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Multifunctional cotton fabrics with graphene/polyurethane coatings
with far-infrared emission, electrical conductivity, and ultraviolet-
blocking properties
Xili Hu
a
,
b
,
1
, Mingwei Tian
a
,
b
,
c
,
**
,
1
, Lijun Qu
a
,
b
,
c
,
*
, Shifeng Zhu
a
,
b
, Guangting Han
b
,
c
a
College of Textiles, Qingdao University, Qingdao, Shandong 266071, PR China
b
Laboratory of New Fiber Materials and Modern Textile, The Growing Base for State Key Laboratory, Qingdao University, Qingdao, Shandong 266071, PR
China
c
Collaborative Innovation Center for Marine Biomass Fibers, Materials and Textiles of Shandong Province, Qingdao University, Qingdao, Shandong 266071,
PR China
article info
Article history:
Received 9 February 2015
Received in revised form
22 August 2015
Accepted 26 August 2015
Available online 29 August 2015
abstract
In order to introduce multifunctional properties into flexible cotton fabric, graphene and waterborne
anionic aliphatic polyurethane composites were prepared and then deposited on the surface of the fabric
substrate through facile pad-dry-cure process. The fabrics thus obtained were characterized by scanning
electron microscopy and Fourier transform infrared spectroscopy, and their functional properties such as
far-infrared emission, electrical conductivity, and ultraviolet (UV) blocking were studied. The coating
process enhanced the far-infrared emissivity up to 0.911 in the wavelength range of 4e18
m
m. In addi-
tion, the ultraviolet protection factor (UPF) of the fabric with 0.8-wt% graphene could reach 500, up to
60-fold higher than that of pristine cotton fabric (UPF 8.19), and its electrical resistivity was decreased
from 1.15 10
7
to 2.94 10
1
U
m, which is almost 8 orders of magnitude. The fabrics have also been
found to be stable even after 10 cycles of laundering.
©2015 Elsevier Ltd. All rights reserved.
1. Introduction
Flexible fibrous textile functional materials have recently
attracted attention for their electrical conductivity [1], antibacterial
[2],fire retardant [3], superhydrophobic [4], and ultraviolet-
blocking properties [5]. Thus, functional properties are commonly
imparted to the fabric via approaches such as pad-dry-cure [6],
ultraviolet curing [7], plasma-induced graft polymerization [8,9],
solegel method [10], magnetron sputter technique [2], and appli-
cation of molecular layer-by-layer self-assembly techniques [11].
Far-infrared rays with a longer wavelength of 6e15
m
m can
penetrate 2e3mm[12] into most biological materials and exert
strong rotational and vibrational effects at the molecular level,
leading to dilation of blood vessels and therefore, enhancement of
blood microcirculation and metabolism [13,14]. Far-infrared-
emitting materials would transform the energy absorbed from
either sunlight or heat of the human body into far-infrared rays
within a specific wavelength range, and then reemit them to the
human body [15]. Because the far-infrared radiation enhances
blood circulation and metabolism as well as promotes the recovery
of fatigued muscles, much attention has been paid to the applica-
tion of germanium and ceramics to textile materials that have close
contact with the skin, such as mattresses, sheet materials, and
clothing for therapeutic and health care purposes [13e16].
Graphene is a one-atom-thick planar sheet of sp
2
-bonded carbon
atoms that are tightly packed into a two-dimensional honeycomb
lattice, and is a basic building block for graphite materials of all other
dimensionalities [17e19]. Because of its unique electronic, optical,
thermal, and mechanical properties, graphene differs from most
conventional three-dimensional materials, and has attracted great
attention as building block for advanced materials with diverse ap-
plications [20,21]. Moreover, functional textiles can also be made
using graphene. For instance, some researchers coated textiles with
graphene or graphene composites and introduced several significant
multifunctional properties such as electrical conductivity [18,22],
*Corresponding author. College of Textiles, Qingdao University, Qingdao, Shan-
dong 266071, PR China.
** Corresponding author. College of Textiles, Qingdao University, Qingdao, Shan-
dong 266071, PR China.
E-mail addresses: tmw0303@126.com (M. Tian), profqu@126.com (L. Qu).
1
These authors equally contributed to this work.
Contents lists available at ScienceDirect
Carbon
journal homepage: www.elsevier.com/locate/carbon
http://dx.doi.org/10.1016/j.carbon.2015.08.099
0008-6223/©2015 Elsevier Ltd. All rights reserved.
Carbon 95 (2015) 625e633
ISSN号
0008-6223
antibacterial activity [17], and thermal conductivity [6]. The potential
of graphene to enhance far-infrared emission has not been explored.
Therefore, in this study, the graphene nanoplate was notably applied
as the functional unit to treat cotton fabric for attaining far-infrared
radiation and other special properties.
In this article, graphene and waterborne anionic aliphatic poly-
urethane composite were reported as a multifunctional finishing
agent for the woven cotton fabric by facile pad-dry-cure process. The
far-infrared radiation emission, electrical conductivity, and
ultraviolet-blocking properties were also investigated. Furthermore,
the durability of the aforementioned properties was evaluated.
2. Experimental
2.1. Materials
A1e3-nm-thick and 20-
m
m-long graphene nanoplate (GNP)
provided by Ningbo Moxi Science and Technology Ltd, China, was
stably dispersed in an aqueous solution of 25-mg/mL concentra-
tion. Waterborne anionic aliphatic polyurethane (WPU) was sup-
plied by Sinopharm Chemical Reagent Co., Ltd (40 wt%, particle
size <100 nm), and distilled water was used in the preparation of
all solutions. Ultrapure (100%) cotton fabric plain weave (190 g/m
2
),
supplied by Jiangsu Hongdou Industrial Co., Ltd, China, was used as
substrate fabric.
2.2. Preparation of multifunctional cotton fabrics
During initial stages of the experiment, GNP and waterborne
polyurethane composite (GNP/WPU) was prepared. GNP is exfoliated
graphite and was used as-received. First, the GNP aqueous solution
was treated continuously with ultrasound (600 W, 40 kHz) for
90 min, and its water bath was kept at a constant temperature of
23
C by circular flow. The concentration of the final GNP suspension
was about 25 mg/mL. Then, the GNP solution was mixed with WPU
aqueous emulsion under vigorous stirring for 2 h, until the mixture
becomes homogeneous. Fig. 1 depicts the GNP/WPU composite and
the corresponding chemical structures of relative compounds [5].
The cotton fabric coating was modified with GNP/WPU com-
posite using pad-dry-cure process as follows: The control fabrics
were first impregnated in aqueous solution of GNP/WPU composite
for 100 min with a liquor ratio of 1:30 at ambient conditions, and
then padded through two dips and two nips with padding nip
pressure set to obtain 100% wet pickup. Afterward, the padded
fabrics were washed with distilled water to remove the unreacted
starting compounds. Then obtained product was dried, followed by
curing in a vacuum oven at 70
C for 10 min and 120
C for 5 min.
The weight of the obtained graphene-coated fabric was 240 mg/m
2
,
and denoted as GNP/WPU-1. Afterward, the above-described entire
process was conducted in the resultant GNP/WPU-1 fabric, which
increased the graphene-coated weight of the fabric to 320 mg/m
2
,
denoted as GNP/WPU-2. Furthermore, the entire process was
applied again on GNP/WPU-2, and the resultant graphene-coated
weight of the fabric was 480 mg/m
2
, denoted as GNP/WPU-3.
2.3. Characterization and measurement
The morphology and structure of GNP material were charac-
terized by the following techniques: the morphology was investi-
gated using scanning electron microscopy (SEM, EVO18, ZEISS,
Germany), high-resolution transmission electron microscopy (HR-
TEM, HITACHI, H-7650, Japan), Fourier-transform infrared (FTIR,
Nicolet 5700, Thermo Nicolet Corp., USA) spectrometer with
wavenumber in the range of 500e4000 cm
1
(KBr disk), and X-ray
photoelectron spectroscopy (XPS Kratos AXIS His spectrometer)
with a monochromatized AI KR X-ray source (1486.6 eV photons) at
a constant dwell time of 100 m s and a pass energy of 40 eV. The
anode voltage and current were set at 15 kV and 10 mA. For peak
synthesis, a Shirley-type background was use.
Moreover, the dispersed state of the GNP in the WPU polymer
matrix was determined by zeta potential measurements. These
measurements were made using a Malvern Zetasizer Nano-ZS90
system with irradiation from a 632.8-nm HeeNe laser. The sam-
ples were filled in folded capillary cells. The zeta potential was
estimated using Smoluchowski approximation as follows [23]:
x¼hm=ε;(1)
where
h
is the solution viscosity and εis the dielectric constant of
the liquid.
The structural characterization of the resultant GNP/WPU
composite-coated fabrics was also determined using SEM (JEOL
JSM-840, Japan) and FTIR (Thermo Nicolet Corp., USA), and their
properties were measured as follows.
IR-2 dual-band infrared emissivity measuring instrument was
used to test the infrared emissivity of the coated fabrics with
wavelengths in the range of 8e14
m
mat37
C through the active
blackbody radiation source to determine normal reflectivity. (Each
sample was tested in six different parts and the average value was
obtained.) Emissivity was measured as a relative value, assuming
that the emissivity of the blackbody is 1. Infrared effect of
graphene-coated fabrics was measured using a thermal infrared
photospectrometer.
In this study, the surface electrical resistivity of the composite-
coated fabric was measured according to the American Association
of Textile Chemists and Colorists (AATCC) Test Method 76-2005 by
four-point probe technique (RTS-8, Probes Tech, China). Each spec-
imen was tested in differentparts of the fabric five times o n each side,
and the average values were obtained. The environmental tempera-
ture and relative humidity were set at 20
C and 65%, respectively.
Thermal properties (thermal conductivity and thermal resis-
tance) were measured using heat flow meter thermal conductivity
instrumentation (NETZSCH HFM 436 Lambda, Germany). The
measurable range of conductivity 0.05e8.0 W m
1
K
1
, and the
measurement method conforms to the American Society for
Testing and Materials (ASTM) standards, C518-04 and E1530-06.
Furthermore, in order to elucidate the dynamic heat transfer of
the graphene-coated cotton fabrics, we used a setup in our labo-
ratory to simulate the dynamic thermal response of fabric speci-
mens under unsteady-state conditions. As shown in Fig. 2, fabric
specimens were homogeneously scrolled into a tubular shape and a
temperature sensor was placed at the center of the scrolled fabric.
Each scrolled fabric specimen was introduced into a 100-
C air bath
from an initial temperature of 23
C, while the fixed temperature
sensor measured the temperature curve, which was recorded by a
computer system at 1-s interval.
The UV-blocking properties of the composite coated fabrics, as
determined by UV protection factor (UPF) and UV transmission
spectra, were recorded by a UV spectrophotometer (UV1000F,
Labsphere Inc., USA). On the basis of the recorded data in accor-
dance with Australia/New Zealand standard AC/NZS 439:1996, UPF
was calculated as follows [24]:
UPF ¼Z
400
290
E
l
S
l
dl
Z
400
290
E
l
S
l
T
l
dl
;(2)
where E
l
is the relative erythemal spectral effectiveness, S
l
is the
solar UV spectral irradiance, T
l
is the spectral transmittance of the
X. Hu et al. / Carbon 95 (2015) 625e633626
specimen (incoming light that passes through the specimen), d
l
is
the wavelength increment (nm), and
l
is the wavelength (nm).
Laundering durability of our prepared fabrics was measured by
subjecting the surface-treated fabrics to the AATCC Test Method 61-
2006. The test was performed using a standard color-fastness in a
washing launder machine (Model SW-12AII, Wenzhou Darong
Textile Instrument Co., Ltd, China) equipped with 500-ml
(75 125 mm) stainless steel lever lock canisters. The fabric was
laundered in a rotating closed canister containing 200-ml aqueous
solution of an AATCC-standard WOB detergent (0.37% w/w) and 10
stainless steel balls. The dimensions of the fabric samples were
50 100 mm for the experimental test.
3. Results and discussion
3.1. Morphology and structure of GNP material
The featured characterization of the GNP material was investi-
gated as shown in Fig. 3. A typical SEM image of GNP was shown in
Fig. 3a, in which layer-by-layer structure of graphene edges could
be observed and the flat sheets have a lateral size in the order of
5e15
m
m. A TEM image of the GNP was shown in Fig. 3b, in which
the fully exfoliated monolayer graphene could be detected, and
some GNP crumple because of the atomic thickness. Furthermore,
the XPS spectrum was analyzed to identify the surface chemical
composition and variation of GNP. The wide scan and C1s spectra of
the GNP were illustrated in Fig. 3c and d, respectively. The atomic
ratio of carbon could reach a high level at 95% according to the
wide-scan spectrum. In addition, the C1s core-level spectrum of the
GNP was presented, which consisted of five different chemically
shifted components that can be deconvoluted into sp
2
C]Cinar-
omatic rings (284.7 eV), CeOH (285.6 eV), CeOeC (286.8 eV),
respectively, and these assignments were in agreement with the
previous studies [25]. Moreover, the oxygen groups were at lower
Fig. 1. Schematic illustration for the GNP/WPU composite and its corresponding chemical structure.
Fig. 2. Apparatus to simulate the dynamic thermal response of fabric specimens under
unsteady-state conditions. (A color version of this figure can be viewed online.)
X. Hu et al. / Carbon 95 (2015) 625e633 627
content compared with the C]C bands, indicating the high carbon
atomic ratio. Therefore, such GNP might have outstanding electrical
properties.
3.2. The characterization of GNP/WPU composite
Zeta potential is an acceptable parameter to evaluate the aqueous
dispersion. In this study, the zeta potential of GNP/WPUwith different
GNP contents was shown in Fig.4a. Under neutral conditions, thezeta
potential of WPU was set at 11.2 mV (Fig. 4a), resulting from a small
number of carboxyl groups remaining on the edge of WPU. After
incorporating GNP, thezeta potential of GNP/WPUcomposite became
more negative, which generally represents sufficient mutual repul-
sion to ensure the stability of a dispersion [26]. Once the weight ratio
of GNP to WPU reached 0.8 wt%, the zeta potential of GNP/WPU
composite solution was set at 30.8 mV. There was no significant
change in the zeta potential of the GNP/WPU composite on further
addition of GNP, indicating that the GNP was fully dispersed with
WPU in the aqueous solutionand cannot be dispersedwith more GNP.
Therefore, the 0.8-wt% weight ratio of GNP to WPU was considered
the optimum value for obtaining well-dispersed GNP/WPU compos-
ite. In this study, the 0.8-wt% GNP was used to obtain well-dispersed
GNP/WPU composite, which was induced onto the cotton fabric
substrate to fabricate functional cotton textile.
Furthermore, GNP/WPU composite solutions with graphene
content in the range of 0e1.6 wt% were coated on the surface of the
cotton fabric by pad-dry-cure process. The electrical resistivity of
the samples was illustrated in Fig. 4b, in which the color of the
composite fabric gradually deepened from white to gray initially
and became pure black finally. Also, the electrical resistivity of the
control fabric could dramatically decrease from 1.15 10
7
to
0.675
U
m at 0.8 wt%. The electrical resistivity of the composite
fabric was constant with the increase of GNP content to 1.6 wt%.
Therefore, in this study, we considered that the GNP content at
0.8 wt% was the percolation threshold, and the GNP/WPU com-
posite solution with GNP 0.8 wt% was the most remarkable char-
acteristic to modify cotton fabric.
3.3. Morphology and structure of GNP/WPU-coated fabric
The SEM images of the treated and untreated cotton fabrics are
shown in Fig. 5. It can be seen from Fig. 5a and b that the control
cotton fabrics show some typical longitudinal stripes with clean
and smooth surface. However, after GNP/WPU composite coating,
the fiber surface of the treated fabrics shows a compact and ho-
mogeneous covering of nanoplates, as shown in Fig. 5ceh, which
removes the original surface strips and makes the fiber surface
rough. Furthermore, many irregular wrinkles and protuberances,
which were thought as graphene, were found to be evenly
distributed, indicating that adequate interfacial bonding existed
between GNP/WPU composite and fiber substrate.
With an increase of graphene-coated weight, the fibers of the
fabric showed a rough surface, and increasing numbers of irregular
graphene wrinkles and protuberances can be found on the fiber
surface (Fig. 5ceh), which showed their uniform distribution.
In order to investigate the interaction between graphene and
polyurethane in hybrid aqueous solution, FTIR spectra of GNP, WPU,
and GNP/WPU composite solution are illustrated in Fig. 6a. The ab-
sorption bands of GNP at 3250 and 1635 cm
1
were assigned to eOH
stretching vibrations in the residual waterand the C]C stretching of
the benzenoid rings of graphene [27]. For WPU, the stretching vi-
brations of the eNH groups occurred at 3320 cm
1
, together with the
carbonyl bands at 1710 cm
1
, which indicated the presence of ure-
thane moieties [28]. The GNP/WPU composite solution performed
two characteristic peaks at 3300e3400 and 1650e1750 cm
1
,
respectively.The peak located at 3300e340 0 cm
1
of WPU and GNP/
Fig. 3. (a) SEM image, (b) HR-TEM image, and (c) C1s XPS spectrum of GNP. (d) Wide-scan spectrum in the figure. (A color version of this figure can be viewed online.)
X. Hu et al. / Carbon 95 (2015) 625e633628
WPU composite solution was curve-fitted as shown in Fig. 6b, and
there were two characteristic bands embedded ineNH peaks of
WPU, including a free eNH band (3498 cm
1
) and a hydrogen-
bonded eNH band (3275 cm
1
). After incorporating GNP, a new
band presented at 3179 cm
1
indicated the NH/O hydrogen bonds
between eNH in WPU and eOH in GNP [29]. Furthermore, the
detailed location and fraction of curve-fitting peaks are listed in
Table 1. Compared with WPU, the lower fraction (10.7%) of free eNH
in GNP/WPU was resulted from the formation of hydrogen bonds
between eNH in WPU and eOH in GNP. This result confirmed the
formation of chemical bonds between GNP and WPU, as shown in
Fig. 1.
3.4. Far-infrared emissivity of coated fabrics
The far-infrared radiation emissivity εof the resultant GNP fabric
was listed in Table 2, compared with far-infrared radiated textile
products on the market (the Venus Styler) [30]. The results indicated
that the emissivity of GNP fabric gradually increased from 0.867
(controlfabric) to 0.911 (GNP/WPU-3), which was alreadybeyond the
emissivity limit of the commercial product (the Venus Styler).
Therefore, low content of graphene (480 mg/m
2
) could obviously
improve the far-infrared emissivity of GNP/WPU-3 fabric matrix. A
material with ε¼1, which can ideally convert heat energy to elec-
tromagnetic wave energy (i.e., no energy loss), was named as black-
body.Generally, the emissivity of a practical material was inthe range
of 0e1. Theconversion of heatenergy to electromagneticwave energy
was considered valuable when ε~1. Therefore, GNP/WPU-3 fabric
(ε¼0.911) possessed a high efficiency to transform heat energy from
sunlight or human body to far-infrared radiation, and the generated
far-infrared radiation might reemit to the human body in the elec-
tromagnetic manner. Then,in order to preserve heat, thehuman body
absorbed the energy and water molecules to produce resonance and
promote blood circulation [31]. Precisely, low content of graphene
could definitely improve the far-infrared radiation properties of ma-
trix, whose mechanism might be investigated in our future work.
Fig. 7a and b shows the images of uncoated and coated cotton
fabrics. There is an obvious difference between the appearances of
the uncoated and coated cotton fabrics, because of the presence of
graphene. The thermal infrared images of GNP/WPU fabrics with
different graphene content were shown in Fig. 7cef. All the images
had the same exposure duration (5 min) after the GNP fabric was
connected to the hand. However, different GNP fabrics showed
different colors in thermal infrared images, which implied that they
could launch different amounts of far-infrared radiation. It is worth
noting that under the same exposure duration, the GNP fabric could
absorb the same heat energy from human hand, but the fabric with
more GNP could transform more heat energy to far-infrared radi-
ation. The far-infrared radiation could reemit to the hand to achieve
the effect of heat preservation.
3.5. Electrical conductivity
The initial electrical resistance of untreated control cotton fab-
rics was about 10
7
U
m. Graphene has a unique property of high
electrical conductivity, and the influence of different graphene-
coated weights on substrate cotton samples for the electrical con-
ductivity was investigated in this study, and the results are pre-
sented in Fig. 8. It was evident that the value of surface electrical
resistivity decreases rapidly when the graphene-coated weight
increased from 240 to 480 mg/m
2
, and reached a maximum value of
2.94 10
1
U
m. After 10 times laundering, the surface electrical
resistivity increased from 2.94 10
1
to 3.35 10
1
U
m for GNP/
WPU-3 graphene-coated fabric, and also slightly increased for all
other graphene-coated weight samples. On the basis of the
morphology of the fabric illustrated in Fig. 5ceh, the GNPs were
deposited on the surface fiber substrate. The higher the graphene-
coated weight, the more uniform the nanoplates dispersed on the
fiber surface (Fig. 5c). However, there was no aggregated con-
struction of GNPs, which could severely reduce the electrical ability
to conductive network. Thus, it can be concluded that more effi-
cient GNPs can distribute well on the fiber surface and improve the
electrical conductivity of the fabric.
3.6. Thermal properties of coated fabrics
Thermal conductivity is an intrinsic property of a material that
indicates its ability to conduct heat, which is calculated as the flux
of heat (energy per unit area per unit time) divided by the tem-
perature gradient (Eq. (3))[32,33]. However, thermal resistance
depends on the ratio of thickness to thermal conductivity of the
fabric, and it is calculated using Eq. (4).
lWm
1
K
1
¼Qh
ADTt (3)
Rm
2
KW
1
¼hðmÞ
lWm
1
K
1
;(4)
where Qis the amount of conducted heat (J), Ais the area through
Fig. 4. Zeta potential of GNP/WPU composite (a) and electrical resistivity of GNP/WPU composite-coated cotton fabric (b) with graphene content in the range of 0e1.6 wt.%. (A color
version of this figure can be viewed online.)
X. Hu et al. / Carbon 95 (2015) 625e633 629
which heat is conducted (m
2
), tis the time of conductivity (s),
D
Tis
the drop in temperature (K), his the fabric thickness (m),
l
is the
thermal conductivity, and Ris the thermal resistance.
Table 3 lists thermal conductivity and thermal resistance of
sample fabrics. The result showed that the increase of graphene-
coated weight enhanced the thermophysical properties (thermal
conductivity and thermal resistance) of cotton fabrics to nearly 30%.
However, heat conduction of the cotton fabrics was enhanced by
the decrease of graphene-coated weight.
In order to verify this prediction, the temperature curves were
plotted against testing time for the samples in our setup (Fig. 2), as
shown in Fig. 9. Compared with four temperature curves, the
scrolled fabric specimen GNP/WPU-3 was kept at the highest
temperature raising speed throughout the heating process, and the
control cotton fabric expressed the most dilatory temperature
response. As a consequence, the shortest duration (5 min 58 s) was
Fig. 5. SEM images of the untreated (a, b) and treated (ceh) cotton fabrics.
X. Hu et al. / Carbon 95 (2015) 625e633630
Fig. 6. (a) FTIR spectra of ultrasonic-treated GNP, WPU, and the GNP/WPU hybrid solution and (b) peak-fitting results of GNP/WPU hybrid solution. (A color version of this figure can
be viewed online.)
Table 1
Location and fraction of curve-fitting peaks in the FTIR spectra.
Sample code Free eNH in WPU Hydrogen-bonded eNH in WPU Hydrogen-bonded eOH in GNP
Location (cm
1
) Fraction (%) Location (cm
1
) Fraction (%) Location (cm
1
) Fraction (%)
WPU 3498 16.7 3275 83.3 ee
GNP/WPU 3487 10.7 3295 84.7 3179 4.6
Table 2
Far-infrared emissivity of graphene coated fabrics.
GNP-coated weight (mg/m
2
) Coated fabrics Far-infrared emissivity Standard deviation
0 Control fabric 0.867 0.008
240 GNP/WPU-1 0.879 0.007
320 GNP/WPU-2 0.908 0.005
480 GNP/WPU-3 0.911 0.006
eVenus styler
a
0.891 e
a
A far-infrared radiating textile product on the market.
Fig. 7. Images of (a) uncoated cotton fabric, (b) graphene-coated fabric, (cef) thermographs of graphene-coated fabrics with different coated weights (control cotton fabric, 240,
320, and 480 mg/m [2] graphene-coated fabrics, respectively). (A color version of this figure can be viewed online.)
X. Hu et al. / Carbon 95 (2015) 625e633 631
achieved by the GNP/WPU-3 fabric to reach the destination tem-
perature, that is, 100
C, while the GNP/WPU-2 fabric took 6 min
30 s and the neat cotton fabric exhausted the longest time, 8 min
45 s. These dynamic curves verified the prediction that the fabrics
coated with graphene could have quick temperature response un-
der unsteady-state conditions.
3.7. The UV protection efficiency of the treated fabrics
The UV transmission spectra of GNP fabrics are illustrated in
Fig. 10a. In the range of the scanned wavelength (250e450 nm), the
spectra illustrated definite difference among the samples. Particu-
larly, the curves of the control fabric expressed high UV trans-
mittance, especially in the longer-wavelength (320e450 nm)
region. The UV transmission spectra of graphene composite-
incorporated control cotton fabric showed a dramatic decline for
different graphene-coated weights, implying that the low content
of graphene could effectively block UV rays.
The rate of UV protection was assessed by UPF values, as shown
in Fig. 10b. It was found that all GNP/WPU composite-coated
samples expressed higher UPF values than control cotton fabric.
The UPF values basically increased with increase of GNP weight
ratio, and for the GNP/WPU-2 fabric, they could reach 500, which
was already far beyond the excellent-protection UPF rating (50þ)of
Australian/New Zealand Standard AS/NZS 4399: 1996 and up to 50-
fold increment of control case (UPF ¼8.19). Furthermore, the
laundering durability of each fabric before and after laundering was
compared by their UPF values. It is evident from Fig. 10b that the
UPF values slightly increased no more than 2%, indicating that even
after 10 times laundering, GNP/WPU composite coating was stable
on the fabric surface and effectively blocked UV rays passing
through the fabric. Therefore, the treated fabrics could have long-
term wearability with remarkable laundering durability.
4. Conclusion
It is evident from this study that the production of a cotton
fabric with remarkable electrical conductivity, UV protection, and
far-infrared emission properties was possible through the aid of
graphene and polyurethane composite polymer. Particularly, such a
multifunctional fabric could be facile, fabricated by an effective
pad-dry-cure process at room temperature. From the surface
morphology study of SEM images, it has been found that a very
uniform and dense deposition of the GNPs was achieved with the
help of polyurethane. After GNP/WPU composite was coated on the
matrix of fabric substrate, the treated fabrics possessed efficient far-
infrared-emitting property with a far-infrared radiation emissivity
of 0.911. Furthermore, the electrical resistivity of the modified
Fig. 8. (a) IeV curve and (b) variation of surface electrical resistivity of GNP/WPU composite-coated fabrics and uncoated fabrics. (A color version of this figure can be viewed
online.)
Table 3
Thermal conductivity and thermal resistance of sample fabrics.
GNP-coated weight (mg/m
2
) Coated fabrics Thermal conductivity (W/mK 10
3
) Thermal resistance (m
2
K/W 10
3
)
0 Control fabric 38.500 24.70
240 GNP/WPU-1 45.680 25.02
320 GNP/WPU-2 48.366 28.93
480 GNP/WPU-3 50.633 31.59
Fig. 9. Dynamic temperature curves of control fabric and graphene-coated fabrics. (A
color version of this figure can be viewed online.)
X. Hu et al. / Carbon 95 (2015) 625e633632
fabrics was decreased from 1.15 10
7
to 2.94 10
1
U
m, almost 8
orders of magnitude, and the graphene-coated samples possessed
excellent and durable UV-blocking property even with very low
graphene content. The UPF values basically increased with the in-
crease of GNP weight ratio, and could reach 500 at 320 mg/m
2
graphene-coated weight, which was already far beyond the excel-
lent protection. Overall, such facile route and the resultant multi-
functional fabrics have proved to be an interesting candidate of
fabrics with excellent electrical, UV-blocking, and far-infrared ra-
diation emission properties.
Acknowledgments
Financial support of this work was provided by Natural Science
Foundation of China (grant No. 51273097 and 51306095), China
Postdoctoral Science Foundation (grant No. 2014M561887 and No.
2015T80697), and Taishan Scholars Construction Engineering,
Shandong, China.
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Fig. 10. (a) UV transmission spectrum of GNP/WPU-coated fabrics and (b) UPF and UVA&UVB transmittance values of sample fabrics (the gray column UPF0represents the UPF
values of these fabrics after 10 times laundering). (A color version of this figure can be viewed online.)
X. Hu et al. / Carbon 95 (2015) 625e633 633
