Journal of Materials Science

, Volume 47, Issue 4, pp 2016–2024

Carbon black–clay hybrid nanocomposites based upon EPDM elastomer

Authors

  • Asish Malas
    • Materials Science CentreIndian Institute of Technology, Kharagpur
    • Materials Science CentreIndian Institute of Technology, Kharagpur
Article

DOI: 10.1007/s10853-011-6000-z

Cite this article as:
Malas, A. & Das, C.K. J Mater Sci (2012) 47: 2016. doi:10.1007/s10853-011-6000-z
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Abstract

The present study explored the effect of nanoclay on the properties of the ethylene–propylene–diene rubber (EPDM)/carbon black (CB) composites. The nanocomposites were prepared with 40 wt% loading of fillers, where the nanoclay percentage was kept constant at 3 wt%. As the modified nanoclay contains the polar groups and the EPDM matrix is nonpolar, a polar rubber oil extended carboxylated styrene butadiene rubber (XSBR), was used during the preparation of nanocomposites to improve the compatibility. Primarily the nanoclay was dispersed in XSBR by solution mixing followed by ultrasonication. After that EPDM-based, CB–clay hybrid nanocomposites, were prepared in a laboratory scale two roll mill. The dispersion of the different nanoclay in the EPDM matrix was observed by wide-angle X-ray diffraction (WAXD) and high resolution transmission electron microscopy. It was found that the mechanical properties of the hybrid nanocomposites were highly influenced by the dispersion and exfoliation of the nanoclays in the EPDM matrix. Thermo gravimetric analysis, scanning electron microscopy and dynamic mechanical thermal analysis was carried out for each nanocomposite. Among all the nanocomposites studied, the thermal and mechanical properties of Cloisite 30B filled EPDM/CB nanocomposite were found to be highest.

Introduction

Carbon black (CB) acts as a strongest reinforcing filler and also used most popularly in the tire industry [1]. Almost 90% of the produced CB, all over the world, is used in the tire industry as reinforcing filler to improve the tear strength, modulus and physical characteristics of tires. In the last 20 years there were many reinforcing fillers were developed as an alternative to CB such as kaolin, silica and sepiolite [2]. As all these fillers are inorganic in nature so these are not compatible with the organic polymer matrices. Due to this incompatibility issue, the reinforcing effect of these fillers in the polymer matrices is very much lower than the CB. Nanoclay-based polymer nanocomposites are being studied intensively by several research groups over the last few decades. Montmorillonite is the most generally used layered silicate and it is naturally available. Polymer-layered silicate nanocomposites have shown drastic improvements in thermal, mechanical and barrier properties at very low loading of these types of inorganic layered silicate [35]. Montmorillonite has high cation exchange capacity, high aspect ratio and large surface area [6]. As the layered silicate nanofillers are also inorganic in nature so it is incompatible with the polymer matrices. For making the layered silicate compatible with the polymer matrices, the silicate layer surfaces have been organically modified by exchanging the alkali cations with alkyl ammonium ions [79]. After the modification of the layered silicate nanofillers the reinforcing effect are increased significantly as well as enhance the physical, mechanical and thermal properties of the polymer-layered silicate nanocomposites than their respective controls [1012]. Possibly three types of nanocomposites have been classified, depending upon the dispersion of the nanoclay in the polymer matrices. The first one is traditional polymeric nanocomposites containing clay platelets, in which the clay platelets are dispersed as a segregated phase. The second one is intercalated polymer–clay nanocomposites where the polymer chain is entered into the gallery space of nanoclay platelets and at the same time silicate sheets maintain the layered stacking structure. The third one is the exfoliated polymer–clay nanocomposites, where the silicate sheets can not able to maintain the layered stacking structure. In the case of exfoliated polymer–clay nanocomposites, there is a good dispersion of clay platelets into the polymer matrix at the nanoscale and resulting in improved physical properties [13, 14]. The improvement in the properties imparted by the organically modified nanoclay to the elastomeric composites have developed a new type of composite, known as rubber–CB–clay hybrid nanocomposites [15]. This type of hybrid nanocomposites facilitates the partial replacement of CB by organically modified nanoclay in elastomeric composites with out hindering its unique properties. According to Arroyo et al. [12], 10 wt% of nanoclay loading in natural rubber matrix showed similar mechanical properties as that of 40 wt% loading of CB in natural rubber. Synergistic reinforcement of CB and nanoclay in natural rubber composites have been studied by Qu et al. [16]. Structure–property correlation of brominated poly(isobutylene-co-para-methyl-styrene) (BIMS)-nanoclay composites have studied by Maiti et al. [17] and observed drastic improvement in mechanical properties. Engelhardt and coworkers have reported the effects of intercalation and exfoliation of clay platelets on the mechanical properties of the cis-1,4-polyisoprene and epoxidized natural rubber [18]. Ha and coworkers have studied the mechanical and dynamic mechanical properties of millable polyurethane–nanoclay composites [19]. Li et al. have reported the effects of exfoliation of organoclay on the mechanical properties and thermal stability of EPDM rubber by melt extrusion method [20]. Schon and coworkers have investigated the effect of nanosilica on the mechanical properties like surface elastic moduli of silica-reinforced styrene butadiene rubber (SBR), ethylene–propylene–diene rubber (EPDM) and SBR/EPDM rubber blends by atomic force microscopy (AFM)-based HarmoniX material mapping [21]. The relationship between the nanoscale fracture process and the microstructure of the unfilled peroxide cured EPDM rubber, and the microstructure of unexposed and hydrogen exposed samples was investigated by Yamabe and Nishimura [22] by using atomic force microscope (AFM). Huang et al. studied the effect of SC-CO2 on the morphology and dynamic rheology of polypropylene/ethylene–propylene–diene terpolymer thermoplastic olefin (TPO) composites by dynamic vulcanization using a twin screw extruder [23]. Zheng and coworkers studied the effect of organically modified montmorillonite and silica on the mechanical and viscoelastic properties of solution styrene butadiene rubber (SSBR) [24]. Achieving the highly disperse organomodified nanoclay in the polymer matrices involves two main aspects. The first aspect involves the compatibility between polymer and nanoclay and the second aspect is the way of preparation of the polymer–clay nanocomposites. Organoclay prefers to disperse into polar polymer matrices than the nonpolar polymer matrices. For that cause a polar polymers can be used as a compatibilizer for the better dispersion of organically modified clay in the mother polymer matrices [25, 26]. There are many polar compatibilizer can be used such as epoxidised natural rubber, oil extended carboxylated styrene butadiene rubber (XSBR), chlorobutyl rubber etc. Several methods are there in use for the preparation of polymer–organoclay nanocomposites such as in situ polymerization intercalation [27], solution intercalation [28], melt intercalation [29] and co-coagulation of rubber latex and clay aqueous suspension [30].

In the present research work ethylene–propylene–diene terpolymer (EPDM), which is a typical nonpolar rubber with good ageing properties and high filler loading capacity and widely used in automobile sectors, was used as a base rubber matrix for the preparation of EPDM/CB/nanoclay nanocomposites [31, 32]. Three types of commercially available organically modified nanoclays, with different organic moiety, were used for this study. As EPDM is incompatible with the organically modified clay, to prepare EPDM-based CB–clay hybrid nanocomposites, organically modified nanoclay was dispersed in the polar compatibilizer named XSBR by solution mixing method, in order to get uniform dispersion of organoclay in the XSBR matrix. In this study we have used three different types of organically modified clays such as Cloisite 15A, Cloisite 20A and Cloisite 30B. After that the XSBR-organoclay composites (XC) were mixed with the bulk EPDM matrix in presence of CB with sulphur as curing agent. The variation in the curing characteristics, morphology, mechanical properties, dynamic mechanical properties and thermal stability of the different clay–CB hybrid nanocomposites had been analyzed and compared with each other and also with their respective controls.

Materials

Ethylene–propylene–diene terpolymer utilized was Royalene 535, purchased from DSM Elastomer B.V., The Netherlands (E/P weight ratio 60/40, ENB 9.4 wt%). XSBR was bought from Lanxess India Pvt. Ltd.

Cloisite 15A (cation exchange capacity of 125 mequiv/100 g clay), Cloisite 20A (cation exchange capacity of 95 mequiv/100 g clay), Cloisite 30B (cation exchange capacity of 90 mequiv/100 g clay) were obtained from Southern Clay Products, Inc., USA, used as nanofillers for the preparation of nanocomposites. CB, type: intermediate super abrasion furnace (ISAF), Grade: N774 was bought from Hi-tech carbon. Other compounding additives like sulphur, zinc oxide, stearic acid, N-cyclohexyl-2-benzothiazyl sulphenamide (CBS), tetramethylthiuram disulphide (TMTD) were obtained from Bayer (M) Sdn Bhd Malaysia.

Methods

Solution mixing

Primarily XSBR was dissolved in Toluene (rubber to solvent ratio was 1:3 weight/volume). To dissolve the compatibilizer (XSBR) fully in the solvent, the solution was stirred vigorously and continuously at room temperature. Then under continuous stirring 50 wt% of nanoclay was added to the solution. Later the total solution was sonicated for 30 min and the whole solution was then poured over a petri dish and left the petri dish in the open air for the evaporation of the solvent completely so as to obtained transparent film. We have made three different XSBR–clay composite by using three different types of nanoclay.

Compounding

Formulation of the rubber compounds were shown in Table 1. An open two roll mixing mill was used for the preparation of the EPDM-based clay–CB hybrid nanocomposites at room temperature; 1:1.4 was the speed ratio of the rotors (front to back). Compression moulding machine was used for the vulcanization of the rubber compounds at 150 °C and the optimum cure time was obtained from the Rheometer.
Table 1

Formulation of the rubber compounds

Ingredients

Designation

Pure EPDM (wt%)

ECB (wt%)

EXC1CB (wt%)

EXC2CB (wt%)

EXC3CB (wt%)

EPDM

100

100

94

94

94

XC

6

6

6

Stearic acid

1

1

1

1

1

CBS

1

1

1

1

1

TMTD

0.5

0.5

0.5

0.5

0.5

Zinc oxide

3

3

3

3

3

Sulphur

1.5

1.5

1.5

1.5

1.5

CB(ISAF-N774)

40

37

37

37

Proc. Oil

2

2

2

2

CBSN-cyclohexyl-2-benzothiazole sulphenamide, TMTD tetramethylthiuram disulphide, ISAF Intermediate Super Abrasion Furnace

Characterization techniques

Cure characteristics

Curing study of the hybrid nanocomposites was carried out in the Monsanto Rheometer R-100 testing instrument at 150 °C with 3° arc for 60 min.

X-ray diffraction

X-ray diffraction analysis of Hybrid compounds and the pure EPDM were done by using a Rigaku Miniflex Diffractometer with Cu Kα radiation at a generator voltage of 40 kV, a scanning rate 1°/min between 1° and 15°, chart speed of 10 mm/2θ, current 20 mA and wavelength of 0.154 nm at room temperature. The d spacing of the nanoclay were obtained from the Brag’s equations nλ = 2d sin θ.

High resolution transmission electron microscopy (HR-TEM)

The morphology of the dispersed nanoclay in the solvent casted sample and in the three different nanocomposites was observed in high resolution transmission electron microscope (HR-TEM, JEOL 2100). For HR-TEM analysis, ultra-thin cross sections of the specimen were cut by using Leica Ultra Cut UCT Ultra microtome instrument equipped with a diamond knife.

Dynamic mechanical thermal analysis (DMTA)

DMTA of the prepared nanocomposites were done by using a TA instrument DMA 2980 model in tension mode at a constant frequency of 1 Hz, a strain of 0.1%, in the temperature range of −80 to +80 °C and at a heating rate of 3 °C/min.

Mechanical testing

Mechanical properties of the hybrid nanocomposites were obtained by using Universal tensile testing machine (Hounsfield H 10KS) under ambient conditions. The tensile stress, modulus and elongation at break (%) were obtained at room temperature. The measured length was 25 mm, and the speed of jaw separation was 500 mm/min.

Scanning electron microscopy (SEM)

SEM analysis of the tensile fractured surface of the nanocomposites was carried out in VEGA TESCAN//LSU instrument after the fractured surface of the samples were gold coated.

Thermo gravimetric analysis (TGA)

TGA of the nanocomposites was done by using a DuPont TGA-2100 thermal analyzer in the temperature range 30 to 700 °C with a heating rate of 10 °C/min.

Results and discussions

X-ray diffraction analysis

Wide-angle X-ray diffraction was used to analyze the state of clay exfoliation in the prepared EPDM-based CB–clay hybrid nanocomposites. Figure 1 shows the X-ray diffraction pattern of Cloisite 15A, XSBR-C15A composite (XC1), EPDM–CB–XC1 (EXC1CB) nanocomposite and pure EPDM–CB (ECB) composite in the diffraction angle range of 1°–10°. Figure 1 shows an intense peak, around 2θ = 2.71°, for Cloisite 15A, corresponding to the basal spacing of 3.32 nm (d001). For the case of compatibilizer-clay (XC1) composite, the main peak of C15A was shifted towards the lower angle (2θ = 1.71°), corresponding to a basal spacing of 5.19 nm indicating an increasing of gallery spacing between the clay layers. This is due to the intercalation of XSBR molecules in between the clay platelets [33]. Two secondary peaks are also formed at 2θ = 3.94° and 6.13°, corresponding to the basal spacing of 2.40 and 1.44 nm, respectively, which may be due to the reaggregation of nanoclay in the XSBR matrix. For EXC1CB hybrid composite, no peak was observed which indicates towards the partial exfoliation of nanoclay platelets in the EPDM matrix. For ECB compound, no peak was formed which also indicates the partial exfoliation of CB in the EPDM matrix.
https://static-content.springer.com/image/art%3A10.1007%2Fs10853-011-6000-z/MediaObjects/10853_2011_6000_Fig1_HTML.gif
Fig. 1

XRD plot for Cloisite 15A, XC1, EXC1CB and ECB

Figure 2 shows the X-ray diffraction pattern of Cloisite 20A, XSBR-Cloisite 20A composite (XC2) and EPDM–CB–XC2 (EXC2CB) nanocomposite. A peak at around 2θ = 3.14°, corresponding to the basal spacing 2.82 nm (d001) was observed for Cloisite 20A. For XC2 composite, the usual peak of Cloisite 20A had been shifted towards lower angle 2θ = 1.75°, corresponding to the basal spacing 4.92 nm which proves that the XSBR polymer chain has entered in between the gallery space of clay platelets and produced an intercalated structure of XSBR-clay composite. Two secondary peaks were observed at 2θ = 4.11° and 6.55°, corresponding to the basal spacing of 2.14 and 1.40 nm, respectively. This may be due to the reaggregation of the nanoclay in the XSBR matrix. There is no such peak was observed for the EXC2CB nanocomposite which proves the partial exfoliation of nanoclay platelets in the EPDM matrix.
https://static-content.springer.com/image/art%3A10.1007%2Fs10853-011-6000-z/MediaObjects/10853_2011_6000_Fig2_HTML.gif
Fig. 2

XRD plot for Cloisite 20A, XC2 and EXC2CB

Figure 3 shows the X-ray diffraction pattern of Cloisite 30B, Cloisite 30B-XSBR composite (XC3) and EPDM–CB–XC3 nanocomposite (EXC3CB). From the figure it was observed that the main peak of Cloisite 30B was elevated at 2θ = 5.10°, corresponding to the basal spacing of 1.76 nm (d001). For compatibilizer-Cloisite 30B composite, the main peak of Cloisite 30B had been shifted towards the lower angle 2θ = 4.82° and as well as the peak intensity was diminished which proves the intercalated structure of the composites and also proves the partial exfoliation of C30B platelets in the XSBR matrix. For EXC3CB nanocomposite, no such peak was observed which proves the partial exfoliation of nanoclay in the bulk EPDM matrix.
https://static-content.springer.com/image/art%3A10.1007%2Fs10853-011-6000-z/MediaObjects/10853_2011_6000_Fig3_HTML.gif
Fig. 3

XRD plot for Cloisite 30B, XC3 and EXC3CB

Cure characteristics

Table 2 shows the curing characteristics of different EPDM–CB–clay hybrid nanocomposites. The CB-nanoclay loaded EPDM compound shows an increased minimum torque value than their respective control. The minimum torque value was related to the viscosity of the nanocomposites. Maximum torque value can be taken as the measure of stock modulus [29]. Different types of clay loaded hybrid nanocomposites show an improvement in maximum torque value. CB-Cloisite 30B clay loaded nanocomposite shows higher maximum torque value than the other clay loaded nanocomposites. This may be due to the better dispersion of Cloisite 30B nanoclay in XSBR matrix as well as in the EPDM matrix. As Cloisite 30B is more polar than the other two nanoclays so it was dispersed better than the other two nanoclays in the polar compatibilizer (XSBR) as well as in the EPDM matrix. Different types of nanoclay loaded EPDM–CB compounds show faster scorch and cure time than the pure EPDM–CB compound (ECB). The fast curing reaction promoted by the large surface area of the nanoclay in the hybrid nanocomposites. Cloisite 30B clay containing hybrid nanocomposite shows better scorch and cure time than the other two nanocomposites.
Table 2

Cure characteristics of the rubber compounds

Sample code

Min. torque (dN m)

Max. torque (dN m)

Torque difference (dN m)

Scorch time (min)

Cure time (min)

Cure rate index

Pure EPDM

19.0

60.0

41.0

3.5

10.0

14.2

ECB

22.9

84.9

62.0

1.9

18.7

6.2

EXC1CB

23.5

88.2

64.7

1.7

17.6

6.1

EXC2CB

25.8

90.2

64.4

1.7

18.0

6.7

EXC3CB

26.9

94.0

67.1

1.5

16.2

5.8

Mechanical properties

Table 3 shows the mechanical characteristics of the EPDM-based CB–clay hybrid nanocomposites. There was an improvement in the mechanical property after the addition of CB in the EPDM matrix than the pure EPDM compound. The mechanical properties of CB-clay filled EPDM compounds were further improved than the EPDM–CB compound. CB-Cloisite 30B filled EPDM nanocomposites shows better mechanical properties than the other two hybrid nanocomposites. This is because of the better dispersion of Cloisite 30B in the compatibilizer (XSBR) as well as in the EPDM matrix due to its higher polarity than the other two types of nanoclay. There was a 66% increment in the tensile strength after the addition of CB in the EPDM matrix. The tensile strength was increased by 87, 82 and 65% for EXC3CB, EXC2CB and EXC1CB hybrid nanocomposites, respectively, than the pure EPDM–CB compound. The modulus (100%) was increased by 17, 15 and 6% for EXC3CB, EXC2CB and EXC1CB nanocomposites.
Table 3

Mechanical properties of the rubber compounds

Designation

Tensile strength (MPa)

% Elongation at break

100% modulus (MPa)

300% modulus (MPa)

Tear strength (N/mm)

Pure EPDM

3.6

400

1.5

2.4

9.9

ECB

6.0

260

2.8

5.9

18.5

EXC1CB

9.8

300

2.9

9.6

20.6

EXC2CB

10.8

310

3.2

10.5

21.0

EXC3CB

11.1

310

3.3

10.6

21.9

SEM analysis

Figure 4a–e shows the tensile fractured surface of Pure EPDM, ECB, EXC1CB, EXC2CB and EXC3CB compounds, respectively. All the three hybrid nanocomposites shows highly rougher surface morphology compared to the pure EPDM and ECB compounds. This may be due to the dispersion of CB and organo-modified clay platelets in the EPDM matrix which alter the crack path depending upon their orientation in the EPDM matrix.
https://static-content.springer.com/image/art%3A10.1007%2Fs10853-011-6000-z/MediaObjects/10853_2011_6000_Fig4_HTML.gif
Fig. 4

a SEM image of pure EPDM compound. b SEM image of pure EPDM-CB compound (ECB). c SEM image of EXCICB nanocomposite. d SEM image of EXC2CB nanocomposite. e SEM image of EXC3CB nanocomposite

HR-TEM analysis

Figure 5a–c shows the HR-TEM images of XC1, XC2 and XC3 composites (compatibilizer–clay composites). The dark lines in the images were identified as layered silicates. The HR-TEM images of compatibilizer–clay composites show the presence of intercalated structure and also confirmed the dispersion of layered silicates in the XSBR matrix. Cloisite 30B nanoclay-loaded XSBR composite shows better dispersion of clay platelets in the XSBR matrix because of its higher polarity than the other two types of nanoclay.
https://static-content.springer.com/image/art%3A10.1007%2Fs10853-011-6000-z/MediaObjects/10853_2011_6000_Fig5_HTML.jpg
Fig. 5

a HR-TEM image of XC1 composite. b HR-TEM image of XC2 composite. c HR-TEM image of XC3 composite

Figure 6a–c shows the HR-TEM images of EXC1CB, EXC2CB and EXC3CB hybrid nanocomposites. It was shown from all the images that the CB and clay platelets were partially exfoliated and few were agglomerated in the EPDM matrix.
https://static-content.springer.com/image/art%3A10.1007%2Fs10853-011-6000-z/MediaObjects/10853_2011_6000_Fig6_HTML.jpg
Fig. 6

a HR-TEM image of EXC1CB hybrid nanocomposite. b HR-TEM image of EXC2CB hybrid nanocomposite. c HR-TEM image of EXC3CB hybrid nanocomposite

DMTA analysis

Figure 7a–c shows the temperature-dependent dynamic storage modulus (E′) and loss factor (tan δ), respectively, of the different hybrid nanocomposites and as well as of the pure gum compound. The CB–clay loaded hybrid compounds shows drastic improvement in dynamic storage modulus compared to that of the controls. After adding the CB in the EPDM matrix, ECB composite shows 20% increase in the storage modulus compared to the pure EPDM at 25 °C. At 25 °C, EXC1CB, EXC2CB and EXC3CB hybrid compound shows 296, 318 and 361% increase in the storage modulus than the pure ECB compound, respectively.
https://static-content.springer.com/image/art%3A10.1007%2Fs10853-011-6000-z/MediaObjects/10853_2011_6000_Fig7_HTML.gif
Fig. 7

a Storage modulus of pure EPDM, ECB, EXC1CB, EXC2CB and EXC3CB compounds. b Storage modulus of pure EPDM, ECB, EXC1CB, EXC2CB and EXC3CB compounds at Room Temperature range. c Tan δ plot for pure EPDM, ECB, EXC1CB, EXC2CB and EXC3CB compounds

The tan δ peak height was decreased after addition of CB in the EPDM matrix than the pure EPDM compound. The tan δ peak height was further decreased for the CB–clay loaded hybrid nanocomposites. This may be due to the reinforcing tendency of the both CB and clay in the EPDM matrix. The CB-Cloisite 30B containing EPDM compound shows lesser dampening characteristics than other two hybrid compounds. This may be due to the better dispersion of Cloisite 30B in the compatibilizers as well as in the EPDM matrix which enhances the reinforcing tendency of CB-Cloisite 30B in the EPDM matrix.

Decrease in the tan δ peak height was may be due to the restriction in the polymer chain mobility because of physical and chemical adsorption of rubber molecules in the filler surface [34]. Glass transition temperature (Tg) of the CB–clay loaded hybrid nanocomposites was decreased than their respective controls, this may be due to the plasticizing effect of the organic surfactant [35, 36] or the organic surfactant creates extra volume at the polymer silicate interface [37, 38].

Thermo gravimetric analysis (TGA)

Figure 8 shows the thermal stability of the different hybrid nanocomposites compared to their respective controls. CB–clay loaded compounds shows improved thermal stability than their respective controls. This may be due to the heat shielding effect of the added CB–clay fillers in the EPDM matrix and formation of mass transport barrier to the volatile products produced during the decomposition of the hybrid nanocomposites. Hybrid compound containing Cloisite 30B shows better thermal stability than the other two hybrid nanocomposites, this may be due to the better dispersion of Cloisite 30B in the compatibilizer as well as in the EPDM matrix with CB due to the same reason discussed earlier.
https://static-content.springer.com/image/art%3A10.1007%2Fs10853-011-6000-z/MediaObjects/10853_2011_6000_Fig8_HTML.gif
Fig. 8

TGA plot for pure EPDM, ECB, EXC1CB, EXC2CB and EXC3CB compounds

Conclusion

EPDM-based CB–clay hybrid rubber nanocomposites were prepared using three different types of organo-modified nanoclay. CB–clay loaded hybrid nanocomposites showed overall improvement in all the properties such as thermal stability, mechanical properties, cure characteristics and dynamic mechanical properties. WAXD results of the different XC composites indicated towards the formation of intercalated, aggregated and partially exfoliated structure. However, partially exfoliated structure was observed for the hybrid nanocomposites. Tensile and dynamic mechanical properties of hybrid nanocomposites improved drastically as compared to pure polymer. Among the nanocomposites Cloisite 30B containing hybrid nanocomposites showed better curing characteristics, mechanical, thermal and dynamic mechanical thermal properties than other two nanocomposites because of its better dispersion in the EPDM matrix, in presence of CB, and more polar nature of organic moiety than the other two modified clays.

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© Springer Science+Business Media, LLC 2011