Aman Khalaf P KGK 2012 6Wi E P 10 0 Kautschuk Nanopartikel Kautschuk Dr. Azza. A Ward National...

ELASTOMERE UND KUNSTSTOFFE ELASTOMERS AND PLASTICS

36 KGK · 1-2 2013 www.kgk-rubberpoint.de

PVC/NBR blends · copper · graphite · nanocomposites · mechanical proper-ties · dielectric properties · conductivity · self-crosslinking

Polyvinyl Chloride (PVC) was blended with nitrile-butadiene rubber (NBR) in different ratios. The influence of diffe-rent concentrations of nanosized filler (graphite and copper) on the properties of PVC/NBR blends using solution cas-ting method was studied. The results obtained from the mechanical proper-ties show that elongation at break in-creases with increasing NBR content in the (PVC/ NBR) blends, while tensile strength values decreases as the filler concentration increases in all composi-tes. The dielectric properties of these samples were studied by means of broadband ac -relaxation spectroscopy in the frequency range between 0.01 Hz to 10 MHz and at 25 °C. The dielec-tric properties and the conductivity we-re found to be influenced by increasing the content of both fillers . According to the values of conductivity, the nano-composite of PVC/NBR (50/50) filled with 5% copper belongs to materials characterized as semiconductors.

Graphit und Kupfer Nanoparti-kel in PVC/NBR Verschnitten PVC/NBR Verschnitte · Kupfer · Graphit · Nanocomposite · mechanische Eigen-schaften · dielektrische Eigenschaften · Leitfähigkeit · Selbstvernetzung

Verschnitte aus Polyvinylchlorid (PVC) mit Nitrilkautschuk (NBR) mit ver-schiedener Zusammensetzung wurden mit nanoskaligen Füllstoffen (Graphit und Kupfer) gefüllt und die Eigen-schaften der Systeme untersucht. Die mechanischen Eigenschaften zeigen dass die Reißdehnung mit dem Anteil an NBR im Verschnitt ansteigt, wäh-rend die Zugfestigkeit mit der Füll-stoffkonzentration abnimmt. Die dielelktrischen Eigenschaften der Pro-ben wurden mittels eines Breitband Relaxations-Spektrometers im Fre-quenzbereich von 0,01 Hz bis 10 MHz bei Raumtemperatur untersucht.

Figures and Tables:By a kind approval of the authors

Polymer composites and blends are ef-fective answers to the challenge of deve-loping new polymers with specific sets of properties. One of the goals of material researches is to create new materials with physical properties tailored to a particular application and to understand the physical mechanisms that determine their properties [1, 2]. Thermoplastic elastomers prepared from blends of rub-ber and plastic have created very much interest in the industrial sector [3-6].

NBR (butadiene-acrylonitrile copoly-mer)/PVC (polyvinylchloride) is a misci-ble physical mixture of commercial im-portance. The elastomeric component, NBR, can act as a permanent plasticizer for PVC applications in which PVC im-proves the chemical resistance, ther-mal ageing and abrasion resistance of NBR, [7,8] that enables the use of this blend in the automotive industry as gaskets, wires and cables, and in the manufacture of soles, footwear, artifi-cial leather, and others [9-13].

Nanocomposites made of polymers and nanofillers have been exhibited sig-nificant change and novel properties of these polymers. These novel properties can derive to novel application potentials [14,15]. In the recent years, synthesis of conducting polymer nanocomposites at-tracted great attention due to their po-tential applications in various high tech-nology aspects, for example, electroche-mical displayers, sensors, catalysis, super capacitors, electromagnetic shielding, radar evasion, rechargeable batteries, conductive inks and antistatic textiles [16]. Conductive fillers include metal powders such as Al, Au, Ag, Cu and stain-less steel or carbon and graphite pow-ders [17-19]. Graphite, which is naturally abundant, has been widely used as a conducting filler in preparing conducting polymer composites [20-22]. Conventio-nal graphite fillers are usually micro-dia-meter powders. In order to get a satisfac-tory conductivity, using conventional graphite fillers, composite loadings are usually as high as 15-20 wt % or even higher. This often results in a material with poor mechanical properties and high density. Like many other nanocom-posites, a polymer nanocomposite made from graphite nanopowder or nanos-

heets may have promising properties, especially good electrical conductivity. However they are rarely reported, owing to the difficulty of preparing the graphite nanopowder or nanosheets.

There are three ways to prepare poly-mer nanocomposites: melt compound-ing, in situ polymerization and solution blending. Because of its thermal instabi-lity, it is necessary to prepare the PVC nanocomposites at low temperature, and the solution process may provide the most desirable conditions to prevent thermal and oxidative degradation du-ring the preparation [23-25].

Self-crosslinking of graphite /NBR is found earlier, resulting in strong interfa-cial interaction [26]. This self cross lin-king may be help to establish a desirable covalently bonded interface in the nano-composites, hence eliminating the use of conventional additives such as curing agent accelerators and activators there-by making it possible to design simple composite for potential applications.

The objective of this work is concerned with the study of some mechanical and electrical properties of PVC/NBR blends. This study also covers the effect of adding nano-graphite and cupper in different concentrations (1, 3 and 5 wt %) on the mechanical, electrical and swelling pro-perties before and after self- curing.

ExperimentalMaterialsPVC resin used in this study was a white powder made by suspension polymeriza-tion with K value of 67. It was supplied by

Graphite and Copper Nano- particles in PVC/NBR Composites

AuthorsA.A.Ward, A. I.Khalaf, M.N. Is-mail, S.Y. Tawfik, S.H. Mansour, NRC Dokki Cairo, Egypt

Corresponding author:Dr. Azza. A. WardNational Research CentreMicrowave Physics and Dielectrics Dept.Physics Division12311 Dokki Cairo, EgyptTel. +20/0233322435E-mail: [email protected]


37KGK · 1-2 2013www.kgk-rubberpoint.de

El-Amerria (Alexandria, Egypt). Acrylonit-rile butadiene copolymer (NBR) from Bay-er AG, Germany with 32 % acrylonitrile content and specific gravity 1.17 ± 0.005 at room temperature was used. Tetrahyd-rofuran (THF) and chloroform were re-agent grade from Merck, Darmstadt, Ger-many. High performance motor oil was supplied by ExxonMobil Egypt.

The fine grade of copper with average particle size varies between 60 –75 nm was obtained from BDH chemicals Ltd, Poole, England. Nanographite powder produced by chemical disintegration of graphite with average particle size 40 nm supplied by Nanjing Emperor Nano Mateial Co., Ltd , China.

Preparation of NBR/PVC blends by the solution-casting The required polymer solutions were prepared by the dissolution of 5 g of the PVC in 100 ml of THF and 1.2 g of NBR in 100 ml chloroform separately. Polymer blend films were prepared through the casting of mixed solutions of different ratios (0/100, 10/90, 20/80, 30/70, 40/60, and 50/50) of NBR to PVC on a glass plate with slow drying at room temperature. Care was taken to control the uniform film thick-ness for all compositions. The film thickness ranging from 0.35 to 0.45 cm was controlled by using the same solu-tion concentration of the polymers un-der investigation.

Preparation of NBR/PVC nanocompositesNBR/PVC nanocomposites were prepa-red by the addition of 1, 3 and 5 wt % of

copper or graphite to the previous prepa-red NBR/PVC blends in the same manner as aforementioned.

TechniquesFourier transform infrared spectroscopyInfrared spectra of untreated and heat treated samples were recorded on a JAS-CO FT/IR 300 E Fourier transform infrared (FTIR) spectrometer.

Mechanical MeasurementsTensile strength and elongation at break were determined at room temperature (25 ±1 °C) using Zwick tensile testing ma-chine (model-1425, Munchen, Germany) according to ASTM D 412-06a. The samples were cut with a dumbbell shaped cutter. Cross-section areas of the dumbbell speci-mens were measured accurately with the aid of a thickness gauge. The mean of five readings were taking into considerations.

Swelling testSwelling experiments were carried out by putting the samples in oil for 24 hours according to ASTM D471-12. The weight of the sample was taken under swollen conditions and the results are expressed in terms of swelling index which is defined as the grams of solvent absorbed per gram of sample. The swel-ling percentage (Q%) of the samples was calculated as follows:

Q% = [(w-w‘)/w‘] x 100 where w and w´ represent the weights of the samples after swel-ling and free from dissolved matter, respectively. All these tests were performed at room temperature (~25 °C), and the reported results were averaged from a minimum of five specimens.

Fig. 1: Dependence of mechanical properties of PVC /NBR blend on NBR content (a). Tensile strength (b). elongation at break %

1

Fig. 2: Dependence of Swelling in oil Q % of PVC /NBR blend on NBR content

100/0 90/10 80/20 70/30 60/40 50/50

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Dependence of mechanical properties of PVC /NBR blend on NBR content(a). Tensile strength (b). elongation at break%

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Dependence of Swelling in oil Q% of PVC /NBR blend on NBR content

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Dielectric MeasurementsCircular discs were cut out from the sheets of the composites with a diameter of 12 mm for dielectric studies. These studies were carried out using an impedance ana-lyzer (Schlumberger Solartron 1260), an electrometer, amplifier, and measuring cell as described before [27]. Using the impedance analyzer, the permittivity ε', loss factor tanδ, and ac resistance Rac were measured at room temperature (25 ±1 °C) and different frequencies 0.01Hz -10MHz.

The measurement was automated by in-terfacing the impedance analyzer with a personal computer through a GPIB cable IEE488. A commercial interfacing and au-tomation software Lab VIEW was used for acquisition of data. The error in ε' and tanδ amounts to 1 % and 3 %, respectively. The temperature of the samples was cont-rolled by a temperature regulator with Pt 100 sensor. The error in temperature mea-surements amounts 0.5 °C. To avoid mois-ture, the samples were stored in desicca-

tors in the presence of silica gel. Thereafter the sample was transferred to the measu-ring cell and left with P2O5 until the mea-surements were carried out.

Scanning electron microscopyThe morphology of composite samples was studied with a JEOL JXA-840A scan-ning electron microscope (SEM) at a ma-gnification of 1000 X. The surface of the polymer was mounted on a standard specimen stub. A thin coating (10 A˚) of gold was deposited onto the polymer surface and attached to the stub before examination.

Self crosslinkingSelf crosslinking was occurred after hea-ting the samples of PVC/NBR (50/50) filled with 1, 3 and 5 wt % of each of graphite or copper for 1h at 160 °C.

Results and Discussion

PVC/NBR blends

Mechanical Properties of PVC/NBR blends

Figure 1a,b show the dependence of the mechanical properties on the blend rati-os (100/0, 90/10, 80/20, 70/30, 60/40, and 50/50) of PVC/NBR. It can be seen that increasing NBR content in the blends decreases the tensile strength which could be attributed to the poor wetting of the PVC by the rubber matrix. This poor wetting leads to poor interfacial adhesion between the PVC and rubber matrix and hence reducing the tensile strength values. Also increasing the NBR content in the blends increases the elon-gation at break, due to the decrease of the stiffness of the blend (Fig.1b).

Oil resistance of PVC/NBR blendsFigure 2 shows that the swelling behavi-or decreases by increasing NBR content. So NBR has been chosen as an oil resis-tant rubber and its blends with PVC pro-duced acceptable limits of swelling re-quired for applications of these thermo-plastic elastomers as oil seals.

Dielectric properties of PVC/NBR blends

The permittivity ε' and dielectric loss ε" for different ratios of NBR/PVC blends were measured over a frequency range 0.01Hz up to 10 MHz. The measurements were carried out at room temperature (25 ±1 °C). The data obtained are illustra-ted graphically in Figure 3 a,b. From this

Fig. 3: The permittivity ε’ and dielectric loss ε” at room temperature ~25 °C of PVC/NBR blends as a function of frequency.

Fig. 4: The permittivity ε’ and dielectric loss ε” versus PVC / NBR content at f = 0.01Hz.

4

10-2 10-1 100 101 102 103 104 105 106 107

5

10

15

20

f [Hz]

(a)

PVC PVC90 PVC80 PVC70 PVC60 PVC50

ε'

10-2 10-1 100 101 102 103 104 105 106 107

10-1

100

101

(b)

ε''

f [Hz]

3

3 The permittivity ε' and dielectric loss ε" at room temperature ~ 25oC of PVC/NBR blends as a function of frequency.

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100/0 90/10 80/20 70/30 60/40 50/50

0

5

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20(b)

ε''

PVC / NBR content

The permittivity ε' and dielectric loss ε" versus PVC / NBR content at f = 0.01Hz.

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16 (a)

ε'

PVC / NBR content

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Figure it is clear that the values of ε' de-crease by increasing the applied frequen-cy showing an anomalous dispersion. In such range the permittivity has a contri-bution from orientation polarization. Al-so it is clear that ε' & ε" increase by incre-asing NBR content in the blend. This in-crease in ε' & ε" with the incorporation of rubber is due to the increase in C≡N dipo-les which leads to an increase in the ori-entation polarization and also to the presence of interfacial polarization [28]. From the same figures, it is clear that the curves relating ε" and frequency are broader than Debye curve [29] indicating that more than one relaxation process is present. These processes could be attri-buted to mechanisms related to the main chain and its related motions [28,30]. In addition, Figure 4 represents the variation of the permittivity ε' and dielectric loss ε" versus NBR content at fixed frequency f = 0.01 Hz. From this fi-gure it is obvious that the addition of NBR increase both ε‘ and ε" respectively. This increase is due to the increase in the polarity of the sample.

PVC/NBR nanocomposites

Mechanical properties of PVC/NBR nanocomposites

The dependence of tensile strength on graphite and copper loading is presented in Figure 5a,b. It is observed that tensile strength decreases as the filler loading increases in all composite samples. This can be referred to the filler-filler interac-tions which result in a graphite or copper agglomeration in the composites. Filler agglomeration was considered as a wea-kening point that leads to the broken of the composite samples so easily when the stress was transferred onto it, thus the tensile strength would decrease once the graphite or the copper concentra-tions increase.

Figure 6a,b reveals the relationship between elongation at break and PVC/NBR blends loaded with graphite and cop-per. It can be seen that incorporation of graphite into the PVC/NBR blends caused a decrease of elongation at break of the composites compared to unfilled speci-men. The reduction of elongation at break values might be due to the decreasing of deformability between the PVC/NBR and graphite. On the other hand the addition of copper to PVC/NBR blends increases the elongation at break. This increase in elongation at break is clearly seen in blend containing high NBR content.

Fig. 5: Dependence of tensile strength of PVC/NBR blends on filler loading.(a). PVC/NBR/graphite (b). PVC/NBR/Copper.

Fig. 7: Dependence of swelling behavior of PVC/NBR blends on the filler loading. (a). PVC/NBR/graphite (b). PVC/NBR/Copper.

Figure 6: Dependence of elongation at break % of PVC/NBR blends on filler loading. (a). PVC/NBR/graphite (b). PVC/NBR/Copper.

Oil resistance of PVC/NBR nanocom-posites

Figure 7a,b illustrates the effect of graphi-te and copper content on the swelling behavior of PVC/NBR blends in oil. The swelling resistance decreases continuous-

ly with increasing graphite and copper concentration. Also it was noted that as the NBR concentration increases the oil resistance of blend PVC/NBR increases. This is due to the polar nature of NBR that enhances the oil resistance of the blend.

0wt% 1wt% 3wt% 5wt%0

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Dependence of tensile strength of PVC/NBR blends on filler loading . (a). PVC/NBR/graphite (b). PVC/NBR/Copper

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Dependence of swelling behavior of PVC/NBR blends on the filler loading.(a). PVC/NBR/graphite (b). PVC/NBR/Copper

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Dependence of elongation at break% of PVC/NBR blends on filler loading. (a). PVC/NBR/graphite (b). PVC/NBR/Copper

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Dielectric properties of PVC/NBR na-nocomposites

The permittivity ε' and dielectric loss ε" of PVC/NBR/graphite (Figures 8 & 9) and PVC/NBR/copper (Figures 10 & 11) nano-composites as a function of frequency and graphite and copper content were il-lustrated. From these figures it is seen that the values of ε' and ε" increase by in-creasing the filler content in the blend. Moreover the values ε' and ε" of PVC/NBR/ copper composites are higher than those of PVC/NBR/graphite composites. This increment is attributed to interfacial

polarization of heterogeneous system. In-terfacial polarization always present in materials comprised of more than one phase like filled polymers. This kind of polarization arising at the interfaces due to the migration of charge carries through different phases of the composite materi-al resulting in differential charge accumu-lation at the interfaces [30]. When these charges are made to move by the applica-tion of an external field, the motion will be hindered at various points of the com-posite material differentially, causing space charge to appear. The appearance

of such space charge can distort the mac-roscopic field and appears as polarization to an external observer. Interfacial polari-zation is present in materials with consi-derable electrical heterogeneity and to-tally absent in materials which electrically homogeneous. Hence composite materi-als will exhibit large interfacial polarizati-on within them under an external field. Moreover metal particles embedded in an insulator matrix can act as charge centers and can contribute increment of the per-mittivity because of interfacial polarizati-on. Another contributing factor for the

Fig. 8: Permittivity ε’ versus frequency f of PVC/NBR blends loaded with different concentrations of nano- graphite at room temperature ~25 °C.

Fig. 9: Dielectric loss ε’’ versus frequency f of PVC/NBR blends loaded with different concentrations of nano-graphite at room temperature ~25 °C.

9

Permittivity ε' versus frequency f of PVC/NBR blends loaded with different concentrations of nano- graphite at room temperature ~25°C.

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Dielectric loss ε'' versus frequency f of PVC/NBR blends loaded with differentconcentrations of nano-graphite at room temperature ~25°C.

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103 PVC90PVC / 10NBR80PVC / 20NBR70PVC / 30NBR60PVC / 40NBR50PVC / 50NBR

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3 wt%

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Fig. 10: Permittivity ε’ versus frequency f of PVC/NBR blends loaded with different concentrations of nano-copper at room temperature ~25 °C.

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Fig. 11: Dielectric loss ε’’ versus frequency f of PVC/NBR blends loaded with different concentrations of nano-copper at room temperature ~25 °C.

11

increment of the permittivity in such composites is the possible increase in the conductivity due to the presence of metal filler particles in the matrix. However the experimental results in these Figures are in agreement with this explanation ta-king into consideration the fact that the conductivity of copper particles are higher than those of graphite.

The permittivity ε' and dielectric loss ε" are plotted graphically versus the filler content and at fixed frequency f =0.01 Hz in Figure 12. From these figures it is clear that, at low content of the filler, the filler

particles are isolated i.e., placed so far apart that there is no interaction between them. As the filler (graphite and copper) content is increased, clusters of particles are formed. A cluster may be considered as a region in the polymer matrix where filler are in physical contact or very close to each other. The average polarization associated with a cluster is larger than that of the individual particle because of an increase in the dimensions of the filler inclusion, and hence, greater interfacial area [31,32]. From this point of view, the values of the permittivity ε' and dielectric

loss ε" of the composites will be higher than those of the pure polymer.

Electrical conductivity of PVC/NBR nanocomposites

The values of the electrical conductivity are determined by means of resistivity measurements for nanocomposites of PVC/NBR loaded with various content of graphite and copper (Figure 13). From the-se figures it is clear that, at low filler the conductivity of the materials is about 10-13 S/cm (for PVC) in the initial stage and this is consistent with the magnitude of an

10-2 100 102 104 106

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Permittivity ε' versus frequency f of PVC/NBR blends loaded with differentconcentrations of nano-copper at room temperature ~25°C.

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Dielectric loss ε'' versus frequency f of PVC/NBR blends loaded with different concentrations of nano-copper at room temperature ~25°C.

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insulator. This value increased with increa-sing NBR content and reaches its maxi-mum value at 50 %NBR (1.68x10-11 S/cm). Also, the electrical conductivity of the composite depends significantly on the type and concentration of the dispersed filler. An increase in the copper content leads to a significant improvement of electrical properties of the investigated nanocomposites. This observation indica-tes that the PVC/NBR nanocomposites loaded with copper may find applications in domains where certain electrical con-ductivity is demanded, like self dischar-ging of the products.

A sharp increase, which is known as the percolation transition Figure 14, emerges when the filler content reaches a critical content. The conductivity levels off after arriving at this critical value. At this stage, the conductivity of PVC/NBR (50/50) is about 1.84x10 –7 S/cm, PVC/NBR (50/50)/5wt % graphite and 1.89x10-5 S/cm for PVC/NBR (50/50)/5wt % of cop-per which is nearly consistent with that of a semiconductor. The difference in the conductive behavior between PVC/NBR/graphite and PVC/NBR /copper at higher filler concentration is attributed to the

Fig. 12: The permittivi-ty ε’ and dielectric loss ε” of PVC / NBR versus graphite and copper content at f = 0.01Hz.

Fig. 13: The conductivity “σ” of PVC/NBR blends versus nano-grapite and nano -copper content at 25 °C.

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12 The permittivity ε' and dielectric loss ε" of PVC / NBR versus graphite and copper content at f = 0.01Hz.

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The conductivity "σ" of PVC/NBR blends versus nano-grapite and nano -copper content at 25 0C.

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enhanced number of conductive paths in the copper composites. The electrical conductivity of the composites exhibited a pronounced transition with the increa-se of filler content, from an insulator to nearly a semiconductor. This transition can be satisfactorily explained and de-scribed by the percolation theory and the formation of the conductive network in the composites [32]. According to this theory, the percolation threshold corres-ponds to the onset of the transition from an insulator to a semiconductor. This transition occurs for PVC/NBR /graphite nanocomposites at 3-4 wt. % graphite but when the filler is replaced by copper it occurs at 1-2 wt %. Clearly, copper na-nocomposites require a much lower per-colation threshold and, in so doing, they are more effective in electrical conducti-vity in comparison with normal graphite nanocomposites.

According to the common used classi-fication of the electrical conducting ma-terials, the materials with electrical con-ductivity lower than 10-6 S. cm-1 are trea-ted as insulators, with electrical conduc-tivity between 10-6 S.cm-1 and 102 S.cm-1 as semiconductors. Thus, in our case the nanocomposites of PVC/NBR (50/50) with 5wt % of copper presented in this work belong to materials characterized as semiconductors (σ = 1.89 x10– 5 S/ cm ) in comparison with PVC/NBR (50/50) with 5wt % of graphite (σ = 1.84 x10 – 7 S/ cm) at 30 °C. However, these values of electrical conductivity increased with in-creasing temperature. This increase as temperature increases above the Tg of the matrix, as revealed in Figure 14, can be caused by the possible flocculation of conductive fillers.

Morphology Dispersion of fillers is also important to the variation of percolation threshold for conductivity transition in the composi-tes. In our experiment, we used intensive stirring to promote fine dispersion for the composites as can be seen in Figure 15a,b. The graphite possesses a layering structure. So for polymer/graphite com-posites, higher and surface area of fillers lead to a lower percolation threshold compared to traditional carbon black [33]. On the other hand if the solution concentration is too high, the higher vis-cosity may hinder the polymer chains from entering the minor pores of the graphite and thus lead to poor dispersion of graphite in the polymer compared to copper Figure 13c,d

Self-crosslinking of PVC/NBR nano-composites

Compared with the conventional chemical process such as peroxide or sulfur induced vulcanization used for crosslinking rubber, self -crosslinking has some advantages [34,35]. The process is fast, clean and re-

quires less energy. It results in the formati-on of a three-dimensional network through union of macro-radicals genera-ted after heating for 1h at 160 °C. The IR -spectra of PVC/NBR (50/50) filled with 5 wt % of graphite and copper nanocomposi-tes before and after self-crosslinking are

Fig. 14: The conductivity “σ” of PVC / NBR (50/50) plotted as a function of nano/graphi-te and copper content and at different temperatures.

Fig. 15: SEM Micrographs of : (a). PVC/NBR/3wt% graphite (b). PVC/NBR/3wt% copper (c). PVC/NBR/5wt% graphite and (d). PVC/NBR/5wt% copper.

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0wt% 1wt% 3wt% 5wt%

(b)30 0C 60 0C90 0C3rd-Order Polynomial Fit

Nano-copper content0wt% 1wt% 3wt% 5wt%

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σ (

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The conductivity "σ" of PVC / NBR (50/50) plotted as a function of nano/graphite and copper content and at different temperatures.

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14



shown in Figure 16. It is reasonable to as-sume that the polar cyanide groups (C≡N) on NBR molecular chain does not take part in the curing as there was no change in the IR- peak at 2236 cm-1. For the uncured na-nocomposite, the peak at ν = 1644 cm-1 corresponds to C=C stretch vibration. Com-pared to the change in peak at ν = 2236 cm-1 after self -crosslinking, the intensity of the peak at ν = 1644 cm-1 is distinctly reduced Fig 16b. This indicates that part of the C=C participates in the curing reaction. The absorption peak at ν = 1744 cm-1 which usually corresponds to a carboxyl group in graphite, is capable of producing a physical interaction with C≡N group.

Effect of self curing on mechanical pro-perties of PVC/NBR nanocomposites

The self-cured nanocomposites filled with graphite possess better tensile strength with acceptable elongation at break compa-red to those filled with copper as it is shown in Figure 17. For example the PVC/NBR/ at 5 wt% graphite has a tensile strength that is respectively 3-times higher than that of the uncured one (Fig. 17a). These notable en-hancement of the mechanical properties may be due to the physical interaction bet-ween the active groups (epoxide and hydro-xyl) on graphite surface [35, 36] and NBR molecules (with C≡N) which enhance the reinforcement of graphite. Moreover, after heating the composites that contain graphi-te in air, free radicals as a consequence of pyrolytic bond cleavage (e.g. evolution of CO2, CO) are formed. These radicals could react with the C=C bonds and adjacent α-H of the rubber macromolecules at elevated temperature, enhancing the interfacial in-teraction and facilitating the reinforcement by graphite. On the other hand copper do not seem to result in chemical or physical bonding at the interface between it and the blend, as copper lacks of active groups.

Effect of self curing on dielectric pro-perties of PVC/NBR nanocomposites

The dielectric loss ε" of PVC/NBR/graphite and PVC/NBR/copper nanocomposites as a function of frequency at different 5wt% of graphite and copper before and after curing is illustrated graphically in Fig. 15a,b respectively. From this Figure 18a,b it is clear that the values of ε" of PVC/NBR/graphite decreased markedly after curing and the peak in the high frequency is shif-ted toward the lower frequency, this shift may be represent a strong evidence of self -crosslinking. However the polar groups on graphite surface e.g. -OH and -COOH, might interact physically and chemically

Fig. 16: IR spectra of PVC/NBR ( 50/50):(a) 5wt% graphite (b) 5wt% copper -nano-composites before and after self-curing at 160 °C for I h.

16

Fig. 17: Mechanical properties of PVC / NBR (50/50) filled with graphite & copper nano-fillers before and after self-curing at 160 °C for 1 h.

16

3000 2500 2000 1500 1000

Wavenumber (cm-1)

(b)

174422

36

2926

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Uncured

Tran

smitt

ance

(%)

1644

2924

(a)

2236 17

44

Self-cured

Uncured

Tran

smitt

ance

(%)

16 IR spectra of PVC/NBR ( 50/50):(a) 5wt% graphite (b) 5wt% copper -nanocomposites before and after

self-curing at 1600C for I h. 17

6

8

10

12

14

16

18

Uncured

Self-cured

(a)

Tens

ile st

reng

th M

Pa

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Self-cured

(c)


200

400

600

800

1000

Uncured

Self-cured

(b)

Elo

ngat

ion

atbr

eak

%

Nano-graphite content0wt% 1wt% 3wt% 5wt%

Uncured

Self-cured

(d)

Nano-Copper content

17

17 Mechanical properties of PVC / NBR (50/50) filled with graphite & copper nano-fillers before and after self-curing at 1600C for 1 h.



Fig. 18: Dielectric loss ε’’ of PVC/NBR ( 50/50) filled with ; (a). 5wt% graphite & (b) 5wt%copper nano-fillers before and after self-curing at 160 °C for 1 h.

18with rubber macromolecules, leading to strong interfacial interactions which redu-ced the mobility of the polymer, meaning that the chains and or/ network grow to a certain scale at which the contribution from dipole relaxation becomes detectible within the measured frequency range. As the mixture reacts the chain and or/ net-work becomes larger and the dipole rela-xation time should be longer (Fig. 18a). On the other hand, The dielectric loss ε" valu-es of PVC/NBR/copper (Fig. 18b) are not largely affected by the heat treatment as copper free from active groups and or/ra-dicals which facilitate the bonding bet-ween them and the polymer.

ConclusionsNanocomposites contains PVC/NBR blend reinforced graphite and copper nanoparticles were prepperd by solution casting method and their mechanical and electrical properties were. The re-sults obtained are concluded as follows:The SEM images show that the nanopar-ticles are well dispersed at low filler con-tent. As the filler (graphite and copper) content is increased, clusters of particles are formed resulting in better conducti-vities of nanocomposites.

The PVC/NBR/copper nanocomposites have higher electrical conductivity and a lo-wer percolation threshold of about 1-2 wt% than that loaded with graphite due to good dispersion of conducting filler entire the PVC/NBR nanocomposites and the compo-sites behave as n- type semiconductor.

The dielectric constant and dielectric loss of composites shows a high value in the frequency range 0.01 to 10 MHz due to the high conductivity of cupper and aspect ratio of graphite which allowed the gene-ration of interfacial polarization, because of both the increase in dipoles formed at filler/matrix interface, and at internal in-terfaces in the fillers of the composite.

The dielectric data on frequency do-mains revealed more than one relaxation mechanism ascribed to the Maxwell–Wagner effect, the main chain, and its related motions.

Copper nanocomposites are most pro-mising alternative candidates for elect-ronic applications over a frequency range of 0.01 to 10 MHz due to their light weight, low cost, ease of processing, good dispersion and conductivities.

References

[1] H. Li, L. Wang, G. Song, Z. Gu, P. Li, C. Zhang, and L. Gao, Iran. Polym. J. 19 (2010) 39.

[2] A. A. Shokri, G. Bakhshandeh, and T. D. Fara-hani, Iran. Polym. J. 15 (2006) 227.

[3] M. Abu-Abdeen and I. Elamer, Materials and Design 31 (2010) 808.

[4] S. M. Gheno, F. R. Passador and L. A. Pessan, J. App. Polym. Sci. 117 (2010) 3211.

[5] A. Mousa, U. S. Ishiaku and I. Z. A. Mohd, Po-lym. Bull. 53 (2005) 203.

[6] M. K. Stockdale, J. Vinyl Technol., 12 (1990) 235. [7] U.S. Ishiaku, F.S. Lim and I. Z. A. Mohd, Polym.-

Plast. Technol. Eng. 38 (1999) 939.[8] Z. Liu, X. Zhu, L. Wu and Y. Li, Polymer 42

(2001) 737.[9] M.C.S. Perera, U. S. Ishiaku and I. Z. A. Mohd,

Eur. Polym. J., 37 (2001)167.[10] A.Y. Coran, Thermoplastic rubber-plastic

blends, in: A.K. Browmick, H.L. Stephens (Eds.), Handbook of Elastomers -New Deve-lopments and Technology Mercel Dekker, New York (1988) 249.

[11] Z. Xiaojiang, J. App. Polym. Sci. 27 (1989) 223.

[12] N.R. Manoj, Polym. Degrad. Stab. 44 (1994) 43.[13] K.E. George, J. App. Polym. Sci. 32 (1986) 2867.[14] F. El-Tantawy, N. Abdel-Aal, A. Al-Hajry and M.

Bououdina, Polym. Compos. 29 (2008) 125.[15] G. Chen, C. Wu, W. Weng, D. Wu and W. Yan,

Polymer 44 (2005)1781.[16] T. Wang, G. Chen, C. Wu and D. Wu, Prog.

Org. Coat. 59 (2007)101.[17] J. M. Margolis, Conductive Polymers and

Plastics (Chapman & Hall, New York, (1989).[18] J. Delmonte, Metal/Polymer Composites,

Van Nostrand, New York (1990).[19] D. M. Bigg,: Metal Filled Polymers, edited by

S. Bhattacharya, Marcel Dekker, New York (1986)165.

[20] D. S. Saunders, S. C. Gala and G. K. Deir-mendjian, Composite 24 (1993) 309.

[21] T. A. Ezquerra, M. Kulescza, and F. J. Baltá-Calleja, Synth. Met., 41 (1991) 915.

[22] G-H. Chen, D-J. Wu, W-G. Weng and W-L. Yan, Polym. Eng. Sci., 41 (2001) 2148.

[23] D. Wang and C. A. Wilkie, J. Vinyl Addit. Technol. 8 (2002) 238.

[24] G. A. Ari and I. Aydin, J. Macromol. Sci., Part B 47 (2008)260.

[25] N.M. Ahmed, S.H. Mansour and S.L. Abd-El-Messieh, Materials and Design 31(2010) 4312.

[26] P.R. Dluzneski, Rubber Chem. Technol. 74 (2001) 451.

[27] A. A. Ward, Dielectric and mechanical pro-perties of filled rubbers in dependence on stress amplitude and temperature. PhD thesis, Cairo University, (2003).

[28] A.I. Khalf and A.A. Ward, Materials and De-sign 31 (2010) 2414.

[29] N. E. Hill, W. E. Vaughan, A. H. Price and M. Davies, Dielectric properties and molecular behaviour. London: Van Nostrand (1969).

[30] A. A. Ward and A. I. Khalf, KGK 62 (2009) 650.

[31] H. A. Pohl, Dielectrophoresis, Cambridge University Press, London, (1978).

[32] V. singh, A. R. Kulkarni and T.R. Rama Mo-han, J. appl. Polym. Sci. 90 (2003)3602.

[33] A. A. Ward and A. I. Khalf, KGK 60 (2007) 623.[34] T. Szabo, O. Berkesi, P. Forgo, K. Josepovits, Y.

Sanakis and D. Petridis, Chem. Mater. 18 (2006) 2740.

[35] Collins R. L., Bell M. D. and Kraus G., J. Appl. Phys. 30 (1959)56.

[36] Y. L. Hawng, C. C.Yang and K.C. Hawng, J. Phys. Chem. A 101( 1997)7971.

Dielectric loss ε'' of PVC/NBR ( 50/50) filled with ;(a). 5wt% graphite & (b) 5wt%copper nano-fillers before and after self-curing at 1600C for 1 h.

10-3 10-1 101 103 105 107

100

101

102

103

(a)

Self-curedUncured

ε''

f [Hz]10-3 10-1 101 103 105 107

(b)

Self-curedU

ncured

f [Hz]

18

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Aman Khalaf P KGK 2012 6Wi E P 10 0 Kautschuk Nanopartikel Kautschuk Dr. Azza. A Ward National...

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