Dielectric elastomers (DE) containing conducting inorganic fillers would have great potential for actuators, capacitive energy storage, elastomer sensors and many other applications. In this regard, ternary composites with metal alloy materials as reinforcing fillers might be an enabler for low dielectric loss and high dielectric constant. Herein, ternary rubber composites were prepared by incorporation of Cu-based alloy into acrylonitrile-butadiene rubbers (NBR). However, material incompatibility between the Cu-Al-Zn alloy and the rubber matrix often results in phase separation, void formation and particle aggregation, with dramatically degraded performance. Through surface modification, Cu-Al-Zn alloy particles were uniformly dispersed onto the NBR rubber matrix via 3-(Trimethoxysilyl) propyl methacrylate (TMSPM) as coupling agent. The effective reinforcement of modified Cu-based alloy particles into NBR was systematically analyzed by SEM (scanning electron microscope) and XRD (X-ray diffraction). The results reveal that the morphology and dispersion state of modified Cu-Al-Zn alloy were critical to the dielectric properties of the NBR compounds. Mechanical properties were greatly enhanced by the reinforcement of modified Cu-based alloy into the NBR matrix. The outstanding performance of NBR composites is due to the uniform dispersion of modified Cu-Al-Zn alloy particles and good interfacial compatibility with rubber matrix, suggesting high performance dielectric composite.
Research Article
Electrical and Mechanical behaviors of rubber composites based on polar elastomers with incorporated Cu-based alloy
https://doi.org/10.21203/rs.3.rs-1757303/v1
This work is licensed under a CC BY 4.0 License
Journal Publication
published 21 Jul, 2024
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Acrylonitrile-butadiene rubber (NBR)
Cu-Al-Zn alloy
Dielectric properties
Mechanical properties
Inorganic/elastomer composites with superior dielectric characteristics, benefiting from good flexibility, lightweight and their easy processing, have considerable industrial interest for several decades [1]. Nowadays, these composites have been most used in multiple areas as electroactive soft robots, flexible electronics, and energy storage systems. Many materials have been mentioned as flexible polymeric matrix, as silicone rubbers, polyurethanes, natural rubber (NR), acrylic elastomers and styrene-butadiene-styrene triblock copolymer [2]. Among these materials, Nitrile rubber (NBR) is a copolymer of butadiene and acrylonitrile. NBR has good mechanical properties, irregular chain structure, oil resistance and do not crystallize on stretching. According to the importance on NBR and have specific properties qualified it to introduce a lot of industries; there is a tendency to develop new technologies which permit to manufacture products of better quality and performance at lower costs. The addition of fillers to elastomers usually conducts to reinforce its mechanical and electrical properties [3].
Metal-alloys are inorganic compounds widely utilized in polymer processing technology. They can be applied as fillers in amounts usually several phr and metal-alloys generally fulfill different functions simultaneously, e.g., a filler and colorant. The main function of metal-alloys is their impact on the processing properties of rubber mixtures, and they are providing appropriate physico-mechanical properties of rubber products [4, 5]. Cu-based shape memory alloys (SMAs) have attracted significant attention and interest in recent years owing to their good shape memory capacity, low production cost, simple fabrication and narrow temperature region of transformation. Cu-based alloys are used application in catalysis, electronic and production of metal matrix composites [6]. The unique thermo mechanical behaviors of Cu-based alloy are their shape memory effect and super elasticity which made them suitable for structural vibration control applications. Improving the interaction between these type of inorganic fillers and elastomers of hydrocarbon nature, different chemical treatments have been practiced to these fillers in order to improve their compatibility with the polymeric matrix. Subsequently, the improvement of inorganic/NR composites for enhanced dielectric constant is highly desirable [7].
The main goal was to study the influence of Cu-based alloy contents on the curing process of rubber compounds, electrical and mechanical properties of the prepared composites. The interactions between Cu-based alloy and NBR matrices were evaluated by SEM and XRD analysis.
2.1. Materials
NBR with acrylonitrile content of 34 ± 1% was purchased from by Bayer AG, Germany. Zinc oxide (ZnO), sulfur (S) and stearic acid in analytical grades were purchased from Aldrich Company, Germany. The other chemicals including CBS (N-cyclohexyl-2-benzothiazole sulfenamide) and TMQ-polymerized 2, 2, 4-trimethyl-1, 2-dihydroquinoline was used without further purification. Cu-Al-Zn alloy DEVARD`s Alloy Extra pure, LOBA CHEMIE PVT.LTD.
2.2. Synthesis
2.2.1. Elastomer composite preparation procedure
The preparation of NBR composites loaded with different amounts of Cu-based alloy are shown in Table 1. The composites were mixed with a sulfur curing system on a two roll mill in accordance with ASTM D3182-07(2012). Subsequently, different phr of Cu-based alloy and NBR were mixed uniformly in presence or absence the prepared coupling agent 3-(Trimethoxysilyl) propyl methacrylate (TMSPM), as shown in Table 1 [8]. The rubber composites sheets were produced by a compression type hydraulic press compression molding in an electrically heated hydraulic press under 40 kg/cm2 and a temperature of 152 ± 1°C.
|
Formula no./Ingredient phr |
N0 |
N1 |
N2 |
N3 |
N4 |
N5 |
N6 |
N7 |
N8 |
N9 |
N10 |
N11 |
N12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Cu-Al-Zn alloy |
-- |
2.5 |
5 |
10 |
15 |
20 |
25 |
2.5 |
5 |
10 |
15 |
20 |
25 |
|
Coupling agent |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
4 |
4 |
4 |
4 |
4 |
4 |
| Notes: Base recipe (in phr): NBR 100; stearic acid 2; zinc oxide 5; CBS (N-cyclohexyl-2-benzothiazole sulfenamide) 1; Paraffin oil 2; S sulfur 3. ∆M is the difference between maximum and minimum torque; TMQ – polymerized 2, 2, 4-trimethyl-1, 2-dihydroquinoline; CRI – cure rate index, where phr is part per hundred parts of rubber | |||||||||||||
2.3. Methods of testing
2.3.1 Scanning Electron Microscopy (SEM) used to identify microstructural characteristics of the NBR composites. (Quanta FEG 250; FEI Co., Hillsboro, OR, USA), with attached energy dispersive X-ray spectroscopy (EDS) attachment. Surface of the specimens was coated with gold paste as a contact material for the SEM measurements.
2.3.2 X-ray diffraction (XRD) was carried out on Pan Alytical Emprean diffractometer with Cu-Kα radiation (λ = 1.5406 Å) The diffraction curves were obtained within the 2θ range of scattering angles 2θ of 4–80 with 0.026 step size and step time 30 sec/step.
2.3.3 Rheological measurements of the rubber composites containing different contents of modified Cu-Al-Zn alloy were observed at 152 ± 1°C in accordance with ASTM D2084-11(2011). Using TA Instruments, New Castle, DE, USA (an oscillating disc rheometer R-100 MDR one)
2.3.4 Mechanical properties namely, E % (elongation at break) and T.S (tensile strength) were characterized in accordance with ASTM D412-06a (2013) using a Zwick testing machine.).
2.3.5 Dielectric measurements were tested at room temperature ~ 30°C, included, tanδ (loss factor ), dielectric constant ε' ( permittivity), and ac-resistance Rac were tested in a broad range frequency (0.1 Hz − 1 MHz). The permittivity ε' is calculated in accordance to; where d is thickness of the sample, c is capacitance of the dielectric, A is area of electrode, and εo is permittivity of vacuum (8.85 x10-12 F/m). While the loss factor “tanδ” is measured on the basis of where δ is the loss angle, f is the frequency, Rp is the equivalent parallel resistance and Cp is the equivalent parallel capacitance, respectively. The measurement was computerized by interfacing the impedance analyzer with a personal PC through a GPIB cable IEE488. A commercial interfacing and automation software program “Lab VIEW” was utilized for data acquisition. The error in tan δ and ε' amounts to ± 1% and ± 3%, respectively. The temperature of the samples was controlled by a temperature regulator with (Pt 100) sensor. The error in temperature measurements is approximately ± 0.5°C. To avoid moisture effects the samples were saved in desiccators. However, ε′ and tanδ were re-calculated once again after performing the experiment to test the measurements’ reproducibility.
3.1. Scanning electron microscopy (SEM)
Figure1. SEM for NBR composite loaded with (a) 0 phr Cu-alloy, (b) 10 phr & (c) 25 phr Cu-alloy without coupling agent and (d) 10 phr & (e) 25 phr Cu-alloy with coupling agent
The surface morphology of NBR filled with Cu- Al-Zn alloy is presented in Fig.1. The results exhibited the mutual reaction between the two phases seems to be little worse with presence of more voids, microcavities and poor filler distribution with rubber-rich areas. Better distributions of Cu-based alloy particles and more homogenous structure are observed in NBR composites samples with the coupling agent TMSPM as in Fig.1(d-e). This is attributed to the functional groups of acrylate emulsion polymer which dominating the filler-filler interactions to prevent agglomeration. The improved adhesion and compatibility between the NBR matrix and Cu- based alloy due to the higher polarity of the rubber matrix especially in the presence of coupling agent (acrylate emulsion polymer) [9].
3.2. X-ray diffraction (XRD)
The registered X-ray diffraction pattern of the Cu-Al-Zn alloy is shown in Fig. 2. The peaks position and relative intensity were extracted and identified using Highscore plus software and PDF database. Quantitative analysis using Rietvled method with the same program revealed that the pattern consists of 79.7% of Cu Al2 (PDF no. 98-004-2518), 17.5% of Al4.2Cu3.2Zn0.7 (PDF no. 98-005-7730), and 2.8% of Fe (PDF no. 98-063-1729). The crystallite size for each phase was determined from the most intense peak using the Scherrer equation after correction for the instrumental broadening.
D = κ λ/β cos(θB) (1)
Where D is the crystallite size, λ is the wavelength, β is the peak sample broadening and K stands for a geometrical factor that depends on crystallite apparent radius ≅1. Table 2 indicating, that all phases of Cu-Al-Zn alloy and crystallite size in the nanometer range.
|
Structure parameter |
Cu Al2 |
Al4.2Cu3.2Zn0.7 |
Fe |
|---|---|---|---|
|
Space group |
I 4/m c m |
R-3 |
I m -3 m |
|
a Å |
6.0678 (5) |
4.118(2) |
2.8683 (7) |
|
c Å |
4.8772 (3) |
25.19(2) |
|
|
α = β |
90 |
90 |
90 |
|
γ |
90 |
120 |
90 |
|
Crystallite size nm |
57(1) |
86(3) |
21(2) |
|
Weight % |
79.7 |
17.5 |
2.8 |
Figure3. Showed the XRD diffraction for pure NBR, NBR loaded with 2.5phr Cu-Al-Zn alloy, and NBR/coupling loaded with 2.5phr Cu-based alloy. For pure NBR a characteristic halo and broad diffraction peak (Humb) at 2θ =20 is observed indicating the amorphous nature of NBR, the same behavior was observed by Zhao Zhang et al [10], besides the broad peaks, a few other peaks were observed for which could be due to the other additive during the vulcanization, like ZnO, S, and stearic acid. These alterations aren't fully understood yet, but they could be linked to particle surface activity, especially at the rubber-ZnO interface, which contains sulfur and stearic acid on the surface. For NBR having 2.5phr Cu-Al-Zn alloy intensity of both halo and broad peak at 2θ-20 s reduced a little, besides new peaks appeared at 2θ=38, 47.49 and 47.9° indicating the existence of CuAl2 phase in the composite. Inspecting the diffractogram of NBR/coupling agent/2.5 phr Cu-Al-Zn alloy, we can observe that no new peaks corresponding to the coupling agent appeared which means that a complete dissolution of coupling agent inside the NBR matrix, accompanied by a variation in the relative intensity of some peaks besides disappearing of the peak at 2θ =42.27°.
Figure 4a shows the XRD diffraction pattern of the NBR and composite (NBR/Cu-based alloy) with different percentages of Cu-based alloy. From this figure we can observe that starting from 5phr metal alloys loaded new peaks appeared at 2θ = 20.7°, 29.44°, 38.0°, 47.4°, 47.9° owing to CuAl2 phase. A new peak developed at 2θ = 44° starting from 10% Cu-Al-Zn alloy loading corresponding to the Al4.2Cu3.2Zn0.7 phase. The intensity of these peaks increases with increasing the percentage of the alloy loaded and no peak appeared corresponding to Fe phase due to its lower concentration. A closer look at this figure we can observe the diffraction pattern become smoother (peak to the noise ratio increases) due to increasing the percentage of Cu-Al-Zn alloy loaded, in addition to the reduction in the intensity of the amorphous peaks. Reduction of the peak intensity of the broadened peak can indicate cutting back the size of stacks or in other words, cutting back the number of layers in each stack and decreasing the crystallinity of the polymer. This is because of the increase in shear stress in the mixing step for the preparation of composites. The crystallinity index of the proposed composites is tabulated in Table 3 and calculated using EVA software based on the following relation:
$$\mathbf{A}\mathbf{m}\mathbf{o}\mathbf{r}\mathbf{p}\mathbf{h}\mathbf{u}\mathbf{s}\mathbf{\%}=\frac{\mathbf{g}\mathbf{l}\mathbf{o}\mathbf{b}\mathbf{a}\mathbf{l} \mathbf{a}\mathbf{r}\mathbf{e}\mathbf{a}-\mathbf{r}\mathbf{e}\mathbf{d}\mathbf{u}\mathbf{c}\mathbf{e}\mathbf{d} \mathbf{a}\mathbf{r}\mathbf{e}\mathbf{a}}{\mathbf{g}\mathbf{l}\mathbf{o}\mathbf{b}\mathbf{a}\mathbf{l} \mathbf{a}\mathbf{r}\mathbf{e}\mathbf{a}} \mathbf{x} 100 \left( 2 \right)$$
$$\mathbf{C}\mathbf{r}\mathbf{y}\mathbf{s}\mathbf{t}\mathbf{a}\mathbf{l}\mathbf{l}\mathbf{i}\mathbf{n}\mathbf{i}\mathbf{t}\mathbf{y}\mathbf{\%}=100-\mathbf{A}\mathbf{m}\mathbf{o}\mathbf{r}\mathbf{p}\mathbf{h}\mathbf{u}\mathbf{s}\mathbf{\%} \left(3\right)$$
|
NBR/phr |
Crystallinity index |
NBR/coupling agent/phr |
Crystallinity index |
|---|---|---|---|
|
0 |
51 |
0 |
51 |
|
2.5 |
48.1 |
2.5 |
50.7 |
|
5 |
45.3 |
5 |
47.9 |
|
10 |
43.6 |
10 |
47.1 |
|
15 |
45.6 |
15 |
49.2 |
|
20 |
46.1 |
20 |
56 |
|
25 |
50.2 |
25 |
52.1 |
The values of the crystallinity index pointed out that it declined with an increment of Cu-Al-Zn alloy till 10 phr then it increases again but still less than NBR. The decreases in the crystallinity indicated to increasing disorder in the rubber matrix while the increasing is due to aggregation. The same behavior was obtained for the composites with a coupling agent Fig. 4b. By comparing the crystallinity values for the composites with and without coupling agent, we notice that TMSPM increases the crystallinity at the same phr%.
3.3. Rheological properties of NBR/ Cu-Al-Zn rubber composites
The vulcanization demeanor of the NBR compounds containing several concentrations of Cu-based alloy in absence or presence coupling agent was studied utilizing rheometric measurements. The rheometric parameters are presented in Table 4(a,b). The maximum and minimum torque indicates the maximum crosslinks and compound’s viscosity level respectively [11]. The difference between maximum and minimum torque values (ΔM = MH-ML) is a slip modulus that indirectly appears crosslink density. The addition of Cu-based alloy to NBR matrix in both cases absence/or present coupling agent, the maximum torque (MH ) decreased by increasing of Cu-Al-Zn alloy content up to 10phr and 2.5phr for absence and present coupling agent respectively, then slight increase by increasing Cu-Al-Zn alloy. The value of maximum torque (MH) improved eventually in presence coupling agents comparison without in a coupling agent. Additionally, the cross link density (ΔM ) increase in presence of coupling agent compared to pure NBR especially at the higher loading of Cu-Al-Zn alloy as shown in Table 4(a,b). The decrease in the value of maximum torque indicated to agglomeration trend of Cu-based alloys inside the NBR matrix. Therefore, the value of maximum torque improved eventually in presence coupling agent in comparison with absence one. On the other hand, the interfacial interaction between NBR matrix and Cu-based alloys was much better with the used of coupling agent as compared to without it. Also, addition of Cu-based alloys into NBR matrix in presence TMSPMA (coupling agent) lead to the decrease in the value of optimum cure time (tc90). This result indicated that Cu-based alloys/ TMSPMA were able to activate the cure reaction of NBR compounds [12].
|
Formula no./Ingredient phr |
N0 |
N1 |
N2 |
N3 |
N4 |
N5 |
N6 |
|---|---|---|---|---|---|---|---|
|
Rheometric characteristic at 152 ± 1°C |
|||||||
|
MH, dNm |
12.16 |
10.85 |
9.03 |
9.29 |
10.72 |
11.5 |
11.68 |
|
ML, dNm |
0.59 |
0.65 |
0.59 |
0.63 |
0.71 |
0.71 |
0.67 |
|
∆M, dNm |
11.57 |
10.2 |
8.44 |
8.66 |
10.01 |
10.79 |
11.01 |
|
Ts2.min |
3.23 |
3.34 |
2.79 |
2.43 |
2.52 |
2. 52 |
4.41 |
|
Tc90, min |
21.19 |
22.17 |
22.38 |
22.42 |
21.92 |
22.26 |
21.15 |
|
CRI, min− 1 |
5.57 |
5.61 |
5.77 |
5.77 |
5.68 |
5.38 |
5.63 |
|
Formula no./Ingredient phr |
N0 |
N7 |
N8 |
N9 |
N10 |
N11 |
N12 |
|---|---|---|---|---|---|---|---|
|
Rheometric characteristic at 152 ± 1°C |
|||||||
|
MH, dNm |
12.16 |
11.68 |
12.17 |
12.56 |
12.54 |
12.74 |
12.9 |
|
ML, dNm |
0.59 |
0.67 |
0.74 |
0.76 |
0.78 |
0.81 |
0.82 |
|
∆M, dNm |
11.57 |
11.01 |
11.43 |
11.8 |
11.76 |
11.93 |
12.08 |
|
Ts2.min |
3.23 |
4.41 |
5.05 |
5.01 |
4.32 |
3.68 |
2.49 |
|
Tc90, min |
21.19 |
21.15 |
19.59 |
18.83 |
18.95 |
19.09 |
19.35 |
|
CRI, min− 1 |
5.57 |
5.63 |
5.95 |
6.1 |
6.09 |
6.04 |
5.93 |
3.4. Mechanical properties
The mechanical properties of rubber composites are highly affected by the type, shape, size, loading and dispersion of the magnetic filler (Cu-alloy), also as the NBR rubber matrix properties and the interfacial adherence between the Cu-alloy and NBR matrix. Effects of Cu-based alloy loadings modified with acrylate emulsion polymer (coupling agent) on the physical properties of NBR compounds are presented in Fig. 5. The tensile strength of NBR composites increase up to 10phr and then tensile strength reduced by increasing the content of modified Cu-alloy. One reason for this is the inferior interfacial bonding between alloy particles and the matrix. Owing to the re in the effective cross-section of the matrix in the composites and there is a rise in internal stress for every point of rubber matrix. Another reason for reduction is the interaction between the copper and NBR matrix is weak and the effect of the interaction increases by increasing Cu-alloy loading. Elongation at break increase with increasing applied fillers content. It can be referred to the decrease of cross-link density of prepared mixeds [9].
The tensile strength and elongation at break of the NBR composites has increased after adding coupling agent (acrylate emulsion polymer). This might be due to an increased crosslink density caused by coupling agent between NBR and Cu-alloy. Also, his might be ascribed to the height specific surface of acrylate emulsion polymer particles, which allows extensive chemical interactions between Cu-alloy and NBR, thus improving polymer-filler interaction. Elongation at break of NBR composites with coupling has increased compared to NBR composites without coupling. This is because the rubber composites produced is not rigid and not stiff, so it is easy to stretch so it has Fig.5. Change of tensile strength and elongation at break of investigated NBR composites a large elongation at break values [13, 14].
3.5. Dielectric Properties of Cu-Al-Zn Alloy
Figure6a, b. The variation of permittivity ε′ and the loss factor and tanδ with frequency at different temperatures for Cu-Al-Zn Alloy versus the frequency (f) and (c) Dependence of the ε′ and tan δ at fixed frequency 100 Hz on temperature.
The variation of the loss factor tan δ and permittivity ε' versus frequency f at several temperatures for Cu-Al-Zn alloy are presented in Fig. 6. It is observed that at low frequencies both permittivity ε' and the loss factor tan δ increased with decreasing frequency. This trend is a characteristic feature for dc-like imperfect charge transport [15, 7]
However, the increase of ε′ and tan δ at with increasing temperatures is due to the increase of the space charge polarization [16]. The space charge polarization (Maxwell–Wanger type interfacial polarization) increases with increasing temperature due to the increase in dc conductivity. Conduction and polarization mechanism are linked up as one promotes another. Various interfaces such as electrode-grain, grain-grain (grain boundary) are the dominating regions where these space charges accumulate which promote polarization. The origin of interfacial polarization is an A.C current in phase with the applied potential. This current arises from the differences in conductivities and permittivity of the substances creating the dielectric material. Further, the variation of the dielectric constant ε′ and tan δ at a fixed frequency (100 Hz) with temperature are shown in Fig. 6c. From this figure, it is observed that both ε′ and tan δ increase with rising temperature. This could be attributed to increase of the number/mobility of charge carriers and enhancement of hopping conduction as will be discussed later [17]. The variation of the total conductivity of Cu-Al-Zn Alloy vs. frequency at different temperature is presented in Fig. 7a. It is noted that total conductivity increase with increasing the temperature showing negative temperature coefficient of resistance (NTCR) behavior. As temperature increases dispersion in conductivity narrows and all the curves of different frequencies at high temperatures merge into a single curve. This is due to the recombination of released space charges at high temperatures. For all samples under investigation, the conductivity pursues a power law relation;
Where ω is the angular frequency, A is a frequency independent parameter and “s” is a power, the values of s are found to be s ≤ 1 that is; 0.75 ≤ s ≤ 0.50, which is governed by electronic hopping processes.
The dc-conductivity was calculated from the power law (Aws) and is plotted as a function of reciprocal temperature in Fig. 7b. The obtained data are fitted according Arrhenius law;
Where σo is the pre-exponential term, Ea is the conduction activation energy, and k is the Boltzmann constant. A plot with different slopes (in the low- and high-temperature regions) suggests the presence of different types of conduction process with different activation energies. Activation energy is the energy required for the polaron to jump over the grain boundaries. As temperature increases, the polarons receive sufficient thermal energy to get activated and cross the barrier. The low activation energy in the high temperature region may be due to the onset of grain boundary contribution to the dc conductivity of the material.
3.6 Dielectric Properties of NBR /Cu-Al-Zn alloy composites
Figure 8 signifies the dielectric properties of NBR/ Cu-Al-Zn alloy in absence and presence of coupling agent 30 oC. At low frequencies, the permittivity (ε') of NBR composites improved with rising Cu-Al-Zn alloy loading in comparison to pure NBR. At high frequencies, the permittivity (ε') reduced sharply owing to the delay in orientation polarization [18, 19]. However, as discussed earlier in Fig. 1, the presence of coupling agent improved the dispersion of Cu-Al-Zn alloy which, in turn, enhances the synergistic effect between Cu-Al-Zn alloy and NBR matrix. Consequently, the permittivity (ε') of treated samples is significantly improved the compared to untreated one (see Figs. 8 and 9).
On the other hand, the high dielectric loss ε" values detected at low frequencies is referred to interfacial polarization effects resulting from heterogeneity of the studied samples. Obviously, the ε" values are increased fast at low frequencies and subsequently reduced somewhat at high frequencies as the testing frequency increased. Moreover, noticeable broad peak at ~ 1 MHz was also observed. This peak referred to the delay in the orientation polarization and segmental motion of the rubber chain. However, it is worth to notice that, the dielectric loss dielectric loss ε" of the treated samples are lower than those of untreated see Figs. 8 and 9. This may possibly due to the polymer-filler interactions were improved by the coupling agent 3-(Trimethoxysilyl) propyl methacrylate (TMSPM) modification. However, the obtained results are in line with those obtained from mechanical properties and supported by SEM findings.
3.7. Electrical Conductivity of NBR /Cu-Al-Zn alloy composites
A plateau in electrical conductivity σ (ω) vs. frequency f plot can be seen at high Cu-Al-Zn alloy content (Fig. 10a, b). Obviously, all NBR composite samples obey the universal power law [20]. However, the electrical conductivity σ (ω) can be used as a measure of the filler dispersion feature in the composite. That is, a severe increase of σ (ω) can be observed when conductive filler particles formed filler network at a certain concentration known as the percolation threshold. As revealed in in, the DC conductivity σdc increases when the percolation threshold of about 5 parts Cu-Al-Zn alloy is reached. This abrupt growth in σdc is a result of the formation of a continuous network of Cu-Al-Zn alloy in NBR host matrix. Additional increase in Cu-Al-Zn alloy loading caused only slight enhancement in σdc, since the percolation threshold had already been accomplished. From Fig. 10, it may also be noticed that the conductivity of the NBR composites filled Cu-Al-Zn alloy was slightly decreased by the addition of the coupling agent 3-(Trimethoxysilyl) propyl methacrylate (TMSPM). On the other hand, the obtained values of the conductivity for NBR composites are in the range of 10− 9 -10− 7 which endorses such composites to be manipulated in antistatic and electrostatic dissipation applications.
Rubber composites with Cu-alloy particles embedded into the NBR rubber matrix were prepared in presence coupling agent, SEM observation confirms the well dispersion of these particles in the NBR matrix. Concerning the mechanical results obtained for NBR composites let us consider the Cu-alloy as reinforcing filler since the elongation at break increase. Moreover, the Cu-alloy modified through the intercalation with TMSPM as coupling agent promotes even more this tendency owing to the greater compatibility with NBR matrix. The intensity of the crystalline peaks of NBR composites increased with increasing the loading of Cu-based alloy was revealed from XRD curves. This work proves that Cu-alloy can effectively improve the dielectric properties of inorganic/polymer composites. NBR composites containing of Cu-based alloy can be manipulated in antistatic and electrostatic dissipation applications.
Acknowledgements
The present work is supported through the National Research Centre Project No. 12010313.
Declarations
Conflict of interest the authors declare that they have no conflict of interest.
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No competing interests reported.