Electromagnetic microwave absorption performances of sulfonated polyacrylonitrile carbon fibers

1.

ELECTROMAGNETIC MICROWAVE
ABSORPTION PERFORMANCES OF
SULFONATED POLYACRYLONITRILE CARBON
FIBERS
D.O. Hrabovyi*, V.A. Moiseienko**, O.O. Barsukov***,
I.P. Matushko*, O.V. Mischanchuk****, and L.M. Grishchenko*
* Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
** Independent Research & Development Laboratory "200k Electronics", Kyiv, Ukraine
*** Institute of Gerontology Academy of Medical Sciences of Ukraine, Kyiv, Ukraine
****O.O. Chuiko Institute of Surface Chemistry, NAS of Ukraine, Kyiv, Ukraine

2.

PURPOSE OF THE RESEARCH
The purpose of this research is to investigate the
preparation methods and electromagnetic microwave
absorption performances of sulfurated and oxidized
polyacrylonitrile carbon fibers in order to develop a
deeper understanding of their potential as
electromagnetic wave absorbing materials. The ultimate
goal is to contribute to the development of more effective
and efficient materials for applications in fields such as
telecommunications, aerospace engineering, and
defense.

3.

problem statement
Increase in demand for electromagnetic and electrical energies
Harmful impact of radiofrequency electromagnetic radiation (EMR) on the environment
and biological systems
Need for protective materials for shielding
Carbon-based radio-absorbing materials, such as laminated carbon fibers (CFs), have
valuable properties
CFs have low density, electrical conductivity, chemical resistance, low-temperature
coefficient of linear expansion, and can combine with most polymers
Obtaining CFs comprises thermal treatment of original polymeric fibers of PAN or
hydrated cellulose fibers
CFs are excellent absorbers of electromagnetic radiation and can be used for military
purposes, protective clothing for soldiers, and military equipment
Proposed modification of the surface of the PAN CFs by chemical methods to create
new chemical and radio-frequency absorbents

4.

METHODS OF THE STUDY
●Scanning electron microscopy (SEM)
●Chemical Analysis (C.A.)
●Thermogravimetric analysis (TGA)
●Thermoprogrammed desorption with IR
registration of products (TPD IR)
●Thermoprogrammed desorption massspectrometry
(TPD MS)
●Vector network analysis method (VNA)

5.

Materials
Commercial PAN CFs have developed nanoporosity
BET surface area SBET equals 900 m2 g-1, and the total pore volume Vtot is
about 0.19 cm3 g-1
Thermal analysis data shows weight loss of about 6% in the temperature range
of 30–800 °C
Functionalization of the CFs with S-containing groups performed in two stages
First stage: Flow of argon saturated with sulfur vapor passed through PAN CFs
heated to the stated temperature of 400°C, 500°C, 600°C, 700°C, or 800°C
Second stage: Sulfurated CFs oxidized with 30% hydrogen peroxide solution at
room temperature, washed with deionized water, filtered, and dried at 120°C
in air
Selected synthesis temperature (T) used to denote the sulfurated and oxidized
PAN CFs samples as PAN/S1/T

6.

Methods
Studies of initial PAN CFs and modified PAN CFs performed using
thermogravimetry (TG) and thermoprogrammed desorption with mass
spectrometric registration of desorption products (TPD MS) on a Selmi instrument
Temperature range of the study was 30–800 °C; heating rate was 10 °C/min
Analysis for sulfur performed using the Eshka method
Scanning electron microscopy (SEM) imaging and energy-dispersive X-ray (EDX)
spectroscopy measurements carried out on a Zeiss EVO-50 SEM microscope fitted
with an X-ray energy-dispersive microanalyzer (Oxford Inca Energy 200)
S11 and S21 are important scattering parameters for measuring microwave
properties
S11 corresponds to the reflection coefficient C of electromagnetic radiation from
the surface of the material
S21 is the attenuation of electromagnetic radiation when it passes through the
tested material

7.

Microwave Absorption Performance of PAN CFs
PAN CFs are potential materials for masking coatings and protecting biological
objects from UHF fields
Measuring their microwave properties is important for understanding their
performance
Standing Wave Coefficient
Measuring minimum and maximum values of standing waves yields the voltage standing
wave ratio (VSWR) or standing wave coefficient
VSWR is related to the reflection coefficient by the equation VSWR = (1 + |C|)/(1 - |C|)
The best antenna equivalents have VSWR = 1.05, and most user equipment works with
VSWR < 2
Measurement Technique
Specialized measuring equipment called a network analyzer
was used to measure VSWR and S21 parameters
The analyzer consists of a generator and an indicator
Studies were carried out in X-band (8-12 GHz) and Ka-band
(24-39 GHz)

8.

Reflection Mode
The indicator unit controlled the generation and sweep of the frequency in the desired range
A standing wave was generated in a paired waveguide and the power magnitude of the
incident electromagnetic radiation was recorded
The electromagnetic wave interacted with the studied PAN CFs sample deposited in one layer
on a metal short-circuit, partially absorbed in it and partially reflected
The network analyzer received the value of the magnitude of the reflection of electromagnetic
radiation from the test material
Transmission Mode
The measurement technique in the transmission mode is similar to that described in the
reflection mode
The coupler immediately connects with a waveguide section with the material under
study applied over the entire cross-sectional area
The electromagnetic radiation that interacted with the PAN CFs was partially absorbed
and partially passed through it

9.

3. Results and discussion

10.

Characterization of Sulfurated and
Oxidized PAN CFs
TPD MS spectra shows CO, CO2, and water as products of
thermal desorption of oxygen-containing groups and
physisorbed water in pristine PAN CFs
Thermal desorption temperature range and SO2 desorption
maxima for sulfurated and oxidized PAN CFs shift to higher
temperatures with increasing synthesis temperature
Most thermally stable samples obtained at sulfur vapor
treatment temperatures of 700 °C and 800 °C
Sulfur concentration decreases with increasing synthesis
temperature, ranging from 0.5 mmol g^-1 to 4 mmol g^-1
TGA results show three sections of mass loss:
First range (30-130 °C) corresponds to thermal desorption of
adsorbed water
Second range (130-500 °C) corresponds to thermodesorption of
sulfo groups and oxygen-containing groups
Third range (500-800 °C) corresponds to thermal desorption of
oxygen-containing groups
PAN CFs modified with sulfur vapors show significant increase
in total weight loss compared to unmodified PAN CFs,
indicating the formation of sulfur-containing and oxygencontaining acidic groups on the surface
Total weight loss of sulfur-containing samples ranges from 0.11
to 0.28 mmol g^-1, corresponding to thermal decomposition of
sulfur-containing and oxygen-containing groups from the
surface
Weight losses and sulfur content in modified PAN CFs decrease
with increasing synthesis temperature.

11.

Microwave Absorption Properties of
Sulfurated and Oxidized PAN CFs
Experimental results of VSWR and absorption for PAN CFs with
surface modification by sulfur-containing groups
Studies performed in microwave frequency range in centimeter
and millimeter bands
Figure shows absorption curves for electromagnetic field for
studied samples annealed at temperatures from 400 to 800 °C
and without annealing
Annealing leads to a 3-fold deterioration of the absorption
properties of the carbon fiber
Samples of sulfurated and oxidized PAN CFs have a minimum
reflectance of microwave energy at frequencies above 40 GHz
Chemical modification changes VSWR by no more than 2-5%
Magnitudes of VSWR and attenuation of signal power S21
passed through one layer of the sulfurated and oxidized PAN
CFs show a close to linear decrease with increasing frequency
Return loss increases with increasing frequency
Transparency windows of about 300 MHz observed at 30 and 36
GHz, potentially useful for masking objects from radars
operating at these frequencies
Annealing of PAN CFs at temperatures up to 800 °C generally
does not lead to changes in VSWR by more than 5%
Signal power attenuation changed in the range from 2 to 5 dB
for PAN CFs treated at temperatures of 600 °C and 700 °C in the
X-frequency range
Additional studies needed to determine reasons for observed
effect at these temperatures

12.

CONCLUSIONS
1. Sulfonation of carbon fiber based on polyacrylonitrile was carried out
and samples containing sulfur-containing groups in a rather large
concentration – up to 4 mmol/g were obtained.
2. The TGA and TPD MS studies showed that the SO2 from decomposed
sulfur-containing surface groups desorbs in a wide temperature range.
The sulfogroups decomposition temperature depends on the
temperature of the sulfurization.
3. It was found that the modification of the PAN CFs with sulfur changes the
VSWR by no more than 2–5%, but the absorption of microwave radiation
by the material becomes three times lower. The latter effect is most likely
associated with the annealing of the PAN CFs at high temperatures. The
prepared samples of sulfurated and oxidized PAN CFs showed a
minimum reflection of microwave energy at frequencies above 40 GHz.