Carbon black–clay hybrid nanocomposites based upon EPDM elastomer
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- Malas, A. & Das, C.K. J Mater Sci (2012) 47: 2016. doi:10.1007/s10853-011-6000-z
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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.
Carbon black (CB) acts as a strongest reinforcing filler and also used most popularly in the tire industry . 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 . 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 [3–5]. Montmorillonite has high cation exchange capacity, high aspect ratio and large surface area . 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 [7–9]. 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 [10–12]. 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 . 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. , 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. . Structure–property correlation of brominated poly(isobutylene-co-para-methyl-styrene) (BIMS)-nanoclay composites have studied by Maiti et al.  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 . Ha and coworkers have studied the mechanical and dynamic mechanical properties of millable polyurethane–nanoclay composites . 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 . 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 . 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  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 . Zheng and coworkers studied the effect of organically modified montmorillonite and silica on the mechanical and viscoelastic properties of solution styrene butadiene rubber (SSBR) . 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 , solution intercalation , melt intercalation  and co-coagulation of rubber latex and clay aqueous suspension .
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.
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.
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.
Formulation of the rubber compounds
Pure EPDM (wt%)
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 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 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
Cure characteristics of the rubber compounds
Min. torque (dN m)
Max. torque (dN m)
Torque difference (dN m)
Scorch time (min)
Cure time (min)
Cure rate index
Mechanical properties of the rubber compounds
Tensile strength (MPa)
% Elongation at break
100% modulus (MPa)
300% modulus (MPa)
Tear strength (N/mm)
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 . 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)
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.