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Curing Characteristics and Tear Properties of Bentonite Filled Ethylene Propylene Diene (EPDM) Rubber Composites
Available online at www.sciencedirect.com
ScienceDirect Procedia Chemistry 19 (2016) 394 – 400
5th International Conference on Recent Advances in Materials, Minerals and Environment (RAMM) & 2nd International Postgraduate Conference on Materials, Mineral and Polymer (MAMIP), 4-6 August 2015
Curing Characteristics and Tear Properties of Bentonite Filled Ethylene Propylene Diene (EPDM) Rubber Composites Nurus Sakinah Che Mat, Hanafi Ismail*, Nadras Othman School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia
Abstract The effect of bentonite clay loading on curing characteristics and tear strength of bentonite filled ethylene propylene diene monomer (EPDM) composite were studied. Compounding was carried out on two -roll mill and vulcanization was done at 1500C. Torque values, scorch time and optimum cure time of the prepared rubber compound were assessed by using Mosanto Disc Rheometer (MDR 2000). Results indicated that the maximum torque of EPDM/Bt composite decreases at high bentonite loading. Increasing in values with increasing bentonite loading was recorded for minimum torque and optimum cure time of EPDM/Bt composite. The increase is related with the increase in viscosity due to the increasing of bentonite clay loading in EPDM matrix. Scorch time was found to be decreasing up to 30 phr bentonite clay. Results also show that tear strength of EPDM/Bt composite increased with increasing bentonite loading up to 90 phr. The reason is probably due to agglomeration occur causes the reduction in properties at high loading above 90 phr bentonite clay. The scanning electron microscopy (SEM) of tear fracture surface of EPDM/Bt composite illustrated that with increasing bentonite loading up to 90 phr bentonite clay, a better dispersion of bentonite clay is achieved as compared to lower loading, resulting in high tear strength value for EPDM/Bt composite. © Published by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license ©2016 2016The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia. Peer-review under responsibility of School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia Keywords: Ethylene propylene diene monomer; bentonite clay; rubber composites
* Corresponding author. Tel.:+60 4 599 6113; fax: + 60 4 594 1011. E-mail address: [email protected]
1876-6196 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia doi:10.1016/j.proche.2016.03.029
Nurus Sakinah Che Mat et al. / Procedia Chemistry 19 (2016) 394 – 400
Nomenclature NR NBR µm sqm/g h gcm-3 0 C phr mm ISO ASTM N/mm
Natural rubber Nitrile Butadiene rubber micronmeters squaremeters per gram hour gram per centimetre cubic degree celcius part per hundred rubber millimeters International Organization for Standardization American Society for Testing and Material Newton per milimeters
1. Introduction Ethylene propylene diene (EPDM) rubber is a saturated polymer that is mostly known as a rubber that have a greater resistance towards ozone and high temperature as compared to other general purpose rubber. Due to its high performance, EPDM rubber is often used in automotive application, building and construction, cable and wire, also as sheeting and sealing 1. Although EPDM has high resistance towards oxygen, ozone and heat, the strength of unfilled EPDM actually are very poor and therefore, the incorporation of filler is required to increase its strength. The filler is usually added into rubber phase to either reinforce the properties of rubber, reducing the cost of production and/or to ease the processing. Among all the filler used, carbon black is more known thanks to its high reinforcement capability. However, its potential to pollute environment, besides low variety of colour usage, urge the researchers to find other more friendly white filler to be used, which among them is silicate layer clay such as bentonite and montmorillonite (MMT). Bentonite is a naturally occurring rock consisting majorly of MMT, sodium and other minerals such as quartz, feldspar and others. MMT have a structure such that the Aluminium octahedral sheet is sandwiched in between the silica tetrahedral sheet. The thickness of the layer is only 1nm which in between the gap gallery, the exchangeable cations take place. These exchangeable cations are important because it is responsible in altering the properties of the rubber 2. The use of clay in nanocomposite rubber was initiated by Toyota R&D group in 1991 with their nanocomposite based on nylon rubber with MMT clay. The improvement in mechanical properties by the use of MMT clay discovered by Toyota had attract the attention of the researchers and the results are plentiful studies of nanocomposites has been reported 3-5. In order to further understanding the benefit of bentonite, the work was focused on studying the effect of bentonite clay loading on curing characteristics and tear properties of EPDM/Bt composite. 2. Experimental 2.1. Material The material used throughout this study are the same as used by Ismail et al, (2011) 6 (Table 1). EPDM, 778Z purchased from Keltan DSM Elastomers consist of ethylene content of 67%, ENB of 4.3% and ML (1+4) 125 0C of 63MM. Bentonite, Bt was supplied by Ipoh Ceramics (M) Sdn. Bhd. Zinc oxide,ZnO, stearic acid, tetramethyl thiuram dsulphide (TMTD), 2-mercapto benzothiazole (MBT) and sulphur were all obtained from Bayer (M) Ltd. The average particle size and specific surface area of Bt are 5.31µ m and 0.975 sqm/g, respectively and the elemental composition of Bt are as shown in Table 2 6.
Table 1: Compounding formulation of EPDM/Bt composite 6.
395
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Nurus Sakinah Che Mat et al. / Procedia Chemistry 19 (2016) 394 – 400
Composite (phr)
C1
C2
C3
C4
C5
100
100
C6
C7
EPDM
100
100
100
100
100
Bt
0
10
30
50
70
90
120
5
5
5
5
5
ZnO
5
5
Stearic Acid
1.5
1.5
1.5
1.5
1.5
1.5
1.5
MBT
0.8
0.8
0.8
0.8
0.8
0.8
0.8
TMTD
1.5
1.5
1.5
1.5
1.5
1.5
1.5
Sulphur
1.5
1.5
1.5
1.5
1.5
1.5
1.5
Table 2: Elemental compositions of Bt 6. Bentonite Content SiO2 Al2O3 MgO CaO Fe2O3 K2 O Na 2O TiO2 BaO P2O5 SrO MnO ZrO2 SO3 Loss of ignition (LOI)
Amount (%) (w/w) 76.0 15.0 2.7 2.0 2.0 1.2 0.36 0.12 0.061 0.037 0.032 0.029 0.024 0.021 0.416
2.2 Preparation of Bentonite- Filled EPDM Composites Prior to compounding of EPDM rubber with Bt clay, Bt was first dried in vacuum oven at 800C for 24h. The compounding process of EPDM/Bt composite was done by using the same ingredients used by Ismail et al., (2011) as in Table 1 where bentonite clay followed by sulphur were incorporated last 6. A laboratory scale (160mm x 320mm) two roll mill, model XK-160 was used during compounding process. Mosanto Moving Die Rheometer (MDR 2000) was then used to determine the cure characteristics of the rubber compound at 150 0C, in accordance to ISO 3417. The curing time (t 90) obtained from the rheograph was then used to compress rubber compound into sheets. The temperature for the compression moulding used was 150 0C. 2.3 Tear Properties In order to obtain the tear sample for tear test, the rubber compound was compressed using a square mould of 2mm in thickness. The samples were then left at room temperature for at least 6 hours before they were cut into trouser shape. The tear sample was tested using Instron 3366 at room temperature with the crosshead speed of 50mm/min in accordance to ASTM D624. 2.4 Morphological Studies The tear fractured surface of the EPDM/Bt samples from the tear test was observed under Supra-35VP field emission scanning electron microscope (SEM) to determine their surface morphology, shape, dispersion and adhesion. Test specimens were mounted on the aluminium using double-sided sticky tape and then coated with a thin layer of Pd-Au before testing.
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Nurus Sakinah Che Mat et al. / Procedia Chemistry 19 (2016) 394 – 400
3. Results and Discussion 3.1 Curing Characteristics of EPDM/Bt composites
60 a)
40 20 0 0
30
60
90
120
Scorch time,ts2
Optimum cure time, t90
Fig. 1 and 2 both displayed the curing characteristics of vulcanizate EPDM/Bt composite. The optimum curing time of vulcanizate EPDM/Bt increased with increasing Bt loading. The increase was attributed to the adsorption of curative that arise from the presence of hydroxyl group at silicate layer of Bt clay. The similar result was reported by Ansarifar et al, (2000) that also found the curing time of rubber delayed as the amount of silica increased. The presence of hydroxyl group was reported able to disrupt the vulcanization process and resulted in the increase in curing time and scorch time 7. Scorch time of EPDM/Bt composites shows increasing trend with increasing amount of Bt only after incorporation of 30 phr Bt clay. At lower loading, a slight decrease in scorch time was probably due to high surface area of Bt that promotes better heat distribution in rubber system. 15 b)
10 5 0 0
Bt clay loading, phr
30
60
90
120
Bt clay loading, phr
Fig. 1. (a) Optimum cure time, t 90 ;(b) scorch time, t s2 of EPDM/Bt composites at different Bt loading.
With incorporation of Bt clay increased the viscosity of EPDM/Bt composite. This is as shown by the increase in minimum torque with increasing Bt content. Increased in viscosity is known indicated for a decrease in molecular movement of rubber that was resulted from the increase amount of Bt content in rubber. With increased viscosity high shear forces are therefore needed to rotate the rotor during vulcanization process. Figure 3b shows that the maximum torque value can be seen to be increasing up to 90 phr Bt clay, supporting the expectation that the increased of filler increased the stiffness of rubber, consequently increased the torque value recorded. A decrease above 90 phr was probably due to the presence of weak EPDM-Bt interaction in the composite. b)
6 4 2 0 0
30
60
90
Bt clay loading, phr
120
Maximum Torque, MH
Minimum torque, ML
a) 8
20 15 10 5 0 0
30
60
90
120
Bt clay loading, phr
Fig. 2. (a)Minimum torque, ML ;(b) maximum torque, MH of EPDM/Bt composites at different Bt loading.
3.2 Microstructure of Bentonite Morphological studies were conducted by subjected rubber samples under SEM at certain magnification. In order to determine the shape and clearly see the surface of bentonite filler, SEM was conducted at different magnification as shown in Fig. 3(a) and 3(b). From Fig. 3(a), it can be seen that bentonite is in the form of
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Nurus Sakinah Che Mat et al. / Procedia Chemistry 19 (2016) 394 – 400
irregular shape. By increasing magnification to 6050x, bentonite surface was actually consisting of pores and voids. These voids and pores are believed able to reinforce properties of EPDM/Bt composite. This is arising from the entrapment of filler at the voids and pores of bentonite that can increase the interaction between rubber and filler.
Fig. 3. SEM micrograph of Bt particles at (a) 1000x ;(b) 6050x magnification.
3.3 Tear Properties
Tear strength, N/mm
Fig. 4 shows the tear strength of EPDM/Bt composite as amount of Bt clay increased. It was found that according to Fig. 4, tear strength increased with increasing Bt up to 90 phr loading. This shows that there is an improvement in tear strength with incorporation of Bt clay in EPDM rubber. The improvement was probably resulted from the molecular chain of EPDM rubber that can orient in the direction of strain upon loading8. The ability to orient and slip around the clay was probably arising from the good interaction between EPDM rubber and Bt clay. High aspect ratio of Bt clay increase its contact surface with EPDM matrices, assisting for a better stress transfer and hence increased the tear strength of EPDM/Bt composite with increasing Bt loading. Similar finding was reported by Samsuri, (2013) claiming that the increase in tear strength was affected from the increasing ability of rubber chain to slip around filler particle9. A reduction in tear strength above 90 phr might arise from the stacked of high amount of Bt clay forming agglomeration. The agglomeration restricts the mobility of rubber chain to slip around the clay and resist the chain to orient well when strained. The interaction of EPDM rubber with Bt clay also become weaker. As a consequence, the stress could not distribute evenly throughout EPDM matrices upon loading, decreasing the tear strength of EPDM/Bt composite.
40 35 30 25 20 15 10 5 0 0
10
30 50 70 90 Bt clay loading, phr
120
Fig. 4.The effect of Bt loading on tensile strength of EPDM/Bt composites.
Nurus Sakinah Che Mat et al. / Procedia Chemistry 19 (2016) 394 – 400
399
Fig. 5. Tear fractured surfaces of EPDM/Bt composites with (a) 0 phr ;(b) 10 phr ;(c) 90 phr ;(d) 120 phr Bt loading [Magnification:300X]
Fig. 5 shows the tearing surface of EPDM/Bt composite at different loading. The tearing surface of unfilled EPDM (Fig. 5(a)) showed a smoother and staggered surface as compared to when increasing Bt loading (Fig. 5b to 5d). The staggered surface can be seen to diminish as Bt filler increased. With increasing Bt clay, the surface roughness of EPDM/Bt also can be seen to be increased. Excess loading at 120 phr caused Bt clay to agglomerate and have a poor surface wetting as shown as in Fig. 5d. The agglomeration causes a reduction in the interfacial interaction of EPDM-Bt and resulted the Bt filler to be pulled out of the EPDM matrix, leaving voids. As compared to at 90 phr loading, the clay can be seen to still attach to the EPDM rubber. This shows that there is a good wetting of Bt clay with EPDM matrix at this 90 phr Bt loading, increasing its strength to adhere well to EPDM matrix and therefore increase its tear strength.
4. Conclusion x x x
Optimum cure time, t90, scorch time, ts2 and minimum torque increased with Bt loading. Maximum torque increased up to 90 phr Bt clay loading. The reason was attributed to the increasing amount of hydroxyl group that depleted the curing process, and increased the stiffness and viscosity of EPDM/Bt composite. Tear strength was increased with increasing Bt loading up to 90 phr loading. A decrease in tear strength at high loading was because of the presence of Bt clay that stacked up to form agglomeration, instead having a weaker adhesion to the rubber matrix and consequently led to the decrease in tear strength. The tear fractured surface of EPDM/Bt clay shown by SEM proved that there was a good adhesion of EPDM to Bt clay with increasing Bt clay loading. The agglomeration and voids that caused by the pull out of the embedded agglomerates were presence at 120 phr Bt loading.
Acknowledgements The author would like to thank GRANT 203.PBAHAN.6071245 (FRGS) and MyBrain15 for the financial support.
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References 1. 2. 3. 4. 5. 6. 7. 8. 9.
Morton M. Rubber technology. Germany: Springer; 1999 Arthur GC, Robert WD. Symposium on industrial applications of bentonite. Clays and Clay Minerals 1961; 10: 272-283. Nik Intan Nik Ismail, Ali Ansarifar M, Mo Song. Improving heat ageing and thermal properties of silicone rubber using montmorillonite clay. J App Poly Sci 2014; 41061: 1-13. Arroyo M, LÓpez-Manchado MA, Herrero B. Organo-montmorillonite as substitute of carbon black in natural rubber compounds. Elsevier Sci. Ltd. 2003; 44:2447-2453. Kim J-t, Oh T-s, Lee D-h. Preparation and characteristics of nitrile rubber (NBR) nanocomposites based on organophilic layered silicates. Polym Int 2003; 52:1203-1208. Ismail H, Mathialagan M. Curing characteristics, morphological, tensile and thermal properties of bentonite-filled ethylene-propylene-diene monomer (EPDM) composites. Polym-Plastic Tech. & Eng. 2011; 50: 1421-1428. Ansarifar M A, Chugh J P, Haghighat S. Effect of silica on the cure properties of some compounds of styrene-butadiene rubber. Iranian Poly J 2000; 9: 81-87. Blanchard AF and Parkinson D. In: Thomas S, Chan CH, Pothen LA, Joy J, Maria H. editors. Natural rubber materials: Comp Nanocomp. UK: The Royal Society of Chemistry; 2014; 2: 80. Samsuri A. Theory and mechanism of filler reinforcement in natural rubber. In: Thomas S, Chan C H, Pothen L A, Joy J, Maria H. editors. Natural rubber materials:Comp Nanocomp.UK: The Royal Society of Chemistry 2014; 2: 80.
ScienceDirect Procedia Chemistry 19 (2016) 394 – 400
5th International Conference on Recent Advances in Materials, Minerals and Environment (RAMM) & 2nd International Postgraduate Conference on Materials, Mineral and Polymer (MAMIP), 4-6 August 2015
Curing Characteristics and Tear Properties of Bentonite Filled Ethylene Propylene Diene (EPDM) Rubber Composites Nurus Sakinah Che Mat, Hanafi Ismail*, Nadras Othman School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia
Abstract The effect of bentonite clay loading on curing characteristics and tear strength of bentonite filled ethylene propylene diene monomer (EPDM) composite were studied. Compounding was carried out on two -roll mill and vulcanization was done at 1500C. Torque values, scorch time and optimum cure time of the prepared rubber compound were assessed by using Mosanto Disc Rheometer (MDR 2000). Results indicated that the maximum torque of EPDM/Bt composite decreases at high bentonite loading. Increasing in values with increasing bentonite loading was recorded for minimum torque and optimum cure time of EPDM/Bt composite. The increase is related with the increase in viscosity due to the increasing of bentonite clay loading in EPDM matrix. Scorch time was found to be decreasing up to 30 phr bentonite clay. Results also show that tear strength of EPDM/Bt composite increased with increasing bentonite loading up to 90 phr. The reason is probably due to agglomeration occur causes the reduction in properties at high loading above 90 phr bentonite clay. The scanning electron microscopy (SEM) of tear fracture surface of EPDM/Bt composite illustrated that with increasing bentonite loading up to 90 phr bentonite clay, a better dispersion of bentonite clay is achieved as compared to lower loading, resulting in high tear strength value for EPDM/Bt composite. © Published by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license ©2016 2016The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia. Peer-review under responsibility of School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia Keywords: Ethylene propylene diene monomer; bentonite clay; rubber composites
* Corresponding author. Tel.:+60 4 599 6113; fax: + 60 4 594 1011. E-mail address: [email protected]
1876-6196 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia doi:10.1016/j.proche.2016.03.029
Nurus Sakinah Che Mat et al. / Procedia Chemistry 19 (2016) 394 – 400
Nomenclature NR NBR µm sqm/g h gcm-3 0 C phr mm ISO ASTM N/mm
Natural rubber Nitrile Butadiene rubber micronmeters squaremeters per gram hour gram per centimetre cubic degree celcius part per hundred rubber millimeters International Organization for Standardization American Society for Testing and Material Newton per milimeters
1. Introduction Ethylene propylene diene (EPDM) rubber is a saturated polymer that is mostly known as a rubber that have a greater resistance towards ozone and high temperature as compared to other general purpose rubber. Due to its high performance, EPDM rubber is often used in automotive application, building and construction, cable and wire, also as sheeting and sealing 1. Although EPDM has high resistance towards oxygen, ozone and heat, the strength of unfilled EPDM actually are very poor and therefore, the incorporation of filler is required to increase its strength. The filler is usually added into rubber phase to either reinforce the properties of rubber, reducing the cost of production and/or to ease the processing. Among all the filler used, carbon black is more known thanks to its high reinforcement capability. However, its potential to pollute environment, besides low variety of colour usage, urge the researchers to find other more friendly white filler to be used, which among them is silicate layer clay such as bentonite and montmorillonite (MMT). Bentonite is a naturally occurring rock consisting majorly of MMT, sodium and other minerals such as quartz, feldspar and others. MMT have a structure such that the Aluminium octahedral sheet is sandwiched in between the silica tetrahedral sheet. The thickness of the layer is only 1nm which in between the gap gallery, the exchangeable cations take place. These exchangeable cations are important because it is responsible in altering the properties of the rubber 2. The use of clay in nanocomposite rubber was initiated by Toyota R&D group in 1991 with their nanocomposite based on nylon rubber with MMT clay. The improvement in mechanical properties by the use of MMT clay discovered by Toyota had attract the attention of the researchers and the results are plentiful studies of nanocomposites has been reported 3-5. In order to further understanding the benefit of bentonite, the work was focused on studying the effect of bentonite clay loading on curing characteristics and tear properties of EPDM/Bt composite. 2. Experimental 2.1. Material The material used throughout this study are the same as used by Ismail et al, (2011) 6 (Table 1). EPDM, 778Z purchased from Keltan DSM Elastomers consist of ethylene content of 67%, ENB of 4.3% and ML (1+4) 125 0C of 63MM. Bentonite, Bt was supplied by Ipoh Ceramics (M) Sdn. Bhd. Zinc oxide,ZnO, stearic acid, tetramethyl thiuram dsulphide (TMTD), 2-mercapto benzothiazole (MBT) and sulphur were all obtained from Bayer (M) Ltd. The average particle size and specific surface area of Bt are 5.31µ m and 0.975 sqm/g, respectively and the elemental composition of Bt are as shown in Table 2 6.
Table 1: Compounding formulation of EPDM/Bt composite 6.
395
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Nurus Sakinah Che Mat et al. / Procedia Chemistry 19 (2016) 394 – 400
Composite (phr)
C1
C2
C3
C4
C5
100
100
C6
C7
EPDM
100
100
100
100
100
Bt
0
10
30
50
70
90
120
5
5
5
5
5
ZnO
5
5
Stearic Acid
1.5
1.5
1.5
1.5
1.5
1.5
1.5
MBT
0.8
0.8
0.8
0.8
0.8
0.8
0.8
TMTD
1.5
1.5
1.5
1.5
1.5
1.5
1.5
Sulphur
1.5
1.5
1.5
1.5
1.5
1.5
1.5
Table 2: Elemental compositions of Bt 6. Bentonite Content SiO2 Al2O3 MgO CaO Fe2O3 K2 O Na 2O TiO2 BaO P2O5 SrO MnO ZrO2 SO3 Loss of ignition (LOI)
Amount (%) (w/w) 76.0 15.0 2.7 2.0 2.0 1.2 0.36 0.12 0.061 0.037 0.032 0.029 0.024 0.021 0.416
2.2 Preparation of Bentonite- Filled EPDM Composites Prior to compounding of EPDM rubber with Bt clay, Bt was first dried in vacuum oven at 800C for 24h. The compounding process of EPDM/Bt composite was done by using the same ingredients used by Ismail et al., (2011) as in Table 1 where bentonite clay followed by sulphur were incorporated last 6. A laboratory scale (160mm x 320mm) two roll mill, model XK-160 was used during compounding process. Mosanto Moving Die Rheometer (MDR 2000) was then used to determine the cure characteristics of the rubber compound at 150 0C, in accordance to ISO 3417. The curing time (t 90) obtained from the rheograph was then used to compress rubber compound into sheets. The temperature for the compression moulding used was 150 0C. 2.3 Tear Properties In order to obtain the tear sample for tear test, the rubber compound was compressed using a square mould of 2mm in thickness. The samples were then left at room temperature for at least 6 hours before they were cut into trouser shape. The tear sample was tested using Instron 3366 at room temperature with the crosshead speed of 50mm/min in accordance to ASTM D624. 2.4 Morphological Studies The tear fractured surface of the EPDM/Bt samples from the tear test was observed under Supra-35VP field emission scanning electron microscope (SEM) to determine their surface morphology, shape, dispersion and adhesion. Test specimens were mounted on the aluminium using double-sided sticky tape and then coated with a thin layer of Pd-Au before testing.
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Nurus Sakinah Che Mat et al. / Procedia Chemistry 19 (2016) 394 – 400
3. Results and Discussion 3.1 Curing Characteristics of EPDM/Bt composites
60 a)
40 20 0 0
30
60
90
120
Scorch time,ts2
Optimum cure time, t90
Fig. 1 and 2 both displayed the curing characteristics of vulcanizate EPDM/Bt composite. The optimum curing time of vulcanizate EPDM/Bt increased with increasing Bt loading. The increase was attributed to the adsorption of curative that arise from the presence of hydroxyl group at silicate layer of Bt clay. The similar result was reported by Ansarifar et al, (2000) that also found the curing time of rubber delayed as the amount of silica increased. The presence of hydroxyl group was reported able to disrupt the vulcanization process and resulted in the increase in curing time and scorch time 7. Scorch time of EPDM/Bt composites shows increasing trend with increasing amount of Bt only after incorporation of 30 phr Bt clay. At lower loading, a slight decrease in scorch time was probably due to high surface area of Bt that promotes better heat distribution in rubber system. 15 b)
10 5 0 0
Bt clay loading, phr
30
60
90
120
Bt clay loading, phr
Fig. 1. (a) Optimum cure time, t 90 ;(b) scorch time, t s2 of EPDM/Bt composites at different Bt loading.
With incorporation of Bt clay increased the viscosity of EPDM/Bt composite. This is as shown by the increase in minimum torque with increasing Bt content. Increased in viscosity is known indicated for a decrease in molecular movement of rubber that was resulted from the increase amount of Bt content in rubber. With increased viscosity high shear forces are therefore needed to rotate the rotor during vulcanization process. Figure 3b shows that the maximum torque value can be seen to be increasing up to 90 phr Bt clay, supporting the expectation that the increased of filler increased the stiffness of rubber, consequently increased the torque value recorded. A decrease above 90 phr was probably due to the presence of weak EPDM-Bt interaction in the composite. b)
6 4 2 0 0
30
60
90
Bt clay loading, phr
120
Maximum Torque, MH
Minimum torque, ML
a) 8
20 15 10 5 0 0
30
60
90
120
Bt clay loading, phr
Fig. 2. (a)Minimum torque, ML ;(b) maximum torque, MH of EPDM/Bt composites at different Bt loading.
3.2 Microstructure of Bentonite Morphological studies were conducted by subjected rubber samples under SEM at certain magnification. In order to determine the shape and clearly see the surface of bentonite filler, SEM was conducted at different magnification as shown in Fig. 3(a) and 3(b). From Fig. 3(a), it can be seen that bentonite is in the form of
398
Nurus Sakinah Che Mat et al. / Procedia Chemistry 19 (2016) 394 – 400
irregular shape. By increasing magnification to 6050x, bentonite surface was actually consisting of pores and voids. These voids and pores are believed able to reinforce properties of EPDM/Bt composite. This is arising from the entrapment of filler at the voids and pores of bentonite that can increase the interaction between rubber and filler.
Fig. 3. SEM micrograph of Bt particles at (a) 1000x ;(b) 6050x magnification.
3.3 Tear Properties
Tear strength, N/mm
Fig. 4 shows the tear strength of EPDM/Bt composite as amount of Bt clay increased. It was found that according to Fig. 4, tear strength increased with increasing Bt up to 90 phr loading. This shows that there is an improvement in tear strength with incorporation of Bt clay in EPDM rubber. The improvement was probably resulted from the molecular chain of EPDM rubber that can orient in the direction of strain upon loading8. The ability to orient and slip around the clay was probably arising from the good interaction between EPDM rubber and Bt clay. High aspect ratio of Bt clay increase its contact surface with EPDM matrices, assisting for a better stress transfer and hence increased the tear strength of EPDM/Bt composite with increasing Bt loading. Similar finding was reported by Samsuri, (2013) claiming that the increase in tear strength was affected from the increasing ability of rubber chain to slip around filler particle9. A reduction in tear strength above 90 phr might arise from the stacked of high amount of Bt clay forming agglomeration. The agglomeration restricts the mobility of rubber chain to slip around the clay and resist the chain to orient well when strained. The interaction of EPDM rubber with Bt clay also become weaker. As a consequence, the stress could not distribute evenly throughout EPDM matrices upon loading, decreasing the tear strength of EPDM/Bt composite.
40 35 30 25 20 15 10 5 0 0
10
30 50 70 90 Bt clay loading, phr
120
Fig. 4.The effect of Bt loading on tensile strength of EPDM/Bt composites.
Nurus Sakinah Che Mat et al. / Procedia Chemistry 19 (2016) 394 – 400
399
Fig. 5. Tear fractured surfaces of EPDM/Bt composites with (a) 0 phr ;(b) 10 phr ;(c) 90 phr ;(d) 120 phr Bt loading [Magnification:300X]
Fig. 5 shows the tearing surface of EPDM/Bt composite at different loading. The tearing surface of unfilled EPDM (Fig. 5(a)) showed a smoother and staggered surface as compared to when increasing Bt loading (Fig. 5b to 5d). The staggered surface can be seen to diminish as Bt filler increased. With increasing Bt clay, the surface roughness of EPDM/Bt also can be seen to be increased. Excess loading at 120 phr caused Bt clay to agglomerate and have a poor surface wetting as shown as in Fig. 5d. The agglomeration causes a reduction in the interfacial interaction of EPDM-Bt and resulted the Bt filler to be pulled out of the EPDM matrix, leaving voids. As compared to at 90 phr loading, the clay can be seen to still attach to the EPDM rubber. This shows that there is a good wetting of Bt clay with EPDM matrix at this 90 phr Bt loading, increasing its strength to adhere well to EPDM matrix and therefore increase its tear strength.
4. Conclusion x x x
Optimum cure time, t90, scorch time, ts2 and minimum torque increased with Bt loading. Maximum torque increased up to 90 phr Bt clay loading. The reason was attributed to the increasing amount of hydroxyl group that depleted the curing process, and increased the stiffness and viscosity of EPDM/Bt composite. Tear strength was increased with increasing Bt loading up to 90 phr loading. A decrease in tear strength at high loading was because of the presence of Bt clay that stacked up to form agglomeration, instead having a weaker adhesion to the rubber matrix and consequently led to the decrease in tear strength. The tear fractured surface of EPDM/Bt clay shown by SEM proved that there was a good adhesion of EPDM to Bt clay with increasing Bt clay loading. The agglomeration and voids that caused by the pull out of the embedded agglomerates were presence at 120 phr Bt loading.
Acknowledgements The author would like to thank GRANT 203.PBAHAN.6071245 (FRGS) and MyBrain15 for the financial support.
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