Effect of Furnace Carbon Black on the Dielectric and ...

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Chloroprene rubber . dielectric properties . microwave properties In this paper, the dielectric and microwave properties of chloroprene rubber (CR) based composites comprising different amounts of furnace carbon black in the range 0-100 phr have been investigated in the frequency range from 1 to 12 GHz. In the frequency range from 1 to 8 GHz the values of the dielectric permittivity and dielectric loss angle tangent are relatively low and do not change significantly with the increase of frequency. In the range from 8 to 12 GHz, the increase in frequency leads to increasing values of relative dielectric permittivity and dielectric loss angle tangent. Increasing the amount of carbon black leads to improved microwave properties of the investigated composites. The composites based on CR containing 60-100 phr furnace carbon black have very good microwave properties and can be used for the needs of anti-radar camouflage and for electromagnetic shielding.

Einfluss von Ofenruß auf die dielektrischen und MikrowellenEigenschaften der Chloroprenkautschuk-Verbundwerkstoffen Chloroprenkautschuk . Dielektrischen Eigenschaften . Mikrowellen-Eigenschaften Untersucht wurden die Dielektrischen und Mikrowelleneigenschaften von Chloroprenkautschuk-Verbundwerkstoffen mit verschiedenen Mengen von Ofenruß (0 – 100 phr) im Frequenzabstand von 1 bis 12 GHz. Im Frequenzabstand von 1 bis 8 GHz sind die Werte der Elektrizitätskonstante und des Dielektrizitätsverlusstfaktors verhältnismässig niedrig und sie verändern sich nicht bedeutend mit der Frequenzzunahme. Im Frequenzabstand von 8 bis 12 GHz führt die Frequenzzunahme zu Anstieg der Werten der relativen Dielektrizitätskonstante und des Dielektrizitätsverlusstfaktors. Die Zunahme der Rußmenge führt zu Verbesserung der Mikrowelleneigenschaften der untersuchten Verbundwerkstoffen. Die ChloroprenkautschukVerbundwerkstoffe mit 60 – 100 phr Ofenruß haben sehr gute Mikrowelleneigenschaften und sie können für Radartarnung und elektromagnetische Abschirmung angewendet werden. Figures and Tables: By a kind approval of the authors

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Effect of Furnace Carbon Black on the Dielectric and Microwave Properties of Chloroprene Rubber Composites In the recent years, considerable attention has been paid to the elastomeric microwave absorbing materials, which is due to the ever increasing use in the manufacture of telecommunication equipment, which is applied in industry, electronics, medicine [1, 2] etc. Depending on microwave absorption and SE at different frequency ranges, these composites have been widely used in the area of electromagnetic/ radio-frequency interference (EMI/RFI) shielding, electrostatic discharge (ESD), elastomer interconnect devices used for integrated circuit (IC) package assembly [3] etc. Rubbers as electrical insulators are transparent to electromagnetic radiation and thus do not provide microwave absorption and electromagnetic interference shielding effectiveness (SE). Both microwave absorption and SE in the rubber based composites can be improved by the formation of a continuous network of conductive fillers throughout the insulating polymer matrix [3]. Composites in EMI shielding and microwave applications based on different rubber matrices have been reported and include nitrile rubber [4], polychloroprene [5, 6], silicone [7-9], polyurethane [10], butyl rubber [11, 12], polysulfide polymer [13], ethylene vinyl acetate (EVA) [14-17], ethylene vinyl acetate blended with natural rubber [17], EVA/ethylene–propylene–ethylidenenorbornene blend [16]. The most often used conductive fillers with high dielectric loss include carbon black [4, 12, 14-18], short carbon fiber [4–6, 1417], graphite particles [7, 13], boron carbide [11, 18]. On the other hand rubber composites containing as fillers high magnetic loss materials are also important for many applications such as microwave absorbers or materials for electromagnetic wave shielding, magnetic data storage media, magnetic field sensors [19-21], etc. Chloroprene rubber (CR) [poly (2-chloro-1,3 butadiene)] is a polar elastomer which is widely used in rubber

industry. Due to its chemical nature, CR has a set of valuable properties such as: good mechanical strength, high ozone and weather resistance, good aging resistance, low flammability, good resistance toward chemicals, moderate oil and fuel resistance and adhesion to many substrates. It is well-known that the chemical nature of the elastomer matrix significantly affects the interaction between the electromagnetic waves and the composite [22]. Unlike the non-polar elastomers, those containing highly polar functional groups or bonds (NBR, CR etc.) provide better microwave properties of the composites designed for microwave absorbers. Despite publications on electromagnetic interference shielding effectiveness and microwave properties of composites based on chloroprene rubber, as well as on the use of carbon black as absorption active filler in terms of electromagnetic waves, we found no detailed study on dielectric (dielectric permittivity and dielectric loss angle tangent) and microwave (coefficients of reflection and attenuation and electromagnetic in-

Authors A. Omar Al-Hartomy, A. Ahmed Al-Ghamdi1, Jeddah, R. Falleh AlSolamy, Tabuk, (Saudi Arabia), N. Dishovsky, M. Mihaylov, V. Iliev, Sofia, (Bulgaria) , F. El-Tantawy, Ismailia, (Egypt). Corresponding author: Mihail Mihaylov, University of Chemical Technology and Metallurgy Dept. Polymer engineering 1756 Sofia, Bulgaria Tel: +3592/81 63/219 e-mail: [email protected] KGK · 10 2012

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terference shielding effectiveness) properties of chloroprene rubber based composites, conducted in a wide frequency range and within a wide range of filling. On the ground of the above said the aim of this paper is to present the results of dielectric and microwave properties and electromagnetic interference shielding effectiveness measurements in the frequency range (1-12 GHz) of chloroprene rubber based composites, filled with standard furnace carbon black in the range from 0 to 100 phr.

TEM micrograph and micrograph in SAED regime (on the right) of standard furnace carbon black Corax N220 particles

1

Experimental Materials

Polychloropren (Baypren 226, Lanxess) with a Mooney viscosity ML(1+4) of 75, was used. Furnace black, namely (Corax N220, Evonik), of primary particle size about 20 nm was used as a reinforcing high dielectric loss filler. Other ingredients such as zinc oxide (ZnO), stearic acid (SA), N-(1,3-dimethylbutyl)N’-phenyl-p-phenylenediamine (Vulkanox 4020, Lanxess), tetramethyl thiuram disulfide (TMTD, Vulkacit Thiuram/C, Lanxess), and magnesium oxide (MgO) were commercial grades and used without further purification. TEM micrograph of the filler used with selected area electron diffraction (SAED) is shown on Figure 1. As it can be seen from the figure, the elementary particles of carbon black form aggregates and agglomerates with different shapes and sizes. From the SAED image presented in Figure 1 it is evident that the investigated carbon black has amorphous structure.

Preparation of rubber composites

Typical formulations of CR composites are presented in Table 1. The filler mixing with rubber was accomplished in an open two-roll mill under identical conditions of time, temperature, and nip gap, with same sequence of mixing of all compounding ingredients to avoid the effect of processing on the properties. The vulcanization of the rubber compounds was carried out in an electrically heated hydraulic press using a special homemade mold at temperature 153 °C and under pressure 150 KN/m2. The optimal curing time was determined by the vulcanization isotherms, taken on an oscillating disc vulcameter MDR 2000 (Alpha Technologies) according to ISO 3417:2002.

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1 Table1: Formulations of chloroprene rubber based composites Ingredient, phr Sample Chloroprene rubber (Baypren 226) Zinc oxide Dioctyl adipate (DOA) Carbon black Corax N220 TMTD Vulkanox 4020 (6PPD) Magnesium oxide

1 100 5 15 0 2.5 1.5 5

Characterization and measurements Microwave properties Reflection and attenuation

Measurements of reflection and attenuation were carried out using the measurement of output (adopted) power Pa in the output of a measuring line without losses, where samples of materials may be included. Because of the wide frequency measurement a coaxial line was used. Samples of materials were shaped like discs with an external diameter D = 20.6mm, equal to the outer diameter of the coaxial line and thickness ∆ = 2mm. The internal diameter

2 100 5 15 20 2.5 1.5 5

3 100 5 15 40 2.5 1.5 5

4 100 5 15 60 2.5 1.5 5

5 100 5 15 80 2.5 1.5 5

6 100 5 15 100 2.5 1.5 5

is depending on the relative dielectric permittivity of the material. Part of the incident electromagnetic wave with power Pin. on the sample was reflected from it. The rest of the wave with power Pp penetrates the material so that the attenuation L depends on the coefficient of reflection |Γ|. His module is determined by a reflect meter. So attenuation is determined by

(1)

where

Pp = Pin. (1-|Γ|2)

(2)



2

R 1

4

3

2

The sample is in the form of a disc with a diameter of 10 mm and thickness about 2 mm. It is placed at the maximum electric field location of the cavity. Because the thickness of the sample is not equal to the height of the resonator, in the place of its inclusion obtains a dielectric with an equivalent permittivity εe, which is determined by (5) and instead εr be saved εe. Then εr is determined by:

εr ≈ εe (k + 1) - k,

Scheme of the equipment for measuring of the microwave properties: 1. a set of generators for the whole range: HP686A and G4 – 79 to 82; 2. Coaxial section of the deck E2M Orion, with samples of material; 3. Power meter HP432A; 4. Scalar reflectance meter HP416A; R Reflect meter, including: - two directional couplers Narda 4222.16 - two crystal detectors Narda 4506-N.

(∆< l) (6)

where k = l/ ∆ and l is the distance from the disc to the top of the resonator.

Dielectric loss (tan δε )

The loss factor tan δε is calculated from quality factor of the cavity with Qε and without sample Qr

3

1

2

3

5

4

Scheme of the equipment for measuring the dielectric properties: 1. Generators for whole range: HP686A and G4-79 to 82; 2. Frequency meters: H 532A; FS-54; 3. Cavity resonator; 4. Sample; 5. Oscilloscope EO 213.

The following scheme was used for testing both parameters (Figure 2):

Shielding effectiveness (S.E.)

This parameter is defined as the sum of the reflection losses R, dB and attenuation L, dB in the material. It can be directly measured or calculated from the measured reflectance and attenuation in the material [23]. In the first case, as measured: incident power on the sample Pin. and adopted after the sample Pa, S.E. is determined by: (3)

The measurement setup uses several cavity resonators for the whole range, generators for the whole range, frequency meter and an oscilloscope. The following scheme was used for measuring of the dielectric properties (Figure 3): All microwave and dielectric parameters were measured in the 1-12 GHz frequency range.

TEM analysis

Where R, dB is the attenuation due to the reflection of power at the interfaces. In the present work the shielding effectiveness was determined by equation (4).

Dielectric properties Relative dielectric permittivity (εr )

In the second, if known reflection and absorption in the material, S.E. is determined, by definition, as:

The determination of complex permittivity is carried out by the resonance method, based on the cavity perturbation technique [24]. Measuring resonance frequency of empty cavity resonator ƒr and then measuring the shift in resonance frequency with the sample material ƒε. Then the dielectric constant εr is calculated from the shift in resonance frequency, cavity and the sample cross sections Sr and Sε respectively:

S.E. = R + L, dB (4)

(5)


(7)

The particle size, size distribution and some specific features of the fillers were determined using a TEM JEOL 2100 at accelerating voltage 200 kV. The specimens were prepared by grinding the samples in an agate mortar and dispersing them in ethanol by ultrasonic treatment for 6 min. A droplet of the suspension was dripped on standard carbon films on Cu grids. Additional data for fillers structure were obtained using SAED method (Selected Area Electron Diffraction).

Results and Discussion Dielectric Properties

Figure 4 shows the dependencies of the complex relative dielectric permittivity (εr) on frequency for the studied composites based on chloroprene rubber (CR), containing different amounts of carbon black N220. Figure 4 shows that with unfilled composites based on chloroprene rubber (CR 0), the relative dielectric perKGK · 10 2012

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4

5

Effect of different amounts of standard furnace carbon black N220 on relative dielectric permittivity of chloroprene rubber based composites

Effect of different amounts of standard furnace carbon black N220 on dielectric loss angle tangent of chloroprene rubber based composites

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Effect of different amounts of standard furnace carbon black N220 on dielectric loss angle tangent of chloroprene rubber based composites

Effect of different amounts of standard furnace carbon black N220 on coefficient of reflection of chloroprene rubber based composites

mittivity (εr) does not change significantly with the increase of frequency. In this case the value of εr in the whole frequency range is about 2.7. Filling chloroprene rubber with carbon black N220 leads to some significant changes in terms of εr. The increase in the amount of the filler leads to an increase of εr at all tested frequencies. Obviously, in the frequency range from 1 to 7 GHz, the values of εr remain approximately constant with the increase of frequency at all concentrations of the investigated filler. Above this frequency range, there is a sharp increase in the εr values and at the highest frequency (12

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GHz) the dielectric permittivity reaches about 7÷9, according to the degree of filling. The nature of variation of all curves is approximately the same /Figure 4/. Figures 5 and 6 show the dependencies of the dielectric loss angle tangent (tan δε) on the frequency for the studied composites based on chloroprene rubber (CR), containing different amounts of carbon black N220. The results of the investigation of the dielectric loss angle tangent (tan δε) are significantly different in comparison with the above parameter. Firstly, it should be noted that up to frequency 8

GHz, the values of tan δε almost do not change with the frequency regardless of the degree of filling. At all frequencies, however, the increase in the amount of carbon black leads to increased values of the dielectric loss angle tangent (tan δε) / Figure 5/. The dependences of tan δεon frequency for the composites comprising 80 to 100 phr carbon black N330 (CR 5 and CR 6) are shown separately in Figure 6. With these relatively high concentrations of the filler, the values of the dielectric loss angle tangent (tan δε) of the studied composites increase significantly and the values reach 0,09. www.kgk-rubberpoint.de


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Effect of different amounts of standard furnace carbon black N220 on coefficient of attenuation of chloroprene rubber based composites

Effect of different amounts of standard furnace carbon black N220 on electromagnetic interference shielding effectiveness of chloroprene rubber based composites

Microwave Properties

The coefficient of reflection |Γ| as a function of frequency and the degree of filling for the chloroprene rubber based composites is presented as a family of curves on Figure 7. Generally, with the increase of the degree of filling and the frequency the coefficient of reflection also increases; the differences between the curves are not very large being approximately proportional to the quantity of filler. The nature of the curves shows that the concentration of 60 phr (CR 60) is a critical concentration for the behavior of the studied composites in terms of the coefficient of reflection. At the beginning of the frequency range its values are higher than those for the composites comprising lower amounts of filler. In the frequency range between 4 and 7.5 GHz its gradient decreases and ends at |Γ| = 0.82, which is less than the values for the composites comprising 20 phr (CR 20) and 40 phr (CR 40) carbon black N220, respectively. For the composites comprising higher filler amounts (CR 80 and CR 100) the variation of |Γ| is much smaller - from about 0.30 to about 0.60, but the values themselves are considerably lower. It is worth noting that for these high degrees of filling at frequencies up to 7 GHz, the coefficient of reflection of the composites is the highest, above 9 GHz it becomes the lowest, and at 11-12 GHz it is even close to that of the unfilled composite. Such an effect has not been observed until now in our investigations. The very good microwave prowww.kgk-rubberpoint.de

perties of composites containing 80 and 100 phr carbon black N220 were confirmed by the results of the absorption coefficient and effectiveness of electromagnetic shielding. The dependence of the attenuation coefficient on the frequency and the amount of filler presented in Figure 8 demonstrates most clearly the properties of the studied composites. In Figure 8 four groups of curves are very clearly distinguished: the first consists of one curve for the unfilled composite (CR 0), the second - two curves for the composites comprising 20 phr (CR 20) and 40 phr (CR 40) carbon black N220, third - again one curve for composite filled with 60 phr carbon black N220 (CR 60) and the fourth which consists of two curves, for the composites comprising highest filler amount (CR 80 and CR 100). Each of them quite clearly demonstrates the process of absorption of electromagnetic waves in the given composite. It is noteworthy that composites containing 80-100 phr furnace carbon black have attenuation coefficients in the range of 30-40 dB/ cm in a very wide frequency range from 1 to 10 GHz, whereas within the range 10-12 GHz they are around 4070 dB/cm. Impressive is also the coefficient of attenuation of these composites at low frequencies (1-4 GHz), which also remains within the 30-40 dB/cm range. All curves reflecting the dependence of the interference shielding effectiveness on frequency and the degree of

filling presented on Figure 9 were reduced to the thickness of the material ∆ = 2mm. This fact should not be ignored because, according to the methodology for measuring the dielectric shielding, the entire thickness of the shielding material is involved. Bearing in mind this fact, the different materials must have the same thickness so that we may compare. In this case we have an interesting result: composites with the highest filler amount (80 and 100 phr), are not the most effective in shielding. Composite containing 60 phr (CR 60) carbon black N220 proves best for this purpose. In examining the quantitative expression of the constituent components of this parameter, namely the reflection and attenuation losses in the material, it is evident that for the composites CR 80 and CR 100 reflection coefficients are not high and do not vary much in a wide frequency range, but attenuation is less than in the case of CR 60. With the composite containing 60 phr carbon black, the coefficients of reflection and attenuation complement each other successfully and this combination results in extremely broadband shielding effectiveness and the average value is about 16 dB in the entire investigated range with thickness of the sample ∆ = 2mm. Since the studied system is linear, it can easily be seen that with increasing the thickness of the shielding coating to ∆ = 4mm, the average efficiency value may increase to about 23 dB under equal conditions which is a promising KGK · 10 2012

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result. In conclusion it can be argued that composites based on chloroprene rubber containing 60-100 phr furnace carbon black have very good microwave properties and can be used for the needs of anti-radar camouflage and for electromagnetic shielding.

Conclusions

The study deals with the dielectric and microwave properties in the frequency range 1-12 GHz of chloroprene rubber based composites comprising different amounts of standard furnace carbon black in the range of loadings from 0 to 100 phr. It was found out that increasing the amount of carbon black N220 in the studied composites based on CR leads to an increase of the dielectric permittivity (εr). In the frequency range from 1 to 7 GHz εr has relatively low values (εr = 2.7 to 4), which do not change significantly with the increase of frequency. In the interval from 7 to 12 GHz, there is sharp increase of εr and its values reach 7 to 9 depending on the filler concentration. It was found out that increasing the amount of carbon black leads to improved microwave properties of the investigated composites. The composites based on chloroprene rubber containing 60-100 phr furnace carbon black have very good microwave properties and can be used for the needs of anti-radar camouflage and for electromagnetic shielding.

Acknowledgements

The present research is a result of an international collaboration program between University of Tabuk, Tabuk, Kingdom of Saudi Arabia and the University of Chemical Technology and Metallurgy, Sofia, Bulgaria. The authors gratefully acknowledge the financial support from the University of Tabuk.

References

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Elastomers and Plastics, 23 (1991) 345. [5] P. B. Jana, A. K. Mallick and S. K. De, J. Mater. Sci., 28 (1993) 2097. [6] P. B. Jana, A. K. Mallick, J. Elastomers and Plastics, 26 (1994) 58. [7] J. P. Kalinoski, US Pat. 910, 524 (1999). [8] D. Yuping, L. Shunhua and G. Hongtao, Sci. Technol. Adv. Mater. 6 (2005) 513. [9] D. W. Kang, H. G. Yeo and K. S. Lee, J. Inorg. Organomet. Polymers, 14 (2004) 73. [10] David C. Lin, Lee Y. Wang and Long Y. Chiang, Synthetic Metals, 81 (1997) 987. [11] F. El-Tantawy and N. Dishovsky, J. Appl. Polym. Sci. 91 (2004) 2756. [12] F. El-Tantawy, J. Appl. Polym. Sci., 97 (2005) 1125. [13] M. A. Cosman, A. Balladares, U.S. Pat. 0220327 (2004). [14] N. C. Das, T. K. Chaki, D. Khastgir and A. Chakraborty, J. Appl. Polym. Sci. 80 (2001) 1601. [15] N. C. Das, T. K. Chaki, D. Khastgir, A. Chakraborty, Adv. Polym.Technol. 20 (2001) 226. [16] N. C. Das, D. Khastgir, T. K. Chaki, and A. Chakraborty, J. Elastomers and Plastics, 34 (2002) 199. [17] N. C. Das, D. Khastgir, T. K. Chaki, and A. Chakraborty, Appl. Sci. Eng., 31, (2000) 1069. [18] P. Ghosh, A. Chakrabarti, Europ. Polym. J. 36 (2000) 1043. [19] K. A. Malini, P. Kurian, M. R. Anantharaman, Mater. Letters, 57 (2003) 3381. [20] E. M. Mohammed, K. A. Malini, Ph. Kurian, M. R. Anantharaman, Mater. Res. Bulletin, 7 (2002) 753. [21] N. Dishovsky, A. Petkov, Iv. Nedkov, Iv. Razkazov, IEEE Trans. on Magnetics, 30 (1994) 969. [22] R. Shtarkova and N. Dishovsky, J. Elastomers and Plastics, 41 (2009) 163. [23] C. R. Paul, Introduction to Electromagnetic Compatibility, John Wiley & Sons, N.Y., (1992). [24] B. Meng, J. Booske and R. Cooper, IEEE Trans. Microwave Theory Tech., 43, (1995) 26

The Authors:

Dr. Omar A. Al-Hartomy is assistant professor of solid state physics in the department of physics, University of Tabuk. He is a director of Nanotechnology Research Laboratory at University of Tabuk. His specialist subjects are semiconductor physics, nanoscale physics and scanning probe microscopies. His current research fields are nanocomposite materials, growth and characterization, nanoelectronics and power electronics properties, oxide nano-

rods and nanoparticles, and synthesis of DWCN. A. A. Al-Ghamdi is a Professor of Solid State Physics in the Department of Physics at King Abdulaziz University. He received his PhD in Physics from University of Sussex at UK in 1990. His fields of interests are in point defects, ion implantations, structural investigations of crystalline and amorphous solid materials by means of X-ray, thermal, optical and electrical properties of thin solid films and nanomaterials. He is also currently working on solar cell devices. Falleh R. Al-Solamy is a Professor of Differential Geometry in the Department of Mathematics at King Abdulaziz University. Currently, he is joining the University of Tabuk and working as a vice rector for graduate studies and scientific research. He received his PhD in Mathematics from University of Swansea at UK in 1998. His fields of interests are Differential Geometry and its Applications, Mathematical Physics, Solitons and Quantum Groups. Nikolay Dishovsky is a full professor of Technology of Rubber, PhD and DSc and Head of Department of Polymer Engineering at the University of Chemical Technology and Metallurgy in Sofia, Bulgaria. Mihail Mihaylov, PhD is an assistant professor of Technology of Rubber in the Department of Polymer Engineering at the University of Chemical Technology and Metallurgy, Sofia, Bulgaria. Vladimir Iliev, PhD is an associate professor at the College of Telecommunications and Posts, Sofia, Bulgaria Farid El-Tantawy is a Professor of Applied Polymer and Ceramics in the Department of Physics, Faculty of Science, Suez Canal University, Ismailia, Egypt. Currently, he is joining the Faculty of Education for Girls in Belgarn, Department of Physics, King Khalid University, Belgarn, Kingdom of Saudi Arabia. His current research interest is the synthesis and fabrication of nanoconducting composites or nanoblends and nanomaterials for real technological applications.
