Dielectric behavior of natural rubber composites in microwave fields

In this article, we report the preparation of conducting natural rubber (NR) with polyaniline (Pani). NR was made into a conductive material by the compounding of NR with Pani in powder form. NR latex was made into a conductive material by the in situ polymerization of aniline in the presence of NR latex. Different compositions of Pani–NR semi‐interpenetrating networks were prepared, and the dielectric properties of all of the samples were determined in microwave frequencies. The cavity perturbation technique was used for this study. A HP8510 vector network analyzer with a rectangular cavity resonator was used for this study. S bands 2–4 GHz in frequency were used. Thermal studies were also carried out with thermogravimetric analysis and differential scanning calorimetry. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2682–2686, 2007     

Tailoring the nonlinear conducting behavior of silicone composites by ZnO microvaristor fillers

Silicone composite filled with zinc oxide microvaristors possesses excellent nonlinear conducting behavior as ZnO varistor does. For better adjusting the composite's electrical behavior to satisfy the practical field‐grading requirement, this article studied the influence of ZnO filler's property on the nonlinearity of the composite. Several groups of ZnO‐silicone composite samples in different filler volume fraction and filler diameter were prepared, the measured J‐E characteristics show that the percolation threshold of ZnO‐silicone composite is around 35%, above which the composites present reliable nonlinear behavior. The switching voltage of the composite exhibits a considerable decrease as filler's diameter increases or filler's volume fraction increases, while the nonlinear coefficient remains stable. Moreover, filler's size also has a little influence on composite's percolation limit. The conclusion above fits very well with the theory of the conducting composites and percolation process. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42645.     

Dielectric properties of high coercivity barium ferrite–natural rubber composites

The effect of frequency, temperature, and BaFe₁₂O₁₉ (BF) content on the dielectric constant $ \acute\varepsilon $ , dielectric loss ε″, and tan δ were studied for barium ferrite—natural rubber composites (RFC). The dielectric constant for barium ferrite was related to the preparation method, meanwhile the dielectric constant of natural rubber (NR) is relatively large compared to the theoretical value. The results showed that $ \acute\varepsilon $ , ε″, and tan δ for RFC decrease as the frequency increases, however, at higher frequencies, the effect significantly weakens. At low ferrite loading, the dielectric properties are strongly influenced by BF content. Strong correlation between magnetic initial permeability and dielectric constant for hard magnetic material polymer composites was also observed. Increasing the content of barium ferrite in NR matrix enhances both ε″ and tan δ. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Low dielectric and high thermal conductivity epoxy nanocomposites filled with NH2‐POSS/n‐BN hybrid fillers

Hybrid fillers of mono‐amine polyhedral oligomeric silsesquioxane/nanosized boron nitride (NH₂‐POSS/n‐BN) were performed to fabricate NH₂‐POSS/n‐BN/epoxy nanocomposites. Results revealed that the dielectric constant and dielectric loss values were decreased with the increasing addition of NH₂‐POSS obviously, but increased with the increasing addition of BN fillers. For a given loading of NH₂‐POSS (5 wt %), the thermal conductivities of NH₂‐POSS/n‐BN/epoxy nanocomposites were improved with the increasing addition of n‐BN fillers, and the thermal conductivity of the nanocomposites was 1.28 W/mK with 20 wt % n‐BN fillers. Meantime, the thermal stability of the NH₂‐POSS/n‐BN/epoxy nanocomposites was also increased with the increasing addition of n‐BN fillers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41951.     

Electrical,mechanical, and piezoresistive properties of carbon nanotube–polyaniline hybrid filled polydimethylsiloxane composites

The electrical, mechanical, and piezoresistive properties of ternary composites based on elastomeric polydimethylsiloxane (PDMS), carbon nanotubes (CNTs), and polyaniline (PANI) were studied and compared with those of binary PDMS–CNT composites. The presence of PANI affected the percolating network of the CNTs. At lower PANI concentrations (2.5 and 5%), the conductive network of the CNTs was constructively modified; this led to an enhancement in the conductivity in the sample containing 2% CNTs. A higher PANI content (7.5%) hindered the flow of main charge carriers through the composite. The piezoresistive response of the binary and ternary composites was studied by cyclic experiments under compression loads. In all of the samples, the electrical resistance increased monotonically up to a 10% strain. The reproducibility of the piezoresistive behavior in the binary and ternary composites provided evidence that the fillers could reversibly recover their initial position together with the PDMS chains without a significant displacement with respect to their original positions. The reduction of the piezoresistive sensibility by PANI addition was attributed to the displacement restrictions of the CNTs within the composite under pressure because of the volume exclusion of PANI particles; this maintained the probability of CNT contact and increased the possibility of the formation of new CNT conductive channels. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44780.     

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     

Enhanced microwave absorbing properties of lightweight films based on polyaniline/aliphatic polyurethane composites in X band

Polymer blends based on nanostructured polyaniline (PANI) doped with hydrochloric acid (HCl) and para‐toluene sulfonic acid (PTSA) introduced into aliphatic polyurethane matrix (PU) are synthesized to produce flexible thin composite films for microwave absorbers. The effects of dopant type, PANI content and film thickness on morphologies, dielectric and microwave absorption properties in the X‐band are studied. It reveals that real and imaginary parts of the complex permittivity are proportional to filler concentrations and type of doped PANI. The PANI‐PTSA/PU films show higher permittivity and better microwave absorbing properties than PANI‐HCl/PU for the same weight fraction of PANI. The minimum reflection loss RL_(dB) values for the PANI‐PTSA/PU are ?37 dB at (20% PANI and 11.6 GHz) and ?30 dB at (15% PANI and 11.3 GHz) for thicknesses of 1.2 and 1.6 mm, respectively. These high values of reflection losses make the obtained lightweight and flexible composites promising radar absorbing materials (RAM). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40961.     

Effect of double percolation on the electrical properties and electromagnetic interference shielding effectiveness of carbon‐black‐loaded polystyrene/ethylene vinyl acetate copolymer blends

In this study, the concept of double percolation and selective location of a conducting additive was used to develop conducting polymer composites composed of polystyrene (PS) and ethylene vinyl acetate copolymer (EVA) filled with carbon black (CB). Scanning and transmission electron microscopy suggested that the CB was preferentially located in the EVA phase. By combining a cocontinuous morphology and selective location of CB in the EVA phase, we achieved the highest conductivity values and better electromagnetic interference shielding effectiveness in the X‐band frequency range for the 70:30 w/w PS/EVA blend. Electromagnetic attenuation occurred by both reflection and absorption mechanisms, although the first was predominant for composites with a higher amount of CB. The percolation thresholds of the PS, EVA, and 70:30 w/w PS/EVA blend loaded with CB were estimated from the dependence of the alternating‐current and direct‐current conductivities. The rheological properties were also used to relate the electrical behavior to the microstructure of the composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43013.     

Dielectric properties of aluminum–epoxy composites

Dielectric properties of Al–epoxy composites were characterized as a function of composition, frequency, and temperature. The dielectric constant increased smoothly with an increase in the concentration of aluminum. An increase in dielectric constant was also observed with an increase in temperature as well as with a decrease in frequency. In general, dissipation factor values for composites with higher concentrations of aluminum were greater than those with lower volume content of aluminum. Also, the dissipation factor showed an increase both with a decrease in frequency and an increase in temperature. The increase in values of dielectric constant and dissipation factor with an increase in concentration of aluminum was attributed to interfacial polarization. The absence of any discontinuity in the plot of dielectric constant versus composition was ascribed to the absence of continuous aluminum chains in the composition range investigated. The increase in dielectric constant with a rise in temperature was attributed to the segmental mobility of the polymer molecules. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3602–3608, 2003     

Ionic liquids as dispersing agents of graphene nanoplatelets in poly(methyl methacrylate) composites with microwave absorbing properties

Graphene nanoplatelets (GNP) is noncovalently functionalized with imidazolium-, pyridinium-, and vinyl-pyridinium-based ionic liquids containing bromide or bis(trifluoromethyl-sulfonyl)imide (TFSI) as the counteranions, and used to prepare poly (methyl methacrylate) (PMMA) nanocomposites by solution casting approach followed by compression molding technique. The PMMA composites loaded with 1.9 and 1.8 wt% of GNP in PMMA/GNP composite and PMMA/GNP/ionic liquids, respectively, were characterized by melting viscosity, thermogravimetric analysis and AC electrical conductivity (σ_AC). The microwave absorption properties at the X-band (8.2–12.4 GHz) frequency were measured for systems with 1 mm thickness using the metal-backed configuration. PMMA nanocomposites loaded with GNP/N-dodecyl-4-vinyl-pyridinium.TFSI (C₁₂ViPy.TFSI) displayed higher thermal stability and higher σ_AC. This system also presented the best response in terms of microwave absorbing properties, with minimum reflection loss (RL) of around −6 dB at 8.7 GHz. Triple layered composite structures with layers of different conductivities and different stacking orders were also investigated in terms of reflection loss. Broadband absorption with minimum RL ≤ −10 dB (90% of electromagnetic attenuation) in the frequency between 10.2 and 12.4 GHz and better absorbing effectiveness were observed for the PMMA/GNP-PMMA/GNP/C₁₂ViPy.TFSI-PMMA/GNP/C₁₂ViPy.Br triple-layered system with 3 mm thickness.     

Influence of ionic liquid on the polymer–filler coupling and mechanical properties of nano‐silica filled elastomer

The natural rubber (NR) nanocomposites were fabricated by filling ionic liquid (1‐allyl‐3‐methyl‐imidazolium chloride, AMI) modified nano‐silica (nSiO₂) in NR matrix through mechanical mixing and followed by a cure process. Based on the measurements of differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), solid state nuclear magnetic resonance spectroscopy, and Raman spectroscopy, it was proved that AMI could interact with nSiO₂ through hydrogen bonds. With the increase of AMI content, the curing rate of nSiO₂/NR increased. The results of bound rubber and dynamic mechanical properties showed that polymer–filler interaction increased with the modification of nSiO₂. Morphology studies revealed that modification of nSiO₂ resulted in a homogenous dispersion of nSiO₂ in NR matrix. AMI modified nSiO₂ could greatly enhance the tensile strength and tear strength of nSiO₂/NR nanocomposites. Compared to unmodified nSiO₂/NR nanocomposite, the tensile strength of AMI modified nSiO₂/NR nanocomposite increased by 102%. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44478.     

Investigation of mechanical properties of alumina nanoparticle‐loaded hybrid glass/carbon‐fiber‐reinforced epoxy composites

This research work investigates the tensile strength and elastic modulus of the alumina nanoparticles, glass fiber, and carbon fiber reinforced epoxy composites. The first type composites were made by adding 1–5 wt % (in the interval of 1%) of alumina to the epoxy matrix, whereas the second and third categories of composites were made by adding 1–5 wt % short glass, carbon fibers to the matrix. A fourth type of composite has also been synthesized by incorporating both alumina particles (2 wt %) and fibers to the epoxy. Results showed that the longitudinal modulus has significantly improved because of the filler additions. Both tensile strength and modulus are further better for hybrid composites consisting both alumina particles and glass fibers or carbon fibers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39749.     

Mechanical,dielectric, and thermal properties of fluorosilicone rubber composites filled with silica/multiwall carbon nanotube hybrid fillers

In this work, hybrid fillers consist of modified silica (SiO₂) and multiwalled carbon nanotube (MWCNT) were used to improve the mechanical, dielectric, and thermal properties of fluorosilicone (FSR) composites via a direct mechanical mixing method. With the increase of CNT loading in SiO₂/CNT hybrid loading ratio, the tensile properties, dielectric constant, electrical conductivity, and thermal properties all increase without a sharp sacrifice of flexibility. The dielectric constant of FSR-S15/C5 achieved 7,370 @1 kHz, which is about four orders of the FSR-S20, and the dielectric loss remains as low as 0.676 @1 kHz. Therefore, the linkage of SiO₂ and FSR chains not only enhances the interfacial interaction between the fillers and FSR matrix but also decreases the agglomeration of the fillers in matrix. What is more, modified SiO₂ and CNT were designed as the effective hybrid filler to improve the performance of the polymeric matrix through synergic effect.     

Carbon–polymer composites with extreme electrical conductivity

The aim of this study was to develop Carbon–polymer composites with extreme electrical conductivity (100 S/cm) combined with good flexural strength. Despite the many optimization methods described in the literature, no comprehensive optimization procedure was to be found because the formulation did not control by itself the final properties. This study showed the major influence of the processing conditions with these peculiar materials. A detailed study of the influence of the processing conditions on the microstructural and macroscopic properties was performed. We, thereby, proposed a comprehensive way to optimize the properties of the final product. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42274.     

Microwave properties of selected thermoplastic conducting composites

Thermoplastic conducting composites of polyparaphenylene diazomethine (PPDA), polythiophene (PTH), poly‐3,4‐Ethylenedioxythiophene (PEDOT), and polyaniline (PANI) with polyvinylchloride (PVC) and polyurethane (PU) were prepared. Conducting composites were prepared by in situ polymerization of thiophene, ethylene dioxy thiophene, and aniline in the presence of polyvinyl chloride and polyurethane using FeCl₃ as the oxidizing agent. PPDA composites were prepared by dispersing PPDA powder in the polymer solution followed by casting. The microwave properties of all the composites were studied in the S band using Vector Network Analyzer and the best composite was selected based on the dielectric properties for microwave applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of microstructure on the dielectric properties of poly(vinyl alcohol)–poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonate) composite films

Poly(3,4‐ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT–PSS) was blended with poly(vinyl alcohol) (PVA) to form 0, 10, 20, 30, 40, and 50 vol % PEDOT–PSS/PVA solutions, and their freestanding films were prepared with a simple and cost‐effective solution casting technique at 27 °C in the absence of additives. Field emission scanning electron microscopy images revealed changes in the cocontinuous network to a rodlike morphology in the composite films from 10 to 50 vol % PEDOT–PSS/PVA. The alternating‐current conductivity was found to obey Jonscher's power law. The obtained values of the dielectric constant at 27 °C were relatively high, and a maximum value of 6.7 × 10⁴ at 100 Hz for 40 vol % PEDOT–PSS'/PVA was observed. The dielectric loss attained a maximum value of about 10⁶ at 100 Hz for 40 vol % PEDOT–PSS/PVA. However, a decrease in the dielectric parameters was observed at 50 vol % PEDOT–PSS/PVA because of locally induced strain in the microstructure. The variations in polarization with respect to the applied electric field (P–E) were determined for 50, 100, and 500 Hz at 500 V for the freestanding composite films of lower concentrations up to 20 vol % PEDOT–PSS/PVA. In summary, the dielectric and P–E measurements confirmed that the electrical characteristics changed in accordance to the contribution from both resistive and capacitive sites in the PEDOT–PSS/PVA composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45079.     

Dielectric and microwave properties of carbon nanotubes/carbon black filled natural rubber composites

Abstract

Natural rubber (NR) based nanocomposites containing a constant amount (50 phr) of standard furnace carbon black and carbon nanotube (CNT) at a concentration from 1 to 5 phr have been prepared. Their dielectric (dielectric permittivity and dielectric loss) and microwave properties (coefficients of absorption and reflection of the electromagnetic waves and electromagnetic interference shielding effectiveness) have been investigated in the 1–12 GHz frequency range. The results achieved allow recommending CNTs as second filler for NR based composites to afford specific absorbing properties.     

The behavior of natural rubber–epoxidized natural rubber–silica composites based on wet masterbatch technique

Natural rubber–epoxidized natural rubber–silica composites were prepared by the wet masterbatch technique and the traditional dry mixing method. Performances of the composites based on different preparation methods were investigated with a moving die rheometer, an electronic universal testing machine, a dynamic mechanical analyzer, a nuclear magnetic resonance crosslink density analyzer, a rubber processing analyzer (RPA), a scanning electron microscope (SEM), and a transmission electron microscope (TEM). The RPA, SEM, and TEM analyses indicated that silica has better dispersion, lower filler–filler interaction, and better filler–rubber interaction in compounds based on the wet masterbatch technique, leading to improvements in mechanical strength and the dynamic mechanical and compression properties of the composites. It also indicates that composites prepared by the wet masterbatch technique have shorter scorch time, faster curing velocity, and higher crosslink density. The composites prepared by the wet materbatch technique also have lower rolling resistance, which is an important property for their use as a green material for the tire industry. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43571.     

Effect of a coupling agent on the electromagnetic and mechanical properties of carbon black/acrylonitrile–butadiene–styrene composites

Titanate coupling agent (TCA) is widely used as a plasticizer in filled polymer processes. In this study, the effect of TCA with different contents (2 and 10 wt %) on the electrical conductivity, wave absorption, and mechanical properties of carbon black (CB)/acrylonitrile–butadiene–styrene (ABS) composites were investigated. The results indicate that with the addition of 2 wt % TCA to the filled CB, the electrical conductivity of CB/ABS composites improved greatly, but its wave absorption performance was weakened. In contrast, the addition of 10 wt % TCA to the filled CB improved the microwave absorption performance of the CB/ABS composites but led to poor electrical conductivity. However, TCA, regardless of the contents of 2 or 10 wt %, greatly improved the mechanical properties of the composites. The probable reasons for this are discussed on the basis of the fracture morphology of the sample, a chemical band between the filling and resin, and the physical coating between the filling and TCA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1839–1843, 2006     

Styrene–butadiene rubber/graphite powder composites: Rheometrical,physicomechanical, and morphological properties

The physicomechanical properties, curing characteristics, and morphological behaviors of styrene–butadiene rubber/graphite powder composites were evaluated. Different weight fractions and particle sizes of graphite powder were used. An increase in the graphite content increased the maximum torque, reinforcing factor, and tensile strength and decreased the elongation at break and equilibrium swelling. Also, a decrease in the particle size of the graphite increased the tensile strength and decreased the equilibrium swelling. Moreover, the dielectric properties were measured at about 30°C and 100 Hz. The values of permittivity and dielectric loss were found to increase with increasing graphite content. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011