THERMAL AGING INFLUENCE ON MECHANICAL ......by melt compounding method by a twin screw extruder followed by injection moulding. Required quantity of Acrylonitrile Butadiene Styrene

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


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


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




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%



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



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




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



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.



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Documents

THERMAL AGING INFLUENCE ON MECHANICAL ......by melt compounding method by a twin screw extruder followed by injection moulding. Required quantity of Acrylonitrile Butadiene Styrene