International Journal of Bioresource Science
Citation: IJBS: 1(1): 57-63 June 2014
©2014 Renu Publishers. All rights reserved
Effect of Helium-Oxygen Plasma Treatment on Physical
and Chemical Properties of Cotton Textile
Kartick K. Samanta*, T.N. Gayatri, A.H. Shaikh, S. Saxena, A. Arputharaj, S. Basak and
S.K. Chattopadhyay
Plasma Nanotech Lab, Chemical and Bio-chemical Processing Division, ICAR-Central Institute for Research on Cotton
Technology, Adenwala Road, Matunga, Mumbai - 400019, India
*Email: [email protected]
Abstract
Plasma, an ionized gas composed of ions, electrons, photos, UV radiation and neutral active species, can be used for nano-scale
surface modification of textile substrates without using water. Among the various types of plasma, only atmospheric pressure
cold plasma (non-thermal plasma) is suitable for surface modification of heat sensitive textile substrates in a continuous manner.
Atmospheric pressure cold plasma was generated in the presence of helium-oxygen (He/O2) mixture and cotton fabric was plasma
treated for 30 s to 4 min. Upon ionization, helium (He) emits photons at wavelengths of 706 nm, 667 nm, 587 nm, 727.5 nm and
oxygen at 776 nm and 844 nm. After plasma treatment, cotton became more hydrophilic due to generation of hydrophilic groups
resulting better water wicking. Plasma treatment increases the surface crystalline index (CI) from 1.09 in the untreated sample to
1.65 in the 2 min He/O2 plasma treated sample. Scanning electron microscope (SEM) images showed etching of fibre surfaces. In
the 2 min and 4 min He/O2 plasma treated samples, there was an improvement in colour value in terms of K/S, a* and c*. Surface
crystalline index (CI), numbers of hydroxyl and carbonyl groups play an important role in colouration of cellulosic textile using
reactive dye.
Keywords: Plasma, Cotton, Textile, Colouration, Water pollution
Wet chemical processing of textile is important because it
imparts highest value to the textile substrates. However,
the process is water and energy intensive. Approximately,
100 litres of water is used to process one Kg of cotton
textile, which is finally discharged as an effluent
contaminated with unused colouring material and
chemicals. Discharge of effluent in the water streams has
a serious impact on flora and fauna and in addition with
fertility of agricultural land. Shortage of water in near future
would have a serious impose in textile. Therefore, textile
industries are now slowly moving towards the
implementation of water-less or low water based
processing technologies, such as digital printing, spray &
foam finishing and plasma processing. The main attraction
of plasma in industrial application is to avoid chemical
effluents. Other advantages are saving of large quantities
of water, chemicals and energy [Banchero et al, 2008].
Plasma, an ionized gas can be used for nano-scale surface
engineering of textile substrates by attaching a small
molecule such as oxygen, nitrogen, fluorine etc or by plasma
reaction of big molecules containing hydroxyl, carbonyl,
carboxyl, acrylate group [Samanta et al, 2006]. Generation
of radicals on the fibre surface followed by plasma reaction
of a precursor could lead to a development of advanced
textiles such as water and oil repellent, hydrophilic,
antimicrobial, flame retardant and UV protective [Samanta
et al, 2008; Samanta et al, 2009; Wang et al, 2011]. Plasma
processing of textile can also be used for improvement in
Samanta, et al.
dyeing, printing and adhesion strength. Mainly, low
pressure plasma has been explored for such applications.
However, the process technology has not been
commercialized in textile due to its several inherent
limitations. On the other hand atmospheric pressure plasma
is an emerging technology that can overcome the limitations
of low pressure plasma hence, gaining attention in the
research community. Plasma has been used to impart
hydrophobic to super-hydrophobic functionality in various
hydrophilic textiles [Samanta et al, 2012; Kale et al, 2011].
It has also been used for hydrophilic functionalization of
hydrophobic textile such as nylon, polyester and
polypropylene [Samanta et al, 2010]. Plasma pre-treatment
of protein fibres such as wool and silk for improvement in
colouration and felting has been also reported [Panda et al,
2012; Nadiger et al, 1985]. However, a little information is
available on plasma treatment of cellulosic substrates
(cotton textile) for improvement in colouration. For apparel
shirting and suiting cotton textile is mainly used because
of its comfort properties associated with soft feel and
excellent moisture management.
frequencies of 3.8-4.2 kV and 21.8 kHz, respectively.
During the plasma treatment, helium gas flow rate was
kept at 400 ml/min and oxygen at 50 ml/min using two
mass flow controllers (Alicat Scientific made, USA). Before
the treatment, the reactor was flushed with He gas for 10
min to remove contaminants such as air. Thereafter, the
samples were plasma treated for 30 s to 4 min in the
presence of He/O2.
Water wicking time
Water wicking time was measured by dipping a rectangular
strip of fabric in water. The fabric was dipped 1 cm in
water and kept straight vertically by putting a weight at the
bottom. The time for water to travel each centimetre in
vertical direction was recorded. Lesser the water wicking
time, better the hydrophilic property and comfortable for
apparel use.
Optical emission spectroscopy of plasma
Light emitted by the excited atoms and molecules over the
wavelength of 300 to 900 nm was analyzed using Optical
Emission Spectrometer (OES), Mikropack model PlasCalc
2000. Offline analysis of OES data was carried out using
Specline 2.1 software.
In this study an attempt was made on generation of heliumoxygen (He/O2) plasma in the presence of cellulosic cotton
textile and its effect on physical and chemical properties
was studied. In addition, the effect of plasma treatment on
colouration of cotton textile has also been reported.
ATR-FTIR analysis
ATR-FTIR analysis of the untreated and plasma treated
samples were carried out in Shimadzu IR Prestige 21
analyser with ATR attachment over the wavelength of 700
to 4500 cm-1.
Materials and Methods
Materials
Desized and bleached 100% cotton woven textile with an
areal density of 123 g/m2 was used to study the effect of
plasma treatment on physical and chemical properties. The
fabric has 110 threads per inch (EPI) in the vertical direction
(warp) and 90 threads per inch (PPI) in horizontal direction
(weft).
Scanning electron microscopy (SEM) and EDX analysis
Surface of the untreated and plasma treated samples were
analyzed using scanning electron microscope, Model Philips
XL 30 at a magnification of 800-1000 KX. The samples
were gold coated before the analysis. EDX analysis of these
samples was carried out in Field Emission Gun Scanning
Electron Microscope (FEG-SEM).
Prior to the plasma treatment, the fabric was rinsed in
acetone and dried in air oven at 90 °C for 10 min to remove
any contamination and trapped moisture in textile structure.
Different gases were procured from Alchemie gases Pvt.
Ltd.
Colouration of textile and measurement of colour
parameters
The untreated and helium-oxygen (He/O2) plasma treated
samples were dyed using cold brand reactive dye (Procion
brill Red M-8B). The shade percentage was kept at 1 on
weight of the fabric. In the dye bath 40 gpl salt and 12 gpl
soad was added and dyeing was carried out for an hour.
Thereafter, the colour parameters such as K/S, L, a*, b*,
c and h values were measured using Perkin-Elmer double
Plasma treatment
Plasma treatment was carried out in an indigenously
developed atmospheric pressure plasma reactor in the
presence of helium-oxygen (He/O2) gases. Plasma was
generated in between the two rectangular aluminium
electrodes of size 7×6 cm2 at discharge voltages and
58
Effect of Helium-Oxygen Plasma Treatment on Physical and Chemical Properties of Cotton Textile
the excited species. As every gas has a distinct excitation
level, it has a particular emission characteristic in excited
state, hence produces a distinct colour. For example, when
He gas is ionized, it gives light bluish purple colour and
when oxygen was introduced along with it, it colour
changed to milky white as shown in Figure 1.
beam spectrophotometer of model Lambda 35 equipped
with integrating sphere. Depth of colour (shade) of the
dyed fabrics was determined in terms of K/S from
reflectance data according to the Kubelka– Munk equation.
K/S= (1-R)2 / 2R
Where, K is the absorption coefficient, S is the scattering
coefficient and R is the reflectance of the treated fabric at
a wavelength of maximum absorption. K/S was determined
at 540 nm (λ max) of the respective dye. Other colour
parameters such as L (lightness-darkness), a* (red-green),
b* (blue-yellow), c (strength/saturation of a particular
shade) and h (hue of a particular shade) were measured
using the Win lab software delta-E 1976.
Figure 2 shows the OES spectrum of He-oxygen plasma.
Upon ionization, He emits photons at different wavelengths
such as at 706 nm, 667 nm, 587 nm, 727.5 nm, 388 nm
and 356 nm. Among the various atomic lines of helium
(He), the He peak at 706 nm is the most prominent. The
other small peaks present in the spectrum particularly, in
the wavelength of 300 nm to 400 nm are mainly due to the
atomic lines of nitrogen. The presence of trace amount of
nitrogen in He gas might have produced such small peaks
at lower wavelengths. In He/O2 plasma, oxygen showed
atomic lines at 776 nm and 844 nm. These are characteristic
atomic lines of oxygen plasma. Similar result has also been
reported in literature [Milosavljeviæ et al, 2014].
Results and Discussion
Generation of plasma and its optical properties
Atmospheric pressure plasma was generated in the presence
of helium-oxygen (He/O2) gaseous mixture. The colour of
particular plasma depends on the atomic and molecular
species present in the plasma zone and photons emitted by
Water wicking
Fig. 1: Colour of the He+oxygen (He/O2) plasma.
Fig. 2: Optical emission spectrum of helium-oxygen (He/O2) plasma.
59
Samanta, et al.
Figure 3 shows the vertical water wicking in the untreated
and 4 min plasma treated cotton woven fabrics. Cotton being
pure cellulosic in nature, it has good liquid absorbency and
transport property. It can be seen that water took
approximately similar time to travel up to 2 cm vertically in
the untreated and plasma treated samples. However, water
took more time (110 s) in the untreated sample to travel up
to 3 cm compared to 4 min plasma treated sample whereas,
it was only 99 s. It can also been seen that the He/O2 plasma
treated samples took significantly lower time compared to
untreated samples to travel same height through the wicking
experiment. The result showed that plasma treatment has
helped in better liquid transportation. This might be due to
etching of the cotton surface by plasma treatment (discussed
SEM section). Bombardment of high energy plasma species
such as electron, ion and neutral active species on cotton
fabric might have increased and opened up some capillaries,
which promotes wicking of water. In addition, formation
more oxygen containing polar groups such as carbonyl,
carboxyl and hydroxyl on the cotton fibres surface by
oxidation of cellulosic has also helped in better transport of
water in concurrence with capillary action.
of oxygen is more in the plasma treated sample compared
to the untreated sample. It was observed that untreated
cotton has 44.5% oxygen and 55.5% carbon. It is similar
to the theoretical value of carbon and oxygen reported in
the literature for the cellulosic substrates [Samanta et al,
2012]. The oxygen percentage increased to 48.2% in the
He/O2 plasma treated sample. This corresponds to 3.7%
increase in surface oxygen. In the plasma treated sample,
3.7% more oxygen might have helped formation of more
oxygen containing molecules such as carbonyl, carboxyl
and hydroxyl. These polar groups are responsible for better
wicking of water in the plasma treated sample.
Fig. 4: EDX images of the untreated and plasma treated cotton textiles.
ATR-FTIR analysis
The changes in the surface molecules up to few
micrometers were studied in attenuated total reflectionFTIR to investigate the effect of plasma treatment on
cellulose chemistry. Figure 5 shows the ATR-FTIR spectra
of the various cotton samples.
Fig. 3: Water wicking time in the untreated and He/O2 plasma
treated cotton fabrics.
EDX analysis
Figure 4 shows the energy dispersive X-ray images of the
untreated and plasma treated cotton samples. Cotton fibre
after chemical treatment to remove fat, waxy and other
contaminants it becomes pure cellulose. As a result of this,
as expected in the untreated and plasma treated samples
only atomic peaks of carbon (C) and oxygen (O) are
present. EDX can not identify the hydrogen (H) atom. It
can be seen from the Figure 4 that intensity of peak height
Fig. 5: ATR-FTIR spectra of different cotton samples: (a) untreated,
(b) 2 min He/O2 plasma treated and (d) 4 min He/O2 plasma treated.
60
Effect of Helium-Oxygen Plasma Treatment on Physical and Chemical Properties of Cotton Textile
It can be seen that in the plasma treated samples such as
(b) 2 min He/O2 and (c) 4 min He/O2, there is a new peak
formed at 1710 cm-1. Denes et al reported the identification
of carbonyl peak that was resulted from oxidation of free
radicals formed by the cleavage of C1-C2 bonds of the
pyranosidic ring of cellulose by argon plasma treatment
[Danes et al, 1997; Garside et al, 2003]. Similar carbonyl
peak at 1710 cm-1 has also been observed in our case when
the cotton fabrics were plasma treated in the presence of
He/O2. Intensity of this peak is more the case of 2 min He/
O2 plasma treated sample. There was an increase in the
intensity at 2850 cm-1 assigned to methylene stretch. This
may be due to increase in cross-linking within the cellulosic
chains. Also there was an increase in intensity of –OH peak
in the range of 3000-3400 cm-1 due to reaction of oxygen
with cellulose. However, there is an increase in intensity of
the carboxylic acid –OH group at 3750 cm-1 in plasma
treated samples due to the formation of carboxylic acid
groups.
plasma treated samples, respectively. This corresponds to
51% and 179% increase in surface crystallinity. The result
indicates that plasma treatment would have increased
surface crystallinity of cotton fibres. With increasing
crystallinity, the intensity of peak at 893cm-1 decreases
and peak at 1420 cm-1 increases.
Fig. 6: ATR-FTIR spectra of the different cotton samples over the
wavaenumber of 700-2000 cm-1 : (a) untreated, (b) 2 min He/O2 plasma
treated and (c) 4 min He/O2 plasma treated.
Table 2: Normalized peak ratio of different molecules in the different
cotton textile
Table 1: Ratio of intensity of A1420 / A893 cm-1 for the different
cotton samples
Different samples
Ratio of corrected
intensities A 1420/A
893 cm-1
Crystalline
Index (CI)
0.0682/0.0626
0.0883/0.0534
0.1203/0.0396
1.09
1.65
3.04
Untreated
2 min He/O2 plasma treated
4 min He/O2 plasma treated
Table 2 shows the normalized peak ratio of the different
molecules of cellulose. In the 2 min He/O2 plasma treated
sample there was an increase in carbonyl peak. However,
in the 4 min He/O2 plasma treated sample, the peak ratio
was similar to untreated sample. It can be seen that the
normalized peak ratio for –OH increased from 3.63 in the
untreated sample to 5.48 and 5.29 in the 2 min and 4 min
He/O 2 plasma treated samples, respectively. This
corresponds to 51% and 45.7% increase in surface –OH
groups. Similar improvement was also observed for –C–H
asymmetric stretching at 2922 cm-1. The increase in –C=O
and –OH oxygen containing hydrophilic groups in the
plasma treated samples has helped the cotton samples to
be more hydrophilic. In the plasma treated sample, water
wicking time was lower possible due to formation of more
hydrophilic groups on the surface.
Different samples
The absorbance at 1420 cm-1 (–CH2 bending) and 893 cm1
(–C–O stretching) are sensitive to the amount of crystalline
portion versus amorphous portion in the cellulosic
substrates. In case of, broadening of these bands reflect
more disordered structure of cellulose. The absorbance
ratio at A1420 cm-1 and A893 cm -1 was defined as an
empirical crystalline index (CI). In 1958, O’Connor
proposed Lateral Order Index (LOI, A1420/A893) to
calculate the crystalline index (CI) for the cellulose material
[O’Connor et al, 1958]. Table 1 shows crystalline index
of the untreated and different plasma treated samples. It
can be seen that untreated sample has crystalline index of
1.09 and it increased to 1.65 and 3.04 in 2 and 4 min He/O2
Untreated
2 min He/O2 plasma
4 min He/O2 plasma
–C=O at
1710 cm-1
–OH in
3300-3400
cm-1
–C–H
asymmetric
stretching
at 2922 cm-1
1.00
1.38
1.00
3.63
5.48
5.29
1.83
2.63
3.00
*Peak ratio was calculated by normalizing the peak height with 1082
cm-1 for glycosidic ether (C–O–C)
3.5 Scanning electron microscope (SEM)
Figure 7 shows the scanning electron micrograph of the
different cotton samples. It can be seen from the Figure
7.a that untreated sample has smooth surface and individual
61
Samanta, et al.
(a)
(b)
Fig. 7: SEM micrograph of the different cotton samples : (a) untreated and (b) He/O2 plasma treated.
From the Table 3, it can be seen that in the 30 s plasma
treated sample K/S value decreased significantly. In the 1
min plasma treated sample also K/S value was lower than
the untreated sample. Unlike 30 s and 1 min plasma treated
samples, in the 2 and 4 min He/O2 plasma treated samples,
there was a significant improvement in the K/S value. The
K/S was 100 in the untreated sample and in increased to 110
in the plasma treated samples. Due to improvement in K/S
value, the red value i.e. a* increased from 46.39 to 47.14 in
the 2 min He/O2 plasma treated sample. Similarly, saturation
value (c) of red colour increased from 46.51 in the untreated
sample to 47.27 and 47.12 in the 2 min and 4 min He/O2
plasma treated samples, respectively. As expected in all the
plasma treated samples there were no significant change in
hue value (h). In the untreated and plasma treated cellulosic
textile reactive dye uptake and resulting K/S value in the
fabric depend on several parameters during dyeing such as
(i) number of hydroxyl groups, (ii) number of carboxylic
acid –OH group, (iii) presence of carbonyl groups, (iv)
surface and bulk crystallinity, (v) surface roughness and
(vi) surface charge i.e. zeta potential. Some of these factors
are in favour of reactive dyeing of cotton and others have
adverse effect. Among the above parameters, the surface
cotton fibres are easily visible. The surface of the cotton
fibre became rougher after treatment in the presence of
He/O2 plasma (Figure 7.b). During the plasma treatment
bombardment high energy ions, electrons, UV light and
photon might have etched the surface by removing the
few surface molecules resulting increase in roughness.
Analysis of colour parameters
Table 3 shows the various colour parameters in the
untreated and He/O2 plasma treated samples. The colour
parameters were measured by measuring the L, a*, b*, c,
h and K/S values. The L denotes the brightness (+) and
darkness (-) of the sample. The positive value of a*
indicates the sample is red in colour and negative value
indicates sample is green in colour. Similarly, positive and
negative of b* indicates the colour of the sample is either
blue or yellow. The c value indicates the saturation
(strength) of particular colour. Higher the value of ‘c’
indicates the stronger that particular colour. And ‘h’ value
indicates hue a particular colour. From the reflectance value
of light, K/S was calculated using the spectrophotometer
software.
Table 3: Colour parameters in the untreated and different plasma treated cotton samples
Plasma treatment time
0s
30 s
1 min
2 min
4 min
L
a*
b*
c
h
K/S
In %
60.84
62.79
61.52
59.78
59.72
46.39
42.99
45.30
47.14
46.97
-3.26
-3.73
-3.72
-3.52
-3.79
46.51
43.16
45.45
47.27
47.12
355.98
355.04
355.30
355.73
355.39
2.493
1.961
2.300
2.742
2.733
100
79
92
110
110
62
Effect of Helium-Oxygen Plasma Treatment on Physical and Chemical Properties of Cotton Textile
crystallinity and presence of carbonyl groups play negative
role. The amount of hydroxyl groups (–OH) has both positive
and negative role in reactive dyeing of cellulose in alkaline
condition. It was observed that after plasma treatment
surface of the cotton fabric became rougher and as a result
of this surface roughness value increased. If the surface of
a material is rougher, specific surface area would also
increase resulting lower K/S value.
crystalline index and (vi) surface charge (zeta potential)
during dyeing of cotton using reactive dye in alkaline
condition. Plasma processing of textile was carried out in
dry state without using water. The emerging plasma
technology would help to save significant amount of water
and energy while reducing the cost of production.
In the plasma treated samples there was formation of more
hydroxyl groups as reported in the ATR-FTIR analysis.
Therefore, it was expected that sample will absorbed more
amount of reactive dye and would produce darker shade
(more K/S). However, in the 30 s and 1 min plasma treated
samples the K/S was lower i.e. less mount of dyed get
absorbed. This may be due to formation of more carbonyl
groups (act as a reducing group) at lower plasma treatment
time and more surface crystallinity. Also the etching away
of waxy surface layer as well as parts of amorphous region
of cellulose and surface cross-linking might have reduced
the reactive dye uptake by the cotton fibres [Choudhury,
2013]. In the case of 2 and 4 min plasma treated samples
dye uptake was more due to possibly less number of carbonyl
group formation and more formation of –OH groups.
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Conclusion
Atmospheric pressure plasma was generated in the presence
of helium-oxygen (He/O2) mixture. It was observed that
upon ionization He/O2 produces milkish while colour.
Cellulosic cotton woven textile was plasma treated for 30
s to 240 s in the above plasma and different physical &
chemical properties were studied in details. It was observed
that after He/O2 plasma treatment, cotton became more
hydrophilic and there was generation of more number of –
OH and –C=O groups. Also after plasma treatment surface
became rougher. Due to increase in surface roughness and
more oxygen containing hydrophilic groups, water wicking
time reduced from 482 s in the untreated sample to 440 s
in the 4 min plasma treated sample. After plasma treatment
surface crystalline index (CI) increased from 1.09 in the
untreated sample to 3.04 in the 4 min He/O2 plasma treated
sample. Unlike 30 s and 60 s He/O2 plasma treated samples,
in the both 2 and 4 min He/O2 plasma treated samples,
there was an improvement in K/S value. The K/S value
increased from 100 in the untreated sample to 110 in the
plasma treated samples. The dye uptake by the fabric and
resulting K/S value of the dyed fabric depends on cumulative
factors such as (i) number of hydroxyl groups, (ii) presence
of carbonyl groups, (iii) presence of carboxylic acid –OH
group, (iv) surface roughness, (v) surface and bulk
63