J Mater Sci (2006) 41:5359–5364

DOI 10.1007/s10853-006-0179-4

Nickel and iron nano-particles in natural rubber composites

D. E. El-Nashar Æ S. H. Mansour Æ E. Girgis

Received: 28 December 2005 / Accepted: 7 April 2006 / Published online: 8 June 2006

Springer Science+Business Media, LLC 2006

Abstract In this work, the mechanical, electrical, and modulus, strength and heat resistance, and decreased
magnetic properties of natural rubber (NR) composites flammability [1]. Polymer nanocomposites using mag-
containing iron or nickel nanoparticles at different netic materials as fillers are important for many
percentage varying from 0 to 120 phr (part of magnetic applications because the magnetic materials are widely
particle per hundred rubber) have been investigated at used in various fields such as magnetic data storage
room temperature. It was found that the optimum media, magnetic field sensors and biomedical applica-
concentration of magnetic fillers in NR is 30 phr, which tions such as drug delivery. Magnets are usually blen-
improve the rheometric characteristics and physico- ded with polymer materials such as rubber to obtain
mechanical properties. Magnetic properties of the magnetic rubber composites, which has many applica-
rubber composites have been investigated using tions [2–5].
vibrating sample magnetometer (VSM) at room tem- Natural rubber (NR) is an unsaturated elastomer
perature. The magnetic measurements show super- characterized by its crystallinity and has some good
paramagnetic behavior for all Ni and Fe nanoparticles properties, such as high strength, outstanding resil-
percentage. The electrical measurements show a strong ience and high elongation at break [6, 7] and it is
dependency of the conductivity on the percentage of economically available [8, 9]. However, NR is very
magnetic nanoparticles. sensitive to heat and oxidation because of the double
bonds in its chains [10]. Furthermore, NR is vulca-
nized with sulfur compounds, which can crosslink the
chains because of the presence of the reactive double
bonds. It has high strength in non black formulations,
Introduction hot tear resistance, retention of strength at elevated
temperature, excellent dynamic properties and gen-
Polymer nanocomposites represent a new alternative eral fatigue resistance, so it has accounted for its use
to conventionally filled polymers due to their filler size in many applications [11, 12]. The incorporation of
and dispersion. Nanocomposites exhibit markedly magnetic fillers with NR leads to the formation of a
improved properties compared to the pure polymers or composite with improvement mechanical, magnetic
their traditional composites. These include increased and electrical properties.
The development of iron powder polymer compos-
ites was expected to broaden the application base for
D. E. El-Nashar Æ S. H. Mansour (&)
Polymers & Pigments Department, National Research metal into high volume alternating current (AC)
Centre, Dokki, Cairo, Egypt magnetic applications [13–15]. It is well known that
e-mail: smansour26@hotmail.com ferromagnetic properties depend on the crystal size of
the used materials [16–19]. Therefore, particular mag-
E. Girgis
Solid State Physics Department, National Research Centre, netic properties are expected for the nanometer-sized
Dokki, Cairo, Egypt Ni-dispersed composites.

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In the present work composite magnetic materials room temperature (25 C ± 1). Average of 5 samples
were prepared by mixing different concentrations of was taken for each measurements point.
magnetic nanoparticles of Fe (hard magnet) or Ni (soft Dielectric measurements permittivity e¢ and dielec-
magnet) with NR matrix to form composites with good tric loss e¢¢ were carried out at 100 Hz and at room
mechanical, magnetic and electrical properties for dif- temperature using a LCR meter type AG-411 B (Ando
ferent applications. electric Ltd. Japan). The capacitance C, loss tangent
tan d and AC resistance R were measured directly from
the bridge from which the permittivity e¢, dielectric loss
Experimental e¢¢ and Rdc were calculated. The cell used for measuring
the solid samples was a guard ring capacitor type NFM/
NR produced in Maliysia of type RSS-1, Ribbed 5T [Wiss Tech. Werkstatten (WTW) GMBH, Ger-
Smoked Sheets with a specific gravity 0.913 + 0.005 many]. The cell was calibrated using standard materials
and Mooney viscosity at 100 C = 60–90r and glass (trolitul, glass, and air) of different thickness ranging
transition temperature Tg = )75 C. from 1 to 5 mm. For each sample, a relation between
Other chemicals such as sulfur, zinc oxide, stearic acid, the thickness d and its capacitance CM was plotted as a
n-cyclohexyl-2-benzothiazole sulphenamide (CBS) and standard curve. The capacitance CM for the standard
phenyl-b-naphthyl amine (PBN) were of technical materials obtained from the standard curves was plot-
grade. ted versus the known permittivity e¢ of each material
The fine grade of iron (Fe) with average particle size (e¢ = 2.5, 7, 1 for trolitul, glass and air respectively).
varying between 26 nm and 45 nm and nickel (Ni) with The relation between CM and e¢ was found to be linear
average particle size varying between 22 nm and 50 nm and thus the permittivity corresponding to any mea-
was supplied by VEB Laborchemie Apolda, Germany. sured capacitance can be deduced. To check the stan-
The formulations of the composites are given in dard curve, two Teflon samples (e¢ = 2.0) [20] with
Table 1. All rubber ingredients were blended on a two- different thicknesses were used. The experimental er-
roll mill (470 mm diameter and 300 mm working dis- ror in e¢ and e¢¢ was found to be ±3% and 5%,
tance). The speed of the slow roll was 24 rpm with a respectively.
gear ratio of 1:1.4. An oscillating disc rheometer model The magnetic properties, magnetization saturation
100 from Monsanto, USA was used for measuring the (Ms), permittivity (Br), and coercive force, Hc were
curing characteristics of the rubber compounds measured for the iron and nickel rubber composites by
according to ISO 289-1994. The compounded rubber using a vibrating sample magnetometer (VSM) model
was vulcanized in a hydraulic press under a pressure of (LDJ 9600-1).
about 4 MPa and temperature of 142 ±1 C for their
optimum cure time (Tc90).
The tensile strength, elongation at break and Results and discussion
Young’s modulus were determined on dumbbell
shaped specimens using a Zwick tensile machine Table 2 summarizes the rheometric characteristics of
(model 1425). This is carried out in accordance with the NR composites. The minimum torque ML is an
ISO 37. indirect measure of the viscosity of the compound [21,
Hardness was measured using the Shore A durom- 22]. The table shows that minimum torque is slightly
eter according to ISO 868. All tests were conducted at increased with increasing Fe loading up to 30 phr then
decreases. In the case of Ni composites no significant
change in ML was observed.
Table 1 NR formulations containing different concentrations of It is clear from Table 2 that the maximum torque
Fe and Ni MH increases with Fe and Ni loading with the maxi-
Ingredients Phr (part per hundred rubber) mum values obtained at a concentration of 30 phr. The
scorch time ts2 values in Table 2 indicate that the
NR 100 samples loaded with Fe and Ni exhibit longer scorch
Stearic acid 1
ZnO 5 times than the unloaded rubber. It is observed that the
CBS 0.6 scorch time increases up to 30 phr and then decreases
PBN 1 with increasing filler content. Tc90 is the optimum cure
Sulfur 1.5 time for vulcanization and it is calculated as follows:
Iron (Fe) 0,10,30,60,90,120
Nickel (Ni) 0,10,30,60,90,120
Tc90 ¼ ðMH
ML Þ  0:9 þ ML

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Table 2 Rheometric
Filler content (phr) ML (dNm) MH (dNm) Tc90 (min) ts2 (min) CRI (min)1)
characteristics of NR
composites Fe
0 3.5 45 11 6 10
10 3 52 16 7 11
30 4.5 61 16.5 9 13.5
60 3.5 58 17 8 11.5
90 3 58 19 6.5 8
120 2.5 54 22 6.5 6.5
Ni
0 3.5 45 11 6 10
10 2 58 13.5 6.5 14.5
ML—minimum torque; 30 3.5 65 14.5 9 18.5
MH—maximum torque; 60 3 63 14.5 8 15.5
Tc90—optimum cure time; 90 2.5 60 15.5 7.5 12.5
ts2—scorch time; CRI—cure 120 2.5 56 16 7 11.5
rate index

This is an important parameter as far as the vulcani-

zation is concerned.
Evaluation of cure time is a prerequisite for molding
the compounds. It is clear that Tc90 values increase
with the addition of magnetic filler.
Cure rate index (CRI) is a direct measure of the fast
curing nature of the rubber compounds and is calcu-
lated with the following relation:

CRI ¼ 100=Tc90 ts2

CRI increases with magnetic filler concentration and

it supports the activation of the cure reaction up to
30 phr of the magnetic filler (Fe and Ni). At higher
loading, there is a poor interfacial interaction between Fig. 1 Effect of filler content on the tensile strength of NR
NR and the magnetic filler [23]. composites

Mechanical properties

The variation of tensile strength, Young’s modulus and

elongation at rupture with magnetic filler loading of Fe
and Ni are presented in Figs. (1–3) respectively. The
tensile strength of these composites increases with
increasing the magnetic filler up to 30 phr and then it
decreases with increasing the filler loading. Increasing
of tensile strength at filler loading 30 phr was due to
the good filler–rubber interaction as a result of better
filler dispersion in the rubber matrix. Strong rubber–
filler interaction would increase the effectiveness of the
stress transferred from rubber matrix to filler particles
dispersed in the rubber matrix [24]. However, the
reduction in strength at filler loading (more than
30 phr) due to the reduction of the stress-induced
crystallization of NR matrix by loading of magnetic Fig. 2 Effect of filler content on the Young’s modulus of NR
filler [8]. composites

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Fig. 3 Effect of filler content on the elongation at rupture of NR Fig. 5 Variation of premativity against filler content
composites

The recorded Young’s modulus also ensures the constant frequency f = 100 Hz. From these figures it is
same behavior (Fig. 2). For the elongation at rupture notable that both e¢ and e¢¢ increase by increasing both
(Fig. 3) no significant changes were observed. filler content. Although the values of e¢ are higher in
The variation of hardness with loading magnetic case of Ni-composites, these higher values are accom-
filler is shown in Fig. (4). It shows that the hardness panied by higher loss values when compared to
increases with increasing filler loading. Fe-composites. This might be due to the formation of
From these data, it is clear that the optimum con- some oxide layer on the Fe particles during processing
centration of magnetic fillers with NR is 30 phr, which the samples that could reduce its conductivity.
improve the rheometric characteristics. It was observed From the above investigation it is clear that iron
that the Fe filler enhances the physico-mechanical composites possess more preferable insulating prop-
properties more than Ni. erties when compared with those of Ni.
The conductivity (r) was calculated from the mea-
Electrical properties sured resistance R using the equation r = L/RA where
A is the area of the sample in cm2 and L its thickness in
It was interesting to study the electrical properties of cm. The variation in conductivity with respect to filler
magnetic rubber composites prepared in the present concentrations is shown in Fig. 7. From this figure it is
work. clear that, r increases by increasing filler content. The
Results of permittivity e¢ and dielectric loss e¢¢ of conductivity data r are found to be 0.59 ) 11.9 · 10)11
various rubber/iron and nickel composites are shown in W)1 cm)1 for the samples containing different con-
Figs. 5 and 6. centrations of iron, while it ranges from 0.76 to
Figures 5 and 6 represent the variation of both e¢ 35.9 · 10)11W)1 cm)1 for the different concentration of
and e¢¢ versus filler content at room temperature and at nickel. These results could lead to the conclusion that

Fig. 4 Effect of filler content on the hardness Fig. 6 Variation of dielectric constant against filler content

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nanoparticles Fe 30 phr show a switching field (Hs) of

0.007728 T and the magnetization saturation (Ms) is
22.75 emu/g. While for Fe 120 phr the switching field is
0.005049 T and Ms is 60.67 emu/g. It is clearly shown
that by increasing the Fe nanoparticles in the rubber
samples, the magnetization (emu/g) increases while the
switching field (Hs) decreases. Increasing the magnetic
nanoparticles in the rubber medium, leads to decrease
the distance between the magnetic nanoparticles.
Decreasing the distance leads to magnetic coupling
between the nanoparticles. This coupling decrease the
switching field because once one particle switched,
Fig. 7 Variation of conductivity against Filler content the other particles started to switch earlier due to the
magnetic coupling. This leads to decrease the switching
the investigated systems are considered to be insulating field and increase the magnetization in the rubber
materials as their conductivity values are in the order medium. Fig. 8c, d shows the hysteresis loops for rub-
of those found in literature (10)8–10)12 W)1 cm)1) [25]. ber samples with 30 phr and 120 phr Ni nanoparticles
respectively. In Ni samples, the switching field (Hs) for
Magnetic properties 30 phr Ni is 0.00438 T and Ms is 18.96 emu/g while the
Hs for 120 phr is 0.003620 T and Ms is 25.03 emu/g.
Figure 8 shows the hysteresis loops measured using From Fig. 8a–d, it is clearly shown that, the Ni sam-
vibrating sample magnetometer (VSM) at room tem- ples show the same behavior as Fe samples except the
perature. Figure 8a, b show the hysteresis loops for switching field which is higher at Fe nanoparticles (hard
rubber samples contain 30 phr and 120 phr of iron magnet) compared with Ni nanoparticles (soft magnet).
respectively. It is clearly shown that the hysteresis Increasing the magnetic particles has an influence on
loops of the magnetic nanoparticles which are distrib- the magnetic properties (due to the coupling between
uted in the rubber (which is a nonmagnetic medium) the magnetic nanoparticles which affect on the switch-
have a superparamagnetic behavior. The magnetic ing field) rather than the electrical properties.

Fig. 8 Hysteresis loops of Ni

and Fe NR composites

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Conclusion 3. Lacoste E, Mantaux O, Danis M (2002) Composites, Part A,

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4. Lokander M, Stenberg B (2003) Polym Test 22:245
Magnetic filler of Fe and Ni were incorporated into NR 5. Lokander M, Stenberg B (2003) Polym Test 22:667
with different loading levels up to 120 phr to obtain 6. Kroswitz JI (1990) Concise encyclopedia of polymer science
rubber composites. engineering. Wiley, London, p 1015
The cure characteristic and the physico-mechanical 7. Mark HF (1970) Encyclopedia of polymer science engi-
neering. Wiley, New York, p 492
properties of rubber composites depend mainly on 8. Mohamed EM, Malini KA, Kurian P, Anantharaman MR
both concentration and type of magnetic filler. (2002) Mater Res Bull 37:753
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and Ni is 30 phr of NR. Iron (Fe) enhances the rheo- 57:3381
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