Thermal Aging Influence on Mechanical Properties and Fatigue Behavior of Acrylonitrile Butadiene Styrene Thermoplastic Polymer Nanoclay Composites

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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://iaeme.com/Home/issue/IJMET?Volume=9&Issue=10 ISSN Print: 0976-6340 and ISSN Online: 0976-6359

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://iaeme.com/Home/issue/IJMET?Volume=9&Issue=10

http://iaeme.com/Home/journal/IJMET 679 [email protected] 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.

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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 2300 C 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

http://iaeme.com/Home/journal/IJMET 681 [email protected] Thermal Aging Influence on Mechanical Properties and Fatigue Behavior of Acrylonitrile Butadiene Styrene Thermoplastic Polymer Nanoclay Composites 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%

http://iaeme.com/Home/journal/IJMET 682 [email protected] Pydi Hari Prasadarao,H.Ravisankar and V Chittaranjan Das 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.

40 40

30 30 a

Pure ABS P

, 0.5% Nanoclay ,

20 20 s

1% Nanoclay s

r 3% Nanoclay t r

S 5% Nanoclay

S Pure ABS After Aging 0.5% Nanoclay after Aging 1% Nanoclay after Aging 10 10 3% Nanoclay after Aging 5% Nanoclay after Aging

0 0 0 5 10 15 20 0 5 10 15 20 Strain % Strain %

Figure 3 Stress-Strain response of ABS Nanoclay Composites Before and After Thermal Aging

40 1600 UTS Before aging Tensile Modulus Before Aging UTS After Thermal aging 1400 Tensile Modulus After Thermal Aging

30 1200 a

M ,

1000

h u t

n d 800

e 20 o

r t

e l e i 600 l i s s n

n e

T T 10 400

200

0 0 0 0.5 1 3 5 0 0.5 1 3 5 Nanoclay weight % Nanoclay Weight %

Figure 4 Tensile Strength and Tensile Modulus ABS Nanoclay Composites

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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.

26 28 ABS Pure ABS after Aging 0% nano clay 24 0.5% Nanoclay after Aging

26 a

0.5% nano clay P 1% Nanoclay after Aging

M 22 3% Nanoclay after Aging

1% nano clay P

M 3% nano clay Pure ABS after Aging e

e 5% nano clay

u 20 t d

22 u p t

i l

p 18 A

m 20

A s

s e

16 s e

18 r e t

r t

16 m

m i

i 12 x

14 a a

M M 12 10

10 8 1e+5 1e+6 1e+7 1e+8 1e+5 1e+6 1e+7 1e+8 Life, number of cycles Life, Number of Cycles 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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