Constitutive Modeling Of Softening In Swollen Elastomers Under Long Term Cyclic Loading.

CONSTITUTIVE MODELING OF SOFTENING IN SWOLLEN

ELASTOMERS UNDER LONG TERM CYCLIC LOADING

HAIRUL EFFENDY AB MAULOD

FACULTY OF ENGINEERING

UNIVERSITI OF MALAYA

CONSTITUTIVE MODELING OF SOFTENING IN

SWOLLEN ELASTOMERS UNDER LONG TERM

CYCLIC LOADING

HAIRUL EFFENDY AB MAULOD

SUBMITTED TO THE FACULTY OF ENGINEERING

UNIVERSITY OF MALAYA, IN PARTIAL

FULFILMENT OF THE REQUIREMENT FOR THE

DEGREE OF MASTER OF ENGINEERING

(MATERIALS AND TECHNOLOGY)

2015

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UNIVERSITI MALAYA

ORIGINAL LITERARY WORK DECLARATION

Name of Candidate: Hairul Effendy Bin Ab Maulod (I.C./Passport No.: 810618-14-5733) Registration/Matrix No.: KGG120009

Name of Degree: The Degree of Master of Engineering

Title of Project Paper/Research Report/Dissertation/Thesis (“this Work”): Constitutive Modeling of Softening in Swollen Elastomers under Long Term Cyclic Loading

Field of Study: Mechanical Aspect of Polymer

I do solemnly and sincerely declare that: (1) I am the sole author/writer of this Work; (2) This work is original;

(3) Any use of any work in which copyright exists was done by way of fair dealing and for permitted purposes and any excerpt or extract from, or reference to or reproduction of any copyright work has been disclosed expressly and sufficiently and the title of the Work and its authorship have been acknowledged in this Work;

(4) I do not have any actual knowledge nor ought I reasonably to know that the making of this work constitutes an infringement of any copyright work;

(5) I hereby assign all and every rights in the copyright to this Work to the University of Malaya (“UM”), who henceforth shall be owner of the copyright in this Work and that any reproduction or use in any form or by any means whatsoever is prohibited without the written consent of UM having been first had and obtained;

(6) I am fully aware that if in the course of making this Work I have infringed any copy- right whether intentionally or otherwise, I may be subject to legal action or any other action as may be determined by UM.

Candidate’s Signature Date

Subscribed and solemnly declared before,

Witness’s Signature Date

ii

ABSTRACT

Nowadays, engineering rubber components such as gasket, seals, bumpers, cushions and tubing are essential in mechanical operations due to their simple yet efficient solution for various engineering problems. This is due to its properties such as hyperelasticity, high strain and resilience. Unfortunately, the urge of the market for biodiesel and organic based lubricants jeopardize the life of engineering rubber products due to susceptibility of rubber components to swell under organic solutions especially those served under dynamic forces as in automotive engines and machine tools. Existing models are insufficient to explain behaviour of swollen rubber filled components. Rubbers were immersed in both biodiesel and conventional diesel until reaching 5% swelling percentage. Afterwards the rubbers underwent multiaxial cyclic load until failure with two different elongation percentage which is 75% and 100% elongation. From the peak stress values obtained of corresponding cyclic load, a fitting plot was done to ascertain the suitability of the model with experimental values. Two models were considered based on previous study of modelling swollen elastomers. Computer software MATLAB was used to determine better fit achieved between the two models. The relationship between interaction parameter χ, swelling percentage with the coefficient of the models were also studied. Adjustments were done on the coefficients in order to achieve a suitable numerical relationship between interaction parameter χ and swelling percentage Js with model’s coefficients. The model was then plotted against the experimental values. Validation of the model was achieved from the good coefficient of determination R2 _achieved.

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ABSTRAK

Masa kini, komponen kejuruteraan getah seperti gasket, pemeterai, bampar, kusyen dan tiub adalah penting dalam operasi mekanikal disebabkan penyelesaiannya yang mudah untuk pelbagai permasalahan kejuruteraan. Ini disebabkan oleh sifat-sifatnya seperti hiperelastik, terikan tinggi dan tahan daya. Namun, kehendak pasaran untuk biodiesel dan pelincir berasaskan organik membahayakan hayat produk kejuruteraan getah kerana komponen getah terdedah untuk membengkak dengan cecair organik terutamanya yang melalui beban dinamik dalam enjin otomotif dan peralatan mesin. Model yang terdapat sekarang tidak cukup untuk mewakili komponen terisi getah yang membengkak. Getah direndam di dalam kedua-dua biodiesel dan diesel konvensional sehingga mencapai 5% peratusan membengkak. Kemudian getah menjalani beban berkitar berbilang paksi sehingga gagal dengan dua peratusan pemanjangan berbeza iaitu 75 dan 100% peratusan pemanjangan. Daripada tegasan puncak kitaran yang tersebut, satu plot penyesuaian untuk menentukan kesesuaian model dengan nilai eskperimen. Dua model dikenalpasti dan dipilih berdasarkan kajian sebelum ini berkenaan elastomer membengkak. Perisian komputer MATLAB telah digunakan untuk menentukan penyesuaian yang lebih baik di antara kedua-dua model. Hubungan antara parameter interaksi χ, peratusan membengkak Js dan pekali model juga telah dikaji. Perubahan terhadap pekali telah dilakukan untuk mencapai hubungan berangka yang sesuai antara parameter interaksi χ, peratusan membengkak Js dan pekali model. Model kemudian diplot semula dengan nilai eksperimen. Penentusahan model telah dicapai berdasarkan nilai pekali penentuan R2 _{yang baik diperolehi.}

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ACKNOWLEDGEMENTS

First and foremost, I would like to express my sincere appreciation to my supervisor, Dr. Andri Andriyana for his consistent supervision and guidance and also patience during my work under him.

I would like to thank also Loo Mei Sze from Department of Mechanical Engineering, University of Malaya (UM). This study would not be complete without your important contributions.

Last but not the least; my utmost gratitude goes to my family, parents Ab Maulod Hamid and Hanimah Hadri, my siblings, Nurulhuda, Hairul Nizam, Khairul Aiman and Khairul Afiq. I will not be who I am today without their love and support.

A special dedication to my wife Noraiham Mohamad and daughters Nurul Iman and Nur Kasih Qaisara. Your support and understanding and late nights will always be treasured. I pray to Allah because I could not reward all of your sacrifices and may all of us, are always looked upon by Allah’s grace and compassion.

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TABLE OF CONTENTS

ABSTRACT ... ii

ABSTRAK ... iii

ACKNOWLEDGEMENTS ... iv

TABLE OF CONTENTS ... v

LIST OF FIGURES ... vii

LIST OF TABLES ... ix

LIST OF SYMBOLS AND ABBREVIATIONS ... x

INTRODUCTION ... 1

1.1 Research background ... 1

1.2 Objectives ... 3

1.3 Scope of the study ... 3

1.4 Organization of thesis ... 4

LITERATURE REVIEW ... 5

2.1 Potential of Biodiesel ... 5

2.2 Elastomers in automotive applications ... 6

2.2.1 Nitrile Butadiene Rubber ... 10

2.3 Rubber Swelling ... 11

2.4 Fatigue of Swollen Rubber ... 14

2.4.1 Crack nucleation approach ... 16

2.4.2 Crack growth approach ... 17

2.4.3 Mullins effect of Swollen Rubber ... 18

2.4.4 Phenomenological models ... 19

2.4.5 Crystallization of Mullins effect ... 22

2.4.6 Constitutive modelling ... 23

METHODOLOGY ... 26

3.1 Materials and chemicals ... 26

3.1 Specimen geometry ... 27

3.2 Equipments ... 29

3.3 Experimental set up ... 29

RESULTS AND DISCUSSION ... 33

4.1 Peak Stress and normalized peak stress... 33

4.2 Normalized peak stress ... 40

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4.4 Constitutive modelling of swollen elastomers ... 44

4.4.1 Rubber specimens with 75% elongation compared to Model 1 ... 45

4.4.2 Rubber specimens with 100% elongation compared to Model 1 ... 47

4.4.3 Rubber specimens with 75% elongation compared to Model 2 ... 50

4.4.4 Rubber specimens with 100% elongation compared to Model 2 ... 52

4.5 Relationship of Flory-Huggins interaction parameter χ, swelling percentage Js and material properties ... 55

4.6 New fit for Damage parameter d, versus number of cycles ... 64

4.7 Constitutive modelling of swollen elastomers with adjusted values ... 68

CONCLUSION AND RECOMMENDATIONS ... 72

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LIST OF FIGURES

Figure 2.1 Location of weatherstrip parts and hose related parts in a car (Hokusay 2012)

... 10

Figure 2.2 Examples of NBR based products for automotive applications (Gasgoo 2015) ... 11

Figure 2.3 Molecular structure of nitrile butadiene rubber (NBR) ... 11

Figure 2.4 Schematic illustration of rubber swelling where (a) chains of elastomers are cross-linked together (black dots), (b) solvent molecules penetrate the chains and cause the volume to expand, and (c) network is extensively swollen (Treloar 1975). ... 13

Figure 2.5 Representation for (a) Simo’s coinciding loading-unloading response and (b) Miehe’s different loading-unloading response... 20

Figure 3.1 Specimen geometry of rubber specimen... 28

Figure 3.2 Rubber specimen with 20 cent MYR as geometrical reference ... 28

Figure 3.3 Fatigue testing machine ... 29

Figure 3.4 Experimental set up (a) stress-free without any mechanical loading and (b) with twist angle θ and ∆L axial extension (Ch'ng, Andriyana et al. 2013) ... 30

Figure 3.5 Actual experimental set up ready for testing ... 31

Figure 3.6 Flow chart of study ... 32

Figure 4.1 (a) Peak Stress versus number of cycles for dry, B100 and B0 specimens at 0.75 stretch ratio, and (b) Peak Stress versus number of cycles for dry, B100 and B0 specimens at 1.00 stretch ratio. ... 34

Figure 4.2 (a) Peak Stress Ratio versus number of cycles for dry, B100 and B0 specimens at 0.75 stretch ratio, and (b) Peak Stress Ratio versus number of cycles for dry, B100 and B0 specimens at 1.00 stretch ratio. ... 36

Figure 4.3 Representation of percentage of volume change versus immersion times for B100 and B0 by Chai et al(Chai, Verron et al. 2013) ... 38

Figure 4.4 Normalized peak stress ratio for dry, B100 and B0 specimens for 75% elongation ... 41

Figure 4.5 Normalized peak stress ratio for dry, B100 and B0 specimens for 100% elongation ... 41

Figure 4.6 Damage parameter versus number of cycles for 75% elongation. ... 42

Figure 4.7 Damage parameter versus number of cycles for 100% elongation ... 43

Figures 4.8 Damage parameter for (a) Dry specimen (b) B100 specimen and (c) B0 specimens at 75% elongation fitted with Model 1 ... 45

Figure 4.9 Damage parameter for (a) Dry specimen (b) B100 specimen and (c) B0 specimens at 100% elongation fitted with Model 1 ... 47

Figure 4.10 Damage parameter for (a) Dry specimen (b) B100 specimen and (c) B0 specimens at 75% elongation fitted with Model 2 ... 50

Figure 4.11 Damage parameter for (a) Dry specimen (b) B100 specimen and (c) B0 specimens at 100% elongation fitted with Model 2 ... 52

Figure 4.12 Maximum damage, a, versus interaction parameter χ multiply swelling percentage Js 1.05 for 75% elongation with Model 2 ... 55

Figure 4.13 Rate of damage, b, versus interaction parameter χ multiply swelling percentage Js 1.05 for 75% elongation with Model 2 ... 56

Figure 4.14 Maximum damage, a, versus swelling percentage Js 1.05 over squared interaction parameter χ for 75% elongation with Model 2 ... 57

Figure 4.15 Rate of damage, b, versus swelling percentage Js 1.05 over squared interaction parameter χ for 75% elongation with Model 2 ... 58

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Figure 4.16 Maximum damage, a, versus interaction parameter χ multiply swelling percentage Js 1.05 for 100% elongation with Model 2 ... 59 Figure 4.17 Rate of damage, b, versus interaction parameter χ multiply swelling

percentage Js 1.05 for 100% elongation with Model 2 ... 60 Figure 4.18 Maximum damage, a, versus swelling percentage Js 1.05 over squared interaction parameter χ for 75% elongation with Model 2 ... 61 Figure 4.19 Rate of damage, b, versus swelling percentage Js 1.05 over squared

interaction parameter χ for 75% elongation with Model 2 ... 61 Figure 4.20 Damage parameter for dry specimens at 75% elongation fitted with Model 2 ... 64 Figure 4.21 Damage parameter for B100 specimens at 75% elongation fitted with Model 2 ... 65 Figure 4.22 Damage parameter for B0 specimens at 75% elongation fitted with Model 2 ... 65 Figure 4.23 Damage parameter for dry specimens at 100% elongation fitted with Model 2 ... 66 Figure 4.24 Damage parameter for B100 specimens at 100% elongation fitted with Model 2 ... 66 Figure 4.25 Damage parameter for B0 specimens at 100% elongation fitted with Model 2 ... 67 Figure 4.26 Constitutive modelling for fatigue of dry rubber specimen undergone 75% elongation ... 69 Figure 4.27 Constitutive modelling for fatigue of swollen rubber specimen in 100% biodiesel (B100) undergone 75% elongation ... 69 Figure 4.28 Constitutive modelling for fatigue of swollen rubber specimen in

conventional diesel (B0) undergone 75% elongation ... 70 Figure 4.29 Constitutive modelling for fatigue of dry rubber specimen undergone 100% elongation ... 70 Figure 4.30 Constitutive modelling for fatigue of swollen rubber specimen in 100% biodiesel (B100) undergone 100% elongation ... 71 Figure 4.31 Constitutive modelling for fatigue of swollen rubber specimen in

ix

LIST OF TABLES

Table 2.1 Advantages and disadvantages of several type of rubbers. ... 8

Table 2.2 Summary of phenomenological models ... 21

Table 3.1 Nomenclature of the samples and its description... 26

Table 3.2 Analysis of biodiesel ... 27

Table 4.1 Treated data of rubber specimens at 75% elongation fitted with Model 1 ... 47

Table 4.2 Treated data of rubber specimens at 100% elongation fitted with Model 1 ... 49

Table 4.3 75% and 100% elongation curve fit data with Model 1 ... 49

Table 4.4 Model 1 and 2 comparison of fit data for 75% elongation ... 51

Table 4.5 Models 1 and 2 comparison of fit data for 100% elongation ... 54

Table 4.6 Material parameters acquired from fitting Model 2 with equation (4.9) and equation (4.10) ... 63

Table 4.7 Coefficient of determination, R2 _{values for Damage parameter d, versus} number of cycles fitted with Model 2 ... 67

x

LIST OF SYMBOLS AND ABBREVIATIONS

B0 Designation for diesel

B100 Designation for biodiesel

CB Carbon Black

CR Chloroprene rubber

Dry Dry unswollen specimen

EG Expanded graphite

∆M Mass change (gms)

Js swelling percentage

NBR Nitrile butadiene rubber

SBR Styrene butadiene rubber

SW1 5% swelling of NBR specimen in B100 Blend

1

INTRODUCTION 1.1 Research background

History has shown that modern human civilization depends on fossil fuels. Starting with coal as a source of energy, then petroleum and its derivatives have brought about major and significant progress in modern evolution.

Biofuels are hailed by its proponents as the best replacement for petroleum and counter environmental issues that come with the usage of petroleum based fuels (Mangla, Ravi et al. 2013). Specifically, biodiesels are a promising alternative to fossil based diesel fuel. It could still maintain performance with lower cost. Any proportions between conventional diesel and biodiesel can be used on existing diesel engine or just by itself.

Malaysia itself acknowledges the emerging importance of this commodity and that the government tabled a strategic plan to further boost its demand in the market (Pakiam 2014)

Biodiesel is defined as long-chain monoalkylic esters mixture obtained from renewable sources either vegetables or animals. Currently, biodiesel is synthesized from sunflower, corn olive and soybean oil (Haseeb, Fazal et al. 2011), palm oil and milkweed oil (Vaughn and Holser 2007, Jakeria, Fazal et al. 2014, Phoo, Razon et al. 2014). Its unique ester molecules give the flammability characteristic approaching the conventional diesel (Jakeria, Fazal et al. 2014). The renewability of its sources guarantee the biodegradability, non-toxicity, reduction in exhaust emission, high flash point (minimum 100°C) and high compatibility with conventional diesel fuel (Jakeria, Fazal et al. 2014). The advantages make it the most promising alternative for fuel regardless its disadvantages such as low calorific value, high freezing point and high nitrous oxide emissions relative to

2

conventional diesel. However, the biggest concern of biodiesel utilization which limit its application is their ability to degrade plastic and rubber components due to its solvents-like behaviour (Jakeria, Fazal et al. 2014). This is crucial since more than half of vehicle’s components are polymeric based. The difference between conventional diesel and biodiesel lies in its resources. The conventional diesel is obtained from crude oil and process at different heating temperature through petroleum refining process. Biodiesel on the other hand, is obtained from natural feedstock and consists of mainly 16 to 18 carbon atoms (Haseeb, Fazal et al. 2011). The incompatibility issue of biodiesel with current automotive components are explained by several researchers in their report (Chai, Andriyana et al. 2011, Fazal, Haseeb et al. 2011, Haseeb, Fazal et al. 2011, Jakeria, Fazal et al. 2014).

Elastomers in their unfilled state, do not have good mechanical properties for engineering application (Mars and Fatemi 2002, Mostafa, Abouel-Kasem et al. 2009). Fillers also improve wear resistance and open more possibility for applications (Wang, Zhang et al. 2012). Carbon black fillers are the most commonly used reinforcing fillers and it imparts important mechanical properties on rubber(Donnet and Custodero 2013).

As mentioned, the challenge of biodiesel has been its solvent-like property and coupled with engineering rubber components poses a challenge to the automotive industry for widespread acceptance. Adding to this is the fact that well established studies on fatigue or cyclic load of rubber are often in their dry state (Mars and Fatemi 2002, Chai, Andriyana et al. 2013). Modelling the response of rubber that mimics its final application will offer tremendous value to the industry in helping not only predict the reliability of their product but also offer insight to designing better products.

3

1.2 Objectives

The objectives of this study can be outlined as the following;

i. To investigate the mechanical response long term cyclic loading of swollen rubber

ii. To investigate the effect of different biodiesel blend and stretch ratio on the mechanical response

iii. To constitute a model that could satisfactorily explain the response of swollen rubber under long term cyclic loading

1.3 Scope of the study

NBR is the common choice of material used for automotive’s fuel transport system (Linhares, Corrêa et al. 2013). NBR has better swelling resistance to fluorocarbon compared to natural rubber (Sirisinha, Baulek-Limcharoen et al. 2001). Biodiesel presents itself as a relevant research subject and ongoing research of compatibility between elastomer and biodiesel is still active. The swelling percentage in this study is 5% and initial results collected based on peak stress response of NBR after 1.75 and 2.00 stretch ratios.

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1.4 Organization of thesis

This dissertation has been organized into 5 chapters. Chapter 1 introduces the rationale of current study on alternative fuels. It discusses the challenges of current research have to undertake. The scope and objectives are also presented

Chapter 2 begins on the literature background of this study. It discusses on engineering rubber components in automotive industry, biodiesel significance in Malaysia, elastomers and NBR, fatigue and Mullins effect and also swollen phenomena of rubber.

Chapter 3 then present the methodology of the study conducted. Chapter 4 then continues with result and discussion of the study. Chapter 5 finally conclude and also future recommendation of this study.

5

LITERATURE REVIEW

Transportation is a crucial industry which demands better and greener solutions in every inches of its aspect whether physically, mechanically, electrically and etc. Various researchers across the world spent money, energy and time to develop better and innovative solutions every day. One of the biggest necessities which guarantee the sustainability of vehicles is fuel. Without affordable fuel, vehicles may limit the usage for only high and middle income community.

2.1 Potential of Biodiesel

Biodiesel is a promising alternative for future greener and low cost fuel compared to fossil fuel based diesel. Biodiesel application could maintain the performance of fossil based diesel with better reduction in prices. It can be used at any proportions with existing diesel or by itself on any standard diesel engines.

Malaysia is blessed with various commercial natural resources such as rubber tree, palm oil, sugarcane, paddy and etc. It is the world’s second largest producer of palm oil after Indonesia. Due to large scale production of palm oil, Malaysian government had come up with a strategic plan to manufacture the palm-based biodiesel and help to boost its demand in the market (Pakiam 2014).

Biodiesel is defined as long-chain monoalkylic esters mixture obtained from renewable sources either vegetables or animals. Currently, biodiesel is could be synthesized from sunflower, corn olive and soybean oil (Haseeb, Fazal et al. 2011), palm oil and milkweed oil (Vaughn and Holser 2007, Jakeria, Fazal et al. 2014, Phoo, Razon et al. 2014). Its unique ester molecules, gives it its flammability characteristic approaching conventional diesel (Jakeria, Fazal et al. 2014). The renewability of its sources guarantee the biodegradability,

non-6

toxicity, reduction in exhaust emission, high flash point (minimum 100°C) and high compatibility with conventional diesel fuel (Jakeria, Fazal et al. 2014). The advantages makes it the most promising alternative for fuel despite its disadvantages such as low calorific value, high freezing point and high nitrous oxide emissions relative to conventional diesel. However, the biggest concern of biodiesel utilization which limit its application is their ability to degrade plastic and rubber components due to its solvents-like behaviour (Jakeria, Fazal et al. 2014). This is crucial since more than half of vehicle’s components are polymeric based. The difference between conventional diesel and biodiesel lies in its resources. The conventional diesel obtained from crude oil and process at different heating temperature through petroleum refining process. Biodiesel on the other hand, is obtained from natural feedstock and consists of mainly 16 to 18 carbon atoms (Haseeb, Fazal et al. 2011). The incompatibility issue of biodiesel with current automotive components are explained by several researchers in their report (Chai, Andriyana et al. 2011, Fazal, Haseeb et al. 2011, Haseeb, Fazal et al. 2011, Jakeria, Fazal et al. 2014).

2.2 Elastomers in automotive applications

Elastomer is a class of materials which exhibits low Young’s modulus with extremely high strain rate to failure. The term “elastomer” is used interchangeably with “rubber”. The properties of elastomers are remarkable and unique if compared to any other solid materials. It shows glassy behaviour from its amorphous structure below the glass transition temperature, Tg and exhibits

rubbery behaviour with some degree of crystallinity above the Tg. Due to its

unique properties, rubbers are incredibly versatile material that are used in many applications either domestic, sports gears, automotive or engineering products.

7

Rubbers are classified into two types; either natural or synthethic. Natural rubber in the form of latex is harvested from the Hevea Brasiliensis tree. The presence of double bond in its repeating units increases its reactivity towards vulcanization and ozonation. After vulcanisation the long polymers of natural rubber are interlinked by sulphur compounds. The chains between these sulphur crosslinks are essentially a 3D zigzag structure with freely rotating bonds that allow the polymer chains to change their length by coiling or uncoiling. Due to its chemical formulation and structure, natural rubber has exceptionally best elasticity of all rubber types except for butadiene rubber. Furthermore, it shows excellent resistance to abrasion and fatigue. Despite the excellent properties, utilization of natural rubber in high temperature application are limited due to its poor resistance to heat, ozone (weather), oils and fuels. Natural rubber finds its major application as matrix material in vehicle’s tyre due to its excellent resilience once reinforced with carbon black. Moreover, it is mainly used in the production of vibration dampers, springs and bearings. For special purposes it is used in hoses seals, conveyor belts, coated fabrics and other products.

The loss in natural rubber supply from the Southeast Asia region due to World War II spurred the development of synthetic rubbers (ICIS 2008, Budinski and Budinski 2010). In addition, the development of automobile industry increases the demands for rubber. Enormous attempts were made to produce man-made rubber. Earlier attempt at producing synthetic rubber were inadequate and could not match the properties of natural rubber. The breakthrough came when Ameripol was developed in 1940 and saw the promising breakthrough in cost effective production of synthetic rubber production. As time passed, several rubber types were developed and exhibited properties comparable to natural

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rubber and in some cases surpassed that of the natural rubber. Table 2.1 shows a summary of properties of a few common rubbers in automotive applications

Table 2.1 Advantages and disadvantages of several type of rubbers.

Type Advantages Disadvantages

Natural rubber (NR)

 They have very good mechanical properties such as tensile strength, resist abrasion very well and high strain rate at low stress values

 They can also able to recover easily from applied stress or deformation

 They have poor resistance towards environmental factors such as high temperature, oil and degrade easily due to weathering and ozone exposure

Styrene butadiene rubber (SBR)

 SBR abrasion and aging resistance are better when compared to NR

 It can also withstand deformation longer at short periods and higher temperatures compared to NR

 They have poor resistance when exposed to organics such as oils and fuels  Its tear growth resistance

is lower compared to NR  Flammable

Butyl rubber (IIR)

 IIR have good environmental resistance from weathering or ozone

 It also exhibits good electrical properties and remain stable at low temperatures  Its dampening properties are good against

periodic oscillation

 Despite good dampening properties its resilience is low

 Almost no resistance from organics attacks such as oil or fuels

Ethylene-propylene rubber (EPDM)

 EPDM have excellent resistance to weathering, ageing, ozone, chemicals, hot water/steam and polar solvents such as acetone, methanol or esters; excellent electrical insulating properties

 They also have very good heat resistance, good low temperature properties

 It has fair resistance to aliphatic and aromatic hydrocarbons (mineral oils, gasoline, fuels)

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“Table 2.1 Continued”

Type Advantages Disadvantages

Nitrile rubber (NBR)

 NBR have very good resistance to organics fuels; good mechanical strength; good compression set properties

 It exhibits good properties in terms of mechanical strength and compression strength

 Comparing to SBR, NBR have better heat resistance

 Its environmental resistance is considered fair

 It can be easily flammable exposed to toxic flue gases Aromatic and polar solvents can degrade NBR

Rubbers elastic and good sealing property makes it ideal for various usage in automotive applications. Three main types of automotive rubber products include weather-strip, hose and seal components. Weather-strip parts fill the space between body and other parts to secure air tightness, thus preventing water, sound and dust from entry. It is also used as shock absorbers for door opening and closing and preventing vibrations. Besides, it has an important function of improving the outside appearance of automobile from an aesthetic point of view. Whereas various functions and performances are required for the so-called hose related parts that are required by the operating environment (inner fluid, surrounding environment, etc.), the installation condition (peripheral part, mating pipe, etc.) and other functions and performances such as internal pressure, etc. The vast rubber based products for weatherstrip and hose parts is summarized in Figure 2.1.

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Figure 2.1 Location of weatherstrip parts and hose related parts in a car (Hokusay 2012) Seals are components to fill the closed spaces that exists between two components being a stationary and moving components. It also helps to prevent any leakage of fluids or lubricants between the components. Its usage is also to prevent harmful contaminant from damaging a machine system. It is a vital component that protects precision constructed components from corrosion or wear.

2.2.1 Nitrile Butadiene Rubber

Nitrile Butadiene Rubber (NBR) or Buna-N is a versatile material due to its structure which has acrylonitrile and butadiene. Its physical and chemical properties depend on the composition of nitrile. It is used extensively in the petroleum and natural gas industries, and in other applications involving water, sewer, carbon dioxide, gasoline, sewer, mineral oil, and vegetable oil due to its excellent resistance to these species. Among other synthetic rubbers, NBR is widely used in vehicle due to its resistance to swelling when immersed in petroleum fuels and oils. The components made out of NBR are gasket, fuel and oil hoses and seals.

Door weatherstrip

Sliding roof Glass run

Rear window weatherstrip Weatherstrip- trunk lid

Locker seal Drain hose

Fuel hose Weatherstrip- rear door quarter panel Air hose

Front windshield weatherstrip Cushion, instrument panel Ventilation hose

Water hose Hood seal Protector (radiator grill) Seal, headlight

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Figure 2.2 Examples of NBR based products for automotive applications (Gasgoo 2015)

NBR’s ability to resist swelling of fluorocarbon is superior when compared to natural rubber (Sirisinha, Baulek-Limcharoen et al. 2001). It is the reason that it is often considered for application that involves immersing in oil or fuel. Figure 2.1 shows the molecular structure of NBR.

Figure 2.3 Molecular structure of nitrile butadiene rubber (NBR)

2.3 Rubber Swelling

Polymer stability and dissolution in different media including of hydrocarbon based is an important area of interest in polymer science and engineering because of its vast applications in industry (Miller-Chou and Koenig 2003, Makitra, Midyana et al. 2011). There are cases where polymer based components are exposed to oil contamination risk (Hanley, Murphy et al. 2008). This is the reason of intensive investigations on swelling and dissolution

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behaviours of polymers especially for rubber over almost a hundred years (Miller-Chou and Koenig 2003).

Unlike nonpolymeric materials, polymers do not dissolve instantaneously, and the dissolution is controlled by either the disentanglement of the polymer chains or by the diffusion of the chains through a boundary layer adjacent to the polymer–solvent interface (Miller-Chou and Koenig 2003). The difference between swelling and solubilisation is that the former condition exits due to the crosslinks maintaining the integrity of the polymer network. The solvent’s forcing itself into the polymer network and the network’s resistance balance out each other towards expansion. The compatibility between rubber and solvent is an important factor which determines the swelling effect due to its mismatch components. The performance of a rubber part may be severely compromised if the rubber and the fluid are compatible in terms of swelling potential. According to Hanley (Hanley, Murphy et al. 2008), the compatibility depends on a number of variables such as 1) fillers and plasticisers, 2) rubber molecule structure, 3) selective swelling action by fluid components, 4) time temperature effects on swelling rates and 5) chemical degradation of the elastomer or fluid.

According to Boonstra cited by Da Costa (Da Costa, Nunes et al. 2001), swelling involves diffusion of relatively small, mobile molecules into a system of chain segments. Though both chain segments and diffusing molecules are different in size, strong valence links and the compatibility of both molecules build into an insoluble three-dimensional network. The diffusion starts at the surface of the rubber where high liquid concentration exists and proceeds to zero concentration at the bulk. Then the molecules beginning at the surface continues into the bulk and as the process continues, rubber component dimension increases

7 Rubbers are classified into two types; either natural or synthethic. Natural rubber in the form of latex is harvested from the Hevea Brasiliensis tree. The presence of double bond in its repeating units increases its reactivity towards vulcanization and ozonation. After vulcanisation the long polymers of natural rubber are interlinked by sulphur compounds. The chains between these sulphur crosslinks are essentially a 3D zigzag structure with freely rotating bonds that allow the polymer chains to change their length by coiling or uncoiling. Due to its chemical formulation and structure, natural rubber has exceptionally best elasticity of all rubber types except for butadiene rubber. Furthermore, it shows excellent resistance to abrasion and fatigue. Despite the excellent properties, utilization of natural rubber in high temperature application are limited due to its poor resistance to heat, ozone (weather), oils and fuels. Natural rubber finds its major application as matrix material in vehicle’s tyre due to its excellent resilience once reinforced with carbon black. Moreover, it is mainly used in the production of vibration dampers, springs and bearings. For special purposes it is used in hoses seals, conveyor belts, coated fabrics and other products.

The loss in natural rubber supply from the Southeast Asia region due to World War II spurred the development of synthetic rubbers (ICIS 2008, Budinski and Budinski 2010). In addition, the development of automobile industry increases the demands for rubber. Enormous attempts were made to produce man-made rubber. Earlier attempt at producing synthetic rubber were inadequate and could not match the properties of natural rubber. The breakthrough came when Ameripol was developed in 1940 and saw the promising breakthrough in cost effective production of synthetic rubber production. As time passed, several rubber types were developed and exhibited properties comparable to natural

8 rubber and in some cases surpassed that of the natural rubber. Table 2.1 shows a summary of properties of a few common rubbers in automotive applications

Table 2.1 Advantages and disadvantages of several type of rubbers.

Type Advantages Disadvantages

Natural rubber (NR)

 They have very good mechanical properties such as tensile strength, resist abrasion very well and high strain rate at low stress values

 They can also able to recover easily from applied stress or deformation

 They have poor resistance towards environmental factors such as high temperature, oil and degrade easily due to weathering and ozone exposure

Styrene butadiene rubber (SBR)

 SBR abrasion and aging resistance are better when compared to NR

 It can also withstand deformation longer at short periods and higher temperatures compared to NR

 They have poor resistance when exposed to organics such as oils and fuels  Its tear growth resistance

is lower compared to NR  Flammable

Butyl rubber (IIR)

 IIR have good environmental resistance from weathering or ozone

 It also exhibits good electrical properties and remain stable at low temperatures  Its dampening properties are good against

periodic oscillation

 Despite good dampening properties its resilience is low

 Almost no resistance from organics attacks such as oil or fuels

Ethylene-propylene rubber (EPDM)

 EPDM have excellent resistance to weathering, ageing, ozone, chemicals, hot water/steam and polar solvents such as acetone, methanol or esters; excellent electrical insulating properties

 They also have very good heat resistance, good low temperature properties

 It has fair resistance to aliphatic and aromatic hydrocarbons (mineral oils, gasoline, fuels)

9 “Table 2.1 Continued”

Type Advantages Disadvantages

Nitrile rubber (NBR)

 NBR have very good resistance to organics fuels; good mechanical strength; good compression set properties

 It exhibits good properties in terms of mechanical strength and compression strength

 Comparing to SBR, NBR have better heat resistance

 Its environmental resistance is considered fair

 It can be easily flammable exposed to toxic flue gases Aromatic and polar solvents can degrade NBR

Rubbers elastic and good sealing property makes it ideal for various usage in automotive applications. Three main types of automotive rubber products include weather-strip, hose and seal components. Weather-strip parts fill the space between body and other parts to secure air tightness, thus preventing water, sound and dust from entry. It is also used as shock absorbers for door opening and closing and preventing vibrations. Besides, it has an important function of improving the outside appearance of automobile from an aesthetic point of view. Whereas various functions and performances are required for the so-called hose related parts that are required by the operating environment (inner fluid, surrounding environment, etc.), the installation condition (peripheral part, mating pipe, etc.) and other functions and performances such as internal pressure, etc. The vast rubber based products for weatherstrip and hose parts is summarized in Figure 2.1.

10 Figure 2.1 Location of weatherstrip parts and hose related parts in a car (Hokusay 2012)

Seals are components to fill the closed spaces that exists between two components being a stationary and moving components. It also helps to prevent any leakage of fluids or lubricants between the components. Its usage is also to prevent harmful contaminant from damaging a machine system. It is a vital component that protects precision constructed components from corrosion or wear.

2.2.1 Nitrile Butadiene Rubber

Nitrile Butadiene Rubber (NBR) or Buna-N is a versatile material due to its structure which has acrylonitrile and butadiene. Its physical and chemical properties depend on the composition of nitrile. It is used extensively in the petroleum and natural gas industries, and in other applications involving water, sewer, carbon dioxide, gasoline, sewer, mineral oil, and vegetable oil due to its excellent resistance to these species. Among other synthetic rubbers, NBR is widely used in vehicle due to its resistance to swelling when immersed in petroleum fuels and oils. The components made out of NBR are gasket, fuel and oil hoses and seals.

Door weatherstrip

Sliding roof Glass run

Rear window weatherstrip Weatherstrip- trunk lid

Locker seal Drain hose

Fuel hose Weatherstrip- rear door quarter panel Air hose

Front windshield weatherstrip Cushion, instrument panel Ventilation hose

Water hose Hood seal Protector (radiator grill) Seal, headlight

11 Figure 2.2 Examples of NBR based products for automotive applications (Gasgoo 2015)

NBR’s ability to resist swelling of fluorocarbon is superior when compared to natural rubber (Sirisinha, Baulek-Limcharoen et al. 2001). It is the reason that it is often considered for application that involves immersing in oil or fuel. Figure 2.1 shows the molecular structure of NBR.

Figure 2.3 Molecular structure of nitrile butadiene rubber (NBR)

2.3 Rubber Swelling

Polymer stability and dissolution in different media including of hydrocarbon based is an important area of interest in polymer science and engineering because of its vast applications in industry (Miller-Chou and Koenig 2003, Makitra, Midyana et al. 2011). There are cases where polymer based components are exposed to oil contamination risk (Hanley, Murphy et al. 2008). This is the reason of intensive investigations on swelling and dissolution

12 behaviours of polymers especially for rubber over almost a hundred years (Miller-Chou and Koenig 2003).

Unlike nonpolymeric materials, polymers do not dissolve instantaneously, and the dissolution is controlled by either the disentanglement of the polymer chains or by the diffusion of the chains through a boundary layer adjacent to the polymer–solvent interface (Miller-Chou and Koenig 2003). The difference between swelling and solubilisation is that the former condition exits due to the crosslinks maintaining the integrity of the polymer network. The solvent’s forcing itself into the polymer network and the network’s resistance balance out each other towards expansion. The compatibility between rubber and solvent is an important factor which determines the swelling effect due to its mismatch components. The performance of a rubber part may be severely compromised if the rubber and the fluid are compatible in terms of swelling potential. According to Hanley (Hanley, Murphy et al. 2008), the compatibility depends on a number of variables such as 1) fillers and plasticisers, 2) rubber molecule structure, 3) selective swelling action by fluid components, 4) time temperature effects on swelling rates and 5) chemical degradation of the elastomer or fluid.

According to Boonstra cited by Da Costa (Da Costa, Nunes et al. 2001), swelling involves diffusion of relatively small, mobile molecules into a system of chain segments. Though both chain segments and diffusing molecules are different in size, strong valence links and the compatibility of both molecules build into an insoluble three-dimensional network. The diffusion starts at the surface of the rubber where high liquid concentration exists and proceeds to zero concentration at the bulk. Then the molecules beginning at the surface continues into the bulk and as the process continues, rubber component dimension increases