processing and mechanical
properties. Thermal degradation due to exposure of higher temperatures causes
degradation of its functional properties of acrylonitrile butadiene styrene (ABS) and
restricts their usage in engineering applications. The effect of degradation can be
reduced by the inclusion of nano fillers in these polymers. The present work is aimed to
study the ability of nanoclay inclusions to reduce the damaging effect of thermal
degradation of ABS at higher temperatures. ABS-nanoclay included thermoplastic
polymer composites were fabricated by melt blend method. These composites are
exposed to higher temperature in an oven to study the effect of thermal aging on
mechanical and fatigue behavior of nanoclay ABS thermoplastic polymer
nanocomposites. Nanoclay loading reduces the thermal degradation effect and
enhances fatigue properties after thermal aging when compared to thermally aged
virgin ABS polymer.
Keywords: Thermal Aging, Acrylonitrile–butadiene–styrene, degradation
Cite this Article Pydi Hari Prasadarao,H.Ravisankar and V Chittaranjan Das, Thermal
Aging Influence on Mechanical Properties and Fatigue Behavior of Acrylonitrile
Butadiene Styrene Thermoplastic Polymer Nanoclay Composites, International Journal
of Mechanical Engineering and Technology, 9(10), 2018, pp. 679–686.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=10
Thermal Aging Influence on Mechanical Properties and Fatigue Behavior of Acrylonitrile
Butadiene Styrene Thermoplastic Polymer Nanoclay Composites
http://www.iaeme.com/IJMET/index.asp 680 [email protected]
1. INTRODUCTION
Thermoplastic polymers are a key part of modern industrial applications in almost every field,
from household commodities to engineering applications. Most of the thermoplastic polymers
restrict their usage in heavy engineering applications owing to their poor mechanical properties.
Several works reported [1-4] to enhance these properties by introducing nanoparticles in the
polymer matrix. Acrylonitrile Butadiene Styrene (ABS) is known as an engineering
thermoplastic polymer owing to its versatility in engineering applications. ABS possesses good
mechanical properties when compared to other thermoplastic polymers however; it needs to be
further improvised for a wide range of applications. Thermal degradation is another problem
for ABS where the properties degrade and diminish. The mechanisms of degradation of
thermoplastic polymers have been published by various authors [5-8]. Degradation of ABS
when exposed to UV irradiation was studied by Ramani and Ranganathaiah [9]. Degradation
of mechanical properties due to recycling and reuse of ABS polymer was observed by
Rosteguiet all[10]. The impact resistance of ABS was greatly affected by the temperature of
thermal aging [11]. The impact resistance decreases dramatically beyond a critical aging time
at a certain temperature and this reduction depends on surface property modifications during
aging. Thermal stability of ABS is augmented with the addition of Carbon Black. The Addition
of carbon black significantly reduces the degradation effect due to high temperature exposures
[12, 13]. Halloysite nanotubes were filled in the blends of polypropylene and ABS to enhance
the thermal stability of the polymer composites. An optimum weight fraction of these fillers
yield notable refinement in tensile strength, tensile modulus and impact strength [14]. The
influence of nanoclay weight fraction in ABS and process parameters of injection molding on
mechanical properties and structural properties were studied by Mamaghani et all [15].
Acrylonitrile–butadiene–styrene (ABS) and tin sulfide (SnS) nano composites were fabricated
and the influence of SnS inorganic phase in ABS on thermal properties of nanocomposites was
investigated [16]. Addition of SNS shifts the decomposition temperatures towards higher side.
Addition of single walled carbon nanotubes destabilizes ABS and starts degradation at lower
temperatures [17]. The effect of organo montmorillonite (OMMT) inclusions in
ABS/polyamide 6 (PA6) blends on the morphology and mechanical properties was reported by
Wei yan et al [18]. Flexural and tensile properties of PA6/ABS nanocomposites were found to
increment with OMMT loading whereas their hardness decreased with OMMT loading. The
impact strength of ABS Carbon black composites decreases greatly by carbon black loading
[19]. However heat stability of ABS/Carbon compounds increases with CB content.
Acrylonitrile-Butadiene-Styrene Copolymer/nanoclay composites were prepared and tested to
study the effect of nanoclay modifications with TSS (tetrasulfane). Thermal degradation
temperatures of the composite rose to a higher temperature and an exponential increase in
tensile strength and elongation at break and moderate increase in stiffness was observed [20].
Increase in both strength and ductility of the composite is the most desired existence for
engineering applications.
Many researchers reported the degradation of the mechanical properties due to thermal
aging of ABS. Thermal aging of ABS and its composites reduces its tensile and flexural
properties. The effect of thermal aging on fatigue behavior of ABS is scarce. The influence of
nano sized particles in ABS matrix on thermal aging behavior with reference to mechanical
properties, degradation temperatures/thermal stability were broadly reported. However the
works on fatigue behavior of ABS polymer nanocomposites and the effect of nano particle
inclusions on fatigue properties of ABS/nanocomposites are seldom found.
The present work is aimed to study the degradation of mechanical properties and fatigue
behavior of ABS nanocomposites due to thermal aging. The role of nanoclay inclusion on
improvement of these properties is also discussed.
Pydi Hari Prasadarao,H.Ravisankar and V Chittaranjan Das
http://www.iaeme.com/IJMET/index.asp 681 [email protected]
2. MATERIALS AND METHODS:
Acrylonitrile Butadiene Styrene (ABS) supplied by Allied agencies, Hyderabad, India and
Nanoclay obtained from Nanoshell, Mumbai, India.
2.1 Sample Fabrication
ABS thermoplastic nanoclay composite specimens for tensile and fatigue tests are fabricated
by melt compounding method by a twin screw extruder followed by injection moulding.
Required quantity of Acrylonitrile Butadiene Styrene (ABS) dried in a vacuum oven for 12
hours at 600C for removal of moisture presence, if any. Acrylonitrile butadiene styrene granules
were mixed extensively with different nanoclay weight fractions (0.5%, 1%, 3% and 5%) using
a high speed mechanical mixer. Before it is fed to the twin screw extruder, a small quantity of
paraffin (approximately 3% by weight of nanoclay) is added to ABS granules. Along the barrel
a temperature of 2300C was set during the construction of the samples and speed of the screw
was set to 100 rpm. The wires of the circular cross section were drawn from the twin screw
extruder pass through the water bath for the ensuing cooling. Wires obtained from the twin
screw extruder were cut into pallets for feeding the injection moulding machine. The moisture
gain, during its passage, through the water bath, was separated by preheating the pallets for 12
hours at 600C in oven. Tensile specimens of dumbbell shape (105x10x4mm) as per ASTM -
D638 were fabricated by vertical spindle injection moulding machine. A fill and cooling times
were set, 10 sec and of 20 sec respectively, with 150 Mpa moulding pressure at pre-specified
temperature.
2.2 Thermal Aging
All varieties of ABS samples are exposed to a constant temperature of 1000C for 24 hours in a
hot air oven to study the effect of thermal aging on tensile and fatigue behavior. After 24 hours
exposure specimens were eradicated from the oven and cooled to room temperature for further
studies.
2.3 Morphology
The level of dispersion of nanoclay in the polymer matrix affects the properties of the nanoclay
composites. To study the dispersion level of nanoclay, fracture surfaces of tensile specimen
were used as scanning electron microscope (SEM) specimens. Morphology studies were carried
out using Zeiss EVO MA15 SEM with an acceleration voltage of 10kv. Samples were sputter
coated with gold before they exposed to SEM as the considered polymers are not conductive.
2.4 Tensile Testing
Tensile tests were carried out on ABS nanoclay composite specimens before and after thermal
aging using Instron 8801.ASTM: D638 standards were adopted with a cross head speed of 1
mm/min during the test.
2.5Fatigue Testing
Fatigue tests were conducted on ABS specimens before and after thermal exposure using
Instron 8801 fatigue testing machine. Tensile-Tensile mode was adopted for fatigue tests to
avoid additional fixtures for preventing buckling in case of tensile compressive mode. An
amplitude ratio� =��������� ���
������ ���= �. � and a stress ratio R=
�������� ���
�������� ���,= 0.1 were
set during the test. Maximum amplitude 0.7 times of the ultimate tensile strength was chosen
initially and the number of cycles before the fatigue damage was recorded. Fatigue life was
Thermal Aging Influence on Mechanical Properties and Fatigue Behavior of Acrylonitrile
Butadiene Styrene Thermoplastic Polymer Nanoclay Composites
http://www.iaeme.com/IJMET/index.asp 682 [email protected]
recorded by gradually decreasing the amplitude stress (0.6, 0.5, 0.4 times of their respective
ultimate tensile strength). 10Hz of frequency was set during the fatigue test.
3. RESULTS AND DISCUSSIONS
3.1 Morphology
Fracture surfaces of ABS nanoclay composite tensile specimens were tested by scanning
electron microscopy (SEM) to study the dispersion level of nanoclay in the polymer matrix.
Some significant SEM images of ABS before and after thermal aging are presented in Fig.1-
2.It is understood that the fabrication process adopted for developing polymer nanocomposites
is able to get good dispersion of nanoclay in the polymer matrix. No noteworthy agglomerations
were found. Thermal aging of ABS thermoplastic polymer at 1000C for 24 hours has no notable
impact on morphology. Fading of color can be noticed at some portion may be at the initial
stage of degradation due to thermal aging. Any abnormal distortions of nanoclay particle are
not noticed due to thermal aging.
Figure 1 Neat Acrylonitrile Butadiene Styrene before and after thermal aging
Figure 2 ABS before and after thermal aging at 3% of inclusions of nanoclay
3.2 Tensile properties
Stress strain curves obtained during test on thermal aged and unaged specimens of all the ABS
nanoclay composites are reported in Fig 3. The influences of the curves are subsequently
reported in Fig 4. It can be reasoned that tensile properties of ABS enhances monotonically
with nano clay additions. Tensile strength of ABS enhances by 25% at 5% nano clay loading.
Similar trend was observed in the case of stiffness. An increment in tensile modulus of 20%
Pydi Hari Prasadarao,H.Ravisankar and V Chittaranjan Das
http://www.iaeme.com/IJMET/index.asp 683 [email protected]
was observed at 5% loading of nanoclay in ABS. The load transfers one region to another region
in the ABS polymer via interfaces of nanoclay particles. Larger surface area is available at
higher percentage of nanoclay additions and even distribution of the load in the matrix may be
the reason for reporting high strength and stiffness. The movement of polymer chains, which is
restricted by the nanoclay particles, may be also a reason for this enhancement.
Results revealed that thermal aging increases the percentage of elongation at the break and
decrease tensile strength and tensile modulus for virgin thermoplastics. It is reported that the
reduction in tensile strength and modulus of ABS due to thermal aging is 20% and 13 %
respectively. Similarly the reduction of these properties is 7% and 5%, respectively at 5%
loading of nanoclay in ABS. Significant reduction is observed, in tensile properties, of virgin
ABS due to thermal aging. However, this proclivity of reduction in tensile properties can be
restricted with addition of nanoclay. Thermal aging may not affect the nanoclay particles, and
therefore, it might be the reason for reducing the decreasing tendency of tensile strength. It can
be noticed that thermal aging has no significant effect on tensile modulus.
Strain %
0 5 10 15 20
Str
es
s ,
MP
a
0
10
20
30
40
Pure ABS
0.5% Nanoclay
1% Nanoclay
3% Nanoclay
5% Nanoclay
Strain %
0 5 10 15 20
Str
es
s ,
MP
a
0
10
20
30
40
Pure ABS After Aging
0.5% Nanoclay after Aging
1% Nanoclay after Aging
3% Nanoclay after Aging
5% Nanoclay after Aging
Figure 3 Stress-Strain response of ABS Nanoclay Composites Before and After Thermal Aging
Nanoclay weight %0 0.5 1 3 5
Te
ns
ile S
tre
ng
th,
Mp
a
0
10
20
30
40
UTS Before aging
UTS After Thermal aging
Nanoclay Weight %
0 0.5 1 3 5
Te
ns
ile M
od
ulu
s ,
MP
a
0
200
400
600
800
1000
1200
1400
1600
Tensile Modulus Before Aging
Tensile Modulus After Thermal Aging
Figure 4 Tensile Strength and Tensile Modulus ABS Nanoclay Composites
Thermal Aging Influence on Mechanical Properties and Fatigue Behavior of Acrylonitrile
Butadiene Styrene Thermoplastic Polymer Nanoclay Composites
http://www.iaeme.com/IJMET/index.asp 684 [email protected]
3.3 Fatigue behavior
Thermal aging effect on fatigue behavior of ABS polymer nanocomposites is studied by
conducting fatigue tests on thermal aged and unaged specimens. Fig 5 reported the fatigue
behavior of ABS nanoclay composites before and after thermal aging, Fatigue life of ABS
nanoclay composites enhances with the weight fraction of nanoclay. It can be observed that
fatigue life of ABS thermoplastic polymer decreases due to thermal aging. Decrease in life of
ABS without nanoclay inclusion is noticed around 23% due to thermal aging. Whereas at 5%
of nanoclay inclusions the decrement in fatigue life of ABS nanoclay composite due to thermal
aging is found to be only 8% . It is evident that nanoclay additions reduce the decrement in the
fatigue life due to thermal aging. This reduction in decrement of fatigue life of nanoclay
included ABS may be due to higher thermal stability of nanoclay. It is reported that the fatigue
life of thermal aged ABS nanoclay composites increases with nanoclay weight fractions.
Fatigue life of ABS thermally aged nano composites at 5 % nanoclay additions by weight,
subjected a maximum stress of 0.7 times its ultimate tensile stress increases around 50%. It is
observed (Fig 5) that for same stress level the fatigue life of nanocomposites increases with
weight fraction of nanoclay.
Life, number of cycles
1e+5 1e+6 1e+7 1e+8
Ma
imu
m S
tre
ss
Am
plit
ud
e,
MP
a
10
12
14
16
18
20
22
24
26
28
0% nano clay
0.5% nano clay
1% nano clay
3% nano clay
5% nano clay
ABS
Life, Number of Cycles
1e+5 1e+6 1e+7 1e+8
Ma
xim
um
Str
ee
ss
Am
pit
ud
e ,
MP
a
8
10
12
14
16
18
20
22
24
26
Pure ABS after Aging
0.5% Nanoclay after Aging
1% Nanoclay after Aging
3% Nanoclay after Aging
Pure ABS after Aging
Figure 5 S-N curves for ABS nanoclay composites before and After Thermal Aging
4. CONCLUSIONS:
In the present study, ABS thermoplastic polymer nanocomposites with nanoclay inclusions
were fabricated by melt compound method and exposed to higher temperature to study thermal
aging behavior. Tensile and fatigue tests were conducted on aged and unaged specimens.
Thermal aging has a significant influence on tensile strength and fatigue properties of
nanocomposites. Addition of nanoclay enhances its tensile and fatigue properties of
nanocomposites and reduces the damage due to thermal aging. An increase of 50 % of fatigue
life of ABS nanoclay composites was observed at 5% nanoclay loading when subjected to 0.7
times of its ultimate tensile strength.
Pydi Hari Prasadarao,H.Ravisankar and V Chittaranjan Das
http://www.iaeme.com/IJMET/index.asp 685 [email protected]
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