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Pigment & Resin Technology Composites of styrene butadiene rubber/modified clay: mechanical, dielectric and morphological properties Salwa H. El-Sabbagh, Doaa Samir Mahmoud, Nivin M. Ahmed, A.A. Ward, Magdy Wadid Sabaa, Article information: To cite this document: Salwa H. El-Sabbagh, Doaa Samir Mahmoud, Nivin M. Ahmed, A.A. Ward, Magdy Wadid Sabaa, (2017) "Composites of styrene butadiene rubber/modified clay: mechanical, dielectric and morphological properties", Pigment & Resin Technology, Vol. 46 Issue: 3, pp.161-171, doi: 10.1108/PRT-03-2016-0034 Permanent link to this document: http://dx.doi.org/10.1108/PRT-03-2016-0034 Downloaded on: 18 April 2017, At: 15:52 (PT) References: this document contains references to 34 other documents. To copy this document: [email protected] The fulltext of this document has been downloaded 52 times since 2017* Users who downloaded this article also downloaded: (2017),"Antibacterial evaluation of cotton fabrics by using novel sulfonamide reactive dyes", Pigment & Resin Technology, Vol. 46 Iss 3 pp. 210-217 http://dx.doi.org/10.1108/PRT-08-2015-0080 (2017),"Multi-objective optimisation on end milling of hybrid fibre-reinforced polymer composites using GRA", Pigment & Resin Technology, Vol. 46 Iss 3 pp. 194-202 http://dx.doi.org/10.1108/PRT-09-2015-0085

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*Related content and download information correct at time of download. Composites of styrene butadiene rubber/modiﬁed clay: mechanical, dielectric and morphological properties Salwa H. El-Sabbagh, Doaa Samir Mahmoud and Nivin M. Ahmed Department of Polymers and Pigments, National Research Center, Cairo, Egypt A.A. Ward Department of Microwave Physics and Dielectrics, National Research Center, Cairo, Egypt, and Magdy Wadid Sabaa Department of Chemistry, Faculty of Science, Cairo University, Egypt

Abstract Purpose – This paper aims to study the role of organobentonite (OB) as a filler to improve the mechanical strength of styrene butadiene rubber (SBR). Organoclay was first prepared by modifying bentonite with different concentrations of N-cetyl-N, N, N-triethyl ammonium bromide. A series of SBR composites reinforced with OB were prepared using master-batch method. Design/methodology/approach – The curing characteristics, mechanical properties, thermal behavior, dielectric properties and morphology of SBR/OB composites were investigated. Findings – The elastic modulus and tensile strength of composites were increased by inclusion of OB, while the elongation at break was decreased, due to the increase in the degree of cross-linking density. Thermal gravimetric analysis revealed an improvement in the thermal stability of the composite containing 0.5 cation exchange capacity (CEC) OB, while the scanning electron micrographs confirmed more homogenous distribution of 0.5CEC OB in the rubber matrix. Also, SBR/0.5CEC OB showed low relative permittivity and electrical insulating properties. Research limitations/implications – Bentonite has been recognized as a potentially useful filler in polymer matrix composites because of their high swelling capacity and plate morphology. Practical implications – OB improves the cured rubber by increasing the tensile strength and the stiffness of the vulcanizate. Social implications – Using cheap clay in rubber industry lead to production of low cost products with high efficiency. Originality/value – The clay represents a convenient source because of their environmental compatibility. The low cost and easy availability make the modified clay used as fillers in rubber matrices, and the resultant composites can be applied in variety industrial of applications such as automobile industries, shoe outsoles, packaging materials and construction engineering. Keywords Composites, Mechanical properties, Fillers, Rubber, Hardness measurement Paper type Research paper Downloaded by EKB Data Center At 15:52 18 April 2017 (PT) Introduction reinforcing agent, and its possibility of being dispersed as individual particles in the rubber matrix is high (Chakraborty The reinforcement of rubber composites involved et al., 2010), but the hydrophilic nature of Na-bentonite create incorporating of reinforcing filler-like layered silicate clay, incompatibility with the hydrophobic rubber matrix (Das carbon black (CB) and silica in rubber matrix to create useful et al., 2011). product after vulcanization (Gujel et al., 2014), but still CB Most earlier efforts were concentrated on promoting the remains the most necessary reinforcing filler in rubber compatibilization rubber matrix and bentonite; it was proved manufacture. However, its black color and polluting nature that through cation exchange reactions, the clay mineral can caused researchers to look out for alternative “white” filler. react with a positively charged surfactant such as N-cetyl-N, Clay has been used in rubber manufacture for many years N, N-triethyl ammonium bromide (CTAB) to form because of its cheap and white color. It behaves as a good organically modified bentonite or organobentonite (OB). In these reactions, the metal cations are displaced by CTAB achieving sufficient organophilicity and rendering the OB more compatible with the rubber matrix (Das et al., 2011; The current issue and full text archive of this journal is available on Mclauchlin et al., 2011). Emerald Insight at: www.emeraldinsight.com/0369-9420.htm

Pigment & Resin Technology 46/3 (2017) 161–171 Received 13 December 2015 © Emerald Publishing Limited [ISSN 0369-9420] Revised 24 July 2016 [DOI 10.1108/PRT-03-2016-0034] Accepted 27 August 2016

161 Composites of styrene butadiene rubber/modiﬁed clay Pigment & Resin Technology Salwa H. El-Sabbagh et al. Volume 46 · Number 3 · 2017 · 161–171

Recently, researchers succeeded in intercalating small using flame photometer in the extracted solution (Zawraha amounts of well-dispersed OB layers into rubber matrix and et al., 2014). CEC can be calculated from the following preparing rubber clay composites with challenging new equation: “white” fillers to exchange CB (either wholly or partially) in rubber products to provide composites with efficient CEC (meq/100g) ϭ meq/L Na ϫ A/Wt ϫ 100/1000(1) reinforcement, functional properties and colored (Maity et al., 2008; Sinha and Okamoto, 2003). where A is the total volume of extract (ml) and Wt. is the This reinforcing effect of OB is caused by the high modulus weight of air dry sample (g). of the clay platelets which have relative to modulus of the ● In total,5gofNa-bentonite was first dispersed in 500 ml rubber matrix that facilitates its dispersion by lowering the of deionized water with mechanical stirring for about 24 h. surface energy of bentonite using chemical modification ● A pre-dissolved stoichiometric amount of CTAB solution (Mclauchlin et al., 2011). was slowly added to the bentonite suspension at 80°C. Generally, rubber/clay composites are classified into three ● Concentrations of used CTAB are 0.5, 1.0 and 2.0 groups according to their structures, i.e. intercalated, mEq/100 gm CEC of the bentonite, respectively. exfoliated or both of these structures. The exfoliated ● The reaction mixtures were stirred for6hat80°C using composites are more required due to that their layers exhibit mechanical stirring. the greatest reinforcement (Yang et al., 2011). ● All products were washed several times with deionized The present work focuses on rubber/organoclay water until no bromide anions were detected. composites that were prepared using master-batch method ● The presence of bromide anions was tested using 0.1 N with different concentrations of OB that is used as a AgNO3 solution. reinforcing filler (able to improve strength and hardness of ● The products were dried at 90°C, ground and sieved rubber composites). This study includes the investigation of through 230 meshes and then stored in vacuum curing characteristics, mechanical properties, dielectric desiccators (Zawraha et al., 2014; El-Sabbagh et al., 2015). properties, thermal behavior and morphology of rubber/OB composites. Preparation of styrene butadiene rubber composites The first step includes the mixing of SBR with its various Experimental ingredients (Table I) in a two-roll mill (diameter 470 mm Materials and width 300 mm) at a standard sequence. Then, rubber Sodium bentonite with 78.42 mEquiv/100 g cation exchange was mixed with the ingredients including OB with different capacity (CEC) which was obtained from Alfa Aesar GmbH loadings (3, 6, 9 and 12 phr) under careful control of and Co. (Karlsruhe, Germany). The CTAB used as a modifier temperature. Vulcanization was carried out in a single-day was purchased from Merck KGaA, Germany. light electrically heated auto controlled hydraulic press Ϯ Styrene butadiene rubber (SBR) copolymer has 23.5 per at 152 1°C and pressure 4 MPa (El-Sabbagh et al., 2015). cent styrene content, specific gravity of 0.945 Ϯ 0.005, moony The chemical properties of the used OB in this study have viscosity ML (1 ϩ 4) at 100°C ϭ 52 Ϯ 3 and glass transition already been studied by Ahmed and El-Sabbagh (2014). Tg ϭϪ60°C, and it was obtained from Transport and Engineering Company (TRENCO) Alexandria. Characterization of rubber composites Downloaded by EKB Data Center At 15:52 18 April 2017 (PT) Accelerators: N-cyclohexyl-2-benzothiazole sulphenamide Curing characteristics (CBS). Trade name: Rhenogran® CBS-80, Vulkacit® CZ The cure characteristics of rubber composites were was obtained from Rheinehemie Germany. determined using a Monsanto Rheometer (model 100) at Antioxidants: polymerized 2, 2, 4-trimethyl-1, 2- 152 Ϯ 1°C according to ASTM D 2084. From graphs, dihydroquinoline (TMQ). Trade name: PILnox® TDQ was optimum cure time, scorch time and cure rate index, purchased from Nocil Limited, Navi Mumbai, India. minimum torque (M ) and maximum torque (M ) were Activators: Stearic acid with specific gravity 0.9-0.97 at L H determined. 15°C, and zinc oxide (ZnO) with density 5.5-5.61g/cm3 at 15°C were supplied by Aldrich Company, Germany. Mechanical testing Curing agent: Sulfur with density 2.04-2.06 g.cm؊3 at room Tensile strength, elongation at break (%) and Young’s temperature (25°C Ϯ 1) was supplied by Aldrich Company, modulus of the rubber composites were determined with a Germany. Zwick 1,425 testing machine (Germany) according to ASTM Solvent: Toluene with pure grade. D412. Dumbbell specimens of 2 mm thickness were cut from the molded sheets with a Wallace die cutter. A cross-head Preparation of organoclays speed of 500 mm/min was used, and the tests were performed The CEC was determined for the raw clay sample by at 25 Ϯ 3°C. Five specimens were used, and the average was saturation with 1 N solution of sodium acetate trihydrate calculated in each case, and then the vulcanized sheets were

(CH3COONa.3H2O) for a while at pH 8.2, and then cut into ﬁve individual dumbbell-shaped specimens by a steel washed for several times with 95 per cent ethanol to get rid die of constant width (4 mm). The thickness of the tested of the excess sodium ion. The reacted sodium (Na؉) with specimen was determined by a gauge calibrated in hundredths the clay was extracted by reaction with1Nammonium of a millimeter, with working part of size 15 mm that was acetate solution followed by determination of the sodium chosen for each tested specimen.

162 Composites of styrene butadiene rubber/modiﬁed clay Pigment & Resin Technology Salwa H. El-Sabbagh et al. Volume 46 · Number 3 · 2017 · 161–171

Table I Formulations and rheological characteristics of SBR loaded with Na-bentonite and OB

Torque ␣ ؊1 Sample no. Filler content, phr ML (dNm) MH (dNm) Tc90 (min) Ts2 (min) CRI (min ) f difference (dN m)

SBR loaded with Na-bentonite

s0 – 2.5 25 18.5 7 8.7 – 22.5

s1 3 2.5 26 16.25 6 9.7 9.01 23.5

s2 6 2.5 25 16 6.25 10 8.4 22.5

s3 9 4 32 15.5 5.5 10 6.35 28

s4 12 5.8 35 15 5 10 6.4 29.2

SBR loaded with 0.5 CEC OB

s5 3 5 37 16.5 5 8.6 8.8 32

s6 6 5.8 35 14 4.75 10.08 7.69 29.2

s7 9 6.3 39 13.5 3.75 10.02 6.3 32.7

s8 12 6.5 44 10.5 3.5 10.43 3.2 37.5

SBR loaded with 1 CEC OB

s9 3 5.5 26 15 4 9.01 7.5 20.5

s10 6 6 38 14 4 10.00 7.2 32

s11 9 6.1 39 13.25 3.75 10.05 3.8 35.5

s12 12 6.5 40 12 3.75 10.2 3.41 35

SBR loaded with 2 CEC OB

s13 3 10 35 15 4.5 9.5 8.9 25

s14 6 13.5 35 13.5 3.75 10.02 4.2 21.5

s15 9 13.5 30 12 3.75 10.2 3.6 16.5

s16 12 13 32 13.5 4 10.05 3.4 19

Notes: Base recipe in phr: SBR 100; stearic acid 2; zinc oxide 5; CBS (N-cyclohexyl-2-benzothiazole sulfenamide) 1; processing oil1; sulfur 2; ML is minimum torque; MH is maximum ␣ torque; tS2 is scorch time; tc90 optimum cure time; cure rate index (CRI) is cure rate index; f is speciﬁc constant for reinforcement of ﬁllers, where phr is part per hundred parts of rubber

Hardness (Shore A) of the vulcanized samples was the secondary electron emission characteristics of the measured using the Shore A durometer according to ASTM overgrowth. D 2,240. Thermal analysis Broadband dielectric relaxation measurements Thermal gravimetric investigation was carried out using The permittivity ␧’ and the dielectric loss ␧“ of SBR loaded Perkin Elmer analyzer equipment, USA. Sample weights with Na-bentonite and OB were measured at 30°C and between 13 and 25 mg were scanned from 50 to 1,000°C frequencies of 0.1 Hz to 5 MHz using an impedance using a nitrogen air ﬂow of 50 ml/min and heating rate of analyzer (Schlumberger Solartron 1,260) an electrometer, 10°C/min.

Downloaded by EKB Data Center At 15:52 18 April 2017 (PT) ampliﬁer and measuring cell as described before (El-Sabbagh et al., 2012), the error in ␧’ and ␧”amounts to Results and discussion Ϯ1 per cent and Ϯ3 per cent, respectively. The temperature Curing tests of the samples was controlled by a temperature regulator Curing characteristics of SBR composites are given in Table I. with Pt 100 sensor, and the error was about Ϯ0.5°C. To Scorch time (t ) and cure time (t ) of SBR composites were avoid moisture, the samples were stored in desiccators in s2 c90 reduced for composites loaded with the different the presence of silica gel. Thereafter, the sample was concentrations of (OB) more than the neat elastomer and transferred to the measuring cell and left with P O until 2 5 composites loaded with Na-B. These results can be attributed the measurements were carried out. to good interactions and interfacial adhesion between OB and Scanning electron microscopy analysis the rubber matrix (Malas and Das, 2013). The concentration Scanning electron microscopy (SEM) (JEOL JX 840) of OB is indirect relationship with the cure rate index (100/

micro-analyzer electron probe (Japan) was used in this work to TC90 –TS2). The increase in cure rate may cause the increase estimate the particle shapes of ﬁller and surface of rubber of vulcanization reaction and make extra active crosslink sites vulcanizates unloaded and loaded with the prepared OB. The within the rubber composites (Pal et al., 2010). Minimum

samples were photographed using SEM, after being coated torque (ML) can be considered as a measure of the stock

with a very thin layer of gold to avoid electrostatic charging modulus and maximum torque (MH) depending on the range during examination. The samples were prepared as follows: of cross-linking between rubber chains and reinforcing ﬁller

the surface of the polymer was mounted on standard specimen (Teh et al., 2004). It was noticed that ML and MH increased stub for scanning electron microscopic observation, and then with increasing OB loading up to 1CEC, any further addition a thin coating (10-6 m) of gold was deposited onto polymer of OB led to a decrease.

surface to the stub prior to examination in the microscope. The torque difference (MH-ML) that measures the extent of The previous step was used to enhance the conductivity and cross-linking, varies drastically from one compound to another

163 Composites of styrene butadiene rubber/modiﬁed clay Pigment & Resin Technology Salwa H. El-Sabbagh et al. Volume 46 · Number 3 · 2017 · 161–171

(Sezna et al., 1989). The OB was found to enhance the curing that the composites exhibited a general increase in the process because it can absorb and thus block the movement of mechanical properties with increasing OB loading in the rubber chains and the cure agents. Therefore, the reduction in rubber matrix (Noriman et al., 2010). The SBR composites torque values can be associated with incorporation of OB in the showed an increase in the tensile strength and a decrease in SBR chains, which prevents the formation of cross-links and thus elongation at break. Figure 1 represented SBR composites reduces the rigidity of the material. The torque difference is loaded with 12 phr 0.5CEC OB which showed the highest related to the cross-link density; its increase causes the tensile strength (6.01 MPa) compared to that of SBR (3.8 enhancement of the tensile strength, modulus, hardness and MPa). This can be due to better distribution of OB in the decrease of elongation at break. SBR matrix which leads to improving the interfacial adhesion of OB/SBR composites by reducing the interfacial Mechanical testing energy among the phases (El-Sabbagh et al., 2015). Also, it The inﬂuence of OB content on the mechanical properties can be noticed that the increase in tensile properties of SBR composites was studied, and the results revealed occurred with a slight decrease in the elongation at break

Figure 1 Variation of tensile strength and elongation at break of SBR vulcanizates loaded with different concentrations of OB Downloaded by EKB Data Center At 15:52 18 April 2017 (PT)

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with the increment of OB content as can also be seen in Figure 3 Variation of hardness of SBR vulcanizates loaded with Figure 1. different concentrations of OB In Figure 2, the modulus at 100 and 200 per cent elongation increased may be due to the good dispersion of OB particles in SBR matrix (Larissa et al., 2011), and their improvement can be detected in the order:

SBR Ͻ Na-B/SBR Ͻ 1CEC OB/SBR Ͻ 2CEC OB/SBR Ͻ 0.5CEC OB/SBR

The effect of OB content on hardness of SBR composites is illustrated in Figure 3, and it can be seen that in presence of 0.5CEC OB, hardness values increased quite rapidly compared to the other concentrations. This observation indicated that 0.5CEC OB is more effective in reinforcing rubber. Also, the increase in the cross-link density probably increases the hardness of these rubber composites. To account for the increment in modulus according to the to be constants for a specific strain level and temperature. ⌽ is different factors such as chemical interaction of surface treated attributed to the volume fraction of fillers within the SBR fillers. New generalized exponential equation was proposed, composites. In log scale, equation (3) takes the form: correlating the modulus and volume fraction of the filler as ϭ ϩ ␾ follows (Changwoon et al., 2003): ln ͑EF/E0͒ ln a b (3)

Ef Values of Ln E /E against different volume fractions of ϭ aeb␾ (2) F o E0 investigated filled composites are plotted in Figure 4. The relation between the different volume fraction and Ln EF/Eo where E is the Young’s modulus, the subscripts F and 0 values for all composites was drawn; the slope of the straight indicate filled and neat rubber samples, a and b are considered line of this figure is the values of the constant. The best fit straight line equation corresponding to the experimental values is represented in equations (4)-(7) as follow: Figure 2 Variation of modulus at 100 and 200 per cent elongation 1 For Na-Bentonite: of SBR vulcanizates loaded with different concentration of OB ϭ Ϫ ϩ ␾ ln ͑EF/E0͒ ln 1.351 12.27 (4)

2 For (0.5CEC) OB:

ϭ Ϫ ϩ ⌽ ln͑EF/E0͒ ln 7.61 52.52 (5) Downloaded by EKB Data Center At 15:52 18 April 2017 (PT) 3 For (1CEC) OB:

ϭ Ϫ ϩ ␾ ln͑EF/E0͒ ln 1.58 10.94 (6)

4 For (2CEC) OB:

ϭ Ϫ ϩ ϫ Ϫ4␾ ln ͑EF/E0͒ ln 0.9865 3.1269 10 (7)

The ﬁller–rubber interactions within the composite were described by the constant b (Zhang et al., 2003; Changwoon et al., 2003). Substantially, big slope represented by (b ϭ and 3.1269 ϫ 10؊4) is for composites 10.94 ,52.52 ,12.27 ﬁlled with Na-B, 0.5CEC OB, 1CEC OB and 2CEC OB, respectively. The dispersion of silicate layers increases the modulus that provides intense interaction through the creation of hydrogen bonds between the silicate layers and polymer matrix. In fact, the mobility of the rubber chains is retarded close to the OB surface, as a result of the strong interaction between polymer chains and the clay surface that successively causes the promotion of Young’s modulus (Helaly et al., 2012). The moduli can be in the following order:

165 Composites of styrene butadiene rubber/modiﬁed clay Pigment & Resin Technology Salwa H. El-Sabbagh et al. Volume 46 · Number 3 · 2017 · 161–171

Figure 4 Variation of Young’s modulus versus volume fraction of SBR composites loaded with (a) Na-B, (b) 0.5CEC(OB), (c) 1CEC(OB) and (d) 2CEC(OB)

SBR composites filled with 0.5CEC OB Ͼ 2CEC OB Ͼ 2CEC OB are given in Figure 5. From Figure 5,itwas Na-B Ͼ 1CEC OB. These results are in high agreement with observed that the filled systems showed higher ␧’ than the later properties (rheological and mechanical). pristine rubber. It is well-known that ␧’ of material increases with the increase in its polarizability (Guojun Downloaded by EKB Data Center At 15:52 18 April 2017 (PT) Dielectric study et al., 2012). However, in the high frequency region, The values of ␧’ and ␧” versus the applied frequency f for polarization effects can be ignored, as the dipoles are not SBR filled with 12 phr of Na-B, 0.5CEC OB,1CEC OB and able to follow the change of the electric field (Ku and

Figure 5 Permittivity ␧’ and dielectric loss ␧” versus frequency f of SBR ﬁlled with 12 phr of Na-B, 0.5CEC OB, 1CEC OB and 2CEC OB

101 14 S0 S0 S4 S4 12 S8 S8 S12 100 S12 S16 S16 10 ε'' ε' 8 10–1 6

4 10–2

10–1 100 101 102 103 104 105 106 107 10–1 100 101 102 103 104 105 106 107 f [Hz] f [Hz] (a) (b)

166 Composites of styrene butadiene rubber/modiﬁed clay Pigment & Resin Technology Salwa H. El-Sabbagh et al. Volume 46 · Number 3 · 2017 · 161–171

Liepins, 1987). As a result, the values of ␧’ decreased with Figure 6 The conductivity “␴” of SBR composites frequency, and they reached rather a constant value at the end of the frequency range. On the other hand, the values of ␧’ increased with filler addition; this is due to the presence of polar groups in layered silicates and intercalation of the polymer chain that took place between the silicate layers. In Figure 5(b), the dielectric loss (␧“) of SBR composites is represented as a function of frequency. At lower frequency, the samples exhibited higher ␧” values due to the effect of conductivity and interfacial polarization. Moreover, due the broadness of ␧” curves, more than one relaxation process can be expected (Ku and Liepins, 1987). These relaxation processes can be related to the mechanisms of the main chain motions (Hill et al., 1969). The relaxation process at high frequency can be due to the segmental motion of the main chain (Ward et al., 2013a, 2013b; Ward and Khalaf, 2007), whereas the lower polarization. This can be also referred to the fact that frequency process is related to Maxwell Wagner effect layered silicate is polar and its presence enhances ␧’ values which is usually found in heterogeneous systems (Ward of composite. In addition, the values of ␧’ for a filled system et al., 2013a, 2013b; Ward and Khalaf, 2007). depends on the filler size, shape, spatial distribution and ␧ ␧ Figure 5 shows that the values of ’ and ” are high in low adhesion between the polymer and filler. The uniform frequency region. This may be due to the increase in space distribution of the filler is a clear indication of good charge mobility and/or polarization (Helaly et al., 2012; Bishai adhesion between filler and rubber (see SEM in Figure 8). et al., 2003). To confirm this previous finding, the This adhesion in turn enhances ␧’; moreover, the sample ␴ conductivity “ ” was calculated from the resistance containing 0.5CEC OB showed the most promising measurements using Schlumberger Solartron 1,260 and dielectric results, which are represented in Figure 7.Inthe represented in Figure 6. From this figure, it is obvious that the figure, higher values of ␧’ and lower ␧” were compared to ␴ addition of CEC OB filler increases “ ”, and this increase by the other filled samples. This result is well supported by the the addition of layered silicate is due to the presence of polar mechanical properties, as this sample possesses the most groups which promote the conducting processes. In addition, promising mechanical properties. the conductivity slightly dropped after addition of 0.5CEC OB, and then increased by increasing the CEC OB. This is attributed to the poor interfacial interaction between SBR and Scanning electron microscopy analysis CEC OB. The dispersion of clay was confirmed and clarified by SEM However, for frequency 100 Hz ␧’ and ␧“ increased by as shown in Figure 8. It can be noted from Figure 8(a) that, increasing CEC OB content, this can be seen in Figure 7. unfilled SBR domains are separated facilely from the SBR The higher values of ␧’ and ␧” that is attributed to the matrix due to the poor interfacial adhesion between them, Downloaded by EKB Data Center At 15:52 18 April 2017 (PT) presence of interfacial polarization and orientation and thus the distribution of these domains into SBR matrix

Figure 7 Permittivity ␧’ and dielectric loss ␧” at ﬁxed frequency (f ϭ 100 Hz) of SBR ﬁlled with 12 phr of Na-B, 0.5CEC OB, 1CEC OB and 2CEC OB

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Figure 8 SEM micrographs of (a) SBR, SBR loaded with 12phr (b) bentonite, (c) 0.5CEC OB, (d) 1CEC OB and (e) 2CEC OB at magniﬁcation 1,000 x102X Downloaded by EKB Data Center At 15:52 18 April 2017 (PT)

is not uniform. Figure 8(b) shows that, an addition of 12 sizes; this behavior can be clariﬁed by the compatibilization phr Na-B led to a decrease in the rubber average effect of OB (Bendjaouahdou and Bensaad, 2013). inter-particle distance, and the average size of the dispersed Figure 8(d) and (e)showed that at higher concentration of rubber phase was found to be about 4.53 ␮m(Kanapitsas OB (1CEC and 2CEC), the rubber domain sizes increased et al., 1998). Figure 8(c) showed that, the average rubber to about 2.61 and 2.96, respectively. It is worthy to note domain size was reduced to about 2.79 ␮m in samples that, in Figure 8(c), the particles size in SBR composites having 0.5CEC OB in the composites, and the distribution loaded with 0.5CEC OB are small and distributed of these rubber domains into matrix becomes more homogenously; this demonstrated the highest value homogenous, with good dispersion. This was observed with obtained for tensile strength at 0.5CEC OB (Kanapitsas low cohesion and a narrow distribution of SBR particle et al., 1998; Tabtiang et al., 2000).

168 Composites of styrene butadiene rubber/modiﬁed clay Pigment & Resin Technology Salwa H. El-Sabbagh et al. Volume 46 · Number 3 · 2017 · 161–171

Thermal gravimetric analysis Finally, from the previous results, it can be concluded that Thermal gravimetric analysis (TGA) has been used to adding 0.5CEC OB to SBR exhibits better thermal stability. evaluate thermal behavior of SBR matrix loaded with Na-B In general, the properties of samples containing 0.5CEC and different OB loadings and CECs. From Figures 9(a), OB and 2CEC OB did not exhibit any decrease, while those the curves showed two degradation stages of the rubber, having 1CEC OB slightly decreased, but they are still which occur normally via bond scission along the chain of higher than unfilled samples or those containing Na-B. This SBR. The higher value of an initial temperature of is due to the degree of aggregation, distribution of OB decomposition was observed by adding OB as a result of the within the SBR matrix, polymer–filler and filler–filler cross-linking with the organoclay which leads to an increase interactions, especially in the cases of using reinforcing filler in the stability of matrix, and the same behavior was as clay. observed for final thermal temperature (Dikobe and Luyt, 2009; Pappa et al., 2011). Moreover, it can be observed that a higher residual weight loss percentage was obtained for Conclusions SBR composites containing 0.5CEC OB; this can be This paper focuses on the development of SBR/organoclay attributed to that the addition of OB brought stability composites for various industrial applications. Clays with toward the dispersed phase due to the presence of 0.5, 1 and 2CEC of surfactant were filled in SBR matrix. surfactant (Arjmandi et al., 2015). Also, it was observed The mechanical, thermal, morphological and solvent that the matrix degradation temperature increases with OB uptake properties of the prepared composites were loading. Furthermore, some exothermic peaks were evaluated. The results showed that the tensile strength and obtained in differential thermal analysis (DTA) curve Young’s modulus were affected by the addition of indicating the vulcanization of SBR composites that was organoclay. Also, the samples containing 0.5CEC OB incompletely curved. There was a shift in exothermic peak showed the best mechanical properties among the prepared (thermal degradation peak temperatures) after adding Na-B rubber/clay composites, while the other samples containing or OB to higher temperature (Pappa et al., 2011; Arjmandi 1 and 2CEC OB exhibited lower properties, although they et al., 2015). are still better than samples having Na-B. The better physical interaction between 0.5CEC OB and SBR matrix Figure 9 TGA curves of (a) weight loss percentage, (b) derivative was demonstrated by SEM observation. The dielectric Wt.% of SBR loaded with 12 phr bentonite and OB properties revealed that SBR containing 0.5CEC OB

1.5 showed promising dielectric properties with low relative 1.4 SBR permittivity and electrical insulating properties. The SBR 1.3 bentonite composites loaded with 0.5CEC OB showed high thermal 1.2 (0.5CEC) OB 1.1 (1CEC) OB stability than other composites filled with different 1.0 (2CEC) OB concentrations (1 and 2CEC OB). 0.9 0.8 0.7 0.6 References Weight loss, % 0.5 0.4 Ahmed, N.M. and El-Sabbagh, S.H. (2014), “The Influence 0.3 0.2 of Kaolin and Calcined Kaolin on SBR composite Downloaded by EKB Data Center At 15:52 18 April 2017 (PT) 0.1 properties”, Journal of Polymer Composites, Vol. 35 No. 3, 0.0 pp. 570-580. –0.1 0 100 200 300 400 500 600 Arjmandi, R., Hassan, A., Eichhorn, S.J., Haafiz, M.K.M., Tempature, °C Zakaria, Z. and Tanjung, F.A.J. (2015), “Enhanced (a) ductility and tensile properties of hybrid montmorillonite/ cellulose nanowhiskers reinforced polylactic acid 100 nanocomposites”, Material Science, Vol. 50 No. 8, pp. 3118-3130.

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