Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

CHAPTER ELEVEN

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers Mehmet Kodal1,2, Nursel Karakaya1, Abdulmounem Alchekh Wis1 and Guralp Ozkoc1,2 1

Department of Chemical Engineering, Kocaeli University, Kocaeli, Turkey Polymer Science and Technology Graduate Program, Kocaeli University, Kocaeli, Turkey

2

Contents 11.1 Introduction 11.2 Differential Scanning Calorimetry 11.2.1 Differential Scanning Calorimetry Instructions 11.2.2 Heat Flux Differential Scanning Calorimetry 11.2.3 Power-Compensated Differential Scanning Calorimetry 11.2.4 Calibration 11.2.5 Characterization of Single Components 11.3 Differential Thermal Analysis 11.4 Differential Scanning Calorimetry Analysis of Carbon Nanofillers Incorporated Rubber Nanocomposites 11.4.1 The Effect of Carbon Black on Rubbers 11.4.2 The Effect of Graphene, Graphite, and Carbon Nanotubes on Rubbers 11.5 Thermomechanical Analysis 11.6 Thermomechanical Analysis of Carbon Nanofiller-Incorporated Rubber Nanocomposites 11.6.1 The Effect of Carbon Black on Rubbers 11.6.2 The Effect of Carbon Nanotubes on Rubbers 11.6.3 The Effect of Graphene on Rubbers 11.6.4 The Effect of Fullerene on Rubbers 11.7 Thermal Gravimetric Analysis 11.7.1 Determination of the Degradation Temperature 11.7.2 Determination of the Thermo-Oxidative Degradation Temperature 11.7.3 Determination of the Oxidation Induction Time 11.7.4 Physical Aging 11.7.5 Moisture Determination 11.7.6 Evolved Gas Analysis 11.7.7 Determination of Filler/Additive Content 11.7.8 Determination of Different Types of Plastics in One Sample 11.7.9 Modulated Thermal Gravimetric Analysis

Carbon-Based Nanofillers and Their Rubber Nanocomposites. DOI: https://doi.org/10.1016/B978-0-12-817342-8.00011-1

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© 2019 Elsevier Inc. All rights reserved.

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11.8 Thermal Gravimetric Analysis of Carbon Nanofiller-Incorporated Rubber Nanocomposites 11.8.1 The Effect of Carbon Black on Rubbers 11.8.2 The Effect of Carbon Nanotubes on Rubbers 11.8.3 The Effect of Graphene on Rubbers 11.8.4 The Effect of Fullerene on Rubbers 11.9 Conclusions References

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11.1 INTRODUCTION Rubber has the ability to return to its original shape after being stretched, and is used in many products from tires and cables to hoses and clothing. According to the Rubber Asia report, the total consumption of rubber worldwide increased to 27.2 million tonnes in 2016 with an annual increase of 1.8% [1]. The most widely used rubbers are cis-polyisoprene (natural rubber, NR), cis-polybutadiene (butadiene rubber, BR), styrene butadiene rubber (SBR), ethylene propylene diene monomer (EPDM), acrylonitrile butadiene rubber (NBR), silicone rubber (SR), and chloroprene rubber (CR). The only nonsynthetic elastomer is NR. The basic monomer of NR is cis-1,4-isoprene. NR is obtained from the Hevea brasiliensis tree which is grown in specific regions of the world. especially Thailand, Indonesia, Malaysia, and India. NR is used in almost all commercial rubber products due to its unique physical properties. NR has a very low glass transition temperature (Tg), approximately 73 C, due to its flexible chain backbone and weak intermolecular interactions. To obtain the desired properties, NR is compounded with oils, fillers, crosslinking agents, antioxidants, and processing aids. It has high wear and tear resistance and electrical resistance, and also chemical resistance to acids, alkalis, and alcohols, together with damping or shock-absorbing properties. On the other hand, due to the reactivity of double bonds in the main chain, NR is highly susceptible to degradation, specifically, it is sensitive to environmental factors, such as ozone, light, moisture, humidity, radiation, and heat. It is known that two-thirds of the overall production of NR is consumed in the vehicle tire-manufacturing factory. Twenty-one kilogram of NR is used for radial tires and nearly 9 kg NR is used for conventional truck tires. In addition, it is used in conveyor belts, hoses, shoe soles, cables, automotive parts (seals, blowers, windshield wipers, mats), sound and shock absorbers, floor coverings, gloves, balloons, and baby bottle nipples [2 8]. The most important and widely used synthetic rubber is SBR [9]. It is obtained by copolymerization of styrene and 1,3-butadiene by using an emulsion technique with free radical polymerization mechanism. It can be produced either at 30 60 C

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

(hot rubber) or near 0 C (cold rubber) temperatures, and the end products differ in some properties. Hot SBR has a branched chain structure and very low Tg, consequently, it is not used in tire manufacturing. For this reason, cold SBR has much more industrial importance nowadays. SBR is a copolymer of butadiene and styrene. The styrene content of SBR ranges from 10% to 25%. As the styrene content of SBR increases, it exhibits higher modulus and mechanical strength. Since SBR is an apolar polymer, it has high resistance to polar solvents. In addition, it immediately swells when exposed to oil and fuels. It can be cured with peroxide, sulfur, or phenolic resin systems. It has a lower heat build-up than NR. SBR is a general-purpose rubber-like NR and its main use is in vehicle tire production. Moreover, it is used in the manufacture of conveyor belts, cable and electric industry, V-belts, and flooring. Polybutadiene rubber is the second most commonly produced synthetic rubber in the world. It is produced by free radical or anionic chain polymerization of butadiene. The product mostly includes ( . 80%) trans-1,4. The cis-1,4 ratio, which is the main determinant of the Tg of BR, can be enhanced by increasing the reaction temperature. As NR, BR can also be vulcanized with sulfur. Different catalysts, such as neodymium, cobalt, nickel, titanium, and lithium are used in the production of BR. The catalyst system used determines the final properties of BR. The low vinyl content of BR results in a very low glass transition temperature (, 90 C). The low Tg of BR causes poor wet traction. BR is generally used in tire production, specifically in sidewalls and tread compounds. Furthermore, low rolling resistance and high abrasion resistance are the other essential advantages of BR [10 12]. EPDM, a saturated carbon hydrogen polyolefinic synthetic rubber, which is obtained by polymerizing ethylene and propylene with a small amount of a nonconjugated diene, possesses high electrical resistivity, excellent thermal aging, ozone resistance, and has high resistance to acids, alkalis, ketones, and alcohols. Nevertheless, it has some drawbacks, such as incompatibility with most oils such as gasoline, kerosene, and aromatic and aliphatic hydrocarbons, due to its nonpolarity, which restricts its versatile applications in the automotive industry. It is mostly used in the manufacture of hose, cable, belting, and sporting goods. Moreover, EPDM plays an important role in the tire industry, particularly for sidewalls. EPDM can be vulcanized by either sulfur or peroxide. EPDM vulcanized by peroxide exhibits higher thermal resistance and lower compression set compared to one vulcanized with sulfur. However, the crosslinking efficiency of peroxide-cured EPDM is lower, since the peroxide vulcanization accompanies side reactions, such as chain scission and disproportionation, which induce rapid consumption of the peroxide without formation of radicals [4,13 17]. NBR, in other words nitrile rubber, is a polar rubber, which is usually used in applications in which excellent oil resistance is required. NBR is obtained by polymerization of acrylonitrile and butadiene monomers. Nitrile rubber has different properties depending on the acrylonitrile (ACN) content, which ranges from 18%

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to 51%. The role of acrylonitrile in the copolymer is to reduce the solubility in hydrocarbons by providing a polar nitrile group. Meanwhile, butadiene provides basic rubbery properties and forms double bonds for vulcanization. Vulcanized NBR compounds are resistant to fuels, oils, lubricants, and gas at temperatures from 40 to 135 C, and also resistant to aging, fatigue, and abrasion. NBR is sometimes carboxylated to improve its physical properties [18 21]. CR is produced by free radical emulsion polymerization of 2-chloro-1,3-butadiene. The advantages of CR can be summarized as: air, ozone and aging, fire resistance, long-term resistance to water and chemicals, low gas permeability, high mechanical properties, and good adhesion to metals. Its high crystallization feature enables its use in the manufacture of adhesives. CR can be vulcanized with sulfur. Seventy-three percent of the CR produced is used in the rubber industry, 17% in adhesive production, and 10% in latex manufacturing. CR is used in the production of fuel hoses, hydraulic hoses, brake hoses, O-rings, chocks, bumpers, gaskets, and wiper blades in the rubber industry [22]. SR, which has a backbone composed of repeating silicon and oxygen bonds, can be classified into three categories, according to their crosslinking mechanism, the viscosity of the polymer and whether they cure at high or room temperature: (1) RTV (cured at room temperature); (2) HTV (cured at elevated temperature); and (3) liquid silicone rubber (LSR) (liquid silicone) has unique properties, such as good chemical stability, oxidation resistance, thermal stability, low-temperature toughness, and low toxicity, which enables its use in various industrial areas such as automotive, medical, aerospace, construction, and textile [23 25]. Rubbers are conventionally compounded with reinforcing fillers such as carbon black (CB) and carbon nanotubes (CNTs) in order to improve their thermal and mechanical properties. CB, a colloidal form of elemental carbon, is the most widely used reinforcing agent in the rubber industry. It is produced by partial combustion or thermal degradation of natural gas, light and heavy crude oils, and aromatic hydrocarbons under controlled oxygen atmosphere. There are several types of CB, such as furnace black, channel black, and thermal black, and 95% of applied blacks in rubber are produced with the furnace method. CB provides elastomers with strength, such as tensile and tear and toughness, enhances tear resistance, abrasion, and flex fatigue, and also improves traction, durability, and tensile modulus [3,26 29]. Another promising reinforcing filler in polymer-based composites is graphene. Graphene is a carbon allotrope with extremely high surface area, superior gas impermeability, and unique functional properties, which has planar monolayer carbon atoms arranged in a twodimensional (2D) honeycomb lattice. Graphene, as a unique one-atom-thick layer composed of sp2-hybridized carbon atoms aligned in a honeycomb lattice, possesses a breaking strength of 130 GPa, high thermal conductivity (up to 5000 W/mK), electrical conductivity up to 6000 S/cm, and an exceptional Young’s modulus (B1 TPa).

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

In addition to graphene, graphene oxide (GO) obtained from the natural graphite by oxidation is widely used to improve the properties of polymers [30 33]. The other promising candidate to improve mechanical and thermal properties of elastomers is CNTs. CNTs are composed of a graphene sheet rolled up into a tubular structure. CNTs can be synthesized by arc-discharge, laser ablation, and various catalytic chemical vapor deposition techniques. They can be classified as single-walled carbon nanotubes (SWCNTs), which are a single hexagonal layer of carbon atoms, and multiwalled carbon nanotubes (MWCNTs), which are a stack of graphene sheets rolled up into concentric cylinders. CNTs have high electrical conductivity (104 S/cm), high aspect ratio (diameter in nanometers to length in microns), high tensile modulus (640 GPa to 1 TPa), and high tensile strength (150 180 GPa). On the other hand, CNTs have a great tendency to agglomerate in polymer matrices due to the van der Waals forces. Therefore, CNTs are chemically functionalized through reactions such as oxidation, halogenation, and ozonolysis to improve its dispersion in polymer matrices [3,34 39]. Another carbon-based nanofiller that can be used as a reinforcing filler is fullerene. Fullerene is another allotrope of carbon that can be obtained by wrapping-up graphene. Fullerenes are hollow molecules composed of carbon in the sp2 hybrid state, which have superconductivity, low thermal conductivity, and hardness higher than that of diamond in the crystal state. C60, which consists of molecular balls made of 60 or more carbon atom clusters linked together, is the most important representative of fullerene [40,41].

11.2 DIFFERENTIAL SCANNING CALORIMETRY Differential scanning calorimetry (DSC), a thermoanalytical technique, measures temperatures and heat flows related to thermal transitions in a material. The difference in the amount of heat required to increase the temperature of a sample and reference is measured in this thermoanalytical technique. Both sample and reference pan, having a well-defined heat capacity over the range of temperatures being scanned, are exposed to the same heating history. The basic principle is simple, that DSC measures the amount of energy absorbed or released by a sample to maintain the same temperature of sample to the reference pan. Physical changes containing glass transition, melting and crystallization temperature, heat of fusion, oxidation induction times (OITs), and solidification can be determined. The technique was developed by E. S. Watson and M. J. O’Neill in 1962, and introduced commercially in 1963 [42]. The DSC set-up is comprised of a measurement chamber and a computer. Two pans are heated in the measurement chamber at the same time. The sample pan

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involves the material being investigated. A second empty pan is used as a reference. To monitor the temperature and regulate the rate at which the temperature of the pans changes, a computer is used. A typical heating rate is almost 10 C/min. The rate of temperature change for a given amount of heat will differ between the two pans. This difference depends on the composition of the pan contents as well as physical changes such as phase changes. The difference in heat output of the two heaters is recorded. The result is a plot of the difference in heat (q) versus temperature (T) [43].

11.2.1 Differential Scanning Calorimetry Instructions There are two main types of differential thermal instruments commercially available, differential thermal analyzers (DTAs) and DSCs. These instruments provide quantitative information about exothermic, endothermic, and heat capacity changes as a function of temperature and time (such as melting, purity, and glass transition temperature). The basic difference between DTA and DSC is that, the former measures temperature differences between the sample and reference pan, whereas DSC measures energy differences [44]. There are two basic types of DSC instruments: heat flux DSC and powercompensated DSC.

11.2.2 Heat Flux Differential Scanning Calorimetry The sample and reference are heated at the same rate from a single heating source in a heat flux DSC system. The temperature difference between the pans is recorded and converted to a power difference that gives the difference in heat flow. There are two types of DSC instruments, disk-type DSC and cylinder type DSC. Fig. 11.1 shows disk-type DSC instruments. Sample

S

R Reference sample Furnace

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ΔTSR

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Calorimetric calibration

Figure 11.1 Disk-type DSC instruments [45].

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Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

11.2.3 Power-Compensated Differential Scanning Calorimetry The sample and reference are heated separately in a power-compensated DSC. The pan temperatures are monitored using thermocouples attached to the disk platforms. The thermocouples are connected in series and measure the differential heat flow using the thermal equivalent of Ohm’s law (Eq. (11.1)). dq ΔT 5 dt RD

(11.1)

where dq/dt is the heat flow, ΔT is the temperature difference between the reference and sample, and RD is the thermal resistance of the disk platform. The heat flow to each pan is adjusted to keep their temperature difference close to zero while the furnace temperature is increased linearly. It is used to obtain qualitative and quantitative information about the physical and chemical changes that materials undergo during heating [43]. Fig. 11.2 shows a power-compensated DSC.

11.2.4 Calibration The reliability of the DSC results depends upon the care taken in calibrating the instrument as close to the transition temperatures of interest as possible. The accuracy of results obtained is strongly dependent on the use of high-purity calibration standards and clean DSC sensors. Well-defined standards and calibration procedures are particularly important when comparing the results of analyses performed using different instruments or at different times. Calibration standards have classically been metals such as indium, tin, bismuth, and lead. Other metals have also been used but to a lesser extent because of toxicity (mercury) and handling problems (gallium). Some workers have proposed using organic compounds as standards when studying organic material because of their significant differences in thermal conductivity, heat capacity, and heat of fusion [46]. It is likely that metals will continue to be popular temperature

S

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TR

T(t) Program Control TS = TR + ΔTSR

Figure 11.2 Power-compensated DSC [45].

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Figure 11.3 DSC thermograms of PLA [49].

and enthalpy standards as a result of their widespread availability and ease of use. Organic standards, however, have interesting potential below 300K, where few traditional standards are available [47]. Separate calibration is required at each scan rate used, and it has been argued that calibration in both heating and cooling modes is necessary to achieve the highest level of accuracy [48].

11.2.5 Characterization of Single Components Single components can exhibit the following thermal behavior: melting, crystallization, boiling, sublimation, dehydration, desolvation, solid solid transitions, glass transitions, and polymorphic transitions. These transitions may be endothermic or exothermic. A standard DSC scan for a semicrystalline polymer undergoing a glass transition, crystallization, melting is shown in Fig. 11.3.

11.3 DIFFERENTIAL THERMAL ANALYSIS An alternative technique, which shares much in common with DSC, is DTA. In this technique, the heat flow to the sample and reference remain the same rather

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

T(t) Program

Crucibles S

ΔTSR

R Sample

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Reference sample Furnace Thermocouples ΔTSR

TR

Figure 11.4 DTA measuring system with freestanding crucibles [45].

than the temperature. When the sample and reference are heated identically, phase changes and other thermal processes cause a difference in temperature between the sample and reference. Both DSC and DTA provide similar information. DSC measures the energy required to keep both the reference and the sample at the same temperature, whereas DTA measures the difference in temperature between the sample and the reference [50]. Fig. 11.4 shows the DTA measuring system.

11.4 DIFFERENTIAL SCANNING CALORIMETRY ANALYSIS OF CARBON NANOFILLERS INCORPORATED RUBBER NANOCOMPOSITES 11.4.1 The Effect of Carbon Black on Rubbers In this section, the effect of CBs on the thermal properties of rubber composites were discussed. Fan et al. [51] investigated the thermal properties of NR latex modified by purple carbon black (PCB). They discovered that the glass transition temperature (Tg) of vulcanized latex film increased by the addition of KH560 silane coupling agent modified PCB. On the other hand, Oliveira et al. reported that DSC is not sensitive enough to detect Tg changes in CB-based NR composites [52]. Similar observations related to the insensitivity of DSC to determine the Tg of the NR/CB composites were found by Kenny et al. [53]. They concluded that the immobilization of small amounts of firmly bound rubber on CB particle surfaces, cause insufficiency of this

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procedure to identify Tg changes in NR/CB composites. In another study, DSC experiments showed that CB increased the heat of reaction during the vulcanization under isothermal conditions, which was due to a higher degree of curing in the presence of CB [54]. Long-term performance of di(2-ethylhexyl) phthalate-containing CB-filled NBR membrane was investigated by Linde et al. [55]. As can be seen in Fig. 11.5, the Tg of the samples aged at 140 and 160 C was higher than that of that without plasticizer, which indicated that oxidative crosslinking had occurred. Sebenik et al. [56] investigated the effect of CB type (N234, N330, and N550) on the properties of in situ cured polyurethane (PU)/hydrogenated nitrile-butadiene rubber (HNBR) compounds. The Tg of HNBR in the HNBR/PU/CB compounds shifted back to that of the plain HNBR with the decreasing reinforcing ability of CB (N234 . N330 . N550). The authors suggested that the surface chemistry of CB may have affected the possibility of interchain crosslinking. In another study by Noriman and Ismail [57], blends of styrene butadiene rubber/recycled acrylonitrile butadiene rubber (SBR/NBRr) with different ratios of carbon black/silica (CB/Sil) hybrid filler were prepared. They revealed that the curing temperature of blends increased as the amount of silica increased and the amount of CB decreased. The effects of some processing parameters, such as mixing time, mixing temperature, vulcanization time, and vulcanization temperature of CB-filled SBR membranes were systematically investigated by Wan et al. [58]. Any distinct endothermic peaks in the DSC spectra of the composites processed with different mixing parameters were observed, as can be seen in Fig. 11.6. –15

–20

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Figure 11.5 Glass transition temperature as a function of aging time for samples taken from the middle of the samples aged at 90 C (x, line a), 120 C (’, line b), 140 C (&, line c), and 160 C (▲; line d) [55].

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

(I) 2 mJ

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Figure 11.6 DSC thermograms of composite membranes. (I) Mixing temperature: 80 C, mixing time: 7 min, nip gap: 4 mm; (II) mixing temperature: 60 C, mixing time: 9 min; nip gap: 4 mm; (III) mixing temperature: 60 C, mixing time: 7 min, nip gap: 3 mm; (IV) optimized mixing parameters; (V) pure BMP crystal [58].

Jun-Xue et al. [59] reported that the glass transition temperature of solutionpolymerized styrene-butadiene rubber (SSBR), including different contents of CB, decreased with increasing loading level of CB, which indicated that there were three kinds of mobility states among the rubber chains: free chains, loosely adsorbed chains, and tightly adsorbed chains. In a recent study, the thermal properties of ternary SR/ CB/TiB2 nanocomposites were investigated by Ismail et al. [60]. These authors found that the melting temperature and the percent crystallinity of SR in the presence of 10 wt.% CB were 42.17 C and 78.6%, respectively. In another study, Jovanovic et al. [61] investigated the effects of CB on the properties of NBR/EPDM rubber blends. They concluded that CB-reinforced EPDM/NBR rubber blend exhibited two separate Tg, an evidence of poor interfacial interactions between NBR and EPDM.

11.4.2 The Effect of Graphene, Graphite, and Carbon Nanotubes on Rubbers In this section, the effect of CNTs on the thermal properties of rubber composites are discussed. The thermal conductivity of NR and epoxidized NR composites, including CNTs, were investigated by Kummerlo¨we et al. [62]. A high increase in thermal conductivity was achieved with a low CNT content. However, it turned out that the thermal resistance at the interface between CNTs and the matrix restricts the increase in thermal conductivity. For epoxy/single-walled CNT composites, an increment of thermal conductivity was found by the incorporation of 1 wt.% CNTs. In another study, NR composites reinforced with pretreated

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CNTs were prepared by Sui et al. [63]. A slight increase in the Tg of NR with the increase of filler loading was specified, since the fillers can impede the activation of the rubber macromolecular chains, and keep macromolecular fragments from acquiring the requested arrangement of the crystal lattices. The vulcanization rate of the NR framework decreased, which was attributable to the addition of CNTs in this study. Thomas et al. [64] reported the thermal analyses for phenol functionalization of CNTs/NR. DSC analysis revealed that Tg of NR stayed unaltered within the presence of both CNT- and phenol-functionalized CNTs. Graphite (GT), thermally reduced graphene oxide (TRG), and a hybrid consisting of TRG and ionic liquid [1-ethyl-2,3-dimethylimidazolium bis (trifluoromethylsulfonyl) imide]-modified carbon nanotubes (IMCNTs) were added to NR in the study of Yaragalla et al. [65]. The thermal characteristics of GT, TRG, and hybrid IMCNT 1 TRG-filled NR composites were studied and it was shown that there were not many significant changes in the glass transition (Tg) of neat NR with the addition of fillers. However, the heat capacity, ΔCp of the systems decreased due to the segmental mobility of polymer chains. The reason for this may be that the filler may stick some portions of the NR polymer chains and leads to restricted segmental mobility of the NR chains. Atieh investigated the effect of modified CNTs on the thermal properties of SBR nanocomposites. A direct change in the Tg of the NR was accomplished with an increase in the amount of both P-CNT and CNT-COOH in the matrix compared to the pure rubber. However, it was resolved that CNT-COOH gave a comparable outcome with respect to the pure CNT incorporated with SBR [66]. De Falco et al. [67] investigated the effects of adding a small amount of MWCNTs on SBR vulcanization reaction with a sulfur/n-t-butyl-2-benzothiazole sulfenamide cure system. A reduction of ΔH and a shift to higher maximum exothermal peak temperature (Tp) values were observed for the composites as the MWCNT loading level increased. It is interesting that the addition of CNTs created a postponing impact in all responses according to the DSC results. The effect of the addition of SWCNTs on the properties of a polypropylene (PP)/ EPDM (80/20) blend was investigated by Narimani and Hemmati [68]. The authors stated that the crystallization temperature (Tc) of PP/EPDM/SWNT nanocomposites fundamentally increased as the SWCNT content was increased. This situation could be ascribed to SWCNTs acting as nucleating agents, resulting in a higher crystallization rate. The fusion of SWCNTs influenced the crystalline content and structure of the polymer network and affirmed the use of SWCNTs as a reinforcement in composite materials. A hybrid compound of multiwalled carbon nanotubes alumina (MWCNTs-Al2O3) was added into silicone rubber of polydimethylsiloxane (PDMS). The results reveal that the addition of CNTs in the PDMS composites induced endothermic changes in the heating curve. As more CNTs were incorporated in the composites, the more vitality was retained as heat. This showed that CNTs improved the

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1.0

0 0.05 0.15

0.8 0.6

Heat flow (a.u.)

0.4 0.2 0.0 –0.2 –0.4 –0.6 –0.8 –50 –40 –30 –20 –10 0 10 20 Temperature (ºC)

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Figure 11.7 DSC heating scan of pure XNBR and XNBR/MWCNT composites [71].

thermal properties of the PDMS composite [69]. Ryu et al. [70] reported that the degree of strain-induced crystallization increased with the increased content of CNT in NBR composites. The Tg of the composite increased in the presence of CB and CNT. Preetha Nair et al. [71] reported the latex stage blend of MWCNTs in carboxylated acrylonitrile butadiene rubber (XNBR) latex. DSC analysis was conducted to determine the effect of MWCNTs on the Tg of XNBR. As can be seen from Fig. 11.7, a small increase in Tg of XNBR was obtained by the incorporation of nanotubes. MWCNT-reinforced silicone rubber (SiR) nanocomposites were prepared by Katihabwa et al. [72]. A decrease in the degree of crystallinity (Xc) and supercooling (ΔT) showed that the crystallization rate of the nanocomposites was increased. The crystallization temperature (Tc) of pure SiR increased with the addition of different loading levels of CNTs. This indicates that the dispersed CNT layer in the matrix acted as nucleation seeds that induce further crystallization in CNT/SiR composites. Abd Razak et al. prepared [73] NR/EPDM blends filled with graphene nanoplatelets (GNPs) and investigated the effects of GNP loading levels. The results indicate that the addition of GNPs at low loading levels affected the thermal heat flow and shifted the Tg to some extent. A graphene/room temperature vulcanized (RTV) SR composite was prepared by Dong et al. [74]. DSC curves of the composites showed a single Tg. With the increase in the graphene concentration, Tg was increased and Tm was decreased. The substantiation was the diminishing of the molecular chain adaptability of PDMS, because of the interactions between graphene and PDMS.

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Composites-0% Composites-2% Composites-4% Composites-6% Composites-8% 111.17ºC 110.46ºC 109.27ºC 108.80ºC 105.53ºC 40

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Figure 11.8 DSC curves of ABS/EPDM composites at different GN contents [75].

Acrylonitrile butadiene styrene (ABS)/ethylene propylene diene monomer (EPDM) composites reinforced with GNPs were prepared by Wang et al. [75]. The result demonstrated that the Tg of ABS/EPDM was enhanced by the addition of GN. As can be seen from Fig. 11.8, no crystallization peak could be found in the presence of GN nanoplates. In a recent study conducted by Yin et al. [76] ionic liquid 1-allyl-3-methyl-imidazolium chloride (AMICI) was used to fine-tune the surface properties of GO sheets for fabricating ionic liquid-functionalized GO (GO-IL)/styrene-butadiene rubber (SBR) nanocomposites. The results reveal that the Tg of GO-IL increased in pure AMICI due to the strong interaction between AMICI molecules and GO. The influence of graphene on the vulcanization kinetics of SBR with dicumyl peroxide was studied by Tang et al. [77]. The results demonstrated that the graphene essentially increased the enthalpy of the reaction. They remarked that graphene presumably participated in the vulcanization procedure. In another recent study [78], several solution-polymerized styrene-butadiene-p-(2,2,2-triphenylethyl)styrene (TPES) rubbers (SBTRs) with different levels of TPES were synthesized by anionic copolymerization. The strong interactions of such TPES groups and pristine GNSs were investigated. It was concluded that the Tg of SBTR-1/GNS composite increased from 31.6 to 27.7 C, showing a strong interaction between the SBTR-1 rubber matrix and GNS engendered by the formation of covalent bonds. The compatibilization of GO in XNBR/SBR blends was validated by DSC experiment in the study by Zhang et al. [79]. DSC results showed that Tg of SBR was shown to shift upward, and Tg of XNBR shifted to a lower temperature in the presence of GO, since GO improved

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

the miscibility and compatibility between them. In another study, functionalized graphene (FG)/styrene-butadiene rubber (SBR) composites were prepared by Schopp et al. [80]. The results show that the thermal transitions of SBR/thermally reduced graphite oxide (TRGO) nanocomposites were not affected by the incorporation of up to 25 phr TRGO. Luo et al. [81] prepared graphene/SSBR composites. DSC results showed that there was insignificant difference between the Tg of a graphene/SSBR composite and neat SSBR. Wu et al. [82] modified GO with polystyrene and polyisoprene to improve its dispersion in SSBR rubber matrix. It was observed that the glass transition temperatures of SSBR-BR composites slightly increased by the addition of graphene compared to the neat SSBR-BR composite. The results suggest that graphene was embedded in crosslinked network and limited the segment movement of chains.

11.5 THERMOMECHANICAL ANALYSIS Thermomechanical analysis (TMA) is a thermal analysis technique, based on the measurement of the dimensional changes in a specimen as a function of temperature or time under load at atmospheric pressure. If the measurements are performed under negligible load, the technique is also called thermodilatometry (TD) [83]. TMA is a technique for precise measurement of position, which consists of a sample platform, furnace, heat sink, temperature-measuring device (thermocouple) surrounding the samples, and a sensitive position transformer (Fig. 11.9). During the Linear motor

LVDT

Signal (position)

Thermocouple Probe Sample

Furnace

Figure 11.9 Schematic diagram of a TMA instrument [83].

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Expansion

Probe displacement

Increased chain mobility Limited or no chain mobility Expansion of Vf

Tg

Tm

Temperature (ºC)

Figure 11.10 A schematic representation of a TMA curve in an expansion—mode experiment [83].

measurements, purge gas, preferably helium (other common gases are nitrogen and air), is used to ensure continuous laminar gas flow. Heating rates in the range of 1 5 C/min can be used, depending on the desired sensitivity, sample size, and purge gas [83,84]. It is recommended that the sample is homogeneous and the upper and lower surfaces are parallel and smooth for precise measurement [84]. Fixtures, generally made out of quartz, are used to hold the samples, and available for expansion, three-point bending or flexure, parallel-plate, and penetration tests [85]. The significant outcomes of TMA include the glass transition temperature (Tg) and the coefficient of thermal expansion (CTE, α). The obtained data for dimensional changes indicate the changes in the material’s free volume. The relationship of free volume to transitions is given in Fig. 11.10. The glass transition temperature, Tg, is related to the expansion of free volume, which allows greater chain mobility above this transition [83,84]. An inflexion or bend in the thermal expansion curve can be used for calculation of Tg, using the method given in Fig. 11.11. TMA, due to its high sensitivity, can be used to measure Tg values that are difficult to obtain by DSC, for example, those of highly crosslinked thermosets [85]. The material’s expansivity (CTE) can be obtained from the same data set of thermal expansion test. The equation below can be used to calculate the CTE (Eq. (11.2)):   1 ΔL ~5 (11.2) L0 ΔT P

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

+0.3

Displacement (%)

+0.1 +0.2

Tg

0.0 Tmg

–1.0

Tlg

–2.0

310

350 390 430 Temperature (K)

470

Figure 11.11 Determination of the glass transition temperature (Tg) from a TMA curve and the corresponding derivative TMA curve [84].

where L0 is the initial length of the sample, ΔL is the change in length of the sample, and ΔT is the temperature range. This value is important in the design of products, consisting of several dissimilar materials in contact, in order to prevent any delamination or failure. It has to be considered that, in the case of heterogeneous or anisotropic materials, CTE should be recorded in all (x, y, and z) directions [85]. Due to the thermal history of the sample, the value of Tg or α may change significantly after the first run. In order to eliminate the thermal history effect, the sample should be tested for two runs to obtain the value of Tg or α values [84]. TMA can also be used for the acquisition of some other physical properties, such as creep, stress relaxation, Young’s modulus, shear modulus, flexural stress, softening point and heat deflection temperature, gel time, the degree of swelling, hard-core volume, and crosslink density [83]. In the modulated temperature TMA technique, a sinusoidal temperature modulation (overlaid on a linear underlying heating, cooling, or isothermal profile) is applied to the sample. This technique enables the differentiation of irreversible dimensional changes from reversible ones, such as shrinkage in oriented fibers and films and creep [83]. The details, regarding thermal properties of rubber-based nanocomposites reinforced with carbon-based nanofillers, determined by TMA technique, are nested below in their respective sections. It is obvious that there are relatively few reports dealing with TMA technique application on rubber-based nanocomposites when compared with the enormous number of studies using DSC or thermal gravimetric analysis (TGA).

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11.6 THERMOMECHANICAL ANALYSIS OF CARBON NANOFILLER-INCORPORATED RUBBER NANOCOMPOSITES 11.6.1 The Effect of Carbon Black on Rubbers Measurement of dimensional changes and CTE in CB-filled rubbers are the main uses of the TMA technique. For example, in the study of Kato et al. [86], CB-filled NR vulcanizates were prepared. CB loading was varied from 5 to 80 phr in the vulcanizates. The dependence of the CTE on the volume fraction of the CB/NR interaction layer was examined by use of TMA, under tensile mode loading of 0.098 N, at a rate of 2 K/min from 273 to 423 K in an N2 gas atmosphere. A sudden change (i.e., the transition point) in the CTE, in the CB loading region of 20 30 phr, was observed. At this transition point, which was caused by carbon black network (CBN) formation, the model of the mixing law presumably changes from a series mechanical model before CBN formation, to a parallel one after the network forms. In a similar study, the effect of phenolic resin in CB/nitrile rubber (NBR) vulcanizates was investigated. TMA was conducted under a static load of 10 g, 10 C/min heating rate in a nitrogen atmosphere. The results reveal that the dimensional change is more obvious when 50 phr CB is used, compared to neat NBR. On the other hand, structural integrity and compactness of the vulcanizate improve when phenolic resin and CB are used in combination, which leads to lower susceptibility toward dimensional changes [87]. Moreover, Jurkowska et al. [88] studied the changes in the topological and molecular structure of BR, during mastication, and mixing with CB using a method of TMA. Their results reveal that CB usage increases the shear forces, which are the reason for macroradical formation, and also changes the topological structure of polybutadiene [88]. In a successive study, similar properties were also analyzed for NR and its blends with polybutadiene (BR), using the same TMA method [89].

11.6.2 The Effect of Carbon Nanotubes on Rubbers Electrical conductive polymer composites consisting of CNTs have attracted huge interest in a variety of applications, and the change in electrical resistance of these composites in heat-related applications remains a key issue. Lee et al. [90] dealt with the concept of excluded volume to suppress the negative temperature coefficient of resistance of a MWCNT/SR composite. In this study, MWCNT/SR composites were prepared, with different loading levels of micro- and nano-silica particles. According to TMA results, the decrease in dependence of the resistance on temperature can be attributed to the enhancement of mechanical modulus and the reduction in thermal expansion of the composites, especially in the use of the nanoparticles.

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

Table 11.1 Tg and CTE Data of PDMS Hybrid Composites [91] xGnP Content (%) Tg ( C) CTE Below Tg ( 3 1026/ C)

0 25 50 75 100

76.5 77.0 77.3 77.4 77.2

65.6 60.0 55.3 53.6 22.4

CTE Above Tg ( 3 1026/ C)

362.2 326.8 314.9 301.1 288.1

It can be drawn from this that effect of mechanical reinforcement and suppression in thermal expansion by the secondary particles is essential for suppressing the temperature dependence of resistance [90]. In another study, composites of PDMS were prepared by incorporating a combination of exfoliated graphite nanoplatelets (xGnPs) and MWCNTs functionalized with hydroxyl groups (MWCNTs-OH). The hybrid filler was used at 4 wt.% in the nanocomposites, where the xGnP content varied at 0%, 25%, 50%, 75%, and 100%. TMA was conducted to measure the CTE of the nanocomposites below and above Tg. The results showed that both CTE values of PDMS hybrid composites decreased with increasing xGnP content in the hybrid filler (Table 11.1). This was due to the fact that CTE of PDMS/MWCNT-OH single-filler composite was higher than that of PDMS/xGnP single-filler composite [91].

11.6.3 The Effect of Graphene on Rubbers Polymers are known to have a higher expansion coefficient compared to metals. On the other hand, use of fillers like graphene or clay reduces the thermal expansion, due to the interaction of fillers with the matrix, which constrains the movement of many polymer chains [92]. In the study by Lin et al. [93], acrylamide-modified reduced graphene oxide (AARGO) and thiophenol-modified silver nanowires (mAgNWs) were used as reinforcements in SR, to enhance its thermal properties. CTEs of nanocomposite samples were characterized by a thermomechanical analyzer (TMA) from 30 to 200 C, which is similar to the application temperature for TIMs (thermal interface materials), under nitrogen at a heating rate of 5 C/min. It was found that 6 and 10 phr AA-RGO/SR nanocomposites showed less thermal expansion behavior than neat SR. This means that embedded AA-RGO can fix polymer chains in the SR matrix and reduce the chain mobility, which lowers the CTE. For samples that incorporated mAgNWs with AA-RGO/SR, even lower CTE was observed since mAgNWs have a low CTE and high aspect ratio, interacting mechanically with the SR matrix, which reduces the thermal expansion. The CTE of the mAgNW/AA-RGO/SR nanocomposites was obtained as 148.3 ppm/ C, which differs considerably from the CTE of neat SR,

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310.0 ppm/ C. This suggests the use of AA-RGO mAgNWs hybrid/SR composites as thermal interface materials [93]. As already mentioned in Section 11.6.2, a hybrid filler, composed of xGnPs and MWCNT-OH, was incorporated into PDMS. According to the TMA results, both CTE values (above and below Tg) of PDMS hybrid composites decrease with increasing xGnP content in the hybrid filler, since the CTE of PDMS/xGnP single-filler composite is lower than that of PDMS/MWCNT-OH single-filler composite [91].

11.6.4 The Effect of Fullerene on Rubbers Jurkowska et al. [94] have studied the effect of fullerene, in concentrations between 0.065 and 0.75 phr, when dispersed within CB, on the properties of NR. In this study, TMA was used to determine the glass transition, Tg, beginning of flow, Tf, compaction factor, Vc, and coefficient of linear thermal expansion in glassy, α1, and rubbery states, α2. Tg and α1/α2 values were found to be slightly dependent on fullerene concentration. The results suggest that the rigidity of the rubber network increases with the increase in fullerene concentration. It was observed that the fullerene particles possibly create high-temperature-resistant junctions.

11.7 THERMAL GRAVIMETRIC ANALYSIS TGA can be defined as a thermal analysis technique, where the change in mass of a polymer is measured as a function of temperature or time in a controlled atmosphere [83,85]. Temperature can be increased up to 1000 C or more, for commercially available TGAs. Different types of purge gas may be used, such as inert (nitrogen, argon, or helium), oxidizing (air, oxygen), or reducing gases (forming gas). Little amount of samples, for example, less than 5 mg, can be analyzed by this technique. The heating rate is generally used in the range of 5 20 C/min, while the slower rate is better to differentiate any overlapping thermal events [83]. In TGA equipment, the sample is placed in a controlled furnace, and the temperature of the furnace is monitored by a thermocouple via the millivoltmeter. Meanwhile, the balance allows the continuous mass determination. In the end, a plot of mass as a function of temperature, or time, is obtained as the result of the analysis, as illustrated schematically in Fig. 11.12. This curve presents the relation between mass change versus temperature data and chemical physical events occurring in the sample measured [95]. TGA can be used to identify thermal events like desorption, absorption, sublimation, vaporization, oxidation, reduction, and decomposition. It gives the opportunity

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

Mass change (%)

0

Tl

–50

Tf –100

Reaction interval Temperature (K)

Figure 11.12 Schematic single-stage TGA plot [84].

to characterize the decomposition and thermal stability of materials under a variety of conditions and to examine the kinetics of the physicochemical processes occurring in the sample [84]. TGA may be used for a variety of purposes, as summarized below.

11.7.1 Determination of the Degradation Temperature Thermal degradation is the molecular deterioration because of overheating. The thermal degradation temperature represents an upper limit to the service temperature of plastics. There are two techniques for determination of degradation temperature. In the isothermal method, the weight loss is measured with time, while the sample is set to a temperature that is between 50 and 150 C above its melting temperature. When the melting temperature of the sample is already known, this method enables identification of the physical aging at high temperatures. A nonisothermal degradation test is performed using an increasing temperature pattern while measuring the weight loss. It is generally used when the degradation temperature is unknown [85].

11.7.2 Determination of the Thermo-Oxidative Degradation Temperature It is known that some polymers undergo thermo-oxidative degradation when exposed to oxygen. If the polymer is to be used in air, information about its thermo-oxidative stability becomes even more important, in order to propose stabilizer systems to inhibit its oxidation. For this purpose, the sample is analyzed under air or oxygen, and a nitrogen atmosphere in separate TGA runs. Comparison of the results can be used as an indicator of thermo-oxidative stability. It is recommended to use slower heating rates (e.g., # 1.5 C/min) to clearly observe the mass gaining oxidation step [83].

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11.7.3 Determination of the Oxidation Induction Time The OIT can be identified by TGA analysis, with the method of heating a sample of less than 10 mg to an isothermal temperature (typically 200 C) in oxygen and waiting until the sample begins to gain mass as oxidation starts. This technique can be utilized to find the unknown amount of an antioxidant in a polymeric sample, and also the most effective antioxidant system for a polymer [83].

11.7.4 Physical Aging TGA provides accelerated testing for prediction of lifetime performance. The lifetime prediction includes the identification of the critical reaction which limits the life of a material and the measurement of its kinetics at high temperature. By extrapolation of the kinetics by the use of proper kinetic expressions, one can calculate the reaction rate at lower temperatures [85,95].

11.7.5 Moisture Determination It is essential to determine the moisture content of hygroscopic plastics since water can decompose the structure of the plastic, and finally weaken the mechanical properties. For this purpose, the sample is kept at a temperature below its melting point (40 60 C below) for 1 2 hours under a nitrogen atmosphere [85].

11.7.6 Evolved Gas Analysis This is a hyphenated technique, where more than one instrument is used simultaneously, to analyze the gaseous products evolved during TGA measurement. In this technique, the quantities of the components, as well as the types of components, may be determined by the use of TGA-MS and TGA-FTIR, and TGA-GC [84,85].

11.7.7 Determination of Filler/Additive Content TGA may be used in order to quantify the filler/additive content in the plastics, by heating the sample to and above its decomposition, with a heating rate of 15 30 C/min [85].

11.7.8 Determination of Different Types of Plastics in One Sample Blending different plastics leads to a material with better properties than those of the individual plastics. In TGA, for identification of the components, the sample is run from room temperature to 100 C above the component having the highest decomposition temperature, with a heating rate of 20 30 C. Although this technique is used, the more accurate method is to use DSC and FTIR testing along with TGA [85].

347

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

11.7.9 Modulated Thermal Gravimetric Analysis Modulated TGA is mainly used to gather continuous kinetic information for processes in which volatile reaction products are produced. This may be observed in the cure of phenolics and decomposition of polymers [83].

11.8 THERMAL GRAVIMETRIC ANALYSIS OF CARBON NANOFILLER-INCORPORATED RUBBER NANOCOMPOSITES 11.8.1 The Effect of Carbon Black on Rubbers In this section, the effect of CB on the thermal stability of rubber composites is discussed. Jankovic et al. [96] investigated the comparative kinetic analysis of a nonisothermal degradation process of acrylonitrile-butadiene/ethylene propylene diene rubber blends reinforced with CB and silica fillers. It was concluded that the samples which contain the highest CB content (50 phr), presented the best self-protective property. As can be seen from Fig. 11.13, the shoulders appeared at lower temperatures when CB NBR/EPDM 70 phr SiO2 NBR/EPDM 35 phr CB/35 phr SiO2 NBR/EPDM 50 phr CB/20 phr SiO2

TG

100

β = 20ºC/min 0.0

d(m)/dT (%/ºC)

Mass (%)

90 80

–0.2

–0.4

–0.6

70

–0.8 DTG –1.0

60 50

100

NBR/EPDM 70 phr SiO2 NBR/EPDM 35 phr CB/35 phr SiO2 NBR/EPDM 50 phr CB/20 phr SiO2

200

300

400

500

600

Temperature (ºC)

β = 20ºC/min 100

200

300

400

500

600

Temperature (ºC)

Figure 11.13 Thermogravimetric (TG) and the derivative thermogravimetric (DTG) curves of the NBR/EPDM 70 phr SiO2, NBR/EPDM 35 phr CB/35 phr SiO2, and NBR/EPDM 50 phr CB/20 phr SiO2 degradation processes under nitrogen atmosphere, performed at a constant heating rate of β 5 20 C/min (CB) [96].

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was used as a filler, indicating that the degradation in the presence of CB was more complex. It was indicated that the interaction between CB and matrix was found to be greater with the increase in CB loading level in the matrix. The thermal stability of the NBR/EPDM blend increased by the addition of CB. Moreover, the incorporation of CB and its content increased from 35 to 50 phr compared to the NBR/EPDM rubber compound reinforced with 70 phr of silica, resulting in an increase in the value of peak temperatures (Tp) from 472.86 to 475.91 C at a heating rate of 20 C/min. In a similar study by Jankovic et al. [97], the nonisothermal degradation of CB reinforced acrylonitrile-butadiene/ethylene propylene diene rubber blends were investigated. The maximum rate of the main degradation step decreased in CB-filled NBR/EPDM blend compared to the virgin rubbers. Moreover, the apparent activation energy of the whole degradation process was improved by the addition of significant amount of CB filler. Thermo-oxidative aging and thermal analysis of CB-filled NR/virgin EPDM and NR/recycled EPDM blends were investigated by Nabil et al. [8]. Fig. 11.14 shows the TGA plots of CB-filled blends. It can be seen that degradation of blends occurred at two stages. The first step of degradation of the blends including CB started at 300 C and was completed at 450 C. In another study, thermally stable elastomeric composites, which contain EPDM and conducting polymer-modified carbon black (CPMCB) additives were prepared by casting and crosslinked by compression molding. TGA results demonstrated that the composites were thermally stable with no obvious degradation. Additionally, CPMCB has been observed to improve the processing of composites [98]. Thermal behavior of NBR reinforced with CB (N-330) was investigated by Samarzija-Jovanovic et al. [99]. 120

Weight loss (%)

100 80 NR/Virgin EPDM (90/10) NR/Virgin EPDM (70/30)

60

NR/Virgin EPDM (50/50) NR/Recycled EPDM (90/10) NR/Recycled EPDM (70/30) NR/Recycled EPDM (50/50)

40 20 0

0

100

200

300 400 Temperature (ºC)

500

600

Figure 11.14 Weight loss as a function of temperature (TGA curves) at a different blend ratio of CB-filled NR/virgin EPDM and NR/recycled EPDM blends [8].

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

The outcomes demonstrated that the organic functional groups of CB surface prompted an increase of the grip at the interface between CB and the rubber matrix, resulting in thermal stability and mechanical properties of the NBR/CB blends. In another study by the same researchers, the effects of different types of CB (N330 and N990) on the thermal properties of NBR were analyzed. They discovered that NBR having 80 phr N990 CB performed the best stability [100]. SBR/CB composites were prepared by Mohanraj et al. [101]. The results revealed that lower-molecular-weight ingredients, such as plasticizer and stearic acid, and polymer underwent thermal degradation, but CB remained unaffected. Blends of SBR/ NBRr reinforced with CB/Sil hybrid were tested by Noriman and Ismail as mentioned above. The level of char residue for blends with Si69 was higher than without Si69 since the compound structure of Si69 was comprised of hydrocarbons, which prompted the development of char during degradation. Therefore, Si69 contributed to the general level of char residue [57]. In a recent study conducted by Jovanovic et al. [102], polyisoprene (NR), polybutadiene (BR), and SBR ternary blend (NR/BR/SBR) reinforced with CB were prepared. The TGA and DTG curves proposed two types of mass loss: (1) the first appeared in the temperature interval of 200 400 C with a mass loss of 32.4 13%; (2) the second appeared in the temperature interval of 400 500 C with a mass loss of 94 67% (Fig. 11.15) [102]. Oliveira et al. [103] prepared the NR and CB composites in different percentages. It was observed from TGA analysis that a mass loss of about 5% for all samples occured between 100 and 250 C and above 456 C, only CB was remained. N330 CB-reinforced NR composites were prepared by Ismail et al. [104]. It was found that both CB and halloysite nanotubes did not alter the degradation mechanism of NR composites but changed the degree of degradation. The TGA results showed that the thermal stability of NR nanocomposites was changed insignificantly with different loading levels of CB/HNTs. In another study, the thermal stability of oil palm ash (OPA), silica, and CB-filled NR vulcanizates was investigated by Ooi et al. [105]. Among the types of filler analyzed, the CB exhibited better thermal stability, compared to the OPA and silica fillers. Table 11.2 shows a summary of the articles discussed in Section 11.8.1.

11.8.2 The Effect of Carbon Nanotubes on Rubbers Hoikkanen et al. [106] studied the effect of MWCNTs on the properties of EPDM/ NBR elastomer blends. TGA results showed that the temperature range for chain degradation of MWCNT-filled EPDM was always higher compared to pure EPDM. Therefore, MWCNTs increased the thermal stability of EPDM.

349

(A)

30

100

0.4 20

40

0

20

–10

Mass lost rate (%/ºC)

10

60

0.2

Heat flow (μV)

Mass (%)

80

0.0 –0.2 –0.4 –0.6 –0.8

–20

0 100

200

300

400

–1.0

500 600 Temperature (ºC)

(B)

200

300

400

500 600 Temperature (ºC)

100

200

300

400

500 600 Temperature (ºC)

1.0

100 90

20

80

10

50 40 30 20

Heat flow (μV)

60

Mass lost rate (%/ºC)

0.5

70 Mass (%)

100

0.0

–0.5

0

10 –1.0

0 100

200

300

400

500 600 Temperature (ºC)

Figure 11.15 TGA and DTG thermograms of: (A) NR/BR/SBR (25/25/50) and (B) NR/BR/SBR/CB blend [102]. Table 11.2 Summary of the Articles Related to the Thermal Stability of CB-Filled Rubber Composites Reference Nanocomposite System Results (Effect of CB on the Thermal Stability)

[96] [97]

NBR/EPDM/CB/Si NBR/EPDM/CB

[8]

NR/virgin EPDM/CB NR/recycled EPDM/CB EPDM/CPMCB NBR/CB (N330) NBR/CB(N330) NBR/CB(N990) SBR/CB

[98] [99] [100] [101] [57] [102] [103] [104] [105]

SBR/NBRr/(CB/Sil) NR/BR/SBR/CB RNP/CB RNP/Si/PP/NR NR/CB(N330) NR/OPA/CB/Si

Thermal stability is significantly improved Very strong self-protective behavior Decreased the maximum rate of the main degradation step High amount of char residue Slight increase in thermal stability; thermally stable Slight increase in thermal stability Increase in thermal stability N330 $ N990 Increase in thermal stability; nitrogen $ oxygen atmosphere Increase in thermal stability; with Si69 $ without Si69 Increase in thermal stability Increase in thermal stability Si $ CB Increase in thermal stability Increase in thermal stability compared to neat NR

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Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

Table 11.3 TGA Results of XNBR and XNBR MWCNT Composites [71] Name Onset Temperature Peak Maximum

Residue

T50

T75

XNBR XNBR .05 MWCNT XNBR .15 MWCNT

13.67 15.91 16.54

450 450 452.63

471 471 475

330 333 334

456 458 459

Preetha Nair et al. [71] prepared MWCNT-reinforced NBR composites. First, MWCNTs were dispersed in sodium dodecyl benzene sulfonate (SDBS) by sonication. Then, dispersed MWCNTs were incorporated in XNBR latex. As can be seen from Table 11.3, both T50 and T75 were slightly higher in the presence of MWCNTs compared to pure XNBR. In addition, as the MWCNT loading level increased from 0.05 to 0.15 phr, the percentage of residual weight increased. In a similar study, properties of MWCNT/elastomer composites were investigated by Perez et al. [107]. It was discovered that the percentage of residual weight increased with increasing amount of CNTs in the SBR and NBR elastomers. It was stated that MWCNTs acted as a physical barrier, resulting in a decrease in thermal degradation of elastomers. In another study, the thermal degradation of HNBR/clay and HNBR/ clay/CNT nanocomposites was investigated by Chen et al. [108]. Fig. 11.16 shows the TGA curves of the samples. It can be seen that the addition of clay and CNTs caused a shift in the mass loss towards a higher temperature. The TGA results showed that CNTs improved the thermal stability of HBNR/clay. Abdullateef et al. [109] investigated the effects of surface-oxidized CNTs on the thermal stability of the NR. It was observed that the addition of CNTs did not improve the thermal stability. On the other hand, the acid-modified CNTs demonstrated improvements in the thermal stability by increasing the degradation temperature by around 10 C. In another study, NR SWCNT composites through latex compounding were prepared by Anoop Anand et al. [110]. TGA results showed that the thermal stability of NR was not affected with SWCNTs at concentrations of up to 2.0 phr. On the other hand, Mohamed et al. [111] reported that MWCNTs increased the thermal stability of the NR-latex due to the barrier effect of MWCNTs. The increase in thermal stability was resulted from homogeneous dispersion of MWCNTs in the polymer matrix by use of the trichain surfactant with terminal methyl groups, that produced a higher density of filler matrix interactions in the nanocomposites. Matos et al. [112] prepared novel functional composite materials obtained by NR latex and a special kind of MWCNT where the cavities were filled by magnetic species. It was shown that NR degradation rate was retarded in the presence of CNTs. Moreover, the amount of residue was found to be higher in the composites. In a recent study, multifunctional MWCNT-reinforced NR composites were prepared by Thomasukutty et al. [113]. The thermal stability of the pure polymer and its nanocomposites were examined by performing TGA under nitrogen atmosphere.

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(A) 100

Residual weight (wt%)

80

60

40

20

HNBR HNBR/clay (100/5) HNBR/clay/CNTs (100/5/0.4) HNBR/clay/CNTs (100/5/0.8)

0 350 (B)

400 450 Temperature (ºC)

500

0.0

–0.5

DTG

–1.0 –1.5 –2.0 –2.5 –3.0 380

HNBR HNBR/clay (100/5) HNBR/clay/CNTs (100/5/0.4) HNBR/clay/CNTs (100/5/0.8) 400

420

440 460 Temperature (ºC)

480

500

Figure 11.16 TGA (A) and DTG (B) curves of different samples at a heating rate of 5 C/min [108].

From the TGA curves (Fig. 11.17) it was evident that NR including filler exhibited relatively good thermal stability compared to a gum sample. It was stated that MWCNTs prevented the thermal degradation of the matrix material due to its good dispersion into the matrix. In the study conducted by De Falco et al. [67], the effects of low loading levels of MWCNTs on the thermal degradation of SBR were studied. TGA results showed that the incorporation of MWCNTs into the matrix did not change the thermal

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Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

110

NR1 NR0 NR2 NR3 NR4

100 90 80 Weight (%)

70 60 50 40 30 20 10 0 –10 0

100

200

300

400

500

600

700

800

Temperature (ºC)

Figure 11.17 Weight-loss TGA curve of the NR/MWCNT nanocomposites with temperature [113].

degradation of the composites significantly. Boonmahitthisud and Chuayjuljit [114] used CNTs and nanosilica as reinforcing fillers in NR/SBR blended latex. They found that the addition of both CNTs and nanosilica enhanced the thermal stability of NR/SBR blend. The temperatures for onset (Tonset) and end set (Tend set) degradation of the nanocomposites were all shifted towards higher temperatures. In another study, chloroprene/CNTs/polyaniline (PANI) nanocomposites were prepared by Massoumi et al. [115]. In this study, MWCNTs were carboxylated (MWCNTCOOH) by a conventional acid oxidation process, and then poly(ethylene glycol) monomethyl ether was covalently attached to the MWCNT-COOH via an esterification reaction. It was concluded that functionalized MWCNTs improved the thermal stability of the CR. Table 11.4 shows a summary of the articles discussed in Section 11.8.2.

11.8.3 The Effect of Graphene on Rubbers While providing reinforcement and conductivity, graphitic fillers improve thermal stability, orientation flexibility, photosensitive properties, etc. of the elastomers. Moreover, among the various graphitic fillers, graphite nanoplatelets (GNPs) and graphene (GE) have superior thermal conductivity, and thermal and dimensional stability, compared to expanded graphite (EG) composites [30]. It is known that the use of graphene as a nanofiller enables the creation of char after thermal degradation. Moreover, graphene acts as a heat retardant, inhibitor, and barrier, which enhances the total thermal stability of the system [116,117]. Due to its inert and hydrophobic surface, graphene is not compatible with many polymers.

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Table 11.4 Summary of the Articles Related to the Thermal Stability of CNT-Filled Rubber Composites Reference Nanocomposite System Results (Effect of CNTs on the Thermal Stability)

[106] [71] [107] [108] [109] [110] [111] [112] [113] [67] [114] [115]

NBR/EPDM/MWCNTs XNBR/MWCNTs NBR/MWCNT, SBR/MWCNTs HNBR/clay/CNTs NR/CNTs NR/SWCNTs NR-latex/MWNCTs NR-latex/CNTs NR/MWCNTs SBR/MWCNTs NR/SBR/MWCNTs Chloroprene/MWCNTs

Increase in thermal stability Slightly increase in thermal stability Increase in thermal stability Slightly increase in thermal stability Increase in thermal stability No change Increase in thermal stability Increase in thermal stability Increase in thermal stability No change Increase in thermal stability Increase in thermal stability

Therefore, there are many studies in the literature, which deal with the modification of its surface to provide it with suitable functional groups that are able to promote good dispersion and strong interactions with the chemical moieties in polymers [73]. Studies about NR/graphene and silicone/graphene have been reviewed by Saleem et al. [118]. It can be concluded that a good dispersion of graphene, achieving good filler rubber interaction, nanocomposite preparation method, and surface modification of the filler were the determining factors of the mechanical and thermal properties of nanocomposites. Table 11.5 aims to also supplement the review with very recent studies using TGA to study the effects of graphene on the thermal properties of rubber-based nanocomposites. Zhan et al. [119] prepared NR/GE composites by an ultrasonically assisted latex mixing and in situ reduction process and showed that the process produced a much better dispersion and exfoliation of GE in the matrix compared to conventional direct mixing. According to the TGA results, regarding the thermal stability of samples, it was noted that the incorporation of GE did not improve the thermal decomposition temperature of NR composites [119]. In a similar study about NR nanocomposites, Matos et al. [120] modified the surface of GO with the surfactant cetyltrimethylammonium bromide (CTAB), and obtained NR/rGO. They followed a green route to obtain NR/rGO and NR/GO, based on latex technology. The composites were characterized by different techniques, including TGA. NR/GO nanocomposites again had similar degradation temperature with the unfilled NR, which means the presence of GO did not affect the thermal stability of the rubber. However, it was observed that nanocomposites with rGO had lower degradation temperature due to the presence of the surfactant CTAB.

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

Table 11.5 Summary of Works Using TGA to Study the Effect of Graphene on Thermal Properties of Rubber-Based Nanocomposites Reference Nanocomposite System Results (Effect of Nanofiller on Thermal Properties)

[119] [120]

[73]

[121] [122] [80] [123] [124]

[125] [126] [127] [128] [129] [130] [91]

NR/GE NR/GO NR rGO—prepared with surfactant CTAB NR/EPDM/GNP NR/EPDM/modified GNPs PEI SBR/GE SBR/CB/reduced graphene SBR/FG SSBR/EG SSBR/MEG SBR/CB/EG and i-MG BR/CB/EG and i-MG SBR/BR/CB/EG and i-MG IIR/CB/EG IIR/CB/MEG IIR/MG NBR/GT SR/graphite oxide Silicone foam/FG LSR/GO LSR/TEVS-GO PDMS/xGnPs/MWCNTs-OH

No change No change The decrease in thermal stability Increase in thermal stability Lower increase in thermal stability compared to unmodified GNP Increase in thermal stability A slight increase in thermal stability No change Increase in thermal stability Increase in thermal stability

Increase in thermal stability Increase in thermal stability Increase in thermal stability Increase in thermal stability Increase in thermal stability Decrease in thermal stability compared to neat LSR Increase in thermal stability compared to neat LSR No change

GE, Graphene; GO, Graphene oxide; GNP, Graphene nanoplatelets; GT, Graphite; FG, Functionalized graphene; EG, Expanded graphite; i-MG, Isocyanate-modified graphite nanoplatelets; MEG, Modified EG; MG, Modified graphene; TEVS-GO, Surface functionalization of GO with triethoxyvinylsilane; xGnPs, Exfoliated graphite nanoplatelets; MWCNTs-OH, Multiwalled carbon nanotubes functionalized with hydroxyl groups.

The effect of noncovalent surface treatment of GNPs by utilizing poly(ethyleneimine) (PEI), on the mechanical, physical, and morphological properties of NR/ EPDM blends was also investigated. TGA analysis was performed to observe the degradation behavior and residue evaluation for NR/EPDM blends in relation to filler surface modification and the amount of loadings. The results revealed that unmodified GNPs retained the excellent intrinsic thermal properties of graphene and increased the resistance of NR/EPDM blends to heat degradation. Nevertheless, the blends filled with modified GNPs PEI experienced poorer thermal stability due to a lower degradation temperature onset and degradation temperature (low Td onset and Td) compared to blends with unmodified GNP nanofiller. The presence of adsorbed polymeric layers on GNP surfaces was responsible for providing a further degradation profile for GNPs PEI [73].

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Xing et al. [121] also used a scalable modified latex compounding method to fabricate graphene (GE)/SBR nanocomposites. In TGA results, the initial degradation temperature (Td) was defined as the temperature at which the mass loss is 5 wt.%. Td of unfilled SBR and GE/SBR with 1 phr loading was found to be 324 and 350 C, respectively. However, a further increase in the GE content did not lead to higher Td. The higher Td of the GE/SBR nanocomposites was due to the increasing path of gas diffusion by the incorporation of GE as well as the p p interaction between GE and phenyl groups of SBR [121]. In another study, simple two-roll mill mixing was used to blend SBR with carbon black-reduced graphene (CB-RG) hybrid filler. The thermal stability of SBR composites filled with CB-RG was only slightly higher than CB-filled SBR, due to the limited amount of graphene (up to 3 phr) used in the composites [122]. As a different compounding process, Schopp et al. [80] prepared SBR/FG nanocomposites by an aqueous dispersion blend technology and subsequent melt compounding without the use of organic solvents. Two different types of FG were produced, TRGO and chemically reduced graphite oxide. It was found that thermal transitions and degradation of SBR/FG nanocomposites do not change with FG addition up to 25 phr [80]. Incorporation of EG in rubber formulations was found to improve the thermal stability of the nanocomposites by various researchers [123 125]. EG and modified expanded graphite (MEG) were used in SSBR with and without CB. Oil-extended carboxylated styrene butadiene rubber was used as a polar compatibilizer in order to disperse polar MEG in nonpolar SSBR matrix. The nanofillers were used as 3 phr in the nanocomposites. An increase in thermal stability of the nanocomposites was observed with the incorporation of EG and MEG into the rubber matrix. This result shows the heat-shielding effect of EG and MEG, and the mass transport barrier effect of the dual-filler system [123]. EG and isocyanate modified graphite nanoplatelets (i-MG) were used in SBR, BR, and SBR/BR blends, which were synthesized by melt blending, in the presence of CB. The nanofillers were used as 3 phr. TGA was performed between 30 and 700 C with 10 C/min heating rate. The thermal stability was enhanced with the use of EG and i-MG for all compounds. This showed that EG and i-MG sheets prevent oxidation by acting as heat shielders by dissipating heat, and not permitting heat build-up within the matrix [124]. EG/CB and modified EG (MEG)/CB were also incorporated into butyl rubber (IIR) by direct mixing in an open two-roll mixing mill, with the amount of nanofiller kept constant at 3 phr. TGA was performed in the temperature range 30 700 C with a heating rate of 10 C/min. Temperatures at 10% and 70% decomposition of the nanocomposites were higher than neat IIR. This reveals that the thermal stability was improved due to the enhanced interaction between nanofillers and elastomer matrix, and the action of nanofillers as a heat absorber prevented the heat build-up within the matrix [125].

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

Lian et al. [126] also studied butyl rubber nanocomposites. They reported the fabrication of well-dispersed modified graphene (MG), with a doping level of 1 10 wt. %, in IIR composites through the solution process. With the TGA technique, DTG peaks were obtained, which indicated the temperature of the maximum reactive velocity. It was found that the temperature at the maximum reactive velocity increased with increasing graphene content, namely, it was increased by 11 C for the 10 wt.% composite compared to pure IIR. This indicated that the thermal stability of IIR was improved by the addition of graphene [126]. Regarding NBR nanocomposites, Rajkumar et al. [127] carried out a study in which NBR/graphite nanocomposites were prepared, with loading levels of 3, 6, and 9 phr. Thermal degradation temperature was increased with an increase in nanofiller loading, which indicates the trend of improvement in thermal stability of nanocomposites [127]. There are several scientific studies about the use of graphene-based nanofillers in SR. In the study by Wang and Dou [128], EG was oxidized and graphite oxide (GO) was obtained. SR/GO was synthesized by using a solution intercalation method. According to the TGA results, the thermal stability of the nanocomposites was improved since the GO could absorb a polar Si O bond and result in the formation of physical crosslinking points. In another work, silicone foam was filled with a FG sheet, with loading levels of 0.10, 0.20, and 0.25 wt.%. The TGA data revealed that the onset and the degradation temperatures increased by up to 16 C and more than 55 C, respectively, and the decomposition of the samples became slower. Therefore, it was observed that the use of nanosheets improved the overall decomposition behavior of the samples, due to an increase in the rigidity of the siloxane chains [129]. Liquid silicone rubber (LSR), which has a broad range of applications, in particular for sealing of electronic devices, was also studied. It was reinforced with both GO and FG oxide (TEVS-GO: surface functionalization of GO with triethoxyvinylsilane), with 0.05, 0.1, 0.15, 0.2, 0.25, and 0.3 wt.% loadings. TGA was performed and 10% weight loss temperature (T10) and the residue at 800oC (R800) were used to evaluate the thermal stability of the composites. It was seen that GO/LSR composites showed a lower thermal stability than pure LSR, and the thermal stability decreased with the increase of GO loadings, whereas the TEVS-GO/LSR composites exhibited a higher thermal stability, and thermal stability increased with the addition of TEVS-GO. Since GO contains many oxygen-containing groups, which easily initiated the degradation of alkyl groups, it resulted in the degradation of SR further. However, when modified with TEVS, GO integrated with the chains of siloxane by in situ polymerization, forming chemical crosslinking points and improving the thermal stability of the composites [130].

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As mentioned earlier, a hybrid filler, which is a combination of xGnPs and MWCNTs-OH, with a loading level of 4 wt.%, was used in PDMS. TGA results revealed that the thermal stability for the PDMS hybrid was best when filled with 75% xGnPs (ratio in the hybrid filler), possibly due to the high thermal conductivity of the composite, which helped facilitate a greater heat flow and dissipation throughout the composite, since PDMS filled with 75% xGnP already had the highest thermal conductivity of all the composites. Nevertheless, it is also noted that varying the ratio of xGnP/ MWCNT-OH did not significantly affect the thermal stability of composites [91]. Table 11.5 shows a summary of the articles discussed in Section 11.8.3 in this study.

11.8.4 The Effect of Fullerene on Rubbers Compared with the enormous number of studies on the application of graphene, there are relatively few reports dealing with applications of fullerene in rubber-based nanocomposites. Cataldo [131] studied the effect of fullerene (C60) in NR (cis-1,4-polyisoprene) and IR (synthetic cis-1,4-polyisoprene), as a thermal stabilizer and antioxidant, by using simultaneous TGA-DTA under nitrogen and air flow, at 20 C/min heating rate. In the absence of oxygen, C60 exhibited a certain stabilizing effect in cis-1,4-polyisoprene, by reacting with the polyisoprene macroradicals originated by a thermally induced chain scission reaction, thus slowing down the degradation reaction. This effect was more evident with IR than with NR [131]. Therefore, a specially designed heating ramp was used in order to confirm that C60 also acts as a stabilizer in the case of NR. It was again found that the free radical chain process is slowed down due to a reaction between the rubber chain macroradicals (formed during the thermal decomposition process) and C60 fullerene [132]. Under thermo-oxidative degradation conditions (in airflow), the presence of small amounts of C60 fullerene ensured better resistance to degradation of NR, at a low heating rate (5 C/min). However, it did not show any antioxidant effect for NR at a high heating rate (20 C/min) [131]. On the other hand, NR and IR samples with different levels of C60 were heated in TGA, under nitrogen flow, up to 350 C, 300 C, 250 C, and 190 C, with the aim of obtaining the heat-treated samples. These samples were then analyzed with spectroscopic techniques to find experimental evidence about the mechanism of reaction between C60 and IR or NR. C60 fullerene was determined to be acting as a polyisoprene crosslinking agent when heated up to 190 C, based on the spectroscopic evidence and the insolubility of the resulting crosslinked reaction product. However, excessive heating (above 300 C) caused the degradation (reversion) of the network and formation of a very weakly alkylated fullerene, likewise in all crosslinked networks [132].

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

Just as in NR, fullerene incorporation in PDMS increases the thermal stability [133,134]. In Kraus and Mullen’s study [133], functionalized fullerenes were incorporated in the PDMS main chain. The resulting nanocomposites showed high thermal stability and good film-forming property. The influence of fullerene on the thermal stability of polystyrene (PS) and PDMS rubber was also investigated. In order to compare the stabilization efficiency, fullerene (C60) and Irganox-1076 (sterically hindered phenol-based commercial antioxidant) were used as 1% by weight, and the data for thermo-oxidative degradation were gathered via TGA curves under air flow. Fullerene showed a comparable stabilizing effect with Irganox 1076, such that degradation started at 365 C, 385 C, and 400 C, for PDMS, PDMS, with 1% of C60, and PDMS with 1% Irganox 1076, respectively [134]. The thermal stabilization effect of fullerene in EPDM and IR was demonstrated in several studies [135 137]. EPDM/C60 composites were prepared and the effect of crosslinking of EPDM by using both UV radiation and thermal methods was investigated. With increasing UV exposure time, TGA revealed a decrease in the thermal decomposition temperature of EPDM/C60 films. The results showed that C60 acted as an oxygen scavenger under UV light exposure [135]. Cataldo et al. [136] studied the grafting of C60 fullerene onto IR (synthetic cis-1,4-polyisoprene) chains, in n-hexane and toluene solutions by the action of γ irradiation at 50 and 150 kGy. TGA was performed under nitrogen flow at a heating rate of 10 C/min and revealed that radiolyzed nanocomposites decompose more slowly and the release of pyrolytic products is much lower than pure polyisoprene. This fact implied the thermal stabilizing effect of C60. By use of FTIR, it was shown that the radical adducts of C60 are thermally reversible and nanocomposite decomposition regenerates free C60 during the pyrolysis under N2 [136]. In a similar study, the γ irradiation of IR and C60 solutions in decalin at 50, 100, and 150 kGy was employed, and a gel was formed. This gel was found to be much more thermally stable than the reference untreated polyisoprene sample, according to TGA results. C60 also improved the thermal stability of the nanocomposites. Abundant residual char was observed in the TGA crucible, containing free C60 fullerene, according to FTIR analysis [137].

11.9 CONCLUSIONS Elastomers are widely used in the polymer industry, such as in tire manufacturing, cable, hose and clothing production due to their unique properties. Various types

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of fillers are utilized in rubbers to provide durability and performance and to reduce the price. Today, CB and silica are the main reinforcing fillers that increase the profitability of rubbers. In recent years, carbonaceous fillers such as graphene, CNTs, and fullerene have played a promising role in the polymer industry due to their high aspect ratio, nanosize diameter, very low density, and excellent physical properties. When selecting both elastomer and filler type for a specific application, many analytical techniques can be used. Thermal analysis is frequently used to characterize the polymers and their composites. Thermal analysis techniques measure the thermal transitions (glass transition temperature, crosslinking temperature, etc.), weight loss, thermal stability, dimensional changes, and CTE of rubbers. Rubbers are often subjected to temperature-dependent structural changes during their production, processing, and applications, which makes thermal analysis very important for materials selection, quality control, and assurance.

REFERENCES [1] ,https://rubberasia.com/2017/04/05/world-rubber-consumption-1-8-2016-says-irsg/.. [2] S.Y. Lee, J.H. Kim, B.K. Kim, Natural rubber blends with epoxidized natural rubber, J. Macromol. Sci. B: Phys. 36 (1997) 579 594. [3] P.M. Visakh, S. Thomas, A.K. Chandra, A.P. Mathew, Advances in Elastomers: Blends and Interpenetrating Networks, Springer-Verlag Berlin Heidelberg, 2013. [4] J.A. Razak, S.H. Ahmad, C.T. Ratnam, M.A. Mahamood, J. Yaakub, N. Mohamad, Effects of EPDM-g-MAH compatibilizer and internal mixer processing parameters on the properties of NR/ EPDM blends: an analysis using response surface methodology, J. Appl. Polym. Sci. (2015). Available from: https://doi.org/10.1002/app.42199. [5] W. Arayapranee, G.L. Rempel, A comparative study of the cure characteristics, processability, mechanical properties, ageing, and morphology of rice husk ash, silica and carbon black filled 75: 25 NR/EPDM blends, J. Appl. Polym. Sci. 109 (2008) 932 941. [6] A. Alipour, G. Naderi, G.R. Bakhshandeh, H. Vali, S. Shokoohi, Elastomer nanocomposites based on NR/EPDM/organoclay: morphology and properties, Int. Polym. Sci. 26 (2011) 48 55. [7] A. Alipour, G. Naderi, M.H. Ghoreishy, Effect of nanoclay content and matrix composition on properties and stress-stain behavior of NR/EPDM nanocomposites, J. Appl. Polym. Sci. 131 (2014) 1275 1284. [8] H. Nabil, H. Ismail, A.R. Azura, Comparison of thermo-oxidative ageing and thermal analysis of carbon black-filled NR/Virgin EPDM and NR/Recycled EPDM blends, Polym. Test. 32 (2013) 631 639. [9] Z. Jia, Y. Luo, S. Yang, M. Du, B. Guo, D. Jia, Styrene-butadiene rubber/halloysite nanotubes composites modified by epoxidized natural rubber, J. Nanosci. Nanotechnol. 11 (2011) 10958 10962. [10] S. Jovanovic, S. Samarzija-Jovanovic, G. Markovic, V. Jovanovic, T. Adamovic, M. MarinovicCincovic, Ternary NR/BR/SBR rubber blends nanocomposites, J. Thermoplast. Compos. Mater. (2017). Available from: https://doi.org/10.1177/0892705717697778. [11] ,http://www.iisrp.com/webpolymers/01finalpolybutadienever2.pdf . . [12] A. Wahab, Butadiene rubber (BR): new catalyst to meet global demand, Polym. Compos. Res. Technol. 1 (2014) 1 10. [13] C. Zhang, J. Wang, Y. Zhao, Effect of dendrimer modified montmorillonite on structure and properties of EPDM nanocomposites, Polym. Test. 62 (2017) 41 50. [14] H. Moustafa, N.A. Darwish, Effect of different types and loadings of modified nanoclay on mechanical properties and adhesion strength of EPDM-g-MAH/nylon66 systems, Int. J. Adhes. Adhes. 61 (2015) 15 22.

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

[15] M.M. Abu Zeid, Radiation effect on properties of carbon black filled NBR/EPDM rubber blends, Eur. Polym. J. 43 (2007) 4415 4422. [16] K.S. Lee, Y.W. Chang, Peroxide vulcanized EPDM rubber/polyhedral oligomeric silsesquioxane nanocomposites: vulcanization behavior, Mech. Proper. Therm. Stab. 55 (2015) 2814 2820. [17] S. Prasertsri, K. Kurakanok, N. Sukkapan, Physico-mechanical properties and automotive fuel resistance of EPDM/ENR blends containing hybrid fillers, J. Polym. Res. (2016). Available from: https://doi.org/10.1007/s10965-016-1123-1. [18] R.O. Aly, Influence of gamma irradiation on mechanical and thermal properties of waste polyethylene/nitrile butadiene rubber blend, Arab. J. Chem. 9 (2016) S1547 S1554. [19] J. Wang, H. Jia, Y. Tang, D. Ji, Y. Sun, X. Gong, et al., Enhancements of the mechanical properties and thermal conductivity of carboxylated acrylonitrile butadiene rubber with the addition of graphene oxide, J. Mater. Sci. 48 (2013) 1571 1577. [20] M. Balachandran, L.P. Stanly, R. Mulaleekrishnan, S.S. Bhagawan, Modeling NBR-layered silicate nanocomposites: a DoE approach, J. Appl. Polym. Sci. 118 (2010) 3300 3310. [21] S. Yang, H. Fan, Y. Jiao, Z. Cai, P. Zhang, Y. Li, Improvement in mechanical properties of NBR/ LiClO4/POSS nanocomposites by constructing a novel network structure, Compos. Sci. Technol. 138 (2017) 161 168. [22] D.C. Blackley, Synthetic Rubbers: Their Chemistry and Technology., Springer, Dordrecht, 1983. [23] H. Sirin, M. Kodal, B. Karaagac, G. Ozkoc, Effects of octamaleamic acid-POSS used as the adhesion enhancer on the properties of silicone rubber/silica nanocomposites, Compos. B: Eng. 98 (2016) 370 381. [24] S. Yang, Z. Jia, L. Liu, W. Fu, D. Jia, Y. Luo, Insight into vulcanization mechanism of novel binary accelerators for natural rubber, Chin. J. Polym. Sci. 32 (2014) 1077 1085. [25] F. Shen, X. Yuan, C. Wu, Investigation on crosslinking behaviors of NBR/PVC filled with anhydrous copper sulfate particles by dynamic mechanical analysis, J. Polym. Sci. B Polym. Phys. 45 (2007) 41 51. [26] Y. Zhang, S. Ge, B. Tang, T. Koga, M.H. Rafailovich, J.C. Sokolov, et al., Effects of carbon black and silica fillers in elastomers blends, Macromolecules 34 (2001) 7056 7065. [27] J.W.M. Noordermeer, W.K. Dierkes, Carbon black reinforced elastomers, Encycl. Polym. Mater. (2015). Available from: https://doi.org/10.1007/978-3-642-36199-9_287-1. [28] V. Jha, Carbon Black Filler Reinforcement of Elastomers (Ph.D. Thesis), Queen Mary, University of London, 2008. [29] Y. Chen, Y. Lin, Y. Luo, D. Jia, L. Liu, Styrene butadiene rubber/carbon black composites modified by imidazole derivatives, Int. J. Polym. Anal. Charact. (2016). Available from: https://doi.org/ 10.1080/1023666X.2016.1168563. [30] K.K. Sadasuvini, D. Ponnamma, S. Thomas, Y. Grohens, Evolution from graphite to graphene elastomer composites, Prog. Polym. Sci. 39 (2014) 749 780. [31] D.G. Papageorgiou, I.A. Kinloch, R.J. Young, Graphene/elastomer nanocomposites, Carbon. N. Y. 95 (2015) 460 484. [32] H. Kang, K. Zuo, Z. Wang, L. Zhang, L. Liu, B. Guo, Using a green method to develop graphene oxide/elastomers nanocomposites with combination of high barrier and mechanical performance, Compos. Sci. Technol. 92 (2014) 1 8. [33] U. Khan, P. May, A. O’Neill, J.N. Coleman, Development of stiff, strong, yet tough composites by the addition of solvent exfoliated graphene to polyurethane, Carbon. N. Y. 48 (2010) 4035 4041. [34] B. Mensah, H.G. Kim, J.H. Lee, S. Arepalli, C. Nah, Carbon nanotube-reinforced elastomeric nanocomposites: a review, Int. J. Smart Nano Mater. 6 (2015) 211 238. [35] K. Subramaniam, G. Heinrich, Carbon nanotubes rubber composites, Encycl. Polym. Mater. (2014). Available from: https://doi.org/10.1007/978-3-642-36199-9_288-1. [36] L. Bokobza, Multiwall carbon nanotube elastomeric composites: a review, Polymer (Guildf). 48 (2007) 4907 4920. [37] Y. Saito, T. Nakahira, S. Uemura, Growth conditions of double-walled carbon nanotubes in arc discharge, J. Phys. Chem. B 107 (2003) 931 934.

361

362

Mehmet Kodal et al.

[38] S. Arepalli, Laser ablation process for single-walled carbon nanotube production, J. Nanosci. Nanotechnol. 4 (2004) 317 325. [39] M. Endo, T. Hayashi, Y.A. Kim, H. Muramatsu, Development and applications of carbon nanotubes, Jpn J. Appl. Phys. 45 (2006) 4883 4892. [40] O.A. Al-Hartomy, A.A. Al-Ghamdi, F. Al-Salamy, N. Dishovsky, D. Slavcheva, F. El-Tantawy, Properties of natural rubber-based composites containing fullerene, Int. J. Polym. Sci. (2012). Available from: https://doi.org/10.1155/2012/967276. [41] T. Kuilla, S. Bhadra, D. Yao, N.H. Kim, S. Bose, J.H. Lee, Recent advances in graphene based polymer composites, Prog. Polym. Sci. 35 (2010) 1350 1375. [42] A. Chauhan, B. Mittu, Modern approach to research by DSC and its advancements, Pharm. Anal. Acta (2012). Available from: https://doi.org/10.4172/2153-2435.1000e129. [43] ,https://polymerscience.physik.hu-berlin.de/docs/manuals/DSC.pdf.. [44] A. Luis, A study of different aspects of DTA calibration, Thermochim. Acta 59 (1982) 133 138. [45] P.K. Gallagher, M.E. Brown, Handbook of Thermal Analysis and Calorimetry, Volume I: Principles and Practice, Elsevier Science B.V, 1998. [46] P. Skoglund, A. Fransson, Accurate temperature calibration of differential scanning calorimeters, Thermochim. Acta 276 (1996) 27 39. [47] S.M. Sarge, W. Hemminger, E. Gmelin, G.W.H. Ho¨hne, H.K. Cammenga, W. Eysel, Metrologically based procedures for the temperature, heat and heat flow rate calibration of DSC, J. Therm. Anal. 49 (1997) 1125 1134. [48] A. Gehenot, R.C. Rao, G. Maire, M. Gachon, Value of thermal analysis in the critical evaluation of classical methods of melting point determination, Int. J. Pharm. 45 (1988) 13 17. [49] R. Al-Itry, K. Lamnawar, A. Maazouz, Improved thermal stability, rheological and mechanical properties of PLA, PBAT and their blends by reactive extrusion with functionalized epoxy, Polym. Degrad. Stabil. 97 (2012) 1898 1914. [50] Z.C. Tan, R. Sabbah, Reference materials for energy and temperature calibrations of DTA and DSC instrumentation in the range 100-300 K, J. Therm. Anal. 41 (1994) 1577 1592. [51] D. Fan, X. Liao, S. Liao, Y. Zhao, J. Sun, Mechanical and thermal properties of natural rubber latex modified by purple carbon black, Adv. Mater. Res. 821 822 (2013) 961 964. [52] F. Oliveira, N. Alves, J.A. Giacometti, C.J.L. Constantino, L.H.C. Mattoso, A.M.O.A. Balan, et al., Study of the thermomechanical and electrical properties of conducting composites containing Natural rubber and carbon black, J. Appl. Polym. Sci. 106 (2007) 1001 1006. [53] J.C. Kenny, V.J. McBrierty, Z. Rigbi, D.C. Douglass, Carbon black filled natural rubber. 1. Structural investigations, Macromolecules 24 (1991) 436 443. [54] M. Arroyo, M.A. Lopez-Manchado, B. Herrero, Organo-montmorillonite as substitute of carbon black in natural rubber compounds, Polymer (Guildf). 44 (2003) 2447 2453. [55] E. Linde, T.O.J. Blomfeldt, M.S. Hedenqvist, U.W. Gedde, Long-term performance of a DEHPcontaining carbon-black-filled NBR membrane, Polym. Test. 34 (2014) 25 33. [56] U. Sebenik, J. Karger-Kocsis, M. Kranjnc, R. Thomann, Dynamic mechanical properties and structure of in situ cured polyurethane/hydrogenated nitrile rubber compounds: effect of carbon black type, J. Appl. Polym. Sci. 125 (2012) E41 E48. [57] N.Z. Noriman, H. Ismail, Effect of carbon black/silica hybrid filler on thermal properties, fatigue life, and natural weathering of SBR/recycled NBR blends, Int. J. Polym. Mater. Polym. Biomater. 62 (2013) 252 259. [58] Y. Wan, C. Xiong, J. Yu, D. Wen, Effect of processing parameters on electrical resistivity and thermo-sensitive properties of carbon-black/styrene butadiene rubber composite membranes, Compos. Sci. Technol. 65 (2005) 1769 1779. [59] Z. Jun-Xue, W. He, S. Xin-Yan, Z. Shu-Gao, Effects of carbon black on chain mobility and dynamic mechanical properties of solution polymerized styrene-butadiene rubber, J. Macromol. Sci. B: Phys. 51 (2012) 496 509. [60] A.M. Ismail, K.R. Mahmoud, M.H. Abd-El-Salam, Electrical conductivity and positron annihilation characteristics of ternary silicone rubber/carbon black/TiB2 nanocomposites, Polym. Test. 48 (2015) 37 43.

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

[61] V. Jovanovic, S. Samarzija-Jovanovic, J. Budinski-Simendic, G. Markovic, M. Marinovic-Cincovic, Composites based on carbon black reinforced NBR/EPDM rubber blends, Compos. B 45 (2013) 333 340. [62] C. Kummerlo¨we, N. Vennemann, S. Pieper, A. Siebert, Y. Nakaramontri, Preparation and properties of carbon-nanotube composites with natural rubber and epoxidized natural rubber, Polimery 59 (2014) 11 12. [63] G. Sui, W.H. Zhong, X.P. Yang, Y.H. Yu, S.H. Zhao, Preparation and properties of natural rubber composites reinforced with pretreated carbon nanotubes, Polym. Adv. Technol. 19 (2008) 1543 1549. [64] P.S. Thomas, A.A. Abdullateef, M.A. Al-Harthi, A.A. Basfar, S. Bandyopadhyay, M.A. Atieh, et al., Effect of phenol functionalization of carbon nanotubes on properties of natural rubber nanocomposites, J. Appl. Polym. Sci. 124 (2011) 2370 2376. [65] S. Yaragalla, B. Sindam, J. Abraham, K.C. James Raju, N. Kalarikkal, S. Thomas, Fabrication of graphite-graphene-ionic liquid modified carbon nanotubes filled natural rubber thin films for microwave and energy storage applications, J. Polym. Res. 22 (2015) 1 10. [66] M.A. Atieh, Effect of functionalized carbon nanotubes with carboxylic functional group on the mechanical and thermal properties of styrene butadiene rubber, Fuller. Nanotubes Carbon Nanostruct. 19 (2011) 617 627. [67] A. De Falco, A.J. Marzocca, M.A. Corcuera, A. Eceiza, I. Mondragon, G.H. Rubiolo, et al., Accelerator adsorption onto carbon nanotubes surface affects the vulcanization process of styrene butadiene rubber composites, J. Appl. Polym. Sci. 113 (2009) 2851 2857. [68] A. Narimani, M. Hemmati, Effect of single-walled carbon nanotube on the physical, rheological and mechanical properties of thermoplastic elastomer based on PP/EPDM, Sci. Eng. Compos. Mater. 21 (2014) 15 21. [69] N. Nosbi, M.A. Hazizan, Thermal properties of multiwalled carbon nanotubes-alumina (MWCNTAl2O3) hybrid filled silicone rubber composites, Adv. Mater. Res. 844 (2013) 330 333. [70] S.R. Ryu, J.W. Sung, D.J. Lee, Strain induced crystallization and mechanical properties of NBR composites with carbon nanotube and carbon black, Rubber Chem. Technol. 85 (2012) 207 218. [71] K. Preetha Nair, P. Thomas, R. Joseph, Latex stage blending of multiwalled carbon nanotube in carboxylated acrylonitrile butadiene rubber: mechanical and electrical properties, Mater. Des. 41 (2012) 23 30. [72] A. Katihabwa, W. Wang, Y. Jiang, X. Zhao, Y. Lu, L. Zhang, Multi-walled carbon nanotubes/ silicone rubber nanocomposites prepared by high shear mechanical mixing, J. Reinf. Plast. Compos. 30 (2011) 1007 1014. [73] J. Abd Razak, S. Haji Ahmad, C.T. Ratnam, M.A. Mahamood, N. Mohamad, Effects of poly(ethyleneimine) adsorption on graphene nanoplatelets to the properties of NR/EPDM rubber blend nanocomposites, J. Mater. Sci. 50 (2015) 6365 6381. [74] J. Dong, P. Wang, D. Sun, Y. Xu, K. Li, Preparation and characterization of graphene/RTV silicone rubber composites, Adv. Mater. Res. 652-654 (2013) 11 14. [75] F. Wang, Y. Zhang, B.B. Zhang, R.Y. Hong, M.R. Kumar, C.R. Xie, Enhanced electrical conductivity and mechanical properties of ABS/EPDM composites filled with graphene, Compos. B 83 (2015) 66 74. [76] B. Yin, X. Zhang, X. Zhang, J. Wang, Y. Wen, H. Jia, et al., Ionic liquid functionalized graphene oxide for enhancement of styrene-butadiene rubber nanocomposites, Polym. Adv. Technol. 28 (2017) 293 302. [77] M.Z. Tang, W. Xing, J.R. Wu, G.S. Huang, H. Li, A.D. Wu, Vulcanization kinetics of graphene/ styrene butadiene rubber nanocomposites, Chin. J. Polym. Sci. 32 (2014) 658 666. [78] M. Huang, J. Lu, B. Han, J. Liu, H. Qiao, L. Zhang, Covalent approach for in situ enhancement of interaction between pristine graphene and styrene-butadiene-p-(2,2,2-triphenylethyl)styrene rubber, J. Appl. Polym. Sci. 134 (2017) 44923. [79] X. Zhang, X. Xue, Q. Yin, H. Jia, J. Wang, Q. Ji, et al., Enhanced compatibility and mechanical properties of carboxylated acrylonitrile butadiene rubber/styrene butadiene rubber by using graphene oxide as reinforcing filler, Compos. B 111 (2017) 243 250.

363

364

Mehmet Kodal et al.

[80] S. Schopp, R. Thomann, K.F. Ratzsch, S. Kerling, V. Altstadt, R. Mu¨lhaupt, Functionalized graphene and carbon materials as components of styrene-butadiene rubber nanocomposites prepared by aqueous dispersion blending, Macromol. Mater. Eng. 299 (2014) 319 329. [81] Y. Luo, R. Wang, S. Zhao, Y. Chen, H. Su, L. Zhang, et al., Experimental study and molecular dynamics simulation of dynamic properties and interfacial bonding characteristics of graphene/solution polymerized styrene-butadiene rubber composites, RSC Adv. 6 (2016) 58077 58087. [82] Y. Wu, L. Chen, J. Li, H. Zhou, H. Zhao, J. Chen, Understanding the mechanical and tribological properties of solution styrene butadiene rubber composites based on partially graphene oxide, Eur. Polym. J. 89 (2017) 150 161. [83] J.D. Menczel, R.D. Prime, Thermal Analysis of Polymers: Fundamentals and Applications., John Wiley & Sons, Inc., New Jersey, 2009. [84] T. Hatakeyama, F.X. Quinn, Thermal Analysis Fundamentals and Applications to Polymer Science., John Wiley & Sons, Inc., West Sussex, 1999. [85] H. Lobo, J.V. Bonilla, Handbook of Plastics Analysis., Marcel Dekker Inc., New York, 2003. [86] A. Kato, Y. Ikeda, R. Tsushi, Y. Kokubo, N. Kojima, A new approach to visualizing the carbon black/natural rubber interaction layer in carbon black-filled natural rubber vulcanizates and to elucidating the dependence of mechanical properties on quantitative parameters, Colloid Polym. Sci. 291 (2013) 2101 2110. [87] V. Nigam, D.K. Setua, G.N. Mathur, Hybrid filler system for nitrile rubber vulcanizates, J. Mater. Sci. 36 (2001) 43 47. [88] B. Jurkowska, Y.A. Olkhov, B. Jurkowski, O.M. Olkhova, Study of butadiene rubber mastication and mixing with carbon black, J. Appl. Polym. Sci. 71 (1998) 729 737. [89] B. Jurkowska, Y.A. Olkhov, B. Jurkowski, O.M. Olkhova, On a structure of NR and BR carbon black filled rubber compounds and vulcanizates, J. Appl. Polym. Sci. 74 (1999) 3305 3315. [90] S.E. Lee, Y. Sohn, K. Chu, D. Kim, S.H. Park, M. Bae, et al., Suppression of negative temperature coefficient of resistance of multiwalled nanotube/silicone rubber composite through segregated conductive network and its application to laser-printing fusing element, Org. Electron. 37 (2016) 371 378. [91] K.T.S. Kong, M. Mariatti, A.A. Rashid, J.J.C. Busfield, Enhanced conductivity behavior of polydimethylsiloxane (PDMS) hybrid composites containing exfoliated graphite nanoplatelets and carbon nanotubes, Compos. B 58 (2014) 457 462. [92] M. Bhattacharya, Polymer nanocomposites—a comparison between carbon nanotubes, graphene, and clay as nanofillers, Materials (Basel) 9 (2016) 1 35. [93] S.C. Lin, C.C.M. Ma, W.H. Liao, J.A. Wang, S.J. Zeng, S.Y. Hsu, et al., Preparation of a graphene silver nanowire hybrid/silicone rubber composite for thermal interface materials, J. Taiwan Inst. Chem. Eng. 68 (2016) 396 406. [94] B. Jurkowska, B. Jurkowski, P. Kamrowski, S.S. Pesetskii, V.N. Koval, L.S. Pinchuk, et al., Properties of fullerene-containing natural rubber, J. Appl. Polym. Sci. 100 (2006) 390 398. [95] B. Wunderlich, Thermal Analysis of Polymeric Materials., Springer-Verlag, Berlin, 2005. [96] B. Jankovic, M. Marinovic-Cincovic, V. Jovanovic, S. Samarzija-Jovanovic, G. Markovic, The comparative kinetic analysis of non-isothermal degradation process of acrylonitrile butadiene/ethylene propylene diene rubber blends reinforced with carbon black/silica fillers. Part II, Thermochim. Acta 543 (2012) 304 312. [97] B. Jankovic, M. Marinovic-Cincovic, V. Jovanovic, S. Samarzija-Jovanovic, G. Markovic, Kinetic analysis of nonisothermal degradation of acrylonitrile-butadiene/ethylene propylene diene rubber blends reinforced with carbon black filler, Polym. Compos. 33 (2012) 1233 1243. [98] S.C. Domenech, L. Bendo, D.J.S. Mattos, N.G. Borges Jr, V. Zucolotto, Elastomeric composites based on ethylene-propylene-diene monomer rubber and conducting polymer-modified carbon black, Polym. Compos. 30 (2009) 897 906. [99] S. Samarzija-Jovanovic, V. Jovanovic, G. Markovic, Thermal and vulcanization kinetic behavior of acrylonitrile butadiene rubber reinforced by carbon black, J. Therm. Anal. Calorim. 94 (3) (2008) 797 803.

Thermal Properties (DSC, TMA, TGA, DTA) of Rubber Nanocomposites Containing Carbon Nanofillers

[100] S. Samarzija-Jovanovic, V. Jovanovic, G. Markovic, M. Marinovic-Cincovic, The effect of different types of carbon blacks on the rheological and thermal properties of acrylonitrile butadiene rubber, J. Therm. Anal. Calorim. 98 (2009) 275 283. [101] G.T. Mohanraj, T. Vikram, A.M. Shanmugharaj, D. Khastgir, T.K. Chaki, Kinetics of thermal degradation and thermo-oxidative degradation of conductive styrene-butadiene rubber-carbon black composites, J. Mater. Sci. 41 (2006) 4777 4789. [102] S. Jovanovic, S. Samarzija-Jovanovic, G. Markovic, V. Jovanovic, T. Adamovic, M. MarinovicCincovic, Mechanical properties and thermal aging behaviour of polyisoprene/polybutadiene/styrene-butadiene rubber ternary blend reinforced with carbon black, Compos. B 98 (2016) 126 133. [103] F.A. Oliveira, N. Alves, J.A. Giacometti, C.J.L. Constantino, L.H.C. Mattoso, A.M.O.A. Balan, et al., Study of the thermomechanical and electrical properties of conducting composites containing natural rubber and carbon black, J. Appl. Polym. Sci. 106 (2007) 1001 1006. [104] H. Ismail, S.Z. Salleh, Z. Ahmad, The effect of partial replacement of carbon black (CB) with halloysite nanotubes (HNTs) on the properties of CB/HNT-filled natural rubber nanocomposites, J. Elastomers Plast. 45 (2012) 445 455. [105] Z.X. Ooi, H. Ismail, A. Abu Bakar, A comparative study of aging characteristics and thermal stability of oil palm ash, silica, and carbon black filled natural rubber vulcanizates, J. Appl. Polym. Sci. 130 (2013) 4474 4481. [106] M. Hoikkanen, M. Poikelispaa, A. Das, M. Honkanen, W. Dierkes, J. Vuorinen, Effect of multiwalled carbon nanotubes on the properties of EPDM/NBR dissimilar elastomer blends, Polym.Plast. Technol. Eng. 54 (2015) 402 410. [107] L.D. Perez, M.A. Zuluaga, T. Kyu, J.E. Mark, B.L. Lopez, Preparation, characterization, and physical properties of multiwall carbon nanotube/elastomer composites, Polym. Eng. Sci. 49 (2009) 866 874. [108] S. Chen, H. Yu, W. Ren, Y. Zhang, Thermal degradation behavior of hydrogenated nitrilebutadiene rubber (HNBR)/clay nanocomposite and HNBR/clay/carbon nanotubes nanocomposites, Thermochim. Acta 491 (2009) 103 108. [109] A.A. Abdullateef, S.P. Thomas, M.A. Al-Harthi, S.K. De, S. Bandyopadhyay, A.A. Basfar, et al., Natural rubber nanocomposites with functionalized carbon nanotubes: mechanical, dynamic mechanical, and morphology studies, J. Appl. Polym. Sci. 125 (2012) E76 E84. [110] K. Anoop Anand, T. Sunil Jose, A. Rosamma, J. Rani, Natural rubber-carbon nanotube composites through latex compounding, Int. J. Polym. Mater. 59 (2010) 33 44. [111] A. Mohamed, A.K. Anas, S. Abu Bakar, A.A. Aziz, M. Sagisaka, P. Brown, et al., Preparation of multiwall carbon nanotubes (MWCNTs) stabilised by highly branched hydrocarbon surfactants and dispersed in natural rubber latex nanocomposites, Colloid Polym. Sci. 292 (2014) 3013 3023. [112] F. Matos, F. Galembeck, A.J.G. Zarbin, Multifunctional materials based on iron/iron oxide-filled carbon nanotubes/natural rubber composites, Carbon. N. Y. 50 (2012) 4685 4695. [113] J. Thomasukutty, M. Grace, S. Salini, J.R. Ann, J.G. Jinu, Multifunctional multi-walled carbon nanotube reinforced natural rubber nanocomposites, Ind. Crops Prod. 105 (2017) 63 73. [114] A. Boonmahitthisud, S. Chuayjuljit, Use of carbon nanotube and nanosilica as reinforcement nanofillers in NR/SBR blended Latex, Adv. Mater. Res. 347-353 (2012) 3197 3200. [115] B. Massoumi, M. Hosseinzadeh, M. Jaymand, Electrically conductive nanocomposite adhesives based on epoxy or chloroprene containing polyaniline, and carbon nanotubes, J. Mater. Sci. Mater. Electr. 26 (2015) 6057 6067. [116] C.I. Idumah, A. Hassan, Emerging trends in graphene carbon based polymer nanocomposites and applications, Rev. Chem. Eng. 32 (2016) 223 264. [117] J.R. Potts, D.R. Dreyer, C.W. Bielawski, R.S. Ruoff, Graphene-based polymer nanocomposites, Polymer (Guildf). 52 (2011) 5 25. [118] H. Saleem, A. Edathil, T. Ncube, J. Pokhrel, S. Khoori, A. Abraham, et al., Mechanical and thermal properties of thermoset-graphene nanocomposites, Macromol. Mater. Eng. 301 (2016) 231 259.

365

366

Mehmet Kodal et al.

[119] Y. Zhan, J. Wu, H. Xia, N. Yan, G. Fei, G. Yuan, Dispersion and exfoliation of graphene in rubber by an ultrasonically-assisted latex mixing and in situ reduction process, Macromol. Mater. Eng. 296 (2011) 590 602. [120] C.F. Matos, F. Galembeck, A.J.G. Zarbin, Multifunctional and environmentally friendly nanocomposites between natural rubber and graphene or graphene oxide, Carbon. N. Y. 78 (2014) 469 479. [121] W. Xing, M. Tang, J. Wu, G. Huang, H. Li, Z. Lei, et al., Multifunctional properties of graphene/rubber nanocomposites fabricated by a modified latex compounding method, Compos. Sci. Technol. 99 (2014) 67 74. [122] H. Zhang, C. Wang, Y. Zhang, Preparation and properties of styrene-butadiene rubber nanocomposites blended with carbon black-graphene hybrid filler, J. Appl. Polym. Sci. 132 (2015) 1 7. [123] A. Malas, C.K. Das, Development of modified expanded graphite-filled solution polymerized styrene butadiene rubber vulcanizates in the presence and absence of carbon black, Polym. Eng. Sci. 54 (2014) 33 41. [124] A. Malas, P. Pal, C.K. Das, Effect of expanded graphite and modified graphite flakes on the physical and thermo-mechanical properties of styrene butadiene rubber/polybutadiene rubber (SBR/ BR) blends, Mater. Des. 55 (2014) 664 673. [125] A. Malas, C.K. Das, Influence of modified graphite flakes on the physical, thermo-mechanical and barrier properties of butyl rubber, J. Alloys Compounds 699 (2017) 38 46. [126] H. Lian, S. Li, K. Liu, L. Xu, K. Wang, W. Guo, Study on modified graphene/ butyl rubber nanocomposites. I. preparation and characterization, Polym. Eng. Sci. 51 (2011) 2254 2260. [127] K. Rajkumar, N. Kumari, P. Ranjith, S.K. Chakraborty, P. Thavamani, P. Pazhanisamy, et al., High temperature resistance properties of NBR based polymer nanocomposites, Int. J. ChemTech Res. 3 (2011) 1343 1348. [128] X. Wang, W. Dou, Preparation of graphite oxide (GO) and the thermal stability of silicone rubber/GO nanocomposites, Thermochim. Acta 529 (2012) 25 28. [129] R. Verdejo, F. Barroso-Bujans, M.A. Rodriguez-Perez, J. Antonio de Saja, M.A. LopezManchado, Functionalized graphene sheet filled silicone foam nanocomposites, J. Mater. Chem. 18 (2008) 2221 2226. [130] X.W. Zhao, C.G. Zang, Y.Q. Wen, Q.J. Jiao, Thermal and mechanical properties of liquid silicone rubber composites filled with functionalized graphene oxide, J. Appl. Polym. Sci. 132 (2015) 42582. [131] F. Cataldo, On the reactivity of C-60 fullerene with diene rubber macroradicals. I. The case of natural and synthetic cis-1,4-polyisoprene under anaerobic and thermooxidative degradation conditions, Fuller. Sci. Technol. 9 (2001) 497 513. [132] F. Cataldo, On the reactivity of C60 fullerene with diene rubber macroradicals. II. The reactivity with cis-1,4-polyisoprene under milder thermal conditions, Fuller. Sci. Technol. 9 (2001) 515 524. [133] A. Kraus, K. Mullen, [60]Fullerene-containing poly(dimethylsiloxane)S: easy access to soluble polymers with high fullerene content, Macromolecules 32 (1999) 4214 4219. [134] E.B. Zeinalov, K. Koßmehl, Fullerene C60 as an antioxidant for polymers, Polym. Degrad. Stab. 71 (2001) 197 202. [135] W. Jin, M.A. Kader, W.B. Ko, C. Nah, Effects of UV irradiation on physico-mechanical properties of EPDM/buckminsterfullerene composite, Polym. Adv. Technol. 15 (2004) 662 668. [136] F. Cataldo, O. Ursini, G. Angelini, Radiation-cured polyisoprene/C60 fullerene nanocomposite. Part 1: Synthesis in hexane and in toluene, Radiat. Phys. Chem. 77 (2008) 734 741. [137] F. Cataldo, O. Ursini, G. Angelini, Radiation-cured polyisoprene/C60 fullerene nanocomposite. Part 2: Synthesis in decalin, Radiat. Phys. Chem. 77 (2008) 742 750.