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: sh-shahidi@iau-arak.ac.ir

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

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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

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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

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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

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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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