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Superhydrophobic/Flame Retardant/EMI Shielding Fabrics: Manufacturing Techniques and Property Evaluations

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  • Tiangong University

Abstract and Figures

Electromagnetic pollution interferes with electronic equipment in proximity and jeopardizes human health, which urges the development of electromagnetic interference (EMI) shielding materials. It is urgent to develop electromagnetic interference (EMI) shielding materials. However, the preparation of materials with superhydrophobicity, flame retardancy and EMI shielding properties is still challenging. In this study, we invented a core-spun yarn feeding device, which uses polysulfonamide (PSA) roving as a coating material and stainless steel wire as the core material to prepare a conductive core-spun yarn, which solves the problem of the wire having an easily exposed fabric surface. The finally prepared conductive fabric was subjected to Waterproof 2P hydrophobic treatment to form a superhydrophobic flame-retardant EMI shielding fabric. The results show that the hydrophobic treatment creates a thin film over the woven fabrics, and the contact angle of the fabric surface can reach 155°. The hydrophobic treatment will not damage the shielding effect and slightly increase the dB value. The average dB value of PSA-SS-1’ and PSA-SS-2’ are increased by 0.82 dB and 1.92 dB, respectively. When composed of conductive wrapped yarns for both the warp and weft yarns, the electromagnetic interference shielding effectiveness (EMI SE) of conductive fabrics is beyond 30 dB at 0–3000 MHz and the burnt depth is shorter than 40 mm. As for real applications, superhydrophobic/flame retardant/EMI SE fabrics can be used in a moist and complex environment with retaining conductivity and shielding effectiveness.
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applied
sciences
Article
Superhydrophobic/Flame Retardant/EMI Shielding
Fabrics: Manufacturing Techniques and
Property Evaluations
Hao-Kai Peng 1,2,3, Yanting Wang 1, Ting-Ting Li 1,2 , Ching-Wen Lou 1,3,4,5,6,7,* , Qi He 1and
Jia-Horng Lin 3,4,6,8,9,*
1Innovation Platform of Intelligent and Energy-Saving Textiles, School of Textile Science and Engineering,
Tianjin Polytechnic University, Tianjin 300387, China; skyphk@163.com (H.-K.P.);
18722122269@163.com (Y.W.); litingting_85@163.com (T.-T.L.); h18622343633@163.com (Q.H.)
2Tianjin and Education Ministry Key Laboratory of Advanced Textile Composite Materials,
Tianjin Polytechnic University, Tianjin 300387, China
3Fujian Key Laboratory of Novel Functional Textile Fibers and Materials, Minjiang University,
Fuzhou 350108, China
4Department of Chemical Engineering and Materials, Ocean College, Minjiang University,
Fuzhou 350108, China
5Department of Bioinformatics and Medical Engineering, Asia University, Taichung 41354, Taiwan
6College of Texitle and Clothing, Qingdao University, Shangdong 266071, China
7Department of Medical Research, China Medical University Hospital, China Medical University,
Taichung 40402, Taiwan
8Laboratory of Fiber Application and Manufacturing, Department of Fiber and Composite Materials,
Feng Chia University, Taichung City 40724, Taiwan
9Department of Fashion Design, Asia University, Taichung 41354, Taiwan
*Correspondence: cwlou@asia.edu.tw (C.-W.L.); jhlin@fcu.edu.tw (J.-H.L.);
Tel.: +886-4-2451-7250 (ext. 3405) (J.-H.L.); Fax: +886-4-24510871 (J.-H.L.)
Received: 27 March 2019; Accepted: 27 April 2019; Published: 9 May 2019


Abstract:
Electromagnetic pollution interferes with electronic equipment in proximity and jeopardizes
human health, which urges the development of electromagnetic interference (EMI) shielding materials.
It is urgent to develop electromagnetic interference (EMI) shielding materials. However, the
preparation of materials with superhydrophobicity, flame retardancy and EMI shielding properties
is still challenging. In this study, we invented a core-spun yarn feeding device, which uses
polysulfonamide (PSA) roving as a coating material and stainless steel wire as the core material to
prepare a conductive core-spun yarn, which solves the problem of the wire having an easily exposed
fabric surface. The finally prepared conductive fabric was subjected to Waterproof 2P hydrophobic
treatment to form a superhydrophobic flame-retardant EMI shielding fabric. The results show that
the hydrophobic treatment creates a thin film over the woven fabrics, and the contact angle of the
fabric surface can reach 155
. The hydrophobic treatment will not damage the shielding eect and
slightly increase the dB value. The average dB value of PSA-SS-1’ and PSA-SS-2’ are increased by
0.82 dB and 1.92 dB, respectively. When composed of conductive wrapped yarns for both the warp
and weft yarns, the electromagnetic interference shielding eectiveness (EMI SE) of conductive fabrics
is beyond 30 dB at 0–3000 MHz and the burnt depth is shorter than 40 mm. As for real applications,
superhydrophobic/flame retardant/EMI SE fabrics can be used in a moist and complex environment
with retaining conductivity and shielding eectiveness.
Keywords:
superhydrophobic; flame retardant; electromagnetic interference shielding; conductive
fabric
Appl. Sci. 2019,9, 1914; doi:10.3390/app9091914 www.mdpi.com/journal/applsci
Appl. Sci. 2019,9, 1914 2 of 12
1. Introduction
Mobile communications and electronic devices have become necessities for people to acquire new
knowledge and communicate with others in the modern world [
1
,
2
]. The use of electronic products
such as laptops and cellphones inevitably generates electromagnetic interference (EMI) [
3
5
]. The
electromagnetic pollution jeopardizes people’s health, which leads to the presence of the EMI shielding
materials [
6
,
7
]. EMI shielding materials attenuate electromagnetic energy propagation by means of
absorption and reflection, thereby refraining electromagnetic interference and pollution. The shielding
materials are qualified when they have a resistivity lower than 10
2
/cm
2
[
8
,
9
]. One simple method
of shielding EMI is adopting the conductivity of metallic materials. However, the applications of
metallic materials are restricted due to having a heavy weight, a high cost, and the diculty of the
process [
10
,
11
] and conductive polymer composites (CPC) have been developed in order to address
the issue [
12
,
13
]. Nazan et al. studied the EMI SE of cotton/metallic composite fabrics and found
that the plain weave fabrics had an optimal shielding eectiveness [
14
]. Lou et al. investigated Cu
and SS conductive fabrics, and the dierences in the lamination layer and lamination angle could
change the electromagnetic interference shielding eectiveness (EMI SE) of materials [
15
]. Chen et al.
compared the methods for gaining EMI SE and subsequently composed a complete shielding network
with improved EMI SE [
16
]. The comfort of conductive fabrics compromises when the constituent
metallic wires could not be enwrapped completely [
17
]. As a result, the conductive fabrics demonstrate
oxidation corrosion, which decreases the shielding eectiveness against electromagnetic waves.
Another issue is the stability of the electrical conductivity and, hence, the EMI shielding eciency
and reliability for the practice application of the CPC. In order to better solve the problem of
electromagnetic radiation, it is also necessary to maintain the stability of the conductivity of the
conductive material. Therefore, the shielding eciency of the conductive material will be reliable
and stable in practical applications [
18
20
]. For example, when conductive metal materials are used
under harsh conditions such as humidity, acidity and alkalinity, the materials are easy to be oxidized
or corroded, especially when the composite yarn cannot wrap the wire well [2123].
Therefore, the conductive material is preferably corrosion resistant. In fact, a fabric having
superhydrophobicity is a good candidate for achieving this goal because the superhydrophobic
material can repel water droplets, thereby preventing the aqueous solution from diusing within
the conductive fabric [
24
,
25
]. In addition to maintaining the stability of conductivity during use, the
material should also have a certain flame retardant eect to prevent fires caused by electronic equipment.
PSA fiber with good acid and alkali resistance has relatively better combustion resistance, heat
resistant property, heat stability, and a limiting oxygen index (LOI) over 33%. However, PSA fibers
have a moisture regain of 5.5%, which has a negative influence on the hydrophobicity of the resulting
conductive fabrics in a moist condition [
26
29
]. In order to develop conductive fabrics with excellent
flame retardancy, excellent hydrophobicity and excellent EMI shielding properties, our laboratory
has invented a feeding device for preparing conductive core-spun yarns, which is compared to
conventional core-spun yarn devices. A custom-made feeding device is used to produce conductive
wrapped yarns, ensuring that one or two metallic wires (i.e., the core) can be precisely wrapped in PSA
roving to prevent the exposure of metallic wires. The conductive wrapped yarns are then made into
conductive fabrics that are then processed with waterproof 2P superhydrophobic treatment, to prepare
a superhydrophobic flame-retardant electromagnetic shielding fabric. After hydrophobic treatment,
the contact angles of fabrics reached 155
and the burnt depth is shorter than 40 mm. The hydrophobic
treatment will not damage the shielding eect for which the EMI SE of PSA-SS-1
0
and PSA-SS-2
0
are
34.08 dB and 34.42 dB with electromagnetic waves of 0–3000 MHz.
Appl. Sci. 2019,9, 1914 3 of 12
2. Experimental
2.1. Materials
316L Stainless steel wires (SS) (Yuanneng Co., Ltd., Shanghai, China) have a diameter of 0.06
mm, breaking strength of 354.36 cN, and an elongation of 29.4%. PSA fibers (Shanghai T & L Co.,
Ltd., Shanghai, China) have a fiber length of 51 mm, a fineness of 1.5D, a specification of 21S/3,
a tensile strength of 207.84 cN and a tensile elongation of 8.9%. Waterproof 2P (Hefei Dong Fang Mei
Jie Molecular Material Technology Co., Ltd., Anhui, China) has a concentration of 2%. Waterproof
2P is composed of a fluorine emulsion polymer, emulsion fluid, and a weak cationic type that is
non-toxic biodegradable.
2.2. Preparation of Conductive Wrapped Yarns
A core yarn feeding device, which is specially made with a spinning frame as a drafting system,
can fully enwrap the SS wires in PSA roving in the spinning process in order to prevent the exposure
and oxidation of metallic wires (Figure 1). The number of metallic wires is adjusted to form core yarns
with dierent functions. The PSA roving with a specification of 4 g/10 m is used as the sheath while
one or two metallic wires are used as the core. The conductive wrapped yarns are made with twist
counts of 50, 60, 80, 100, and 120 turns/10 cm.
Appl. Sci. 2019, 9, x FOR PEER REVIEW 3 of 12
316L Stainless steel wires (SS) (Yuanneng Co., Ltd., Shanghai, China) have a diameter of 0.06
mm, breaking strength of 354.36 cN, and an elongation of 29.4%. PSA fibers (Shanghai T & L Co.,
Ltd., Shanghai, China) have a fiber length of 51 mm, a fineness of 1.5D, a specification of 21S/3, a
tensile strength of 207.84 cN and a tensile elongation of 8.9%. Waterproof 2P (Hefei Dong Fang Mei
Jie Molecular Material Technology Co., Ltd., Anhui, China) has a concentration of 2%. Waterproof
2P is composed of a fluorine emulsion polymer, emulsion fluid, and a weak cationic type that is
non-toxic biodegradable.
2.2. Preparation of Conductive Wrapped Yarns
A core yarn feeding device, which is specially made with a spinning frame as a drafting system,
can fully enwrap the SS wires in PSA roving in the spinning process in order to prevent the
exposure and oxidation of metallic wires (Figure1). The number of metallic wires is adjusted to
form core yarns with different functions. The PSA roving with a specification of 4 g/10 m is used as
the sheath while one or two metallic wires are used as the core. The conductive wrapped yarns are
made with twist counts of 50, 60, 80, 100, and 120 turns/10 cm.
Figure 1. The schematic diagram of the preparation process for conductive wrapped yarn.
2.3. Preparation of EMI Shielding Fabrics
A semi-automatic weaving machine (DWL 5016, Hangzhou Tianma Textile Machinery,
Zhejiang, China) is used to produce conductive woven fabrics. The PSA yarn and conductive yarn
are used as warp or weft. The four fabric specifications are shown in the Table1 (PSA-SS-1: for warp
and weft yarn is a conductive yarn wrapped in a single wire; PSA-SS-W1 indicates that the warp
yarn is PSA yarn and the weft is a conductive yarn wrapped with a wire; PSA/SS-60 means feeding
one wire with a twist of 60 turns/10 cm; PSA/SS-60‘ means feeding 2 wires, with a twist of 60
turns/10 cm, and so on).
Table 1. The characteristics of conductive woven fabrics.
Fabric Code Warp Yarn Weft Yarn Fabric Weight
(g/m2)
Thickness
(mm)
Number of
Warp Yarns
(ends/10 cm)
Number of
Weft Yarns
(picks/10 cm)
PSA-SS-1 PSA/SS-60 PSA/SS-60 228.74 0.41 120 110
PSA-SS-2 PSA/SS-60 PSA/SS-60 233.64 0.41 120 110
PSA-SS-W1 PSA PSA/SS-60 210.92 0.38 120 110
PSA-SS-W2 PSA PSA/SS-60 214.36 0.38 120 110
2.4. Preparation of Superhydrophobic/Flame Retardant/EMI Shielding Fabrics
Figure 1. The schematic diagram of the preparation process for conductive wrapped yarn.
2.3. Preparation of EMI Shielding Fabrics
A semi-automatic weaving machine (DWL 5016, Hangzhou Tianma Textile Machinery, Zhejiang,
China) is used to produce conductive woven fabrics. The PSA yarn and conductive yarn are used as
warp or weft. The four fabric specifications are shown in the Table 1(PSA-SS-1: for warp and weft
yarn is a conductive yarn wrapped in a single wire; PSA-SS-W1 indicates that the warp yarn is PSA
yarn and the weft is a conductive yarn wrapped with a wire; PSA/SS-60 means feeding one wire with a
twist of 60 turns/10 cm; PSA/SS-60‘ means feeding 2 wires, with a twist of 60 turns/10 cm, and so on).
Table 1. The characteristics of conductive woven fabrics.
Fabric Code Warp Yarn Weft Yarn Fabric Weight
(g/m2)
Thickness
(mm)
Number of Warp
Yarns (ends/10 cm)
Number of Weft
Yarns (picks/10 cm)
PSA-SS-1 PSA/SS-60 PSA/SS-60 228.74 0.41 120 110
PSA-SS-2 PSA/SS-600PSA/SS-600233.64 0.41 120 110
PSA-SS-W1 PSA PSA/SS-60 210.92 0.38 120 110
PSA-SS-W2 PSA PSA/SS-600214.36 0.38 120 110
Appl. Sci. 2019,9, 1914 4 of 12
2.4. Preparation of Superhydrophobic/Flame Retardant/EMI Shielding Fabrics
The conductive fabrics are immersed in waterproof 2P (2% o.w.f.) and compressed with a pick-up
rate of 60%, which is repeated for another cycle. Samples are then dried at 80
C for 5 min and then
stored at room temperature. Figure 2shows the resulted superhydrophobic/flame retardant/EMI
shielding fabrics.
Appl. Sci. 2019, 9, x FOR PEER REVIEW 4 of 12
The conductive fabrics are immersed in waterproof 2P (2% o.w.f.) and compressed with a
pick-up rate of 60%, which is repeated for another cycle. Samples are then dried at 80 °C for 5 min
and then stored at room temperature. Figure 2 shows the resulted superhydrophobic/flame
retardant/EMI shielding fabrics.
2.5. Characterizations
The microstructure of the superhydrophobic and conductive composite fabric was investigated
by using a scanning electron microscope (TM3030, HTTACHJ, Tokyo, Japan) at an accelerating voltage
of 5 kV. The contact angles (CAs) of the composite fabric were measured by using an optical CA
measuring device (OCA20) and a 5 μL water droplet was chosen for each CA measurement. The
thermogravimetric measurement was conducted with a thermogravimetric analyzer (TG 209F3,
NETZSCH, Bavaria, Germany) with dry nitrogen gas at a flow rate of 60 mL·min
1
. The relative
mass loss of the samples was recorded from 50 °C to 800 °C at a heating rate of 10 °C·min
1
. The
thermal properties were analyzed using a differential scanning calorimeter (NETZSCH DSC200F3,
Bavaria, Germany). Samples were heated from room temperature to 500 °C at 30 °C/min and held
for 3 min to remove the thermal history. Subsequently, the samples were cooled to 30 °C at a
cooling rate of 10 °C/min and heated again to 500 °C at 10 °C/min. The tensile properties of the core
yarns were measured using a universal force meter (HT-9101, Hong da Instrument, Shanghai,
China) with the distance between the gauges being 250 mm and the tensile rate being 300 mm/min.
EMI shielding performance of the composite fabrics was evaluated by using a spectrum analyzer
(Advantest R3132, Burgeon Instrument, Taiwan). All samples were sliced into small circular plates
with a diameter of 150 mm for the EMI shielding tests.
Figure 2. The schematic diagram of the processing procedures of hydrophobic/flame retardant/
electromagnetic interference (EMI) shielding fabrics.
3. Results and Discussion
Figure 3a,b shows the cutting section of the conductive wrapped yarns where the metallic
wires are confirmed to be wrapped in PSA roving regardless of the number of metallic wires. The
observation indicates that the employment of the custom-made feeding device produces wrapped
yarns with an intact morphology and thus solves the corrosion problem caused by the exposure of
metallic wires. Figure 3c shows the morphology of the control group (PSA-SS-W1) that is not
processed with waterproof 2P, whereas Figure 3d shows the morphology of the experimental group
(i.e., PSA-SS-W1) that undergoes superhydrophobic treatment using waterproof 2P, and the fabric
is covered with a transparent breathable film. The major component of the hydrophobic agent is
fluorine-containing an emulsion polymer. Polysiloxane is aligned along the same direction with
hydrophobic agent-CH3 being aligned outwards. Moreover, waterproof 2P is composed of silicon
Figure 2.
The schematic diagram of the processing procedures of hydrophobic/flame retardant/
electromagnetic interference (EMI) shielding fabrics.
2.5. Characterizations
The microstructure of the superhydrophobic and conductive composite fabric was investigated by
using a scanning electron microscope (TM3030, HTTACHJ, Tokyo, Japan) at an accelerating voltage of 5
kV. The contact angles (CAs) of the composite fabric were measured by using an optical CA measuring
device (OCA20) and a 5
µ
L water droplet was chosen for each CA measurement. The thermogravimetric
measurement was conducted with a thermogravimetric analyzer (TG 209F3, NETZSCH, Bavaria,
Germany) with dry nitrogen gas at a flow rate of 60 mL
·
min
1
. The relative mass loss of the samples
was recorded from 50
C to 800
C at a heating rate of 10
C
·
min
1
. The thermal properties were
analyzed using a dierential scanning calorimeter (NETZSCH DSC200F3, Bavaria, Germany). Samples
were heated from room temperature to 500
C at 30
C/min and held for 3 min to remove the thermal
history. Subsequently, the samples were cooled to 30
C at a cooling rate of 10
C/min and heated again
to 500
C at 10
C/min. The tensile properties of the core yarns were measured using a universal force
meter (HT-9101, Hong da Instrument, Shanghai, China) with the distance between the gauges being
250 mm and the tensile rate being 300 mm/min. EMI shielding performance of the composite fabrics
was evaluated by using a spectrum analyzer (Advantest R3132, Burgeon Instrument, Taiwan). All
samples were sliced into small circular plates with a diameter of 150 mm for the EMI shielding tests.
3. Results and Discussion
Figure 3a,b shows the cutting section of the conductive wrapped yarns where the metallic wires
are confirmed to be wrapped in PSA roving regardless of the number of metallic wires. The observation
indicates that the employment of the custom-made feeding device produces wrapped yarns with
an intact morphology and thus solves the corrosion problem caused by the exposure of metallic
wires. Figure 3c shows the morphology of the control group (PSA-SS-W1) that is not processed with
waterproof 2P, whereas Figure 3d shows the morphology of the experimental group (i.e., PSA-SS-W1
0
)
that undergoes superhydrophobic treatment using waterproof 2P, and the fabric is covered with a
transparent breathable film. The major component of the hydrophobic agent is fluorine-containing an
emulsion polymer. Polysiloxane is aligned along the same direction with hydrophobic agent-CH3
Appl. Sci. 2019,9, 1914 5 of 12
being aligned outwards. Moreover, waterproof 2P is composed of silicon and oxygen atoms that
interact with some atoms of the fibers to form coordination bonds and hydrogen bonds. Subsequently,
the vapor and air can penetrate the fabrics instead of the water droplets. The fabrics demonstrate a
good hydrophobic eect with CAs of 155
. The microstructure of the core-spun yarns after FR testing is
shown in Figure 3e–h. It can be showed that the fabrics do not demonstrate distinct shrinkage, cracking,
and dripping during the combustion, after which the fabrics exhibit carbonization and have a crisp
edge, retaining good fabric morphology. A film is formed on the surface of the PSA-SS-W1 fabric after
hydrophobic treatment. The outermost film will destroy the flame retardant eect of the PSA-SS-W1
fabric. This is also the damaged length of the PSA-SS-W1 sample, which is higher than that of PSA-SS-
W1’. Figure 3i shows that water droplets with dierent pH values displayed on the surface of the
superhydrophobic fabric, including acid and alkali water droplets that can stand well on the fabric
surface. This phenomenon shows that the superhydrophobic fabric can be used in harsh conditions
such as humid, acid and alkali environments. The thermal properties of fabrics were investigated by
PSA-SS-W1 and PSA-SS-W1’. The results show that the hydrophobic treatment will not destroy the
stability of the thermal properties. A more detailed discussion is shown in thermogravimetric analysis.
Appl. Sci. 2019, 9, x FOR PEER REVIEW 5 of 12
and oxygen atoms that interact with some atoms of the fibers to form coordination bonds and
hydrogen bonds. Subsequently, the vapor and air can penetrate the fabrics instead of the water
droplets. The fabrics demonstrate a good hydrophobic effect with CAs of 155°. The microstructure
of the core-spun yarns after FR testing is shown in Figure 3e–h. It can be showed that the fabrics do
not demonstrate distinct shrinkage, cracking, and dripping during the combustion, after which the
fabrics exhibit carbonization and have a crisp edge, retaining good fabric morphology. A film is
formed on the surface of the PSA-SS-W1 fabric after hydrophobic treatment. The outermost film
will destroy the flame retardant effect of the PSA-SS-W1 fabric. This is also the damaged length of
the PSA-SS-W1 sample, which is higher than that of PSA-SS- W1’. Figure 3i shows that water
droplets with different pH values displayed on the surface of the superhydrophobic fabric,
including acid and alkali water droplets that can stand well on the fabric surface. This phenomenon
shows that the superhydrophobic fabric can be used in harsh conditions such as humid, acid and
alkali environments. The thermal properties of fabrics were investigated by PSA-SS-W1 and
PSA-SS-W1’. The results show that the hydrophobic treatment will not destroy the stability of the
thermal properties. A more detailed discussion is shown in thermogravimetric analysis.
Figure 3. (a,b) The scanning electron microscope (SEM) image of Core yarn with different number of
wires; (c) SEM image of the warp yarn is PSA yarn and the weft is a conductive yarn wrapped with
a wire (PSA-SS-W1); (d) SEM image of PSA-SS-W1; (e,f) SEM image after burning of
PSA-SS-W1conductive fabric (g,h): SEM image after burning of PSA-SS-W1 conductive fabric; (i)
Photograph displaying water droplets with different pH values on the superhydrophobic fabric
surface; (j) and (k) Thermal properties of fabrics before and after superhydrophobic treatment.
3.1. Breaking Strength of Conductive Wrapped Yarns
Figure 4 shows the breaking strength of conductive wrapped yarns as related to the twist
counts. The breaking strength is correlated with the level of twisting. Increasing the twist counts
first increases and then decreases the breaking strength. As for the wrapped yarns composed of one
metallic wire, the optimal twist counts is 60 turns/10 cm with a maximum breaking strength of 1.67
cN/dtex. As for the wrapped yarns composed of two metallic wires, the optimal twist counts is 60
turns/10 cm with a maximum breaking strength of 1.02 cN/dtex. A low twist count renders the
wrapped yarns with uneven strength lengthwise, which generates a greater number of rounds for
weak ring arrangement. Hence, the wrapped yarns have a higher strength where the weak rings are
Figure 3.
(
a
,
b
) The scanning electron microscope (SEM) image of Core yarn with dierent number of
wires; (
c
) SEM image of the warp yarn is PSA yarn and the weft is a conductive yarn wrapped with a wire
(PSA-SS-W1); (
d
) SEM image of PSA-SS-W1
0
; (
e
,
f
) SEM image after burning of PSA-SS-W1
0
conductive
fabric (
g
,
h
): SEM image after burning of PSA-SS-W1 conductive fabric; (
i
) Photograph displaying water
droplets with dierent pH values on the superhydrophobic fabric surface; (
j
,
k
) Thermal properties of
fabrics before and after superhydrophobic treatment.
3.1. Breaking Strength of Conductive Wrapped Yarns
Figure 4shows the breaking strength of conductive wrapped yarns as related to the twist counts.
The breaking strength is correlated with the level of twisting. Increasing the twist counts first increases
and then decreases the breaking strength. As for the wrapped yarns composed of one metallic wire,
the optimal twist counts is 60 turns/10 cm with a maximum breaking strength of 1.67 cN/dtex. As for
the wrapped yarns composed of two metallic wires, the optimal twist counts is 60 turns/10 cm with
a maximum breaking strength of 1.02 cN/dtex. A low twist count renders the wrapped yarns with
uneven strength lengthwise, which generates a greater number of rounds for weak ring arrangement.
Appl. Sci. 2019,9, 1914 6 of 12
Hence, the wrapped yarns have a higher strength where the weak rings are situated rather than other
parts. An increase in the twist counts causes the fibers to incline and decreases the axial force of the
core yarns. Therefore, the wrapped yarns demonstrate a lower strength. In addition, the twisting
process exerts prestress onto the fibers, attenuating the ability of fibers to withstand a force. To sum
up, the core and the sheath of the wrapped yarns jointly form a compact structure and contribute to
a greater cohesion when the twist counts increase. Meanwhile, the amount of PSA roving per unit
length also increases, which improves the strength and elongation of the wrapped yarns. Conversely,
excessive twist counts have a negative influence on the axial force of the wrapped yarns which, in turn,
interferes with the mechanical properties.
Appl. Sci. 2019, 9, x FOR PEER REVIEW 6 of 12
situated rather than other parts. An increase in the twist counts causes the fibers to incline and
decreases the axial force of the core yarns. Therefore, the wrapped yarns demonstrate a lower
strength. In addition, the twisting process exerts prestress onto the fibers, attenuating the ability of
fibers to withstand a force. To sum up, the core and the sheath of the wrapped yarns jointly form a
compact structure and contribute to a greater cohesion when the twist counts increase. Meanwhile,
the amount of PSA roving per unit length also increases, which improves the strength and
elongation of the wrapped yarns. Conversely, excessive twist counts have a negative influence on
the axial force of the wrapped yarns which, in turn, interferes with the mechanical properties.
0.0
0.4
0.8
1.2
1.6
140
120
100
80
60
Tenacity (cN/dTex)
50
(a)
turns/10cm
0.0
0.2
0.4
0.6
0.8
1.0
1.2
120'
100'
80'
60'
Tenacity (cN/dTex)
50'
(b)
turns/10cm
Figure 4. The breaking strength of conductive wrapped yarns as related to the twist counts. (a) one
metallic wire; (b) two metallic wires.
3.2. EMI Shielding Effectiveness of Conductive Fabrics
The four types of fabrics all demonstrate an EMI SE that is highly dependent on whether the
metallic wires and fabrics build a complete shielding network. Furthermore, the employment of
superhydrophobic treatment has a positive influence on the EMI SE. When composed of a higher
density, the fabrics have a smaller porosity and greater EMI SE [30,31]. After the superhydrophobic
treatment, the fabrics are enwrapped in transparent films that decrease the distance among fibers to
a certain extent and thus strengthens the EMI SE of the conductive fabrics. Figure 5 shows that
when both the warp and weft yarns are composed of conductive wrapped yarns, the conductive
fabrics exhibit a higher EMI SE comparing to those composed of conductive wrapped yarns as weft
yarns. In particularly, PSA-SS-1, PSA-SS-2, PSA-SS-1, and PSA-SS-2 have EMI SE values of 33.26,
32.50, 34.08, and 34.42 dB at frequencies of 0–3000 MHz respectively, which refers to a 99%
shielding effectiveness, suggesting that the conductive fabrics have a good EMI SE. Especially at
1000–2500 MHz, the fabrics have EMI SE of 3050 dB. Furthermore, the number of metallic wires
only has a marginal influence on the EMI SE because EMI SE is primarily related to a
well-established shielding network.
The shielding materials that suit the majority of electronic products are required to be able to
shield incident electromagnetic waves between 30 and 1000 MHz, and an EMI SE of 35 dB is
deemed to effectively block electromagnetic waves. Accordingly, the proposed conductive fabrics
are also suitable for industry and commercial electronic equipment. With PSA roving as warp yarns,
the conductive fabrics have an average EMI SE lower than 10 dB, indicating a low EMI SE.
Although the difference in both of the number of laminations as well as lamination angle is helpful
to the EMI SE, it also increases the thickness of the fabrics which is detrimental to the specific
shielding effectiveness (SSE, the SE per unit volume). The EMI SE is based on the formation of a
shielding network that is formed in the conductive fabrics. Using conductive yarns as both the
warp and weft yarns can build a complete shielding network and yields a good shielding effect. If
the conductive fabrics only have conductive yarns as the weft yarns, the absence of a shielding
network leads to a low EMI SE.
Figure 4.
The breaking strength of conductive wrapped yarns as related to the twist counts. (
a
) one
metallic wire; (b) two metallic wires.
3.2. EMI Shielding Eectiveness of Conductive Fabrics
The four types of fabrics all demonstrate an EMI SE that is highly dependent on whether the
metallic wires and fabrics build a complete shielding network. Furthermore, the employment of
superhydrophobic treatment has a positive influence on the EMI SE. When composed of a higher
density, the fabrics have a smaller porosity and greater EMI SE [
30
,
31
]. After the superhydrophobic
treatment, the fabrics are enwrapped in transparent films that decrease the distance among fibers to a
certain extent and thus strengthens the EMI SE of the conductive fabrics. Figure 5shows that when
both the warp and weft yarns are composed of conductive wrapped yarns, the conductive fabrics
exhibit a higher EMI SE comparing to those composed of conductive wrapped yarns as weft yarns. In
particularly, PSA-SS-1, PSA-SS-2, PSA-SS-1
0
, and PSA-SS-2
0
have EMI SE values of 33.26, 32.50, 34.08,
and 34.42 dB at frequencies of 0–3000 MHz respectively, which refers to a 99% shielding eectiveness,
suggesting that the conductive fabrics have a good EMI SE. Especially at 1000–2500 MHz, the fabrics
have EMI SE of 30–50 dB. Furthermore, the number of metallic wires only has a marginal influence on
the EMI SE because EMI SE is primarily related to a well-established shielding network.
The shielding materials that suit the majority of electronic products are required to be able to
shield incident electromagnetic waves between 30 and 1000 MHz, and an EMI SE of 35 dB is deemed to
eectively block electromagnetic waves. Accordingly, the proposed conductive fabrics are also suitable
for industry and commercial electronic equipment. With PSA roving as warp yarns, the conductive
fabrics have an average EMI SE lower than 10 dB, indicating a low EMI SE. Although the dierence in
both of the number of laminations as well as lamination angle is helpful to the EMI SE, it also increases
the thickness of the fabrics which is detrimental to the specific shielding eectiveness (SSE, the SE
per unit volume). The EMI SE is based on the formation of a shielding network that is formed in the
conductive fabrics. Using conductive yarns as both the warp and weft yarns can build a complete
shielding network and yields a good shielding eect. If the conductive fabrics only have conductive
yarns as the weft yarns, the absence of a shielding network leads to a low EMI SE.
Appl. Sci. 2019,9, 1914 7 of 12
Appl. Sci. 2019, 9, x FOR PEER REVIEW 7 of 12
To further demonstrate the highly efficient EMI shielding of the conductive composite fabrics,
the shielding effectiveness per unit volume (SSE) and specific SSE/t of the fabric based EMI
shielding material are discussed in Figure 5d and Table 2 [31,32]. It can be found that the PSA-SS-1
and PSA-SS-2 superhydrophobic and conductive composite fabric in this study possesses a very
high SSE/t (1623 dB·cm2/g and 1617 dB·cm2/g). The SSE value of the conductive fabric is related to
the thickness of the fabric, the density of the fabric, and the total dB value. The larger the SSE value,
0 500 1000 1500 2000 2500 3000
0
10
20
30
40
50
60
70
80
Frequency (MHz)
PSA-SS-W1
PSA-SS-W2
PSA-SS-1
PSA-SS-2
EMI SE(dB)
46.27dB
31.63dB
a
0 500 1000 1500 2000 2500 3000
0
10
20
30
40
50
60
70
Frequency (MHz)
PSA-SS-W1'
PSA-SS-W2'
PSA-SS-1'
PSA-SS-2'
EMI-SE(dB)
44.89dB
33.8dB
b
0246810
X Axis Title
PSA-SS-W1 PSA-SS-W2 PSA-SS-1 PSA-SS-2
5
10
15
20
25
30
35
average EMI SE (dB)
Hydrophobic fabric
sample
c
0 500 1000 1500 2000 2500 3000
0
500
1000
1500
2000
2500
Frequency(MHz)
PSA-SS-W1'
PSA-SS-W2'
PSA-SS-1'
PSA-SS-2'
SSE/t(dBcm
2
g
-1
)
d
Figure 5. (a) The electromagnetic interference shielding effectiveness (EMI SE) of four fabrics
without hydrophobic treatment; (b) the EMI SE of four fabrics with hydrophobic treatment; (c) The
average EMI SE value of samples before and after hydrophobic treatment; (d) the shielding
effectiveness per unit volume (SSE) values of hydrophobic fabrics.
Table 2. The shielding effectiveness per unit volume (SSE) and SSE/t of four types of fabrics.
Fabric Type Thickness
(mm)
Density
(g/cm3)
EMI SE
(dB)
SE/t
(dB/mm)
SSE
(dB cm3g-1)
SSE/t
dB cm2g-1
PSA-SS-W1 0.41 0.56 10.64 25.95 19 463.43
PSA-SS-W2 0.41 0.57 9.38 22.87 16.46 401.33
PSA-SS-1 0.38 0.55 34.08 89.68 61.96 1623.98
PSA-SS-2 0.38 0.56 34.42 90.57 61.46 1617.38
3.3. The Permittivity of Conductive Fabrics
The permittivity’ real part (ε’) represents the polarization level of the conductive fabrics in an
external electric field. A high permittivity real part indicates the higher polarization ability of the
material. Similarly, the permittivity’s imaginary part (ε’’) represents the energy loss caused by the
rearrangement of the electric dipole moment for the conductive fabrics in an external electric field.
A high imaginary part indicates a greater loss capacity against electromagnetic waves. In addition,
the loss tangent characterizes the absorption attenuation capability of the materials, and thus a
greater loss tangle means an equivalently better absorbing property [33–35].
Figure 6 shows that PSA-SS-1 and PSA-SS-2 which are composed of conductive yarns as both
warp and weft yarns have ε’ and ε’’ values that are higher than those of PSA-SS-W1 and
PSA-SS-W2 which have only weft yarns that are composed of conductive yarns. PSA-SS-1 and
Figure 5.
(
a
) The electromagnetic interference shielding eectiveness (EMI SE) of four fabrics without
hydrophobic treatment; (
b
) the EMI SE of four fabrics with hydrophobic treatment; (
c
) The average
EMI SE value of samples before and after hydrophobic treatment; (
d
) the shielding eectiveness per
unit volume (SSE) values of hydrophobic fabrics.
To further demonstrate the highly ecient EMI shielding of the conductive composite fabrics,
the shielding eectiveness per unit volume (SSE) and specific SSE/t of the fabric based EMI shielding
material are discussed in Figure 5d and Table 2[
31
,
32
]. It can be found that the PSA-SS-1
0
and
PSA-SS-2
0
superhydrophobic and conductive composite fabric in this study possesses a very high SSE/t
(1623 dB
·
cm
2
/g and 1617 dB
·
cm
2
/g). The SSE value of the conductive fabric is related to the thickness
of the fabric, the density of the fabric, and the total dB value. The larger the SSE value, the better the
shielding eect.
Table 2. The shielding eectiveness per unit volume (SSE) and SSE/t of four types of fabrics.
Fabric Type Thickness
(mm)
Density
(g/cm3)
EMI SE
(dB)
SE/t
(dB/mm)
SSE
(dB cm3g1)
SSE/t
(dB cm2g1)
PSA-SS-W100.41 0.56 10.64 25.95 19 463.43
PSA-SS-W200.41 0.57 9.38 22.87 16.46 401.33
PSA-SS-100.38 0.55 34.08 89.68 61.96 1623.98
PSA-SS-200.38 0.56 34.42 90.57 61.46 1617.38
3.3. The Permittivity of Conductive Fabrics
The permittivity’ real part (
ε
’) represents the polarization level of the conductive fabrics in an
external electric field. A high permittivity real part indicates the higher polarization ability of the
material. Similarly, the permittivity’s imaginary part (
ε
”) represents the energy loss caused by the
rearrangement of the electric dipole moment for the conductive fabrics in an external electric field.
A high imaginary part indicates a greater loss capacity against electromagnetic waves. In addition, the
loss tangent characterizes the absorption attenuation capability of the materials, and thus a greater loss
tangle means an equivalently better absorbing property [3335].
Appl. Sci. 2019,9, 1914 8 of 12
Figure 6shows that PSA-SS-1 and PSA-SS-2 which are composed of conductive yarns as both
warp and weft yarns have
ε
’ and
ε
” values that are higher than those of PSA-SS-W1 and PSA-SS-W2
which have only weft yarns that are composed of conductive yarns. PSA-SS-1 and PSA-SS-2 have a
higher storage energy capacity, higher dielectric loss capability, and better EMI SE than PSA-SS-W1 and
PSA-SS-W2 because of a higher polarization ability and more loss capacity. Additionally, the shielding
mechanisms of EMI SE are absorption, reflection, and multiple reflections. Taking PSA-SS-1 as an
example, the
ε
’ is between 4 and 6 and the
ε
” is between 0 and 1.2, and the latter is smaller than the
former. Due to the low absorbing ability and high polarization, PSA-SS-A thus shields electromagnetic
waves primarily by means of reflection.
Appl. Sci. 2019, 9, x FOR PEER REVIEW 8 of 12
PSA-SS-2 have a higher storage energy capacity, higher dielectric loss capability, and better EMI SE
than PSA-SS-W1 and PSA-SS-W2 because of a higher polarization ability and more loss capacity.
Additionally, the shielding mechanisms of EMI SE are absorption, reflection, and multiple
reflections. Taking PSA-SS-1 as an example, the ε’ is between 4 and 6 and the ε’’ is between 0 and
1.2, and the latter is smaller than the former. Due to the low absorbing ability and high polarization,
PSA-
0 200 400 600 800 1000
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Frequency (MHz)
PSA-SS-1
PSA-SS-2
PSA-SS-W1
PSA-SS-W2
a
Permittivity' real part (ε')
0 200 400 600 800 1000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Permittivity' real part (ε '')
Frequency (MHz)
PSA-SS-1
PSA-SS-2
PSA-SS-W1
PSA-SS-W2
b
0 200 400 600 800 1000
-0.1
0.0
0.1
0.2
0.3
0.4
Frequency (MHz)
PSA-SS-1
PSA-SS-2
PSA-SS-W1
PSA-SS-W2
c
tanθ
Figure 6. The influence of different wire content fabrics on the (a) permittivity’s real part (ε’); (b)
permittivity’s imaginary part (ε’’) and (c) loss tangent (tanθ).
3.4. The Effects of Superhydrophobic Treatment on TG, DSC and Fabric Burnt Length
Figure 7a–c and Table 3 show that the samples before and after the hydrophobic treatment did
not destroy the flame retardant property of the PSA. As for PSA-SS-W1, the thermo-gravimetric
process of the PSA fiber can be divided into two stages. In the first stage, the weight loss ratio is
small because it is caused by the evaporation of the residual solvent and small-molecule auxiliaries.
In the second stage, the weight loss rate is high because of the decomposition of the PSA fiber.
Specifically, the heat loss rate of the PSA fiber reaches the maximum at 450.8 °C, which is generally
defined as its thermal decomposition temperature. With the temperature increasing to 800 °C, the
residue accounts for 50.67%, with half of the material not being decomposed. When it comes to the
superhydrophobic-treated PSA-SS-W1, the surface is covered by waterproof 2P that consists of
more water and small molecules. They undergo a volatile cracking process continuously with the
rising temperature and thus the residue is only 29.74 % at 800 °C. However, PSA-SS-W1 has a
thermal decomposition temperature of 454.0 °C, which is comparable to that of PSA-SS-W1, because
the PSA fiber starts to decompose at this specified temperature. Usually, materials with a high
thermal decomposition temperature have a better thermal stability. Moreover, the high residue
content at the termination of the temperature indicates that there is less combustible gas. The
residue has a relatively higher heat absorption, which leads to a decrease in heat energy released by
the burning material. Subsequently, it is difficult to render fibers with thermal cracking, which
prevents the combustion of materials and improves the combustion resistance and refractory [36–
Figure 6.
The influence of dierent wire content fabrics on the (
a
) permittivity’s real part (
ε
’);
(b) permittivity’s imaginary part (ε”) and (c) loss tangent (tanθ).
3.4. The Eects of Superhydrophobic Treatment on TG, DSC and Fabric Burnt Length
Figure 7a–c and Table 3show that the samples before and after the hydrophobic treatment did not
destroy the flame retardant property of the PSA. As for PSA-SS-W1, the thermo-gravimetric process of
the PSA fiber can be divided into two stages. In the first stage, the weight loss ratio is small because
it is caused by the evaporation of the residual solvent and small-molecule auxiliaries. In the second
stage, the weight loss rate is high because of the decomposition of the PSA fiber. Specifically, the heat
loss rate of the PSA fiber reaches the maximum at 450.8
C, which is generally defined as its thermal
decomposition temperature. With the temperature increasing to 800
C, the residue accounts for 50.67%,
with half of the material not being decomposed. When it comes to the superhydrophobic-treated
PSA-SS-W1
0
, the surface is covered by waterproof 2P that consists of more water and small molecules.
They undergo a volatile cracking process continuously with the rising temperature and thus the residue
is only 29.74 % at 800
C. However, PSA-SS-W1
0
has a thermal decomposition temperature of 454.0
C,
which is comparable to that of PSA-SS-W1, because the PSA fiber starts to decompose at this specified
temperature. Usually, materials with a high thermal decomposition temperature have a better thermal
Appl. Sci. 2019,9, 1914 9 of 12
stability. Moreover, the high residue content at the termination of the temperature indicates that there
is less combustible gas. The residue has a relatively higher heat absorption, which leads to a decrease
in heat energy released by the burning material. Subsequently, it is dicult to render fibers with
thermal cracking, which prevents the combustion of materials and improves the combustion resistance
and refractory [
36
38
]. Therefore, PSA roving has a good refractory and is proven to be an eective
material in this study.
Appl. Sci. 2019, 9, x FOR PEER REVIEW 9 of 12
38]. Therefore, PSA roving has a good refractory and is proven to be an effective material in this
study.
100 200 300 400 500 600 700 800
20
30
40
50
60
70
80
90
100
110
Mass(%)
Temperature (℃)
PSA-SS-W1
PSA-SS-W1'
a
400 500 600
60
80
100
100200300400500600700800
-4
-3
-2
-1
0
DTG(%/min)
Temperature (℃)
PSA-SS-W1
PSA-SS-W1'
b
100 200 300 400 500
Heat Flow(mW/mg)
Temperature (℃)
PSA-SS-W1
PSA-SS-W1'
Endo
c
PSA-SS-1 PSA-SS-2 PSA-SS-W1 PSA-SS-W2
20
24
28
32
36
40
burning damage length(mm)
Sample
Hydrophobic treatment
d
Figure 7. (a–c) The effect of hydrophobic treatment on thermal properties of fabrics; (d) the effect of
hydrophobic treatment on fabric burning damage length.
Table 3. The Thermogravimetric analysis (TG) and differential thermogravimetry analysis (DTG)
data of fabrics under a nitrogen atmosphere as related to the employment of hydrophobic
treatment.
Sample T 5wt% (°C) Tmax1 (°C) Tmax2 (°C) Residue at 800 °C%
PSA-SS-W1 435.4 450.8 519.4 50.67
PSA-SS-W1 210.6 454.0 510.9 29.74
Based on the DSC curves, the employment of superhydrophobic treatment does not affect the
melting peaks. The DSC curves fluctuate significantly at 400450 °C, which means that the fibers
undergo a drastic reaction equivalently. Meanwhile, no carbonized phenomenon occurred,
indicating that within this temperature range, thermal cracking occurs to the fibers. Moreover, the
burned length of fabrics is dependent on the density, porosity, and structure of the fabrics. To
minimize the error, each sample processed with superhydrophobic treatment is used to compare
the length before and after combustion. Figure 7d shows that the flame-retardant property of
fabrics does not compromise for the employment of superhydrophobic treatment. The burned
length of PSA-SS-1, PSA-SS-2, PSA-SS-W1, and PSA-SS-W2 is 33.0 mm, 34.5 mm, 37.5 mm, and 36
mm, which is 1 mm, 3 mm, 4 mm, and 3 mm longer than the original length, respectively. The
average burned length of samples is shorter than 40 mm. The fabrics do not demonstrate distinct
shrinkage, cracking, and dripping during the combustion, after which the fabrics exhibit
carbonization and have a crisp edge, retaining good fabric morphology. The smoldering and
continuous burning times are both zero, and therefore, the thermal behaviors of fabrics are not
correlated with the superhydrophobic treatment.
4. Conclusions
Figure 7.
(
a
c
) The eect of hydrophobic treatment on thermal properties of fabrics; (
d
) the eect of
hydrophobic treatment on fabric burning damage length.
Table 3.
The thermogravimetric analysis (TG) and dierential thermogravimetry analysis (DTG) data
of fabrics under a nitrogen atmosphere as related to the employment of hydrophobic treatment.
Sample T 5wt% (C) Tmax1 (C) Tmax2 (C) Residue at 800 C(%)
PSA-SS-W1 435.4 450.8 519.4 50.67
PSA-SS-W10210.6 454.0 510.9 29.74
Based on the DSC curves, the employment of superhydrophobic treatment does not aect the
melting peaks. The DSC curves fluctuate significantly at 400–450
C, which means that the fibers
undergo a drastic reaction equivalently. Meanwhile, no carbonized phenomenon occurred, indicating
that within this temperature range, thermal cracking occurs to the fibers. Moreover, the burned length
of fabrics is dependent on the density, porosity, and structure of the fabrics. To minimize the error, each
sample processed with superhydrophobic treatment is used to compare the length before and after
combustion. Figure 7d shows that the flame-retardant property of fabrics does not compromise for the
employment of superhydrophobic treatment. The burned length of PSA-SS-1, PSA-SS-2, PSA-SS-W1,
and PSA-SS-W2 is 33.0 mm, 34.5 mm, 37.5 mm, and 36 mm, which is 1 mm, 3 mm, 4 mm, and 3
mm longer than the original length, respectively. The average burned length of samples is shorter
than 40 mm. The fabrics do not demonstrate distinct shrinkage, cracking, and dripping during the
combustion, after which the fabrics exhibit carbonization and have a crisp edge, retaining good fabric
Appl. Sci. 2019,9, 1914 10 of 12
morphology. The smoldering and continuous burning times are both zero, and therefore, the thermal
behaviors of fabrics are not correlated with the superhydrophobic treatment.
4. Conclusions
This study proposes using a specially designed feeding device to produce conductive corn yarns
with PSA roving as the coated material and metallic wires as the core material. The conductive corn
yarns are made into conductive fabrics and then processed with superhydrophobic treatment, forming
superhydrophobic/flame retardant/electromagnetic shielding fabrics. The test results show that treated
with waterproof 2P, the fabric CAs reached 155
and the EMI SE is also increased accordingly. The
EMI SE value of PSA-SS-1
0
and PSA-SS-2
0
is 34.08 dB and 34.42 dB with electromagnetic waves of
0–3000 MHz. Comparing to the control groups, the EMI SE value of PSA-SS-1
0
and PSA-SS-2
0
is 0.82 dB
and 1.92 dB higher. The shielding eectiveness of 99.9 % proves that the conductive fabrics are suitable
for use in harsh conditions such as humid, acid and alkali environments. Based on the permittivity
results, when composed of conductive yarns for both the warp and weft yarns, the conductive fabrics
have a polarization ability and greater loss ability against electromagnetic waves than those made of
only weft yarns being conductive yarns in an external electric field. The fabrics shield electromagnetic
waves by means of reflection. After the hydrophobic treatment with waterproof 2P, the PSA fiber
retains its inherent thermal properties demonstrated by a burned length of the conductive fabrics being
shorter than 40 mm.
Author Contributions:
In this study, the concepts and designs for the experiment are supervised by J.-H.L.
and H.-K.P.; Experiment and data processing are conducted by Y.W.; Text composition and results analysis are
performed by H.-K.P. and Y.W.; The experimental result is examined by T.-T.L., C.-W.L. and Q.H.
Acknowledgments:
This work was supported by National Natural Science Foundation of China [grant numbers
51503145, 21806121, 11702187]; the Natural Science Foundation of Tianjin City [grant numbers 18JCQNJC03400,
17JCQNJC08000]; the Natural Science Foundation of Fujian Province [grant numbers 2018J01504, 2018J01505]; the
Opening Project of Green Dyeing and Finishing Engineering Research Center of Fujian University (2017001A,
2017001B, 2017002B and 2017004B), and the Program for Innovative Research Team in University of Tianjin [grant
number TD13-5043].
Conflicts of Interest: The authors declare no conflict of interest.
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(CC BY) license (http://creativecommons.org/licenses/by/4.0/).
... In detail, the SE/t (dB cm −1 ), SSE (dB cm 3 g −1 ) and SSE/t (dB cm 2 g −1 ) were calculated according to Equations (3)-(5) and given in Table 4, where the h was the thickness and S was the areal density in Table 3. It was found that both SSE value and SSE/t value of the sample S2 at specific frequency was much smaller by comparing with other EMI fabrics [39,40], while the SE/t value was stable and higher than 960 dB cm −1 . The difference was caused by the combination of the Song Brocade fabric components and the Song Brocade fabric structure. ...
... (dB cm 2 g −1 ) were calculated according to Equations (3)-(5) and given in Table 4, where the h was the thickness and S was the areal density in Table 3. It was found that both SSE value and SSE/t value of the sample S2 at specific frequency was much smaller by comparing with other EMI fabrics [39,40], while the SE/t value was stable and higher than 960 dB cm −1 . The difference was caused by the combination of the Song Brocade fabric components and the Song Brocade fabric structure. ...
Article
Full-text available
The fabrics with electromagnetic interference (EMI) have been used in various fields. However, most studies related to the EMI fabrics focused on the improvement of the final electromagnetic shielding effectiveness (EM SE) by adjusting the preparation parameters while the breathability of the EMI fabrics was affected and the visible surficial patterns on the EMI fabric was limited. In this work, the two samples based on the Song Brocade structure were fabricated with surficial visible pattern ‘卐’. One was fabricated with silver-plated polyamide (Ag-PA) yarns and the silk yarns, the another with polyester (PET) yarns and the silk yarns. The weaving structure of the two samples were investigated by scanning electronic microscopy (SEM) and laser optical microscopy (LOM). The resistance against the EM radiation near field communication (NFC) and the ultraviolet (UV) light was also evaluated. Besides, the surface resistance, the air permeability and the water evaporation rate were investigated. The results revealed that the ‘卐’ appeared successfully on the surface of the two samples with stable weaving structure. The Ag-PA yarn-incorporated Song Brocade fabric had the EMI shielding effectiveness value around 50 dB, which was supported by the low surface resistance less than 40 Ω. The excellent NFC shielding of the Ag-PA yarn-incorporated Song Brocade was also found. The ultraviolet protection factor (UPF) value of the Ag-PA yarn-incorporated Song Brocade fabric was higher than 190. The air permeability and the evaporation rate of the Ag-PA yarn-incorporated Song Brocade fabric was higher than 99 mm/s, and 1.4 g/h, respectively. As a result, the Ag-PA yarn-incorporated Song Brocade fabrics were proposed for both the personal and the industrial scale utilization
... Superhydrophobic and conductive textiles with breathability and flexibility, not only have the characteristics of self-cleaning, anti-fouling and waterproofing [7,8], but also absorb and reflect electromagnetic waves, which is expected to prolong the lifespan. It can be widely used in the field of electromagnetic shielding textiles, such as protective sleeves for precision electronic instruments, electromagnetic radiation protective clothing, etc. [9,10]. And multi-functional textiles with high additional properties emerge gradually, which could better meet people's needs. ...
Article
Full-text available
In this work, graphene/Ag (GA/Ag) composite aerogels with the micro rough porous structure and conductive property and polydimethylsiloxane(PDMS) with the low surface energy were used to prepare super-hydrophobic cotton fabric (GA/Ag/PDMS@cotton) with conductive property was successfully prepared. The surface morphologies, chemical composition, wettability, conductive property and microwave absorption property of GA/Ag/PDMS@cotton fabric were characterized. It was shown that GA/Ag and PDMS were successfully coated onto the surface of cotton fabrics. The water contact angle of GA/Ag/PDMS@cotton was 157°. And it could make the luminous diode shining continuously. The treated cotton fabrics exhibited excellent super-hydrophobic and conductive properties. The minimum reflection loss of GA/Ag/PDMS@cotton fabric was − 28 dB, and it had a larger effective absorption bandwidth. In addition, the treated cotton fabric also showed excellent anti-fouling and self-cleaning properties. The GA/Ag/PDMS@cotton fabric cannot be wetted and polluted by water, fruit juice, milk and black tea. And it also had excellent washing durability, acid and alkali corrosion and storage stability.
... Super-hydrophobic and conductive textiles with breathability and exibility, not only have the characteristics of self-cleaning, anti-fouling and waterproo ng [7,8] , but also absorb and re ect electromagnetic waves, which is expected to prolong the lifespan. It can be widely used in the eld of electromagnetic shielding textiles, such as protective sleeves for precision electronic instruments, electromagnetic radiation protective clothing, etc [9,10] . And multi-functional textiles with high additional properties emerge gradually, which could better meet people's needs. ...
Preprint
Full-text available
In this work, graphene/Ag (GA/Ag) composite aerogels with the micro rough porous structure and conductive property and polydimethylsiloxane(PDMS) with the low surface energy were used to prepare super-hydrophobic cotton fabric (GA/Ag/PDMS@cotton) with conductive property was successfully prepared. The surface morphologies, chemical composition, wettability, conductive property and microwave absorption property of GA/Ag/PDMS@cotton fabric were characterized. It was shown that GA/Ag and PDMS were successfully coated onto the surface of cotton fabrics. The water contact angle of GA/Ag/PDMS@cotton was 157°. And it could make the luminous diode shining continuously. The treated cotton fabrics exhibited excellent super-hydrophobic and conductive properties. The minimum reflection loss of GA/Ag/PDMS@cotton fabric was − 28dB, and it had a larger effective absorption bandwidth. In addition, the treated cotton fabric also showed excellent anti-fouling and self-cleaning properties. The GA/Ag/PDMS@cotton fabric cannot be wetted and polluted by water, fruit juice, milk and black tea. And it also had excellent laundering durability, acid and alkali corrosion and storage stability.
... But the associated problem with core-spun composite yarn is the malfunctioning of the fabric due to exposure of conductive core under certain conditions. Coating a hydrophobic material on the conductive component plays a role in solving this problem without compromising the shielding performance of the fabric [103]. Another associated problem with fabrics woven and knitted from metallic yarn has lowering of their SE after dyeing, washing and pilling test due to the migration of metal fibers of the yarn structure [104,105]. ...
Article
Full-text available
The rapid proliferation of electronic devices and their operation at high frequencies has raised the contamination of artificial electromagnetic radiations in the atmosphere to an unprecedented level that is responsible for catastrophe for ecology and electronic devices. Therefore, the lightweight and flexible electromagnetic interference (EMI) shielding materials are of vital importance for controlling the pollution generated by such high-frequency EM radiations for protecting ecology and human health as well as the other nearby devices. In this regard, polymeric textile-based shielding composites have been proved to be the best due to their unique properties such as lightweight, excellent flexibility, low density, ease of processability and ease of handling. Moreover, such composites cover range of applications from everyday use to high-tech applications. Various polymeric textiles such as fibers, yarn, woven, nonwoven, knitted, as well as their hybrid composites have been extensively manipulated physically and/or chemically to act as shielding against such harmful radiations. This review encompasses from basic concept of EMI shielding for beginner to the latest research in polymeric-based textile materials synthesis for experts, covering detailed mechanisms with schematic illustration. The review also covers the gap of materials synthesis and their application on polymeric textiles which could be used for EMI shielding applications. Furthermore, recent research regarding rendering EMI shielding properties at various stages of polymeric textile development is provided for readers with critical analysis. Lastly, the applications along with environmental compliance have also been presented for better understanding.
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High-performance EMI shielding of a core-shell nanocomposite of Ni-Co MOF (core) wrapped by a heterogeneous layer of FeBTC MOF and polymeric polypyrrole (PPy) (shell) named Ni-Co/[email protected] is reported. Herein, the spherical structure Ni-Co MOF was firstly prepared and employed as nucleation sites for polymerization of pyrrole monomer utilizing FeCl3 as an in situ oxidant. Surprising, ionic iron not only played the role of oxidizing agent in the polymerization but was also able to interact with the 1,3,5-benzenetricarboxylate (BTC) organic linker existing in the frame of Ni-Co MOF to generate a new metallic MOF named FeBTC. The simultaneous formation of [email protected] in the one step polymerization inadvertently enriched both the variety of chemical components and uptake of the specific surface area to the productive nanocomposite. The as-synthesized Ni-Co/[email protected] nanocomposite displayed its best shielding efficiency at a weight ratio of 1:3 of Ni-Co MOF: pyrrole monomer, with a maximum shielding SET value of 34.1 dB compared to its value of 20.5 dB and 4 dB for the individual components of PPy and Ni-Co MOF, respectively. The sustainable EM attenuation property of Ni-Co/[email protected] can be ascribed mainly to dielectric loss along with interfacial polarization, multiple internal reflection, and multiple scattering.
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Flexible and excellent electromagnetic interference (EMI) shielding materials have attracted increasing attention due to the rapid development of intelligent flexible electronic. Herein, the lightweight, flexible, conductive and efficient EMI shielding silver (Ag)/ magnetic carbon nanotubes (mCNTs) composite coatings were decorated on polypropylene (PP) fabrics via a facile spray deposition technique. The mCNTs were fabricated with hydrogen bonding between Fe3O4 and functionalized CNTs. The conductivity and EMI shielding properties of the Ag/mCNTs composite coatings were significantly enhanced by the introduction of mCNTs. In the frequency of 8.2-12.4 GHz, the Ag/mCNTs composite coatings possessed superior EMI shielding effectiveness (SE) of 61.1 dB and specific SE (SSE/t) of 2811.78 dB cm²/g, which also displayed great stability, maintaining 91.6%, 80.2% and 69.8% of EMI SE after washing, abrasion and bending tests. Therefore, the Ag/mCNTs coated PP fabrics can be a reliable candidate to explore high-performance EMI shielding flexible electronic.
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We studied for the first time the synergistic dispersion effect of the carbon nanotube (CNT)/graphene (Gr) and polypropylene (PP)/polycarbonate (PC) (1:1) double percolation structures on conductive polymer composites (CPCs). PP/PC/CNT/Gr films with different CNT/Gr ratios are prepared by melt blending and hot pressing. Results showed that a CNT/Gr ratio of 1:1 facilitated the creation of co‐continuous double percolation structures of matrices, and the electronic conductivity reached 33.11 S/m, which was five times greater than that of the matrices containing only CNT. Results showed that the synergistic dispersion effect and the co‐continuous double percolation structures provided the matrices with conductivity through an additive effect. Meanwhile, PP/PC/CNT/Gr composite films possessed good thermal stability and hydrophobicity. They also did not exhibit thermal degradation at 300°C and had a water contact angle of 94.5°. However, PP and PC were incompatible, causing considerable brittleness of composite films macroscopically, and the films can hardly curve. To respond to this downside and improve the flexibility, a small amount of thermoplastic polyurethane (TPU) was added to the system. The presence of TPU helped combining the two materials in different phases, thereby strengthening the continuity. However, the presence of TPU adversely affected the double percolation structures and dispersion state of fillers, and subsequently decreased the conductivity.
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Electromagnetic pollution often interferes with nearby electronic equipment and poses a serious threat to the health of people. There is an urgent need to develop soft and lightweight electromagnetic interference (EMI) shielding materials. In this study, a layer-by-layer self-assembly strategy was used implemented to prepare [email protected]@[email protected] ([email protected]) films with unique core-shell and sandwich composite microstructures for electromagnetic interference (EMI) shielding. Results showed that the conductivity of the composite films was the highest at 898.72 S/m after in situ polymerization of pyrrole at low temperatures. The mechanical properties of the conductive films also increased from the initial 16.81 MPa to 22.54 MPa. The average shielding effectiveness (SE) and SSE/t of the composite films with two layers reached as high as 23.81 dB and 6764.20 dB cm² g⁻¹, respectively. This performance was caused originates from by the layer structure of the PAN film and multiple internal reflections from the interconnected core-shells and sandwich microstructures in of the [email protected] films. Therefore, this work study gave provides a new novel strategy for fabricating conductive polymer composites (CPCs) with high-performance EMI shielding.
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This research utilizes a plasma electrolysis technique to clean the surface of stainless steel 316. The resulting microstructure enhances the self-cleaning properties of the stainless steel surface. The position of the cathode electrode is varied to enlarge the total surface being processed and achieves a uniform processing surface. We propose a self-made plasma electrolysis reaction system supplemented with a 3-axis platform to control the speed at which the cathode electrode moves. The electrolyte is an aqueous solution of sodium bicarbonate (NaHCO3) and water. We obtain the optimal parameters for applied voltage, moving speed of the specimen at the cathode, and electrode distance using a one-factor-at-a-time experimental approach to achieve uniform distribution of the surface microstructure. We then observe and measure surface micrographs showing the surface roughness of the specimens after experiments, using a scanning electron microscope (SEM) and an atomic force microscope (AFM). The contact angle is experimentally proven to be greater than 100°, indicating that the surface is hydrophobic.
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We present a comprehensive experimental study on laser-induced hierarchic nano-micro periodic surface structures on brass that influences wetting behavior. Using ultra short laser pulses with a wavelength of 1030 nm, large scaled areas completely covered by laser-induced periodic surface structures (LIPSS) are generated with these areas being superimposed by ablation trenches and u-ripples. The influence of the incident laser fluence and pulse overlap on the apparent contact angle for coverage of the surface with distilled water with a surface tension of 74 mN/m are examined with its temporal evolution being observed over a period of two weeks. Our results show an initial drop in the apparent contact angle below the angle of an unstructured surface. Using atomic force microscopy, the roughness factor described by the Wenzel model is determined and compared to the roughness factor given by the apparent contact angle measurement. The ascertained difference in roughness cannot be entirely attributed to the topography of the laser-structured surface. We suggest that changes in the surface chemistry additionally alter the wetting behavior as confirmed by X-ray photoelectron spectroscopy (XPS) measurements. On a time scale of days after laser irradiation, the apparent contact angle increases into the hydrophobic range. Both the absolute apparent contact angle and this temporal change reveal a pronounced dependence on the applied laser fluence and pulse overlap. In particular, increasing both, the fluence and the pulse overlap leads to smaller apparent contact angles directly after the irradiation and to higher apparent contact angles after an observation period of two weeks.
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Electromagnetic radiation pollution has become a serious threat to human health. Wearable materials with high electromagnetic interference (EMI) shielding are highly desirable to protect people far from electromagnetic radiation. In this study, we prepared flexible and wearable materials with ultrahigh EMI shielding via a facile wet electroless deposition of Ag on surface of cotton fibers ([email protected]) in non-woven fabrics. High conductivity of ∼3333 S/m and excellent EMI shielding effectiveness (SE) of ∼71 dB were achieved by only costing the wet deposition time of 10 s with 1.61 vol% Ag coating layers, which was far more than the requirement for common commercial EMI SE of 30 dB. The EMI SE of the materials could reach ∼111 dB when the Ag plating time was 3 min. The ultrahigh EMI shielding performance was ascribed to cell-like configuration, which is the abundant interfaces and porous structure in the [email protected] non-woven fabrics, and the voids in Ag layers. The electromagnetic radiation, which was reflected at the interfaces and then absorbed in the composites, was hard to escape from the cell-like configurations. Moreover, the prepared [email protected] films could also maintain high EMI SE by suffering dozens of washing times or one thousands of bending times. For example, there were only reduction of a few dB in the EMI SE for the non-woven fabrics with the coating time of 3 min after washing 20 times or bending 1000 times. Therefore, this work gave a new strategy for fabricating wearable materials with high-performance EMI shielding.
Article
High-performance electromagnetic interference (EMI) shields are urgently needed due to the rapid development of modern electronics industry. Herein, biomass-derived highly conductive macroscopic carbon grids (MCGs) were fabricated through the carbonization of wood-pulp fabric matting. The resultant MCGs with thickness of ~0.3 mm exhibited not only exceptional EMI shielding effectiveness (SE) of ~20.3-45.5 dB positively related with their carbonization temperature or negatively associated with their empty grid size, but also semi-transparent characteristic with the transparency of ~15%-56% originated from their grid-like configurations. Moreover, an accurate EM model was constructed for the SE simulation of the MCGs in the 3-D full-wave simulation. Furthermore, it is demonstrated that the EMI SE of double-layered MCG sample could be conveniently tuned by changing the interleaving degree of the stacked grids through tiny translational motion under constant thickness, showing potential for the design of EM attenuating devices with tunable performance.
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Flammability of polymers is a major issue limiting their applications where fire safety is paramount, and a great challenge is to make polymers flame-retarding with no sacrifice of their mechanical performance. This work employed a low-cost graphite intercalation compound (GIC) as a multifunctional additive to improve the flame retardancy and mechanical strength of an elastomer by melt compounding. As characterized by cone calorimetry which presents real fire conditions, the average peak heat release rate and mass loss rate were reduced by 55% and 54% and the fire performance index enhanced by 60% at 12.0 vol% GIC, which implies a lot more time for fire victims to escape and to be saved. It inhibited the elastomer flammability through two consequential processes: (i) endothermic chemical reactions during the GIC expansion and (ii) char layer formation on composite surface protecting the polymer beneath from burning. Tensile strength, Young's modulus, elongation at break and tear strength were respectively improved by 230%, 100%, 220% and 200%. These findings demonstrate that GICs can provide both flame retardancy and reinforcement to elastomers which are extensively used in industries.
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A layer of superhydrophobic coating having good electromagnetic shielding and self-cleaning performance was fabricated on a wood surface through an electroless copper plated process. The superhydrophobic property of the wood surface was measured by contact angle (CA) and roll-off angle (RA) measurements. The microstructure and chemical composition of the superhydrophobic coating were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The analysis revealed that the microscale particles were uniformly distributed on the wood surface and the main component of the coating is metallic copper. The as-prepared Cu coatings on wood substrate exhibit a good superhydrophobicity with water contact angle about 160° and rolling angle less than 5°.
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Future electronics are expected to develop into wearable forms and an adequate stretchability is required for the forthcoming wearable electronics considering various motions occurring in human body. Along with stretchability, transparency can increase both the functionality and esthetic features in future wearable electronics. In this paper, we demonstrate, for the first time, a highly stretchable and transparent electromagnetic interference (EMI) shielding layer for wearable electronic applications with silver nanowire percolation network on elastic PDMS substrate. The proposed stretchable and transparent electromagnetic interference shielding layer shows a high electromagnetic wave shielding effectiveness even at a high tensile strain condition. It is expected for the silver nanowire percolation network based electromagnetic interference shielding layer to be beyond the conventional electromagnetic interference shielding materials and to broaden its application range to various fields that require optical transparency or non-planar surface environment such as biological system, human skin, and wearable electronics.
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In this paper, polyester woven fabric was selected as the fundamental fabric. Ferrite and silicon carbide were the underlying and surface layer absorbing agents, respectively. The influence of the content of the ferrite and silicon carbide absorbent and coating thickness on dielectric constant were discussed. Through the optimization of electromagnetic parameters, ferrite/silicon carbide double-coating polyester woven fabric absorbing materials with the best wave absorption performance were prepared. The results showed that through optimization, at high frequency (10⁵ Hz < f < 10⁷ Hz), when the ferrite content was 60%, the ferrite coating (bottom layer) had a thickness of 1.00 mm, the amount of silicon carbide was 48%, the silicon carbide coating layer (surface layer) was 0.50 mm, and the coated fabric had the best absorbing performance.