J. Plasma Fusion Res. SERIES, Vol.5 (2002) 255-260

Application of Low Temperature Plasma on Modificationof Polypropylene
RASHIDI Abosaed, MOUSSAVI POURGHARBI Hossein, MIRJALILI Mohammad
and GHORANNEVISS Mahmoodr

Textile Section, Science & Research Campus of Tehran Islamic Azad University,
Tehran 14665-678, Irant Plasma Physics Research Center, Science & Research Campus of Tehran Islamic Azad. University,
Tehran 14665-678. Iran(Received: ll December 2001 / Accepted: 17 September 2002)

Abstract
Low temperature plasma is a useful technique to change the physical and chemical properties oftextile materials. In this experiment, the effect of low temperature plasma discharge treatment (helium)on physical, mechanical and chemical properties of polypropylene fibers and fabrics has been
investigated for the different duration with variation of magnetic field. Plasma treatment causes mainly
physical changes by creating microcrack on fiber surface and increasing surface friction. The wettability
and dyeability of fiber are increased by the treatment in such a way. As to increase in the dyeability, lightreflection decreases and the fibers get duller with the treatment. The results show that in longer timetreatments not only increase the surface friction but also increase the abrasion resistance, without muchdamage to the fiber strength. This may be a method for production of dull and semi dull polypropylene
fibers.

Keywords:
abrasion resistance, dye exhaustion, fabric, fiber, low temperature plasma treatment, polypropylene,strength, surface modification

1. Introduction

include the plasma induced polymerization processes,
the glow - discharge synthesis of new macromolecular
structures, and the surface modification and surface
grafting of polymers [3]. The ion bombardment action
on fibers can reveal the detail surface and internal
structures of the fibers [4,5] make the molecules of
surface layer of fibers activated. It is known that thesurface characteristics such as wetting, light reflection,
handling, friction coefficient and dye absorption play animportant role in textile processing. Surface modifica-

The stable low temperature plasma offers a unique

way to induce new characteristics of polymers andpolymer combination for special applications inadvanced technologies. Plasma can be a mixture of inert
gas molecules, ions of both positive and negative, freeradical, electrons and photons, with a net electric chargeof zero and low degree of ionization []. The easy way
to produce plasma is the use of magnetic field. Theplasma produced by DC technique is very stable and in
this system the test can be done in long periods anddifferent conditions [2]. Plasma techniques are used tomodify the characteristics of polymers. These techniquestion is effective for improvement in functionality
without changing the bulk characteristics of fibers.
@2002 by The Japan Society of Plasma
Science and Nuclear Fusion ResearchCorre sponding author' s e-mail: MSIDI50 @ yahoo. com

255

Rashidi A. et al., Application of Low Temperature Plasma on Modification of Polypropylene

Especially, the surface modification by discharge
treatments, such as low temperature plasma, sputteringand corona discharge, is of great interest because thesetreatments could be carried out without using large

amount of water and surfactant and are effective forenergy saving because of dry system [6]. There aremany techniques to control surface characteristics offibers with regard to textile processing. Usually, liquidsystems are mainly in textile processing applied but atpresent time dry systems such as plasma, sputtering, andion beam are of much interest. Therefore, it is necessary
to select the best technique complying with the purpose.
Low temperature plasma treatment causes mainly
chemical implantation, etching, polymerization, free
radical formation, crystallization, crosslinking, improves
the hydrophilic/hydrophobic and adhesive properties [3].
Towards the end of the 50's the first commercial
polypropylene fibers appeared and were then given a
prediction of a fantastic future as a christening present,

based upon their physical and chemical analyses.
However, some of the presumptions were not confirmed
in practice. This initiated in some of the countries athorough and systematic research into properties,
processing and uses of the fibers with the aim to cover
every possible aspect of the area. Teams of researchers

Fig. 1 Equipment's applied to perform low temperatureplasma treatment; (1) Gas inlet, (2) Valve, (3)Vacuum gauge, (4) Glass jar, (5) Specimen, (6)Vacuum pump, (7) Brass electrodes, (8) Powersupply.

from chemical, textile and engineering research6712 Tex warp, 6712 Tex weft, warp density 22lI cm,weft density lUl cm and weight of 442 glm were treatedinstitutes set about this task trying to investigated thenew material fully from the fiber formation polymer,
through spinning the polymer right up to thedevelopment of a wide range of textile products [7].
It was proposed to modify the fibers in the course

by helium low temperature plasma. The use ofequipment is shown in Fig. l. The yarn sample waswarped around the two clamps of chamber. The fabric
was fastened between two electrodes. The vacuum of
the 10-3 torr was achieved by a rotary pump followed bya diffusion pump, which was then increased to 10-6 torr.
By introduction of helium gas the pressure was adjusted
to 0.5 torr (66.6 Pa.). DC plasma reactor produced
helium low temperature plasma. The potential difference
between the electrodes varied from 1 kV to 3 kV. The
electron temperature was 3 eV and plasma current
changes from 30 to 50 pA. The electron temperatureand density 2 x 1010 / cm3 were measured by Langmuirprobe. According to Fig. I the magnetic field wasapplied in a long cylindrical tube from out side. Due tomagnetic field and magnetic force plasma focused inthis case, degree of ionization increase and impurity
decreased. In this experiment magnetic field can bechanges from 0 to 800 gausses and we select stablecondition for plasma in 380 gausses.
The tests were performed at 0.5 torr using heliumgas at the duration of 4, 8, 12, 16 and 20 minutes, thenthe samples were taken for further investigation.

of both their production and their processing. A
foremost aim of the modifications was the improvementof dyeability or - to put it more precisely - thepossibility of making the fibers surface dyeable. The
dyeability problem has not been solved yet and this is
why the fibers are best dope-dyed even nowadays. The
attempts to modify the fiber surface by grafting have notyet found any practical use either.

In this paper, surface modification of polypropylene fibers by helium low temperature plasma
treatment has been investigated on the basis of abrasion
resistance, surface friction factor, thermal analysis(DSC), FT-IR, strength and elongation values anddyeability measurement.

2. Experiments (Samples and Low
Temperature Plasma Treatment)
During this research, lO0 Vo Polypropylene 140
Tex yarn and 100 Vo polypropylene plain weave with256

Rashidi A. et al., Application of Low Temperature Plasma on Modification of Polypropylene

3. Results (Dyeability of Samples)

exhaustion percent value is increased with the treatment
time showing the effect of plasma treatment onPlasma treated and virgin polypropylene samples

were dyed in an AHIBA dyeing system with C.I.
Disperse Blue 56. The dyebath was comprised 3 cm-3
acetic acid lO Vo and I cm-3 dispersing agent 10 7o(Setamole WS). The liquor ratio was kept at 50:1. The
bath temperature was set at 60oC for 5 minutes. Thenthe temperature was raised to 130'C by a thermal

improving the dyeability of polypropylene fibers. Onereason for this result is that plasma irradiation produces
microcrack of the surface layer on the fiber, which
increase surface contact. This effect is shown in thegradient of 2"C/min and dyeing operation was continuedfor 45 minutes. At the end of the dyeing operation, the4. Physical Properties (Abrasion Resistanceand Friction Factor)

given SEM images.

dye concentration of each bath was measured by

The rates of abrasion resistance modification inabsorption spectrophotometer technique.
All measurements were done at room temperatureand the following relation calculated the exhaustion

treated and untreated samples were measured by yarnabrasion tester, the results are given in Table 2. As it isshown in the table, by increasing plasma treatment time
to about 16 min., abrasion resistance is increased andhen decreased. This increased abrasion resistance ispercent:A-At
E=\-n'xl00-

important for polypropylene fibers used in carpets dueto their durability. The reason of this increase can be
related to forming cross-linkage in fiber surface layers
treated by helium plasma irradiation, which causes

4

where E was exhaustion percent in time t, 46 : absorption of dye solution in time 0 and Ar : absorption of dyesolution in time r.
The results from dyeing treatment are given in
Table 1.
One of the important parameters in dyeing is theexhaustion percent in the balanced state which depends
considerably on available dye absorbing places in fibers
which have dye absorbing functional group and on dye

formation of powerful polymer layer on the fiber
surfaces. These modifications are shown in Fig. 2.

The surface friction factor change rates of treatedand untreated samples were examined by measuringsliding angle by Shirley fabric friction tester, results are
given in Table 2. The results show that the plasma
treatment cause fabric friction factor to be increased anddiffusion ability in amorphous of fibers lacking dye

Table 1 The change of dye uptake of polypropylene un-time increase doesn't have much effect on increasing thefriction factor. It also increases the fiber entanglement
adhesion and adherence between fibers. which are useful
to improve yarn quality.

treated and treated with low temperature

SEM images of treated and untreated samples areabsorbing functional group. After treatment theplasma.
Treatment time Residual dye in batch Dye uptake Exhaustionmin.

EllCll

Va

00.15

0.15

50.2

40.13130.168756.4

80. l 388

t20.1225

o.r712o.t77559.3

l60.1 183

0.181760.78

200.1 168o.1832

6r.3

Porous substraie

57.29

Table 2 The change of abrasion resistance and friction
factor of treated and untreated Polypropylene.

olymerizationl Por€siz€€te material(7o)

261

4297

13.8

0.6

8343

31.4

0.611

t2

350

34.1

o.612

l6

370

41.8

0.6

20365

39.8

0.6

Cross-linking Functionalization
surface (grafting)of substEt€

Cross-linking ofconvsntional polimer coallng

0.514

0I

reduaion

WIUM

Treatment time Abrasion Increase of abrasion Friction factor( p)resistance resistancemin.

Nonporous substrateI

ffi

Fig. 2 Surface modification of polymers by plasma treatment.
257Rashidi A. et al., Application of Low Temperature Plasma on Modification of Polypropylene

Fig.3 SEM photographs of polypropylene untreated and treated with low temperature helium plasma,x 14000; (A) Untreated, (B) 4 min., (C) 8 min., (D) 12 min., (E) 16 min., (F) 20 min.

polypropylene fibers; strength, elongation percent,tenacity and work of rupture of treated and untreatedyams were examined by use of Instron strength tester.

0minl

The obtained results show that helium low temperatureplasma treatment causes a little reduction in strength and4minaSmintenacity of polypropylene yarn, and this reduction

I12m,n^remains constant after 8 minutes.

16 min-'.""...".-...-..r20+ min ^Table 3 The change of physical properties of treatedand untreated polypropylene fiber.

-Treatment Strength

200 300 M

Elongation Tenacity Work oftime

500 600 700 Eoo

Wayelength (nm)Fig.4 Reflectance spectra of polypropylene Fabric untreated and treated with low temperature plasma.

shown in Fig. 3. They show that plasma treatment
produce some microcrack on the fiber surfaces. By

increasing treatment time the effects of surface

min.

NVo

0

38.81

36.58

437.41

33.76

835.4233.26

1235.3330.04

l635.16

32.03

zo

35.06

32.O8

cN/Texrupture
cN.cm

27.72 288.2
26.76 261.2
25.3 272.2
25.24 222.64
25.06 23r
25,M 317.82

unevenness changes. This structural change increases

Table 4 The change of thermal properties and crystallization of treated and untreated polypropylene.

the surface friction factor, causes irregular light

Treatment

timemin.

reflection and leads to dull fibers. In Fig. 4 the change
rates of light reflection in treated and untreated samplesare shown.

5. Mechanical Properties
In order to test plasma treatment intensity and its

effect on strength and elasticity properties of258

Melting Degradation Enthalpy Crystallitepointpointilg

04t70.64

194.7rr69.0919t.2

8r68.68

190.7812168.63

t86.7216

168.57191.98)(l168.6

r89.76

86.73
97.46
90.3
94.7
91.54
93.4t

39.87
44.8

41.52
43.54
42.09
42.92

Rashidi A. et al., Application of Low Temperature Plasma on Modification of Polypropylene

The considerable point in the results from thisexperiment shows reduction in elongation at break. The
reason may be due to formation of crystals near thesurface of fibers. Results are given in Table 3. In orderto study the changes made in structure and arrangementof molecular chains and functional groups of treatedpolypropylene samples, they were examined by use ofthermal analysis (DSC) and FT-IR spectrometry
techniques. The results from thermal analysis (DSC)
show that helium plasma treatment leads to slight fall in

melting point, but thermal range required melting thesample begins to increase with treatment time and thenremain constant. The crystallization percent is increasedtoo (Table 4). Increase in crystallization percent andslight decrease in melting point may be related to0.@

1m.00,00,m

degradation of large crystals and formation of small
crystals, which were expected, affected the abrasion
resistance. DSC diagram of an untreated and treated for
4 minutes is provided in Fig. 5. Results from FT-IR
spectrometry of a polypropylene sample treated by&0.m

Fig.5 DSC diagram of polypropylene. A) Untreated,B) Treated for 4 min.

helium low temperature plasma indicate that nostructural change occurred in molecular chains ofpolypropylene before and after plasma treatment (Fig.
6).

6. Conclusions
The application of low temperature plasma on
polypropylene has shown effects that can be used to
improve the fiber performance. The results indicate thatsuch plasma application changes all chemical properties
in such a way to enable the dyeing ofpolypropylene andoffers a new spectrum in chemical process of thesefibers. The physical properties change when larger
surface crystals are broken down and replaced bysmaller crystals which are shown by maintaining themelting points but changing the melting range thatsuggested by DSC data. This greatly increases theabrasion resistance of yarns.

100.0

YoT
90.0

t0.0

There was not much effect on detected strength but

70.0

reduction in extensibility was noticeable. The surface
roughness appears in the SEM photomicrographs. These

60.0
50.0

result from chemical reactions and microcracks on thefiber surface. The surface roughness is not a primaryreason for improved wettability, but may increase it.

,10.0

30.0
20.0
10.0

References

tll,l0llo 3500 3ln0 2500 2m0 l?50 1500 1250 l@0 750 500
Wavenumber l/cm

t2l

Fig. 6 FT-IR diagram of polypropylene, A) Untreated,B) Treated for 20 min.
259

V.E. Golant, A.D. Zhilinsky and I.E. Sakarov, Fundamentals of Plasma Physics, 20 (1987).
M. Sarmadi, A.R. Denes and F. Denes, Textile
Chemist and Colorist, June 1996, 17 (1996).

Rashidi A. et al., Application of Low Temperature Plasma on Modification of Polypropylene

t6l T. Wakida and S. Tokino, text. Res. J. 21, March,

t3l M. Sarmadi and F. Denes, Tappi Journal 79 No.8,
189 (1996).

1996,69 (1996).
O.
t7l Pajgrt, B. Reichstadter and F. Sevcik, Production and Application of Polypropylene Textiles, I I

t4l Yu Weidong and Yan Haojing, J. China Text. Uni.
(English edition) 10 No. 3, 17 (1993).
t5l Yan. Haojing and Yu Weidong, J. China Text. Uni.
(English edition) 10 No. 2, 2 (1985).

(1983).

260