Dielectric properties of nanotube reinforced butyl elastomer composites

Dielectric relaxation behavior of multiwalled carbon nanotube reinforced butyl rubber composites has been studied as a function of variation in filler in the frequency range of 20–2 × 106 Hz. The effect of variation in filler loadings on the complex and real parts of impedance was distinctly visible, which has been explained on the basis of interfacial polarization of fillers in a heterogeneous medium and relaxation dynamics of polymer chains in the vicinity of fillers. The electric modulus formalism has been used to further investigate the conductivity and relaxation phenomenon. The frequency dependence of AC conductivity has been investigated by using Percolation theory. The phenomenon of percolation in the composites has been discussed based on the measured changes in electric conductivity and morphology of composites at different concentrations of the filler. The percolation threshold as studied by AC conductivity occurred in the vicinity of 6–8 phr of filler loading. Scanning electron microscope microphotographs showed agglomeration of the filler above this concentration and formation of a continuous network structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dielectric relaxation of conductive carbon black reinforced chlorosulfonated polyethylene vulcanizates

The frequency dependent dielectric relaxation behavior of conductive carbon black reinforced chlorosulfonated polyethylene (CSM) vulcanizates has been studied for different filler loadings in the frequency range of 10²–10⁶ Hz over a wide range of temperatures (30–120°C). The effects of filler loadings on the dielectric permittivity (ε′), dielectric loss tangent (tan δ), impedance, and electrical conductivity were studied. The variation of the dielectric permittivity with the filler loadings was explained on the basis of interfacial polarization of the filler in the polymer matrix. The frequency dependence of ac conductivity has been investigated using percolation theory. The effect of filler loading on the complex and real parts of impedance was clearly observed, which can be explained on the basis of relaxation dynamics of polymer chains in the vicinity of fillers. The percolation threshold occurred near 30 phr of filler loading. Scanning electron microphotographs showed the agglomeration of the filler on and above these filler loadings. Additionally, the effect of temperature on dielectric loss tangent, dielectric permittivity, ac conductivity, and Nyquist plot of conductive black reinforced CSM vulcanizates has been studied. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Effect of fillers on the relaxation behavior of chlorobutyl vulcanizates

The effect of addition of fillers (carbon black (CB), carbon silica dual phase filler (CSDPF), and nanoclays) on the relaxation behavior of chlorobutyl vulcanizates has been studied. The primary relaxation (α‐transition, the glass transition) was studied by dynamic mechanical analysis as a function of temperature (?60 to +100°C) and positron annihilation life time spectroscopy (?70 to +110°C). Irrespective of the filler and its loading, all the composites showed the glass transition temperature in the range of –29 to –33°C, which was explained on the basis of relaxation chain dynamics of polyisobutylene in the vicinity of fillers. The secondary relaxation (α* or β relaxation) was studied using dielectric relaxation spectra in the frequency range of 100–10⁶ Hz. Nanoclays had a profound influence on the secondary relaxation, whereas CSDPF and CB had a marginal effect. The nonlinear strain dependent dynamical parameters were also evaluated at double strain amplitudes of 0.07–5%. The nonlinearity in tan δ and storage modulus has been explained on the concept of filler–polymer interactions and the interaggregate attraction (filler networking). The “percolation limit” of the fillers in the composites has been studied by DC conductivity measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3161–3173, 2006     

Dielectric relaxation of conductive carbon black reinforced ethylene‐octene copolymer vulcanizates

The dielectric relaxation behavior of different conducting carbon black‐filled ethylene‐octene copolymer (EOC) vulcanizates prepared by melt‐mixing method has been studied as a function of frequency (100 Hz–5 MHz) over a wide range of temperatures (25–100°C). The effect of filler loading and frequency on AC conductivity, dielectric permittivity, impedance, and dielectric loss tangent (tanδ) has been studied. The nature of variation of the dielectric permittivity with the filler loadings was explained on the basis of interfacial polarization of the filler in the polymer matrix. The effect of filler loading on the real and complex part of the impedance was explained by the relaxation dynamics of the polymer chains in the vicinity of the fillers. The effect of filler and temperature on dielectric loss tangent, dielectric permittivity, AC conductivity, and Nyquist plot was also reported. The bound rubber (BR) value increases with increase in filler loading suggesting the formation of strong interphase, which is correlated with dielectric loss. Thermal activation energy (E_a) was found to be decreasing with the temperature, which follows the Arrhenius relation: τ_b = τ₀ exp(−E_a/K_BT) where τ_b is the relaxation time for the bulk material. From the plot of lnτ_b versus inverse of absolute temperature (1/T), the activation energies (E_a) were found to be 0.37 and 0.44eV, respectively. The percolation threshold was observed with 40 phr carbon black loading. POLYM. COMPOS., 37:342–352, 2016. © 2014 Society of Plastics Engineers     

Polyurethane/conducting carbon black composites: Structure,electric conductivity,strain recovery behavior,and their relationships

The polyurethane composites with conducting carbon black (CB) were prepared by a solution‐precipitation process, which was followed by melt compression molding. The polyurethane used has good shape memory effect. The morphology of CB fillers in polyurethane matrix and the resulting conductivity of the composites were investigated. It has been found that CB fillers exist in the forms of aggregates. The percolation threshold is achieved at the CB concentration of 20 wt %. The presence of CB fillers decreases the degree of crystallinity of polycaprolactone (PCL) soft segments of the polyurethane. However, the composites still have enough soft‐segment crystals of polyurethane to fulfil the necessary condition for the shape memory properties. Dynamic mechanical data show that CB is an effective filler for the reinforcement of the polyurethane matrix, but does not deteriorate the stable physical cross‐link structure of the polyurethane, which is necessary to store the elastic energy in the service process of the shape memory materials. Addition of CB reinforcement in the polyurethane has influenced the strain recovery properties, especially for those samples with CB concentrations above the percolation threshold. The response temperature of the shape memory effect T_r has not been affected too much. Strain fixation S_f, which expresses the ability of the specimens to fix their strain, has been improved in the presence of the CB fillers. The final recovery rates R_f and strain recovery speeds V_r of the shape memory measurements, however, have decreased evidently. It is expectedly ascribed to the increased bulk viscosity as well as the impeding effect of the inter‐connective structure of CB fillers in the polymer matrix. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 68–77, 2000     

Effect of modified carbon black on the filler–elastomer interaction and dynamic mechanical properties of SBR vulcanizates

A new modified carbon black (GCB) was prepared by adding special RFL latex into N220. Dynamic properties were obtained over a wide range of temperatures and strains on vulcanizates filled with GCB and unmodified carbon black, respectively. The results show that the GCB can effectively decrease the tan δ value at 60 and 90°C of SBR vulcanizates compared with that of the common unmodified carbon blacks, which responds to the fact that GCB is beneficial to lower rolling resistance and heat generation of the vulcanizates in comparison to that of the unmodified carbon black. Among the factors responsible for this, filler networking and filler–elastomer interaction play a dominant role. The effects of filler loading on mechanical properties of vulcanizates were also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3707–3712, 2006     

Effect of a carbon black surface treatment on the microwave properties of poly(ethylene terephthalate)/carbon black composites

A surface treatment was applied to carbon black to improve the electrical and microwave properties of poly(ethylene terephthalate) (PET)-based composites. Three different formamide solutions with 1, 2, and 3 wt % concentrations were prepared to modify the surface chemistry of carbon black. Microwave properties such as the absorption loss, return loss, insertion loss, and dielectric constant were measured in the frequency range of 8–12 GHz (X-band range). Composites containing formamide-treated carbon black exhibited enhancements in the electrical conductivity, electromagnetic interference (EMI) shielding effectiveness, and dielectric constant values when compared to composites with untreated carbon black. In addition, increases in the formamide solution concentration and carbon black content of composites resulted in an increase in the electrical conductivity, EMI shielding effectiveness, and dielectric constant values. The percolation threshold concentration of PET composites shifted from a 3 to 1.5 wt % carbon black composition with the surface treatment. The best EMI shielding effectiveness was around 27 dB, which was obtained with the composite containing 8 wt % carbon black treated with a 3 wt % formamide solution. Moreover, this composition gave the lowest electrical resistivity and the highest dielectric constant among the produced composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

甲基丙烯酸锌与炭黑共同补强天然橡胶的研究

在开放式炼胶机上,分别以直接添加和原位生成2种方法向天然橡胶(NR)基体中添加甲基丙烯酸锌(ZDMA),制备了2种类型的ZDMA与炭黑共同补强的NR硫化胶,X射线衍射(XRD)分析证实,成功制备了ZDMA。扫描电镜(SEM)研究表明,原位生成ZDMA硫化胶的断面比直接添加ZD-MA硫化胶的粗糙很多,表现出更强的界面结合力。力学性能研究表明,用ZDMA部分替代炭黑,可以有效提高硫化胶的力学性能。在相同添加量下,原位生成ZDMA硫化胶的力学性能优于直接填充ZD-MA硫化胶的。     

炭黑与白炭黑增强聚烯烃弹性体硫化胶的比较

研究了炭黑、白炭黑对聚烯烃弹性体(POE)硫化胶的增强作用,考察了交联剂过氧化二异丙苯(DCP)和炭黑及白炭黑的用量对POE硫化胶物理机械性能的影响,并用扫描电子显微镜对其微观结构进行了观察.结果表明,用DCP交联POE,POE的主要物理机械性能比未交联前有所下降;用炭黑、白炭黑增强POE硫化胶,其物理机械性能显著提高,说明增强效果明显,炭黑、白炭黑最佳用量分别为60份和40份.     

Preparation of carbon black/polypropylene nanocomposite with low percolation threshold using mild blending method

A new approach, mild blending method, to prepare carbon black (CB) filled polypropylene (PP) nanocomposite using CB aqueous suspension was reported in this study. In this compounding process, the CB particles were first dispersed in aqueous suspension by using an ultrasonic irradiation. Subsequently, the CB suspension was blended with melting PP using an extruder with low shear strength screw configuration, followed by removing the vapor from the vent by vacuum. The morphological observation showed that the CB particles were dispersed at a nanometer level in the nanocomposites as they were in aqueous suspension and distributed homogeneously in PP matrix. The CB/PP nanocomposite prepared by this method exhibited a very low percolation threshold, i.e., 2.49 vol %, and a high‐critical resistance exponent t (t = 5.82). These phenomena, which deviated from the classical percolation theory, were likely to come down to the homogeneous distribution of CB particles and the tunneling conduction. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Relaxation behavior of conductive carbon black reinforced chlorosulfonated polyethylene composites

Dynamic mechanical analysis and dielectric relaxation spectra of conductive carbon black reinforced chlorosulfonated polyethylene (CSM) composites were used to study their relaxation behavior as a function of temperature and frequency, respectively. A marginal increase in glass transition temperature has been observed upto 30 phr carbon black filled polymer composite, beyond which it decreases, which has been explained on the basis of aggregation of filler particles in the polymer matrix. The strain dependent dynamical parameters were evaluated at dynamic strain amplitudes of 0.1–200%. The nonlinearity in storage modulus increases with increase in filler loading. It can be explained on the basis of filler–polymer interaction and aggregation of the filler particulates. The frequency dependent dynamical mechanical analysis has also been studied at frequency range of 0.1–100 Hz. The variation in real and complex part of impedance with frequency has been studied as a function of filler loading. The effect of filler loading on ac conductivity has been observed as a function of frequency. An increase in conductivity value has been observed with increase in filler loading. This can be explained on the basis of formation of conducting paths between filler particulates. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Copper phthalocyanine oligomer grafted acrylic elastomer nanocomposites with high dielectric constants

For many applications of dielectric elastomer (DE) actuators, it is desirable to endow the DE with a high dielectric constant (ε), high breakdown field, and good flexibility. In this study, a high‐ε nanocomposite acrylic elastomer (ACM)‐g‐copper phthalocyanine (CuPc) was fabricated, in which the CuPc oligomer was grafted onto the backbone of ACM. This grafted composite exhibited several benefits over the physically blended one. Transmission electron microscopy micrographs indicated that the size of the grafted CuPc was in the range 15–30 nm, which was more than 25 times smaller than that of the simply blended one. At room temperature, ε of ACM‐g‐CuPc (with 15 wt % CuPc) reached 303 at 100 Hz. The remarkable enhancement in the dielectric response could be attributed to the greatly strengthened exchange coupling effect and the Maxwell–Wagner–Sillars polarization mechanism. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39975.     

Approach to the fabrication of acrylic elastomer nanocomposites with high dielectric constants

Dielectric elastomers (DEs) are a type of electroactive polymer that can deform in an electric field. The possession of a high dielectric constant is critical for DEs if they are to be suitable materials for the application of actuators. A novel elastomeric nanocomposite (ACE‐g‐CuPc) was fabricated by copper phthalocyanine oligomer (CuPc) grafting directly onto an acrylic elastomer (ACE) backbone. Compared with other synthetic methods, esterification has several advantages; these include fewer impurities and a simpler synthetic route. Transmission electron microscopy showed that the size of the CuPc particles of the ACE‐g‐CuPc was in the range 15–30 nm; this range was significantly smaller than that of ACE/CuPc (500 nm). The results of thermogravimetric analysis show that the thermal stability of the grafting composite was higher than that of the blending composite. At 100 Hz, the dielectric constant of the grafting composite (with 11 wt % CuPc) reached 173 at room temperature. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43904.     

炭黑/环氧树脂复合材料导电行为的研究

分别采用不同的混合分散方法制备炭黑/环氧树脂(CB/EP)复合材料(CB牌号为F101、XE2,EP牌号为E-54、E-51和E-44),研究了制备工艺、CB用量和CB结构等对复合材料导电性能的影响。结果表明:不同方法制得的复合材料体积电阻率的大小依次为机械混炼法离心混合法超声分散法;CB/EP复合材料的导电性能随CB用量增加而显著提高,并且F101/E-54、XE2/E-54复合材料体系均表现出明显的导电渗流行为;CB结构对复合材料的导电性能影响较大,F101/E-54、XE2/E-54复合材料体系的导电渗流阈值分别为3.85%、0.47%。     

炭黑增强氯丁橡胶硫化胶压缩Mullins效应的强化

研究了炭黑增强氯丁橡胶硫化胶的力学性能和压缩Mullins效应的强化效应,探讨了炭黑用量对其压缩Mullins效应的增强机制。结果表明,炭黑增强后的氯丁橡胶硫化胶的屈服强度和模量均得到明显提高,且力学性能在炭黑用量为30份(质量)时达到最佳;在单轴循环压缩过程中,随着炭黑用量的增加,氯丁橡胶静态硫化胶的Mullins效应不断增强,并且在给定的压缩应变下,其最大压缩应力在首次加载-卸载循环压缩时达到峰值,在随后的4次循环压缩中仅发生不同程度的下降。此外,提高炭黑用量及增大压缩应变均可明显增强氯丁橡胶硫化胶的Mullins效应。     

Alternating electric field induced agglomeration of carbon black filled resins

This letter reports on our observation that an alternating electric field is able to induce the formation of an electrically conducting network in carbon black (CB) filled resins well below the zero-field percolation threshold. Compared with the recently presented dc method, the ac agglomeration is more efficient in two respects: it proceeds significantly faster under equivalent conditions and is still effective at higher ionic concentration. In contrast to the ramified form of dc-induced CB networks, ac agglomeration favors the formation of parallel CB chains. The experimental results can be explained taking into account ionic conductivities of the matrices as well as charges and field induced dipoles on the CB particles.     

Agglomeration and electrical percolation behavior of carbon black dispersed in epoxy resin

In conductive polymer compounds, the filler volume fraction at which a network of touching particles is formed is not a constant but depends on the manufacturing process. By applying three main features—particle-particle interaction, dynamics of agglomeration, and structure of agglomerates—which are well known in colloid science to filled polymers, the electrical percolation behavior can be understood. Thus, it is possible to explain the hitherto found low percolation thresholds of less than 0.5 vol% in carbon-black-filled resins and, hence, further reduce the threshold to 0.06 vol%. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1741–1746, 1997     

Relaxation behavior of conductive carbon black reinforced EPDM microcellular vulcanizates

Dynamic mechanical analysis and dielectric relaxation spectra of conductive carbon black reinforced microcellular EPDM vulcanizates were used to study the relaxation behavior as a function of temperature (−90 to +100°C) and frequency (0.01–10⁵ Hz). The effect of filler and blowing agent loadings on dynamic mechanical and dielectric relaxation characteristics has been investigated. The effect of filler and blowing agent loadings on glass transition temperature was marginal for all the composites (T_g value was in the range of −39 to −35°C), which has been explained on the basis of relaxation dynamics of polymer chains in the vicinity of fillers. Strain-dependent dynamical parameters were evaluated at dynamic strain amplitudes of 0.07–5%. The nonlinearity in storage modulus has been explained based on the concept of filler–polymer interaction and interaggregate attraction (filler networking) of carbon black. The variation in real and complex part of impedance with frequency has been studied as a function of filler and blowing agent loading. Additionally, the effect of crosslinking on the dielectric relaxation has also been reported. POLYM. ENG. SCI., 47:984–995, 2007. © 2007 Society of Plastics Engineers     

Improvement of actuation performance of dielectric elastomers by barium titanate and carbon black fillers

Dielectric elastomers are promising materials for actuators resembling human muscle. Among elastomers, acrylic rubbers (ACM) have shown good actuation performance but its use is limited by the high operating voltages required. The present work demonstrates that simultaneous incorporation of nanostructured carbon black and dielectric fillers offers an increase in a dielectric permittivity and a suitable modulus of the elastomers matrix, enabling an improved electro‐mechanical actuation performance at low voltages. By the use of reinforcing carbon black and barium titanate in an acrylic elastomer matrix a sixfold increase in the dielectric permittivity was realized. A fine tuning of the actuation stress and, consequently, actuation strain can be done by a judicial selection of the different filler concentrations in the soft rubber matrix. Finally, a synergistic effect of the fillers was observed in the improved actuation performance of the developed materials. This work may pave the way to design dielectric elastomers for actuator fabrication. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44116.     

Dynamic mechanical properties of conductive carbon black‐reinforced closed cell microcellular oil‐extended EPDM rubber vulcanizates: Effect of blowing agent,temperature, frequency,and strain

Dynamic viscoelastic properties of Vulcan XC 72 (excess conductive carbon black)‐reinforced solid‐ and closed‐cell microcellular controlled long chain branching grade oil‐extended EPDM (Keltan 7341A) rubber vulcanizates were studied at four frequencies of 3.5, 11, 35, and 110 Hz, and at a temperature range of ?100 to 160°C.The effect of blowing agent (ADC 21) loading on storage modulus (E′) and loss tangent (tan δ) was studied. The log of storage modulus bears a linear relationship with the log of density for both solid and microcellular rubber. Relative storage modulus (E/E) decreases with decrease in relative density (ρ_f/ρ_s). Both E′ and tan δ were found to be dependent on frequency and temperature. The master curves of the storage modulus versus log temperature‐reduced frequency were formed by superimposing E′ results and by using shift factors calculated by Arrhenius equation. Strain‐dependent isothermal dynamic viscoelastic properties were carried out for dynamic strain amplitude of 0.08–7%. Cole–Cole plots of microcellular vulcanizates show a circular arc with blowing agent (density). Empirical relationship between tan δ versus E′ is found to be linear, whose slope is independent of blowing agent loading or density. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1600–1608, 2006