ORIGINAL RESEARCH
Effect of Plasma Pretreatment Followed by Nanoclay Loadingon Flame Retardant Properties of Cotton Fabric
Sheila Shahidi • Mahmood Ghoranneviss
Published online: 12 November 2013
� Springer Science+Business Media New York 2013
Abstract In this research work the effect of plasma
treatment with nitrogen gas followed by nanoclay treat-
ment on flame retardancy of cotton fabrics is studied. The
flame retardancy of the samples was characterized by
limiting oxygen index and the char yield. The thermal
decomposition behaviors, the chemical structures and
morphologies of the fabrics were investigated using thermo
gravimetric analysis, Fourier transform infrared and scan-
ning electron microscopy, respectively, and a possible
flame retardant mechanism is discussed. It shows that,
nitrogen plasma pretreatment has synergistic effect on
nanoclay for improving the flame retardant properties of
cotton samples.
Keywords Flame retardant � Plasma treatment �Nano clay � Cotton � Fabric
Introduction
Cotton is comfortable, a natural product, a renewable
resource, and environmentally friendly [1].
Cotton fabric is the one most commonly used in domestic
applications (clothes, beddings, furniture, wall-hangings,
etc.). Also cotton fabrics have been widely used in both mil-
itary and civilian areas due to their excellent properties.
However, it is also one of the most flammable materials. It is
thus of primary importance for public safety to find ways to
render this material less flammable and of course, in a most
economically and environmentally friendly manner. The real
obstacle of a wider application for cotton fabrics is their
flammability. Various kinds of techniques for imparting the
durable flame retardancy to cotton fabrics have been devel-
oped in the past decades. But their applications are not
desirable during processing and use [2, 3].
Therefore, there is an urgent need to develop an envi-
ronmentally-friendly and effective approach for flame
retardant finishing of cotton fabrics.
Clays are natural environment-friendly materials with high
specific surface area. Nano Clays are hard ceramic material
and are widely applied in many fields such as polymer nano-
composites, adsorbents for heavy metal ions, catalysts, pho-
tochemical reaction fields, ceramics, paper filling and coating,
sensors and biosensors, due to their high specific surface area,
chemical and mechanical stabilities, and a variety of surface
and structural properties [4–6].
Nanoclay is made from montmorillonite mineral
deposits known to have ‘‘platelet’’ structure with average
dimension of 1 nm thick and 70–150 nm wide. Nanoclays
are known to enhance properties of many polymers such as
nylon 6, EVA, epoxy, PET, PE and PP leading to better
clarity, stiffness, thermal stability, barrier properties to
moisture, solvents, vapors, gases and flavors; reduced static
cling and UV transmission in film and bottles; improved
chemical, flame, scratch resistance, and dimensional sta-
bility in injection molded products [7].
Dispersion and morphology of dispersed clays and other
particles at the nano level are considered to be essential if
fire performance properties are to be optimized.
The advantage of this method is that in principle it may be
applied to any textile substrate retrospectively and so offers
S. Shahidi (&)
Textile Engineering Department, Faculty of Engineering, Arak
Branch, Islamic Azad University, Arak, Iran
e-mail: [email protected]
M. Ghoranneviss
Plasma Physics Research Center, Science and Research Branch,
Islamic Azad University, Tehran, Iran
123
J Fusion Energ (2014) 33:88–95
DOI 10.1007/s10894-013-9645-6
great opportunity for enhancing the heat and fire resistance of
a range of textile substrates [8–11].
Nanoclays can be applied to both synthetic and natural
textile materials by different methods.
To enhance nanoclay adsorption on cotton fabric and
increase the uniformity of its distribution, it is necessary to
develop ripple like pattern on the cotton surface.
Therefore, to enhance nanoclay binding, it can be useful to
have some etching and functional groups on the surface of cotton
fibers. To achieve this, one of today’s established methods is the
Low temperature plasma (LTP) treatment of cotton.
LTP is a totally or partially ionized gas. Plasma, a dis-
tinct fourth state of matter, is a gaseous body that contains
an energetic assortment of ions, free electrons, free radicals
and visible, ultraviolet and infrared radiation. One potential
application of plasmas to textiles involves using these
active species within the plasma discharge to drive func-
tional groups onto the surface of the substrate [12, 13].
It is aimed in this work to study the effect of plasma
treatment with nitrogen gas followed by Nanoclay treat-
ment on flame retardancy of cotton fabrics.
Experimental
Materials
Woven Cotton fabrics were kindly supplied by the Baft Azadi
Co (Tehran, Iran). Before treatments, in order to minimize the
chance of contamination, samples were washed with 1 % non-
ionic detergent solution in 70 �C water for 15 min and then
rinsed with water for another 15 min, and dried at room tem-
perature. Nitrogen gas (high purity) was supplied by the Air
Company (Iran). Acetic Acid was purchased from Fulka Co.
The nanoclay used was a natural dimethyl dehydrogenated tal-
low quaternary ammonium exchanged montmorillonite
2M2HT (Cloisite 15A) supplied by Southern Clay Products, Inc.
Cold Plasma Process
A Direct Current (DC) magnetron-sputtering device was
used for plasma treatment; the photo of plasma reactor is
presented in Fig. 1. Nitrogen gas was used as working gas.
An Aluminum (Al) post cathode was used because of its
lower sputtering rate. Fabric samples were put on the anode
in plasma reactor. The chamber was pumped down to
2 9 10-3 torr using a rotary pump, and then N2 was
admitted into it up to a pressure of 5 9 10-2 torr. During
the Plasma treatment, power was very important. After a
long series of preliminary experiments, the most suitable
experimental conditions for the low pressure plasma acti-
vation of the fabric surface were found and the samples
were activated with best condition of plasma. The current
and voltage of the system were kept constant at 200 mA
and 1,000 V, respectively. It was found that, 5 min expo-
sure time is enough for activation of the samples. It should
be mentioned that both sides of fabric samples were acti-
vated by plasma treatment.
Fig. 1 Photo of plasma reactor
J Fusion Energ (2014) 33:88–95 89
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Nanoclay Exhaustion Treatment
The aqueous finishing dispersions were prepared by 5 wt%
Nanoclay with L:G = 40:1 in an ultrasonic bath. The
cotton fabric was then impregnated in the dispersed solu-
tion for 45 min in 80 �C. The treated samples were rinsed
in ultrasonic bath for 5 min to remove un-bonded nanoclay
from the fabric surface. Finally, the (FR) finished fabrics
were conditioned at 21 ± 1 �C and 65 ± 5 % RH for 24 h
prior to any treatment.
Characterization and Testing
FTIR Analysis
The functional groups on the surface of samples were
examined using Fourier transform infrared (FTIR) spec-
trometer (Bomem MB-100, made in Canada).
Scanning Electron Microscopy (SEM)
The surface morphology of prepared fabrics was observed
using a scanning electron microscope (SEM, Philips,
XL30, Netherland) with an accelerating voltage of 25 kV.
The samples were pre coated with gold, using a sputter
coater (SCDOOS, Bal-Tec, Swiss made).
Char Yield
The measuring of char yield can be an appropriate factor
for study the influence of FR. In this order, the weight of
each sample before and after complete burning was mea-
sured and char yield was calculated according to Eq. (1).
Char yield ¼W2 = W1� 100 ð1Þ
where W1, W2 are weight of sample before and after
complete burning, respectively.
Limited Oxygen Index (LOI) Measurement
Limiting oxygen index (LOI) values of some samples were
measured according to ASTM D2863-09 standard method. In
this order, 5 specimens of each sample were prepared in
5 9 15 cm2 and a mixture of oxygen and nitrogen is passed up
through a cylinder containing the fabric specimen supported
vertically. The minimum fraction of oxygen in a mixture of
oxygen and nitrogen in which one specimen will just sustain
burning is determined and reported as the LOI value.
Thermal Analysis
Thermo gravimetric analysis (TGA) and differential ther-
mal analysis (DTA) were carried out using a Perkin Elmer
TG–DTA analyzer, model Pyris1, operating under nitrogen
atmosphere with initial sample weights of 8 mg. Once the
sample has been prepared, it should be placed into the TGA
sample pan and distributed evenly across the pan bottom.
The standard platinum sample pan (0319–0264) is used for
this application. The runs were performed over a temper-
ature range of 50–600 �C at a heating rate of 10 �C/min
under a continuous N2 flow of 100 ml/min.
Results and Discussions
FTIR
FTIR was used to examine the functional groups of the
untreated and plasma-treated samples. The results are
shown in Fig. 2. As shown in the figure, an increase in
absorbance at the 1,720 cm-1 (C = O) band, and
1,080–1,300 cm-1 (C–O) group was noticed after plasma
treatment [14–17].
The OH and NH bands overlapped in the 3,400 cm-1
region. These functional groups were produced on the
fabric by the reaction between the active species induced
by the plasma in the gas phase and the fabric surface atoms.
The peak at 1,545 cm-1 appears owing to the presence of
NH2 and NH deformations in amides. The peak at
3,357 cm-1 in a broad region 3,100–3,470 cm-1 can be
attributed to OH, NH or NH2 stretch.
In the treated fabric, certain absorption bands can be
observed in the 1,180–1,360 cm-1 range (C–N stretching
vibration) as well as a distinct band at 1,170 cm-1 which
Fig. 2 The FTIR results of both untreated and nitrogen plasma
treated cotton for 5 min
90 J Fusion Energ (2014) 33:88–95
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are characteristic of C–O stretching deformation. Also, we
can see that the absorption peak of nitrile groups at
2,240–2,270 cm-1 is prominent after nitrogen plasma
treatment [17–21].
SEM
The SEM micrographs of untreated, Nanoclay treated, N2
plasma-treated and N2 plasma/Nanoclay treated fabrics are
shown in Figs. 3 and 4 with different magnifications. SEM
micrographs show that after LTP treatment ripple-like
patterns oriented in the fiber axis developed. As shown in
Fig. 4, more nanoclay particles were bonded to the surface
of pre functionalized sample. The average nanoclays size
on the surface of nitrogen pretreated sample was deter-
mined and is about 35 nm.
Char Yield and LOI Values of Samples
The char yield and LOI values of the untreated, nanoclay
treated, N2 Plasma treated and N2 Plasma/nanoclay treated
samples is calculated and reported in Table 1. It is
observed that the char yield of the untreated sample before
treatment was 1.9 %, and for the treated samples increased
greatly. The char yield of the sample which was treated
with nanoclay is 10.20 % which is 5 times more than
untreated sample. Also the results show that, N2 plasma
treatment causes increase the flame retardant properties of
cotton sample. It is observed that, Nitrogen plasma has
synergistic effect on nanocaly for flame retardant proper-
ties. As it is seen, the char yield value for N2 plasma/
nanoclay treated cotton increase to 12 %. Also the same
results for LOI values have been achieved. By plasma
pretreatment and nanoclay exhaustion, the LOI values
increase up to 23.5 %.
Presence of nanoclay leads to the formation of a barrier
layer that limits the propagation of fire inside the material
but increases the flame-spread rate over the surface of the
specimen.
Thermal Stability
In order to investigate effect of performed treatment on
cellulose pyrolysis process, TGA, DTA and DTG curves of
untreated and treated samples are presented in Figs. 5, 6
and 7 respectively. The pyrolysis is a complex reaction in
Fig. 3 The SEM images of untreated and nitrogen plasma treated cotton with different magnifications
J Fusion Energ (2014) 33:88–95 91
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which various reactions; endothermics bond rupture, vol-
atilization, and exothermic bond formation can be happen
simultaneously. However, the DTA thermogram shows
only the net change [22].
The weight loss of samples in each pyrolysis stages can
be known from TGA curve profile. As reported in the lit-
erature, cotton decomposes through three steps: At first, all
TGA curves are liner that is related to the initial pyrolysis
stage in which damage on cellulose occurs mostly in the
amorphous region of the polymer, some physical properties
of the fabric change and a little weight loss is observed. In
second stage, high slope in curves observed related to large
weight loss of sample. At this stage the pyrolysis of
cellulose takes place in the crystalline region of the poly-
mers. Finally curves are observed in liner form related to
char pyrolysis [6, 22, 23].
The most important differences of the untreated and the
treated fabrics in TGA curves were the initial decomposi-
tion temperature and the final char residue. It can be
observed in Fig. 5 that the most weight loss is related to the
untreated sample. In this sample the remained char is
7.6 %. In nitrogen plasma treated sample, the weight of
residual materials is rather higher than the untreated one
and due to the pre-functionalization of the sample, the final
char increases to 8.6 %.
This can be explained by the addition of nitrogen con-
taining groups, which helps to form more non-flammable
char residue. The amount of char formed from the treated
samples correlates well with the LOI values of the treated
fabrics. The increased amount of char formed contributes
to greater LOI values of the treated fabrics. In addition,
nanoclay treated samples show higher residues with respect
to cotton and nitrogen treated cotton. The higher final char
residue at high temperatures suggests that addition of
nanoclay can change the pyrolysis mode of the cotton
Fig. 4 The SEM images of nanoclay treated samples
Table 1 Values related to char yield and LOI of untreated, nanoclay
treated, plasma treated, plasma/nanoclay treated samples
Samples LOI Char yield (%)
Untreated 18.5 1.9
Nanoclay treated 22.5 10.21
N2 plasma treated 21.8 8.7
N2 Plasma/nanoclay treated 23.5 12
92 J Fusion Energ (2014) 33:88–95
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fabric when heated and nanoclay functions as an efficient
char forming resulting a char with high resistance against
heat at high temperatures. Thus, it can conclude that the
nanoclay improved flame retardant property with increas-
ing char content and the activation energy of cotton
decomposition as reported by other researchers [6, 8, 11,
24, 25]. The existence of nanoclay on the surface had better
barrier property to heat and oxygen transport due to which
ignition of the composite delayed. More study about
mechanism and kinetic of thermal degradation in cotton
fabric treated with this flame retarding system can be also
considered.
The TGA curve of the untreated and treated samples
indicates the onset of the cellulose depolymerization at about
330 Æ C. The main stage of pyrolysis is in the range of
320–380 �C during which a rapid weight loss is occurred and
much of the pyrolysis products such as levoglucosan is pro-
duced. The final stage of pyrolysis is occurred above 400 �C.
Fig. 5 TGA curve of untreated
and treated samples
Fig. 6 DTA curve of untreated
and treated samples
J Fusion Energ (2014) 33:88–95 93
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Adding nanoclay increases the Tmax comparing with
untreated cotton. Also a large endothermic peak in DTA curves
of the untreated samples is observed at main pyrolysis stage
that related to the weight loss and vaporization of pyrolysis
products [6]. The endothermic peak of nitrogen treated and
nanoclay treated cotton is weaker than the untreated one.
Conclusion
In this research work the effect of plasma treatment with
nitrogen gas followed by Nanoclay treatment on flame
retardancy of cotton fabric were investigated. The results
show that Nanoclay is an effective flame retardant for
cotton fabrics. The char yield of the sample which was
treated with nanoclay is 10.20 % which is 5 times more
than untreated sample. It was concluded that, N2 plasma
treatment causes increase the flame retardant properties of
cotton sample. It is observed that, Nitrogen plasma has
synergistic effect on nanocaly for flame retardant proper-
ties. Also more amounts of nanoclay are absorbed on sur-
face of plasma pretreated cotton. The char yield value for
N2 plasma/nanoclay treated cotton increase to 12 % after
complete burning. Also the same results for LOI values
have been achieved. The improvement of flame retardancy
of the treated samples is attributed to the earlier decom-
position of nanoclay to drive the char formation, which
could inhibit the transmission of heat, energy and O2
between flame and cotton fabrics.
Acknowledgments We would like to thank Iran National Science
Foundation (INSF) for providing grant of members.
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