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MATERIALE PLASTICE
https://revmaterialeplastice.ro
https://doi.org/10.37358/Mat.Plast.1964
Mater. Plast., 61 (2), 2024, 75-89 75 https://doi.org/10.37358/MP.24.2.5720
Characterization of Some Functional Polymeric Composites in a
Synergistic Regime of Protection at Electromagnetic Shielding
and Electrostatic Transfer
ALINA RUXANDRA CARAMITU1, IOANA ION1, MIHAI MARIN1,
ADRIANA MARIANA BORS2*, ROMEO CRISTIAN CIOBANU3,
CRISTINA SCHREINER3, MIHAELA ARADOAEI3
1 National Institute for Research and Development in Electrical Engineering ICPE - CA Bucharest, 313 Splaiul Unirii,
030138, Bucharest, Romania
2INOE 2000-IHP, General Hydraulics Department, 14 Cutitul de Argint Str., 040558, Bucharest, Romania
3 Gheorghe Asachi Technical University, Department of Electrical Measurements and Materials, 67 Dimitrie Mangeron
Blvd., 700050, Iasi, Romania
Abstract: The paper presents the characterization of 5 polymer composite materials with a poly-
propylene (PP) matrix obtained with different (mass) concentrations of strontium ferrite (Fe12SrO19)
reinforcement that have synergistic protective properties against electrostatic discharges (ESD) and
electromagnetic impulses (EMI). These types of composites can be used to protect electronic equipment.
To this purpose, suitable polymer composites were developed using SrFe12O19 type filler in two forms
(powder and concentrate). The weight ratio of the PP/SrFe12O19 composites obtained by the extrusion
process and injection from the melt is 75/25 and 70/30. The characterization of these composite
materials consisted of carrying out some physico-chemical tests to determine the hydrostatic density and
the resistance to the action of water, as well as FTIR, UV-Vis analyzes and dielectric, magnetic and
functional tests to identify the simultaneous protection performance at electromagnetic shielding and
electrostatic discharges, which can occur in the electro-technical, electronics and automotive industries.
It is also found that all composite materials presented reflection shielding properties (SER) in the range:
-71.5 dB...to -56.7 dB, indicating very low absorption shielding. The best performing material was the
PP/SrFe12O19 powder composite with a weight ratio of 70/30. At the same time, EDS tests were also
carried out on these materials. For these applications, the surface resistance Rs and the point-to-point
resistance Rp were tested. Recommended composites for simultaneous EMI and sensitivity to
electrostatic discharges (ESD) functionality, in order of their performance, are M2 (with 30% ferrite
powder) and M1 (with 25% ferrite powder). M4 composite (with 30% ferrite powder concentrate) can
also be used at the limit. Following the research carried out, the obtained results recommend the
composite with promising simultaneous operations as M2 (with 30% ferrite powder). The element of
originality consists of obtaining polymer composites with simultaneous properties of protection against
electromagnetic impulses and electrostatic discharges.
Keywords: strontium ferrite, PP/ SrFe12O19, polymer composites, electromagnetic radiation, magnetic
permeability, electro-static discharge (ESD), electromagnetic impulses (EMI)
1. Introduction
Radio waves, television waves, microwaves, X-rays, visible light waves are all examples of
electromagnetic waves [1, 2], they differ from each other only in wavelength or frequency. High-
frequency electromagnetic waves (MHz, GHz) transmitted by electronic equipment such as microwave
oven, antennas for 4G, 5G mobile communications, etc. have a harmful effect on the health of plants,
animals and people because these waves applied at high frequencies decrease the resistance of animal
and human organism leading to the appearance of various diseases and even death [2, 3]. Therefore,
exposure to electromagnetic waves must be minimized by shielding them with different composite
shielding materials [4, 5]. The continuous increase in electricity production due to the ever-increasing
*email: bors.ihp@fluidas.ro
MATERIALE PLASTICE
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https://doi.org/10.37358/Mat.Plast.1964
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demand of consumers, which generates electromagnetic fields, leads to an increase in electromagnetic
pollution of the environment in various rooms/spaces/deposits/offices [6].
At the same time, all electronic devices, which have become so indispensable in everyday life, induce
an increased sensitivity to electrostatic discharges (ESD), which imposes finding new, high-performance
materials to ensure protection against these discharges [7-10]. Electromagnetic and electrostatic
pollution, constantly increasing, can lead to the deterioration of human health [11-13] and living matter
[14-21], so it is impetuously necessary to reduce it by researching and designing different new materials,
effective for this purpose. These materials must simultaneously ensure an acceptable attenuation of
electromagnetic waves, as well as a protection against electrostatic discharges as a result of phenomena
associated with other local contaminations on humans and the environment [22, 23].
The usual filler materials for the realization of composite materials used as protective shields for
electromagnetic waves are metal powders [24] or ferrite powders at sizes below 30 nm [25, 26], which
present exceptional shielding properties. Over the years, there have been researches carried out to obtain
composite materials using rubber as a polymer matrix [27] and Cr and Mn ferrite filler, materials that
find their utility in absorbing microwaves in the 8-12 GHz range, at the same time, a silicone/
NiCr0.2Fe1.8O type composite was obtained for use in obtaining permanent magnets [28].
Most of the research carried out so far on these composite materials has been carried out in order to
diversify the performances of permanent magnets. Research in terms of finding new composite materials
that simultaneously fulfil the condition for electromagnetic shielding, but also as protection against
electrostatic discharges, has not been carried out. That's why, in this work, we set out to obtain and
characterize polymeric composites of the PP/Fe12SrO19 type with simultaneous applications in the
protection against electromagnetic impulses and electrostatic discharges from electronic devices existing
in the electro-technical, electronics and automotive industries. Thus, in the paper also presented the
results obtained in the ESD functional tests that qualify the composites that simultaneously meet the
conditions of protection and both to electromagnetic impulses and to electrostatic discharges.
The characterization of these materials consisted in performing dielectric tests, tests to determine the
magnetic permeability with the estimation, by calculation, of the electromagnetic shielding efficiency
and functional tests for ESD applications. As a result of these researches, it has been demonstrated that
polymer composite materials (thermoplastics) with superior simultaneous EMI and ESD shielding
properties can be obtained. These composites are easy to make on a large scale, cheap, with minimal
concentration in ferrite powder type filler, but mostly they are easy-to-process thermoplastic materials
for applications in the electrical, electronics and automotive industries.
2. Materials and methods
The following raw materials were used to obtain polymer composite materials:
• Polypropylene polymer matrix - RESINEX with the code PP RXP 2004 NATURAL (PP/25/1300
μm) [29]. Its characteristics are presented in Table 1.
Table 1. Properties of polypropylene [29]
Properties
Standards
Value
UM
General
Melt flow index (MFI)
(230oC/2,16kg)
ISO 1133
25
g/10min
Density
ISO 1183
0,900
g/cm3
Thermal
Vicat Softening Temperature
(Condition A120)
ISO 306
150
oC
Mechanical
Tensile Stress at Yield
ASTM D638
33
MPa
Charpy Impact Strength
(23°C / Notched)
ISO 179
2,5
kJ/m2
Flexural Modulus
ISO 178
1400
MPa
MATERIALE PLASTICE
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https://doi.org/10.37358/Mat.Plast.1964
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-Fe12SrO19 powder filling - from the company TODA Ferrite, Korea with the properties presented in
Table 2 [30].
Table 2. Properties of Fe12SrO19 powder [30]
Property Name
Property Value
Molecular Weight
1061.7
Melting point
> 450°C (lit.)
Density
5.18 g/ mL at 25°C (lit.)
Solubility
Soluble in organic solvents
-Filler - F1 type Fe12SrO19 concentrate granules with coding HM 1213 -PA12 + 85% Fe12SrO19 -
company Mate Co. Ltd [31]; the properties are presented in Table 3.
Table 3. Properties of Fe12SrO19 granular concentrate, type F1[31]
Properties
Type F1-HM 1213-PA12+85%
Fe12SrO19
Specific gravity
3.2 g/cm3
Melting point
190 oC
Residual magnetic field strength
235 mT
Coercive force
177 kA/m
Intrinsic coercive force
251 kA/m
Maximum stored energy
10.9 kJ/m3
Density after ripening
3.21 g/cm3
Flow index at 270oC/10 kg
130 g/10 min
Resistance to bending
125 MPa
Impact resistance
28 kJ/m2
Obtaining the composite materials consisted in the mechanical mixing and primary homogenization
in the polymer mass of the percentages established of filler from ferrite powder/ferrite concentrate,
followed by the introduction of the mixture thus formed, on the machine screw of injection from melt
according to [32]. The processing temperatures of these materials are in the range of 180 - 250°C, and
the working pressure is in the range of 138-155 kN being used to achieve disc-shaped materials with a
diameter of 30 ± 0.1 mm and a thickness of 2 ± 0.1 mm. The concentrations of the obtained composite
materials, as well as their coding, are presented in Table 4 and Figure 1.
Table 4. Sample composition and coding
Composite
material
Composition (%)
PP/ Fe12SrO19
Composition (%)
PP/concentrated of
Fe12SrO19
Figure 1. Obtained
composites materials
M0
100/0
M1
75/25
M2
70/30
M3
75/25
M4
70/30
The composites with the maximum percentage of filler were also aged for 168 h at 65oC to identify
the changes occurring in the thermal degradation process. FTIR and UV-Vis tests were performed on
these aged samples.
2.1. Equipment and method
The obtaining and characterization of these materials was carried out with the following equipment:
a mechanical mixing device/turbine and a melt injection machine Dr. Boy 35 A- Germany [32].
MATERIALE PLASTICE
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Mater. Plast., 61 (2), 2024, 75-89 78 https://doi.org/10.37358/MP.24.2.5720
For the composites characterization, various devices were used depending on the determinations
made:
• The hydrostatic density was determined with the XS204 Analytical Balance, precision: 0.1mg;
linearity: ± 0.2mg; density kit for solids and liquids;
To perform these tests, the applied procedure was according to ASTM D792-20 [33].
The working temperature was 22oC (ambient). The density was determined as the mean value
between 4 measurements performed on 4 different samples. Density of the composites obtained by
injection from the melt was determined by the Archimedes method, on 4 cylindrical samples, 30 mm in
diameter and 2 mm in height.
• The determination of resistance to the action of water was carried out with the XS204 analytical
balance, precision: 0.1mg; linearity: ± 0.2mg and a Memmert oven;
The effectiveness of an electromagnetic shield can be affected by various factors, including exposure
to water. There are several ways in which water could potentially affect the functionality and integrity
of an electromagnetic shield: *corrosion- exposure to water can lead to rusting or oxidation. This process
weakens the material and may compromise its ability to effectively block electromagnetic radiation;
*conductivity: Water could potentially interfere with the shield's ability to direct electrical current. This
would only be significant if water were able to penetrate or come into contact with the conductive
layer(s) within the shielding material; *structural integrity: exposure to water could compromise the
structural integrity of shielding material (if its composed of multiple layers) by causing swelling,
delamination, or other forms of degradation, which might result in gaps or openings within the shield
that would allow electromagnetic radiation to penetrate and affect electronic devices inside.
Thus, to maintain the effectiveness of an electromagnetic shield in a water-exposed environment, it
is essential that the material is corrosion-resistant, minimizes the risk of structural degradation due to
exposure to moisture, and prevents contaminants from entering or affecting its integrity. Therefore, the
polymer material obtained is waterproof and without cumulative effect for water conductivity.
Water absorption determination tests are performed according to ISO 62:2008 (EN) point 6.4 method
2 [34] on 3 samples from each experimental composite model with a 24h test cycle.
Tests were carried out at 4 test cycles, respectively 24h, 48 h, 96h and 192h. The following formulas
are used to calculate the amount of water absorbed (in %):
%100
1
12 x
m
mm
c−
=
(1)
where:
c - amount of water absorbed (%)
m1 - sample mass (mg) dry, before immersion,
m2 - sample mass (mg) after immersion
The magnetic tests consisted of carrying out the comparative hysteresis cycle for M2 and M4
(materials with a 30% filler concentration) and the tests to determine the magnetic permeability.
Each sample was prepared as a hollow cylinder having an external diameter of 20 ± 0.1 mm, an
internal diameter of 16 ± 0.1 mm, and a thickness of 2 ± 0.1 mm to measure the inductance at the ends
of the wire. When the cylindrical sample is inserted into the Test Fixture kit, an ideal, single-turn
inductor, with no flux leakage, is formed. Permeability is derived from the inductance of the core with
the fixture. The real (μ′) and imaginary parts (μ′′) of magnetic permeability were determined from the
inductance measurements over the frequency range of 8-30 MHz, according to following equations [35,
36].
(2)
MATERIALE PLASTICE
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(3)
where: l is the average length of the magnetic core, Leff is the coil inductance, Reff is the equivalent
resistance of the magnetic core losses including the wire resistance, N is the number of windings, Rw is
the wire resistance, A is the cross-sectional area of the magnetic core, is the angular frequency ( =
2f), f is the linear frequency (Hz), and µ0 is the permeability of vacuum (µ0 = 4 × 10-7 H/m).
The total efficiency of the electromagnetic shielding of samples with a thickness of approx. 2 mm is
given by the sum between reflection and absorption (4) [35, 36].
SE = SER + SEA (4)
The reflection shielding efficiency is given by formula (5)
=
0
16
log10)(
r
AC
RdBSE
(5)
exde
d
dBSE ACr
Rlog
2
20log20)(
==
(6)
where:
d - the thickness of the screen (in m) representing the depth with which the radiation penetrates the
material,
SEA - absorption shielding efficiency,
SER - reflection shielding efficiency,
r - real magnetic permeability,
r - real permittivity
tg - dielectric loss
log e - propagation term used in logarithmic function for the adsorption loss calculation
tgfro
2=
(7)
Substituting results [36]:
To estimate the shielding efficiency, we used formula 8.
2
log20)
16
log(10)(
eddBSE +
(8)
• The magnetic characterization was carried out on a VSM-7304 Lake Shore vibrating sample
magnetometer (VSM);
• Magnetic permeability was determined with an impedance analyzer type 4294A (Agilent
technology, Japan, Ltd.) equipped with a 16454A magnetic property measurement kit;
• FTIR analyzes were performed with a JASCO FTIR 4200 spectrometer (Jasco inc., JP) [37]
equipped with an ATR (Attenuated Total Reflection) PRO470H device, at a resolution of 4 cm-1, in the
spectral range 400-4000 cm-1, 100 accumulations/spectrum;
• UV-Vis analyzes were performed with the Jasco V-570 spectrometer (Jasco inc., JP) [38];
• The dielectric characterization was carried out with the help of the dielectric spectrometer Solartron
Analytical, UK [39];
• ESDI functional tests were performed with the Novocontrol measuring device.
MATERIALE PLASTICE
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https://doi.org/10.37358/Mat.Plast.1964
Mater. Plast., 61 (2), 2024, 75-89 80 https://doi.org/10.37358/MP.24.2.5720
3. Results and discussions
3.1. Determination of hydrostatic density
From the experimental data obtained as a result of these tests, it can be seen that the densities of the
composites are quite close due to the very close concentrations of the filler. However, the highest values
are presented by the composites coded with M2 and M4. This can be explained by the fact that they have
the highest concentration of the filler (Fe12SrO19 powder and Fe12SrO19 concentrate granules),
respectively 30%. According to them, the composites with concentrations of 25% of the filler
respectively M1 and M3 and, as expected, the natural polymer M0 have the lowest densities.
The experimental data were presented in Table 5 and Figure 2.
Table 5. Classification of composites according to density
Code
Density ± std. dev.
(g/cm3)
Figure 2. Hydrostatic density
M0
0.89
0.0022
M1
1.077
0.0015
M2
1.157
0.0019
M3
1.068
0.019
M4
1.157
0.0013
3.2. Water absorption
The amount of water absorbed by the composite materials studied were analyzed by comparison with
the control, namely natural polypropylene (M0).
Table 6 shows the absorption of these materials (WA) as a function of time.
The experimental results obtained for water absorption were presented in Figure 3.
Table 6. Water absorption of composites (%)
Code
WA 24h
(%)
WA 48h
(%)
WA 96h
(%)
WA
192h
(%)
Figure 3. Water absorption
M0
0.0091
0.0122
0.0244
0.0244
M1
0.0073
0.0223
0.0339
0.0363
M2
0.0105
0.0143
0.0258
0.0344
M3
0.0103
0.0284
0.0438
0.049
M4
0.0072
0.0264
0.0479
0.0551
The insignificant water absorption by the composite is mainly due to the fact that the strontium ferrite
filler contains -OH functions that form hydrogen bonds with water. From these tests it is found that in
the case of composites made with fillers from Fe12SrO19 concentrate granules (M3 and M4) the water
absorption is somewhat higher than in the case of composites with only Fe12SrO19 powder filler (M1 and
M2). This can be explained by the fact that in the process of homogenization in the melt of the polymer
with the two types of fillers (powder and concentrate) in the case of the concentrate, the polymer that
constitutes the shell of the concentrate granule (respectively PA12) intervenes in the mixture and
between them certain phenomena at the interface appear, thus creating more voids compared to the
polymer blend with only Fe12SrO19 powder. These voids allow for faster water absorption.
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The water adsorption values recorded for both the ferrite powder and the concentrate even after 192
h are insignificant. This aspect proves a good resistance of the electromagnetic shielding effect of these
polymer composites to the action of water.
3.3. FTIR analyses
FTIR spectra were recorded on the primary ferrite and on neat PP polymer samples (Figure 4).
Figure 4. Comparative FTIR spectra recorded on primary ferrite and neat PP polymer samples
Figure 5 shows the spectra recorded on the PP/Fe12SrO19 polymer composites (M1-M4).
Figure 5. Comparative FTIR spectra recorded
on the obtained polymer composites
For M3, the sample obtained was studied in comparison with the one subjected to heat treatment
(aged sample) for 168 h/ 65oC (Figure 6).
MATERIALE PLASTICE
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Figure 6. Comparison of FTIR spectra for initial
and thermally aged samples
The recorded FTIR spectra (Figure 4-6) show characteristic bands of the analyzed materials.
Polypropylene (PP) shows specific maxima at: 2950 cm-1 (CH3 asymmetric stretching), 2918 cm-1
(CH2 asymmetric stretching), 2870 cm-1 (CH3 stretching), 2839 cm-1 (CH2 stretching) [40, 41], 1450cm-
1 and 1377 cm-1 (CH3 symmetric bending), 1166 cm-1 (C-H and CH3), 997 cm-1 (C-C and CH3), 973cm-
1 (C-C and CH3), 840 (C-H) and 808 (C-C) cm-1. Strontium ferrite shows FTIR maxima [39] in the low
frequency spectral range at 580 cm-1 and 539 cm-1 characteristics of Fe-O and Sr-O tetrahedral bonds,
respectively at 428 cm-1 and 442 cm-1, characteristic of octahedral bonds Fe-O and Sr-O.
The FTIR spectra recorded on the strontium ferrite granules (Figure 4) show, in addition to the
characteristic peaks of ferrite (428 cm-1 and 580 cm-1) also the characteristic peaks of the powder coating
matrix with bands characteristic of polyamide [42-46]. The FTIR spectra recorded on the PP/Fe12SrO19
composite samples (Figure 5) show all the characteristic bands above, no major spectral changes being
highlighted. However, depending on the added ferrite concentration, a variation in the intensity of the
characteristic ferrite peaks (428 cm-1 and 580 cm-1) is observed. Exposure to an external stress factor
(such as temperature) did not show spectral changes suggesting certain degradation of the material
structure (Figure 6).
3.4. UV-Vis analyses
The experimental results obtained from these analyzes are presented in Figure 7.
(a)
(b)
Figure 7. UV-Vis spectra for (a) the non-thermally treated composites
M0 - green, M1 - black and M2 - pink and (b) the thermally treated composites
(thermally aged samples) 168 h at 65°C M2 - red and M4 - blue
0.5
1.3
0.6
0.8
1
1.2
200 800400 600
Abs
Wavelength [nm]
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The samples of composite materials, based on PP/filler (Fe12SrO19 powder/ Fe12SrO19 concentrate
granules) analyzed, show broad absorption maximum values with a plateau between 500-600 nm and
absorbance around 1.3 arbitrary units. The appearance of the UV-Vis spectra indicates the homogeneity
of the samples obtained with the functional filler of strontium ferrite.
Ageing the samples with temperature (168 h/65°C) resulted in minor changes in the UV-Vis
spectrum.
In conclusion, ageing for 168 h at 65oC does not lead to perceptible changes.
3.5. Dielectric tests
Dielectric tests were performed in the range 10 kHz - 8 MHz for the classification of composite
materials in terms of electrical conductivity, which is calculated using formula (6).
Figure 8 shows the variations of tg and for the studied composite materials.
(a)
(b)
Figure 8. Variations of (a) tg and (b) with frequency of the analyzed composite materials
From the comparative analysis of the obtained experimental data related to tg for the composite
materials with fillers compared to the natural polymer, it can be said that the addition of fillers leads to
an increase in dielectric losses and at the same time in electrical conductivity.
Table 7 shows the percentage increase in tg and values compared to the natural polymer (M0).
Table 7. Variations of tg and , relative to the natural polymer (M0)
% increase
compared to M0
tg M1
M1
tg M2
M2
tg M3
M3
tg M4
M4
10.92
15.86
15.43
21.69
17.79
17.54
20.16
18.60
It is found that the composites with the highest percentage of Fe12SrO19 and M2 powder respectively
(It is found that the composites with the highest percentage of Fe12SrO19 and M2 powder respectively
(about 22%) show the greatest increases in electrical conductivity. If one analyzes the increase in
electrical conductivity of the composites relative to the PP polymer matrix, it can be said that, when
adding 30% ferrite, M2 increases with about 22% relative to PP, while M4 increases with about 19%
relative to PP. This can be justified by the fact that in the Fe12SrO19 concentrate there is a small amount
of PA12, used in ferrite powder encapsulation.
3.6. Magnetic tests
3.6.1. The hysteresis cycles (Figure 9) were performed on samples with maximum filler concentration
(e.g., M2 and M4). These indicate that at the same percentage of added ferrite, Sr ferrite powder provides
a higher magnetic moment than ferrite concentrate. It should also be noted that no sample reached
magnetic saturation.
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Figure 9. Hysteresis cycle for M2 and M4
3.6.2. The estimation of the electromagnetic shielding efficiency was calculated with the help of
formulas 3-8 using the magnetic permeability values. For the analyzed electromagnetic materials, the
magnetic permeability was determined in the range of 40Hz - 25MHz. Figure 10 shows the variation of
magnetic permeability with frequency in alternating current of composite materials M0-M4 with
maximum ferrite concentration.
Figure 10. Variation of magnetic permeability for
composite materials M1- M4
It is found that the materials with maximum percentage of filler (respectively 30%) have the highest
magnetic permeability, as shown in Figure 10.
The experimental values of the magnetic permeabilities allowed the calculation of SE reflection and
SE absorption using formula 8.
It is found that for these materials, up to 30 MHz there is shielding by reflection (SER) and a very
small shielding by absorption (SEA), this being almost negligible.
This can be explained by the fact that absorption shielding also depends on the thickness of the
samples, which is very small, between 1.9 - 2.75 mm. The variation of the reflection shielding efficiency
(SER) and absorption shielding efficiency (SEA) with the frequency for the M1-M4 composite materials
is shown in Figure 11.
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(a)
(b)
Figure 11. a) Reflection shielding efficiency (SER) and b) absorption shielding
efficiency (SEA) for the M1-M4 composite materials
The maximum values of the SER and SEA for the analyzed materials are summarized in Table 8.
Table 8. Maximum values of SER and SEA for the M1-M4 composite materials
Sample
code
SER
(dB)
SEA
(dB)
Frequency
(Hz)
SrFe12O19 powder/concentrate
content (wt.%)
M1
−67.8
0.01
4.05E+06
25
M2
−71.5
0.06
6.58E+06
30
M3
−56.7
0.04
4.96E+06
25
M4
−60.1
0.14
8.66E+06
30
In Table 8 one can notice that the M2 material has the highest reflection shielding efficiency (SER)
among the analyzed materials. If we compare the SER results for the M1 and M2 materials made with
SrFe12O19 powder filler, it is found that an increase in filler concentration from 25 to 30 wt.% leads to
an increase in the SER value by about 11%, while for the M3 and M4 materials with SrFe12O19
concentrate, an increase of about 6% is observed. This means that the powder leads to better shielding
properties. The values for the same concentration samples (M4-M2 composites with 30% concentration
and M3-M1 with 25% concentration) recorded maximum reflection SE of about 76 % for M4 relative
to M2 and about 82 % for M3 relative to M1.
This is explained by the fact that when obtaining composites using SrFe12O19 concentrate as a filler
(M3 and M4), homogenization with the polypropylene (PP) polymer matrix is hampered by the
polyamide (PA) existent in the F1-type ferrite concentrate, which is not miscible with polypropylene
and during rheological mixing in the melt creates repulsive forces that lead to the appearance of defects,
resulting in a decrease in reflection SE.
3.7. ESD functional tests
Testing of the ESD properties of the composites was carried out in an accredited Renar EMC-EMI
laboratory of the Technical University of Iași with up-to-date calibrated equipment.
Tested:
- Surface resistance Rs according to Standard Test EN 61340-2-3
- Point-to-point resistance Rp according to Standard Test EN 61340-5-1
The minimum requirements for materials usable as protection against electrostatic discharges are:
- Surface resistance Rs maximum 106-108 Ω x m [47]
- Point to point resistance Rp 104 - 1010 Ω [48]
The experimental results obtained are presented in Table 9.
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Table 9. Comparative dielectric and ESD data
Code
10Hz permittivity
ΔTg 10 Hz
Surface resistance Rs
Point to point
resistance Rp
M0
2.25
10-4
1014
1016
M1
3.46
1.75x10-2
2.2x107
4x109
M2
3.73
2.7x10-2
1.2x107
2x109
M3
3.19
1.4x10-2
9.5x107
4x1010
M4
3.31
2x10-2
7x107
2x1010
Composites recommended for simultaneous EMI and ESD functionality are in order of their
performance, namely: M2 (with 30% ferrite powder) and then M1 (with 25% ferrite powder). The M4
composite (with 30% ferrite concentrate) which has surface resistivity and point resistance very close to
the imposed value can also be used at the limit.
4. Conclusions
In this work, 5 experimental models of PP/Fe12SrO19 polymer composite materials with mass
concentrations of 100/0, 75/25 and 70/30 and coding M0-M4 were obtained by melt injection and
characterized. Strontium ferrite (Fe12SrO19) was used in powder form for samples M1 and M2 and
concentrate for samples M3 and M4. Among these, those that show performance in simultaneous
applications in protection against electrostatic discharges and electromagnetic pulses were chosen. The
determined values analysis and the characterization of the obtained polymer materials was carried out
based on the results of the experimental tests performed.
Following these characterizations, the composite coded with M2 with the composition PP/Fe12SrO19
in a concentration of 70/30 was chosen as the optimal variant. By comparing the behavior of powder
and granule type composite materials, it is found that those obtained using ferrite concentrate are more
homogeneous but present lower SER values than those with ferrite powder filler. All the samples of
composite mixtures based on ferrite presented insignificant values regarding the degree of water
adsorption. This shows that they have a good stability to the action of water, therefore a good resistance
to both the electromagnetic shielding effect and the electrostatic transfer of the materials.
The paper concludes with functional tests for ESD and EMI applications. For these applications, the
surface resistance Rs and the point-to-point resistance Rp were tested. The composites recommended
for simultaneous EMI and ESD functionalities in the order of their performance are samples M2 (with
30% ferrite powder), M1 (with 25% ferrite powder) and at the limit the composite M4 (with 30%
concentrate with ferrite powder) which presents characteristics (surface resistivity and point resistance
very) close to the imposed value.
The final conclusion of the obtained experimental results demonstrates that composites with superior
simultaneous EMI and ESD shielding properties can be made. The advantages of these composites are:
- can be carried out on a large scale,
- are cheap,
- have ferritic powder type filling in minimum concentration, and
- they are easy-to-process thermoplastic materials for applications in the electrotechnical, electronics
and automotive industries.
Acknowledgments: This work was supported by Romanian Ministry of Research, Innovation and
Digitalization, project number 25PFE/30.12.2021-Increasing R-D-I capacity for electrical engineering-
specific materials and equipment with reference to electromobility and “green” technologies within
PNCDI III, Programme 1 and project number PN23140201-42N/2023, carried out within National
Institute for Research and Development in Electrical Engineering ICPE—CA Bucharest.
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Manuscript received: 12.04.2024
