Non Aqueous Treatment Using Plasma_Canup_Thesis

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ABSTRACT

CANUP, LAURA KATHERINE. Non Aqueous Treatment of Fabrics Utilizing Plasmas.

(Under the direction of Marian McCord)

The contents of this paper present information from work conducted by utilizing

plasma technology for fabric treatment. Initially, experimentation was done in low-

pressure plasma systems to change the hydrophilic properties of denim fabric. From

these experiments, data was collected that proved denim fabric, both sized and desized,

could obtain hydrophobicity through a fluorocarbon plasma treatment. Using C3F6

fluorocarbon gas provided a greater level of hydrophobicity than using CF4 plasma gas.

The desized denim showed a greater amount of hydrophobicity, in both gases, than the

sized denim. These results can be found in chapter IV. The remaining work, found in

chapters II and III, focuses on the utilization of atmospheric plasmas on the treatment of

nylon 6,6 fabric. Atmospheric plasmas could allow continuous treatment of fabric and

shorter treatment times for fabric, all of which would be better suited for industrial

processing, more specifically in textiles. Nylon 6,6 fabric was treated with air-He plasma

as well as air-He-O2 plasma, where the levels of O2 varied. A significant decrease in

tensile strength was found in treatments lasting five minutes or longer. However,

micrographs of the fiber surface illustrate instances of surface treatment, even at times

less than five minutes. Continuing work on the project includes the building of a

prototype machine for industry (currently in progress), the treatment of many different

kinds of fabrics, and the evaluation of their mechanical, chemical, and physical properties

and functionability thereafter.


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NON AQUEOUS TREATMENT OF FABRICS UTILIZINGPLASMAS

by

LAURA KATHERINE CANUP

A thesis submitted to the Graduate Faculty of

North Carolina State University

In partial fulfillment of the requirements for the Degree of

Master of Science

TEXTILE ENGINEERING AND SCIENCE

Raleigh

2000

APPROVED BY:

Dr. Orlando Hankins Dr. Yiping QiuMinor Committee Member Committee Member

Dr. Marian McCordChair of Advisory Committee


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Dedication

This work is dedicated to all of my family, whose support throughout

school has meant the world to me; to my beloved fiance, who has changed my

life completely and helped me to become all that I am today; and finally to the

wonderful professors I have had at NCSU, who have inspired me throughout my

moment there Dr. William Kimler - (History), Dr. Martin, Dr. Silber (Math),

Dr. Richard Johnson, Dr. Silverburg (Mechanical Engineering), Dr. Bilbro

(Electrical Engineering), Dr. Wayne Skaggs (Biological and Agricultural

Engineering), Dr. Jon Rust, Dr. Tim Clapp, Dr. Perry Grady, Dr. Sam Hudson,

Dr. Marian McCord (Textile Engineering & Textile Chemistry), and Dr.

Mohamed Bourham (Nuclear Engineering).


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Biography of the Author

Laura Katherine Canup was born in Greenville, North Carolina on June 11, 1976.

At a young age her family moved to Fayetteville, North Carolina where she completed

her high school education at Seventy-First Senior High. She attended North Carolina

State University immediately thereafter where she graduated with a Bachelor of Science

degree in Textile Engineering and a Bachelor of Science degree in Textile Material

Science in May of 1998. After completing a summer internship at Glen Raven Mills, Inc.

in Burlington, North Carolina, she continued her education at North Carolina State

University to achieve a Master of Science degree in Textile Engineering (December

2000), focusing her thesis research on plasma technology in the textile industry. She is

currently working as a research engineer for Milliken & Company, located in

Spartanburg, South Carolina, in their Fashion, Apparel, and Specialty Fabrics division.


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Acknowledgements

I would like to thank North Carolina State University for providing the resources

needed to start and complete my graduate work. I would also like to thank the National

Textile Center for providing funds for the project on which I worked throughout graduate

school. I will take this opportunity to thank and acknowledge all of those who helped

with guidance and experimentation through the project:

Mr. Jinho Hyun

Miss Traci Jones

Miss Elizabeth Tapaszi

Mr. Vincent Chian

Mr. Brian L. Bures

Mrs. Wrennie Edwards

Mrs. Carla MacClamrock

Mrs. Susan Olsen

Ms. Diane Harper

Ms. Jane Perry

Dr. Peter Hauser

Dr. Mohamed Bourham

Dr. Yiping Qiu


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v

TABLE OF CONTENTS

List of Tables ..................................................................................................................... ix

List of Figures..................................................................................................................... x

I. INTRODUCTION ...................................................................................................... 1

A. About Plasmas ........................................................................................................ 3

B. Plasma Treatments: The Industrial Plasma Machines ............................................ 8

B.1 Vacuum Plasma Devices..................................................................................... 8

B.2 Atmospheric Plasma Devices ........................................................................... 10

C. Plasma Treatments: Previous Research Findings ................................................. 17

C.1 Traditional Fabric Processing........................................................................... 17

C.2 Cotton................................................................................................................ 18

C.2.1 Main Problems.......................................................................................... 19

C.2.2 Plasma Treatments .................................................................................... 20

C.2.2.1 Desizing ................................................................................................ 20

C.2.2.2 Dyeability.............................................................................................. 20

C.2.2.3 Water Repellency.................................................................................. 20

C.2.3 Summary................................................................................................... 21

C.3 Nylons and Polyamides..................................................................................... 21

C.3.1 Main Problems.......................................................................................... 22

C.3.2 Plasma Treatments .................................................................................... 22

C.3.2.1 Dyeability.............................................................................................. 22

C.3.2.2 Filtration................................................................................................ 25

C.4 Other Plasma Treatments of Interest................................................................. 27

C.4.1 Wool Fiber ................................................................................................ 28

C.4.2 Silk Fiber................................................................................................... 29

C.4.3 Polypropylene ........................................................................................... 29

C.4.4 Other Fibers .............................................................................................. 29

C.5 Fabric Treatments with Atmospheric Plasma................................................... 30

C.5.1 Cotton Fiber .............................................................................................. 30

C.5.2 Polypropylene ........................................................................................... 30


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C.5.3 Polyethylene terephthalate ........................................................................ 31

C.5.4 Wool.......................................................................................................... 31

D. Bibliography ......................................................................................................... 34

II. Modification of Nylon Fabrics with Atmospheric Pressure Plasmas; Part I:

Treatment of Nylon Fabric with He and O2 Plasmas........................................................ 38

A. Abstract................................................................................................................. 38

B. Introduction........................................................................................................... 39

C. Experimental ......................................................................................................... 40

C.1 Materials ........................................................................................................... 40

C.2 Plasma treatment............................................................................................... 40

C.2.1 Instrumentation ......................................................................................... 40

C.2.2 Procedure .................................................................................................. 41

C.3 Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy

(EDS) ........................................................................................................................ 41

C.4 Fabric tensile test .............................................................................................. 42

C.5 Statistical analysis............................................................................................. 42

D. Results and Discussion ......................................................................................... 42

D.1 Scanning Electron Microscopy......................................................................... 42

D.2 EDS Analysis of Fiber Surface......................................................................... 43

D.3 Fabric Strength Measurements ......................................................................... 44

E. Conclusions........................................................................................................... 44

F. Acknowledgments................................................................................................. 45

G. References............................................................................................................. 45

III. Modification of Nylon Fabrics with Atmospheric Pressure Plasmas; Part II:

Treatment of Nylon Fabric with He and O2 Plasmas........................................................ 55

A. Abstract................................................................................................................. 55

B. Introduction........................................................................................................... 56

C. Experimental ......................................................................................................... 56

C.1 Materials ........................................................................................................... 56

C.2 Plasma treatment............................................................................................... 57

C.2.1 Instrumentation ......................................................................................... 57


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C.2.2 Procedure .................................................................................................. 57

C.3 Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy

(EDS) ........................................................................................................................ 58

C.4 Fabric tensile test .............................................................................................. 58

C.5 Statistical analysis............................................................................................. 58



D.2 EDS Analysis of Fiber Surface......................................................................... 59

D.3 Fabric Strength Measurements ......................................................................... 60

E. Conclusions........................................................................................................... 60


G. Bibliography ......................................................................................................... 61

IV. Investigation into the Modification of Cotton Using Low Pressure Plasmas........... 73

A. Abstract................................................................................................................. 73

B. Introduction........................................................................................................... 74

C. Experimental ......................................................................................................... 75

C.1 Materials ........................................................................................................... 75

C.2 Instrumentation ................................................................................................. 75

C.2.1 Plasma Chamber ....................................................................................... 75

C.2.2 Goniometer ............................................................................................... 75

C.2.3 Scanning Electron Microscopy (SEM)..................................................... 76

C.3 Procedure .......................................................................................................... 76


D.1 Hydrophobicity Measurements from Vacuum Plasma..................................... 76


E. Conclusions........................................................................................................... 80


G. References............................................................................................................. 81

V. Appendix A: Evaluation of Capacitively Coupled Atmospheric Plasma................ 99

VI. Appendix B: Atmospheric Plasma System Modeling ............................................ 103

A. Plasma Circuit Model and Matching Network ................................................... 106


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A.1 Matching Circuit Configuration:..................................................................... 107

B. Matching Conditions:.......................................................................................... 108


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LIST OF TABLES

Table I-1: Characteristic Operating Parameters of Atmospheric Plasma Machines........ 16

Table I-2: Regular Treatments on Cotton and the Possible Plasma Treatment

Replacement.............................................................................................................. 21Table I-3: Plasma Treatments and the Resulting Property Effects for Cotton ................. 21

Table I-4: Plasma Treatments and Resulting Property Effects for Nylon and Polyamides

................................................................................................................................... 27

Table I-5: Atmospheric Plasma Treatments and Property Effects.................................... 33

Table II-1: Tensile Strength of plasma-treated nylon 6,6 fabrics ..................................... 47

Table III-1: Sample Carbon Counts EDS Measurements .............................................. 62

Table III-2: Tensile Strength of plasma-treated nylon 6,6 fabrics.................................... 63



Table IV-1: C3F6 Capacitively Coupled Plasma Experimental Control Parameter Design

................................................................................................................................... 82

Table IV-2: Capacitively Coupled CF4 Plasma Experimental Control Parameters.......... 83

Table IV-3: Inductively Coupled CF4 Plasma Experimental Control Parameters............ 84


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LIST OF FIGURES

Figure I-1: Inductively Coupled Industrial Plasma Chamber [11] ..................................... 6

Figure I-2: Schematic of Upper Chamber of OAUGDP Device [11]................................. 7

Figure I-3: KPR-180, Vacuum Plasma, Batch Processing Machine [13]........................... 9Figure I-4: Ldz Continuous Processing Vacuum Plasma Machine [15]........................... 9

Figure I-5: Dielectric Barrier Discharge and Corona Discharge, respectively [9] ........... 11

Figure I-6: Pyrex Glass Reactor [39] where (a) is the apparatus: 1, upper electrode; 2,

lower electrode; 3 and 4, glass plates; 5, Pyrex tube; 6, Pyrex bell-jar; 7, O-ring and

(b) is the brush-style electrode.................................................................................. 12

Figure I-7: OAUGDP Device from University of Tennessee [11]................................... 13

Figure I-8: Schematic of PALADIN [40] ........................................................................ 14

Figure I-9: Atmospheric Pressure Glow Discharge Model from Plasma Ireland [9] ....... 15

Figure I-10: Hirano Kohon, Ltd Atmospheric Plasma Device [41]................................. 15

Figure I-11: Atmospheric Device Built Experimentally by the Technology Research

Institute of Osaka Prefecture in Japan [41]............................................................... 16

Figure I-12: Process Flow of Fabric Preparation.............................................................. 17

Figure I-13: Chemical Structure of Cotton and a Picture of the Morphology of Cotton

[45]............................................................................................................................ 19

Figure I-14: Chemical Structures of Nylon 6 and Nylon 6,6 [45].................................... 22

Figure I-15: Three-Phase Model Schematic Diagram of PET or Nylon 66 Fibers [48]... 24

Figure I-16: Possible Cleaving Mechanism of Polyamide Chain [49] ............................ 26

Figure I-17: Possible Crosslinking Mechanism of Polyamide Chain [49] ....................... 26

Figure I-18: Chemical Structures of Wool, Silk, and Polypropylene [45,50] .................. 28

Figure I-19: Oxygen plasma treated wool under atmospheric pressure. Column 1 is at 10

(a) and 20 (b) minute treatment times. Column 2 is at 25 (a) and 30 (b) minute

treatment times [41]. ................................................................................................. 32

Figure II-1: Basic elements of a capacitively-coupled plasma chamber .......................... 48

Figure II-2: Circuit diagram of atmospheric plasma chamber and equivalent plasma

elements .................................................................................................................... 49

Figure II-3: SEM micrographs of non-exposed nylon samples. Left micrographs at

magnification 4000, while right ones are at 800 . ................................................ 50


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Figure II-4: SEM micrographs of exposed nylon samples in atmospheric helium plasma

for 2 min. Left micrographs at magnification 3000, while right ones are at 800 .51

Figure II-5: SEM micrographs of exposed nylon samples in atmospheric helium-oxygen

plasma for 5 min. Left micrographs at magnification 4000, while right ones are at

800 . ........................................................................................................................ 52

Figure II-6: SEM micrographs of exposed nylon samples in atmospheric helium-oxygen

plasma for 10 min. Left micrographs at magnification 4000, while right ones are at

800 . ........................................................................................................................ 53

Figure II-7: EDS analysis of nylon samples: (a) non-exposed, (b) exposed in atmospheric

helium plasma, and (c) exposed in atmospheric helium-oxygen plasma.................. 54

Figure III-1: Basic elements of a capacitively-coupled atmospheric plasma chamber .... 66

Figure III-2: Untreated nylon 6,6 magnified at 4000 and 500...................................... 67

Figure III-3: He plasma treated, 2 min exposure time, magnified at 4000 and 700..... 68

Figure III-4: O2 plasma treated, 30 sccm flow rate, 3 min exposure time, magnified at

4000 and 1000. ..................................................................................................... 69

Figure III-5: O2 plasma treated, 60 sccm flow rate, 1.5 min exposure time, magnified at

4000 and 1000. ..................................................................................................... 70

Figure III-6: O2 plasma treated, 90 sccm flow rate, 0.5 min exposure time, magnified at

4000 and 1000. ..................................................................................................... 71

Figure III-7: O2 plasma treated, 90 sccm flow rate, 3 min exposure time, magnified at

5000 and 1000. ..................................................................................................... 72

Figure IV-1: Basic Elements of Capacitively Coupled Atmospheric Plasma Chamber... 85

Figure IV-2: Diagram of Contact Angle Measurement with Goniometer........................ 86

Figure IV-3: Average Wet-Out C3F6 Capacitively-Coupled Treatment Sized Denim..... 87

Figure IV-4: Average Wet-Out C3F6 Capacitively-Coupled Treatment Desized Denim. 88

Figure IV-5: Average Wet-Out CF4

Capacitively-Coupled Treatment Desized Denim .. 89

Figure IV-6: Average Wet-Out Time CF4 Plasma Inductively Coupled Sized Fabric

(Sample R1.3 treated upside-down).......................................................................... 90

Figure IV-7: Chemical Attachment of Fluorocarbons on the Fiber Surface with a

Fluorinated Acrylate Ester Film [14]........................................................................ 91


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Figure IV-8: Oil and Water Repellency versus the Number of Fluorinated Carbon

Atoms[13,14] ............................................................................................................ 92

Figure IV-9: Untreated Sized Denim magnified at 4000................................................ 93

Figure IV-10: CF4 treated Sized Denim (75mTorr, 300W, 4 min pulsed for 8 minutes)

magnified at 5000 and 800. .................................................................................. 94

Figure IV-11: C3F6 treated Sized Denim (100mTorr, 50W, 60seconds) magnified at

5000 and 250. ....................................................................................................... 95

Figure IV-12: Untreated Desized Denim magnified at 5000.......................................... 96

Figure IV-13: CF4 treated desized denim (50mTorr, 100W, 30s) magnified at 5000... 97

Figure IV-14: C3F6 treated desized denim (150mTorr, 50W, 30s) magnified at 5000. 98

Figure VI-1: Detailed Model of Atmospheric Plasma, Model #1 .................................. 104




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I. INTRODUCTION

Industry is always in search of new treatments and new technology that will lower

costs, increase productivity, and decrease waste and waste treatment. Plasma treatment

of textile materials has emerged as a major possibility for replacing many current wet-

chemical processes, or at least enhancing them. Plasmas can be defined as gaseous states

of matter that consist of a dynamic mix of ions, electrons, free radicals, metastable

excited species, molecular and polymeric fragments, and large amounts of visible, UV,

and IR radiation [1,2]. Known as the fourth state of matter, plasmas are typically thought

of in reference to solar objects such as the sun and natural occurrences such as lightning.

Decades of development have allowed researchers and scientists to contain and control

such matter and to develop applications such as materials processing, waste reduction,

and alternative energy sources [3-5]. Although plasma treatments have been used for

years to process materials including semiconductors, microchips, and other electrical

devices, the textile industry has only recently opened their doors to such a process [3-5].

There have been only a few companies that have actually used the process for

manufacturing [6]. Most of the information found regarding plasma treatment on textile

materials remains in the research phase.

Plasmas modify the surface of materials through the transfer of energy from the

excited plasma particles to the substrate. Through this interaction, it is possible to obtain

both chemical and physical modification. Ar-He gas plasma has been successful in

bleaching materials. Fluoro-monomer plasma has been proven to provide a

waterproofing treatment [6]. It has also been shown that plasma can improve dyeability

and anti-soil properties. The mechanisms for these modifications include surface etching,

surface activation, crosslinking, chain scission, decrystallization, oxidation, and chemical

reactions on the surface. The type of reaction largely depends on the type of reaction gas

used. For instance, inert gases such as argon and helium typically cause surface

activation to take place. Compounds that contain oxygen are commonly used as etching

gases [7,8]. Nitrogen gas will tend cause reduction reactions since it is a reducing gas.

In current research, most plasma treatments used are conducted at low pressures

(under vacuum) with a variety of gases. Using vacuum chambers for treatments is not


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well suited to the typical continuous processing that is often used in the textile industry

and many other industries. Nevertheless, using low-pressure treatments allow for very

controlled conditions where detailed research can be conducted and optimized. Through

the utilization of these devices, plasma treatment opportunities can be found. In the

research presented in this paper, Chapter IV reviews a study performed on cotton (denim

fabric) treated with low-pressure plasma. Eventually, research conclusions and data from

low-pressure plasma treatments will be used as a point of comparison and optimization

for more industry-oriented plasma processes.

The following two chapters of this paper discuss research conducted on nylon 6,6

fabric with plasmas operating at atmospheric pressure. Atmospheric pressure plasmas

have only in the past few years emerged as a potential means of treating textile materials.

In the past, these plasmas have been found to result in extremely non-uniform treatments

and be very uncontrollable [9]. Recently, however, it has been found that under certain

key conditions, atmospheric treatments can be performed safely, reliably, and uniformly

[10]. Plasmas that operate at atmospheric pressure open up a world of opportunity to the

industry. Because of the operating pressure, there is a strong possibility for continuous

processing, which would infer treatments without waiting for the fabric to dry or for the

vacuum machine to pump down to the appropriate pressure.

The overall focus of this research was to provide preliminary investigations of the

usefulness and treatment quality of plasmas that can be used for continuous industrial

materials processing, or the atmospheric pressure plasmas. Oxygen and helium plasmas

were both used for treating nylon 6,6 fabric under atmospheric pressure. The mechanical

and surface properties of the fabric were evaluated accordingly. A study was also

conducted on the application of low-pressure fluoromonomer gas plasmas to denim fabric

(100% cotton), in order to increase its hydrophobicity. The data will eventually be

compared to similar treatments that will be performed at atmospheric pressure. In the

remainder of the introduction, a review of plasmas, plasma machinery, and recent plasma

research on textiles will be reviewed.


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A. About Plasmas

As mentioned previously, plasmas are gaseous states of matter that consist of a

dynamic mix of ions, electrons, free radicals, metastable excited species, molecular and

polymeric fragments. Industrial plasmas have found large markets in the electronics

industry, for production or modification of computer chips, semiconductors, aircraft and

automobile parts, machine tools, medical implants, and integrated circuits. There are

many types of plasmas that are used for industrial processing. They differ in the way

they are formed and the range of their characteristics after they are produced. In general,

all plasmas are characterized by the same basic parameters no matter the system to which

they are coupled. These parameters can be grouped as either internal (qualities of the

plasma itself) or external (qualities of the operating control parameters). The main

internal parameters of concern are:

Plasma temperature the average individual temperature of the electrons or ions in

the plasma.

Plasma density the number of activated species in a plasma.

Plasma frequency and collision frequency

Many of these parameters are measured directly from the plasma or are applied

intentionally through the plasma controls. Each one of them affects the outcome of the

treatment, and the plasma itself. The plasma temperature refers to the temperature of the

activated electron and ion (separate species and temperatures) particles. These

temperatures are usually measured in the energy unit of electron-Volts (eV), which is

analogous to 11,600 K, however it is not the overall plasma temperature (which remains

at room temperature in many cases). This parameter can be measured, although it can be

difficult depending on the nature of the plasma. The plasma temperature greatly affects

other parameters, such as plasma density and particle velocity. As seen in the equation

for each, an increase in temperature usually means an increase in particle density and an

increase in velocity.

Plasma density can be found through equation (1). This is commonly known as

Boltzmanns equation.

KTe

enn

= 0 (1)


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Here, n0 is the particle density of the gas used (known constants), k is Boltzmanns

constant, e is the charge on a single particle (electron), T is plasma temperature, and is

the potential, or voltage, applied [11].

The natural plasma frequency is commonly given by equation (2) where pe is the

plasma electron frequency and pi is the plasma ion frequency. These individual

frequencies can be found through equation (3) [11]. In the equations given, 0 is the

permittivity of free space and me or mi is the mass of either an electron or ion,

respectively.

( ) 21

22

ie ppp += (2)

====

m

nep

0

2

, where

=

i

i

p

m

eni

0

2

and

=

e

e

p

m

ene

0

2

(3)

There are a variety of particle velocities that can be calculated when referring to

particles in a plasma state. The most commonly used equation for velocity is the mean

thermal velocity. The equation for the mean thermal velocity is shown in equation (4).

21

8

====

m

kTv

where

21

8

====

e

e

em

eTv

and

21

8

====

i

i

im

eTv

(4)

The collision frequency is the average number of collisions that a particle makes

in a certain time period. This parameter can be found through equation (5). In this

equation, n1 is the number of particles (of a homogeneous type) per unit volume, is the

cross-sectional area for the particular interaction, and is the particle velocity, usually

given by a Maxwellian distribution [12]. The bracketed section is integrated over the

appropriate distribution function.

vnc 1= (5)

In the case of a capacitively coupled plasma (with parallel plates), the magnitude

of the electric field is usually found through the simple equation shown in equation (6).

E is the electric field, V is the voltage or potential applied between the plates, and d is the

distance between the plates. This equation holds true prior to plasma initiation, however,

after the plasma starts, E can become complicated.

d

VE ==== (6)


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There is a unique breakdown voltage, or potential (Vb), at which every gas will

strike a plasma state. Vb is dependent on the pressure of the gas and the electrode

spacing. The equation for the breakdown potential for a given gas is shown in equation

(7). Here, A and B are constants for a given gas under particular ranges. P is the

pressure (in Torr), d is the distance between the electrodes, se is the secondary electron

emission at the cathode [11,12].

( )

( )

+

=

se

b

PdA

PdBV

11lnlnln

(7)

Industrial plasmas can be produced in a variety of ways. Only two methods were

used in this research, but they are the most common techniques of creating plasmas for

materials processing. The first form is through an inductively coupled system. This

system is characterized by one or two induction coils that produce a voltage, which

causes the plasma to initiate. For materials processing, there is typically one coil located

on top of an electrode that produces the voltage. A diagram of this process can be seen in

Figure I-1. The electrode plates serve no other purpose than a floating and grounded

surface for the coil and substrate. For operation of these plasmas, it is necessary to know

the potential (found from the induction current and magnitude of inductor), as well as the

chamber pressure, power, operating frequency, and the gas used. Inductively coupled

plasmas are formed via an oscillating magnetic field. Although other inductively coupled

plasmas operate at much higher power levels, the inductive parallel plate plasma reactor

can operate at powers up to 2 kW, which is still higher than capacitively coupled devices.

Because of the high power, high electron densities can also be obtained. Typically,

inductively coupled plasmas operate at very low pressures, under vacuum. When a

plasma is at a low pressure, longer mean free paths of the plasma particles can be

obtained and very little scattering of particles occurs before they hit the substrate. This

means that it is possible to carefully control the way in which the plasma particles modify

the surface because the particles are less likely to collide with one another. This plasma

type is used for very controlled etching and deposition applications. [11,12]


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Figure I-1: Inductively Coupled Industrial Plasma Chamber [11]

The other form of initiating a plasma is through capacitive coupling. In this

device, parallel plates, or electrodes, are connected to the power supply and sustain a

voltage across the space between the plates, where the plasma will initiate. Figure I-2gives a representation of this type of plasma device. The external parameters that help to

define a capacitively coupled plasma are the potential (or voltage between the

electrodes), distance between the plates, chamber pressure, power, operating frequency,

and the type of gas used. Capacitively coupled plasmas operate through an oscillating

electric field. If under vacuum pressures, operation can occur at power ranging from

50W 500W [11]. If at atmospheric pressure, the power can range from 10W 150W.

Heating of the plasma and substrate is usually not as high as in an inductively coupled

plasma. Also, operation at atmospheric pressure is possible. A detailed analysis of

capacitively coupled plasma systems, which operate at atmospheric pressure, can be

found in Appendix B [11,12].


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Figure I-2: Schematic of Upper Chamber of OAUGDP Device [11]

Basic plasma theory revolves around the relationships of induced electric and

magnetic fields with gases under various and, sometimes, extreme conditions. Once a

gas is ionized by being subjected to an electric and/or magnetic field, the plasma particles

may eventually come to an equilibrium state in their velocities and energies. Although

particles within the gas are all moving at different velocities, they equilibrate in the form

of a distribution function. If kinetic or thermodynamic equilibrium is reached, the

velocity and energy distributions take the form of the Maxwell-Boltzmann distribution

function. There are few plasmas that reach or come near to thermodynamic equilibrium,

including DC archs, RF plasma torches, and a few other thermal plasmas. In the case of

thermodynamic equilibrium, all particles are close to the same temperature. Most

plasmas that do reach equilibrium attain only kinetic equilibrium, which is the case for

capacitively-coupled atmospheric-pressure discharges. In this case, ion and neutral

particle temperatures remain close to room temperature and the electrons have a raised

kinetic temperature [11,12].

For the purpose of materials processing, plasmas can be produced from two types

of power sources, direct current (DC) and radio frequency (RF). In DC plasma

discharges, the most basic of plasmas, true current is drawn from the power to the

electrodes. The plasma, in this case, must be directly connected to the electrodes. In RF

discharges, the particles are oscillating due to an oscillating electric or magnetic field. If

the oscillations are low, lower than the plasma ion or electron frequencies, the plasma


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will act as a DC discharge. If the oscillations are at a frequency comparable to the

electron plasma frequency or the ion plasma frequency, the current drawn is a

displacement current. Displacement current means that the power supply interacts with

the plasma through displacement rather than through real currents. Even in oscillating

fields, however, real currents are possible but they are insignificant in magnitude. When

displacement currents dominate, the electrodes do not have to be in contact with the

plasma, meaning a dielectric can be placed in between the plasma and the electrodes to

protect the electrodes, and to control the formation of arcs. The placement of a dielectric

between the plasma and the electrodes can also improve plasma reliability and

reproducibility [11,12].

B. Plasma Treatments: The Industrial Plasma Machines

B.1 Vacuum Plasma Devices

Plasma treatments under low vacuum pressures have been the most common

plasma treatments conducted on textiles. Until recently, plasmas at vacuum pressure

were the only treatments researched because corona discharges (the only plasma thought

to operate at atmospheric pressure) proved to induce many problems. These problems

included high voltages, release of ozone and nitrogen oxides, corrosion of equipment, and

non-uniform, barely effective treatments [6,13].

Armed with this knowledge, many research groups focused their efforts on design

of an economical vacuum plasma machine for the treatment of textile materials. Two

vacuum machine designs emerged and have been used by some textile manufacturers

throughout the world. The first design is a batch vacuum machine built by researchers at

the Neikmi Institute in Russia, KPR-180. Technoplasma, SA and Intes, Messrs Mascioni

(an Italian machine builder) are jointly involved in the development of this machine andare already developing the next industrial model (KPR-270) [13]. A schematic of the

KPR-180 vacuum batch-processing plasma machine is shown below in Figure I-3. This

machine is a large pressure vessel that can handle material rolls up to 65 inches (~170

cm) in diameter. Its operational speed ranges from 8-80 m/min, producing 30-40,000

m/day [1,14]. The operational pressure is under a vacuum of around 10-500 Pa [14].


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Figure I-3: KPR-180, Vacuum Plasma, Batch Processing Machine [13]

The second design is actually a continuous process. Developed at the Textile

Institute in Ldz around 1989, this machine consists of a four-stage vacuum system thatis a step-by-step scaling up process. This process uses the cascade principle with a three-

stage pump system. The pressure is lowered in each separate chamber that the fabric

passes through. The chamber with the lowest pressure, which is the location of the

plasma treatment, is found in the center of the machine. Upon exit, the fabric passes

through chambers that increase the pressure until the fabric has completely exited the

system. A schematic of the device is shown in Figure I-4 [15,16]. The pumping capacity

of this device is about 5400 m3/h with an obtainable pressure of 50 Pa. The operating

frequency is 13.56 MHz and the average RF energy density is 0.12 W/cm3

[15].

Figure I-4: Ldz Continuous Processing Vacuum Plasma Machine [15]

Although developed for using in the textile industry, both of these machines are

still operating under vacuum pressures and require a lot of energy. In a textile


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manufacturing facility, conditions that are needed for operation of the pumps and vacuum

treatment may not be well maintained. Regardless, most of the studies published on

plasma treatment of textiles use a vacuum plasma technology to treat textile materials.

B.2 Atmospheric Plasma Devices

Atmospheric plasma generation and application has been of great interest in

recent years. Much has been done in the area of building devices capable of generating

plasmas at atmospheric pressure, but there is still a need to understand the mechanism of

the plasma bulk and its interaction with substrates. The following devices have been

built in recent years for one atmosphere plasma generation and various applications.

1. RF Glow Discharge; used for a variety of treatments ranging from materialtreatment in low pressure processes to atmospheric processes, can also be used

for chemical neutralization and surface sterilization [9-11,17-23]

2. Plasma Jet; also known as Jet Sprayers, can be used for decontamination,

cleaning, and detoxification methods due to effectiveness, rapid degradation,

and no corrosion effects [24-27].

3. RF Induction and DC Plasma Torch; mainly used for the metal industry, dish

heating, and waste stream treatments, also being used in the investigation of

thermal diamond CVD (diamond and diamond-like films) [28-33].

4. DC Arcjet; used for propulsion and space applications [33-35].

5. DC Glow Discharge; used mainly for surface treatments of materials (see RF

Glow Discharge) [36-37].

6. Microwave Discharge; used for fiber treatment [38].

Although all of these atmospheric plasma techniques exist, the only ones

applicable to treating textiles at this time are the glow discharges, although microwave

drying methods have been recently employed for quick drying of fabric. The other listed

devices tend to cause significant heating of the substrate. Textiles require lower plasma

densities and energies so that heating will not alter the fabric or fabric treatment. If the

plasma heats the fabric, rearrangement of molecules and recrystallization can occur and

alter the bulk properties of the fabric. The technology behind atmospheric plasma


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generation was developed after it was proven that, in 1988, a glow discharge operating at

atmospheric pressure can be uniform, homogeneous, and stable [10]. Until this point in

time, techniques depended on that of corona discharge and dielectric barrier discharge.

Corona discharges have no dielectric, are very uncontrollable, and form arcs easily. Both

corona and dielectric barrier discharges are inhomogeneous and quickly fall to low power

densities [9]. They also tend to require very low electrode spacings [2]. A diagram of

these phenomena can be seen in Figure I-5.

Figure I-5: Dielectric Barrier Discharge and Corona Discharge, respectively [9]

The proof that plasmas at atmospheric pressure could be stable and uniform

developed through the use of a Pyrex glass reactor, shown in Figure I-6. It was found

that an atmospheric-pressure glow discharge could be well developed and stabilized

under the following conditions [10]:

1. Helium is used as the dilute gas.2. An insulating plate (or dielectric) should be set on the lower electrode. The

material must be selected based on the necessary heat resistance for the

application.

3. A brush-style electrode for the top electrode helps to produce a better plasma.


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A couple years after this publication, another technology group in Japan added that

kilohertz or radio frequencies were necessary for this type of plasma [39].

Figure I-6: Pyrex Glass Reactor [39] where (a) is the apparatus: 1, upper electrode;2, lower electrode; 3 and 4, glass plates; 5, Pyrex tube; 6, Pyrex bell-jar; 7, O-ring

and (b) is the brush-style electrode

Presently there are a few machines built for treating polymeric materials with

plasma at atmospheric pressure. The first and most detailed of the information found was

by J. Reece Roth on the OAUGDP device (one atmosphere uniform glow discharge

plasma). Figure I-7 shows the schematic of this capacitively coupled device. The upper

plasma chamber includes the plasma reactor with secondary RF transformer, the

matching network, and the reactor electrodes [11].


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Figure I-7: OAUGDP Device from University of Tennessee [11]

The OAUGDP device uses high voltage RF excitation at kilohertz frequencies in

order to produce a steady-state uniform glow discharge at one atmosphere of pressure for

many different gases. As shown, the device contains two parallel electrode plates across

which a RF electric field is applied or imposed. Table I-1, at the end of this section,

gives the operating parameter ranges for the machine. The RF frequency must be in the

right range of operation for a uniform plasma. If the frequency is too low the plasma will

not initiate. If it is too high, the plasma will form filamentary discharges, or arcs,

between the plates. The electric fields in this sort of device (few kV per cm) are normally

too low to break down a gas for plasma initiation if it is applied as DC only. However,

helium and argon gases will break down under these conditions in a RF field at the right

frequency. With the most desirable frequency applied, the ion population will be trapped

in the plasma bulk (between the plates) while the electrons can freely travel to the

electrode plates where they recombine or build up a surface charge. Ionic species cannot

move as freely due to their large size, comparatively. Moving ions would require more

power and a low operating frequency. Therefore, the frequency must be high enough to


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trap ions in the discharge, but not so high as to also trap the electrons. The more mobile

the electrons, the more uniform and desirable the plasma [11].

Another atmospheric device has been built at North Carolina State University.

The name given to the device is PALADIN (Parallel Plate Atmospheric Plasma Device

for Industry). A schematic of the device is shown in Figure I-8.

Figure I-8: Schematic of PALADIN [40]

The device is powered by an RF power supply. It was not designed for a DC

power supply due to the possibility of arc formation that may stretch through its

plexiglass frame. It is a capacitively coupled device with copper electrode plates. The

plate distance can be changed and the dielectrics around the plates hold them in place.

An exhaust system was built into the device to control the gas volume within the chamber

and the gas flow out of the chamber. Particular gases, depending on their reactivity and

toxicity, may have to be evacuated from the chamber into a fume hood before opening.

Also, pressure inside the chamber is controlled so that it will not get too high, possibly

causing damage [40]. The operational parameters of PALADIN can be seen in Table I-1

at the end of this section. An elemental circuit model of this device has also been

included for reference in Appendix B.


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Very recently, Plasma Ireland has advertised a machine for continuous

atmospheric treatments on textiles, labeled AP-100. With a combination of the

mechanisms found in Figure I-5, a glow discharge can be formed that is more stable and

uniform. Their Atmospheric Pressure Glow Discharge (APGD) is drawn in Figure I-9

and their operational parameters are shown, also, in Table I-1.

Figure I-9: Atmospheric Pressure Glow Discharge Model from Plasma Ireland [9]

The entire AP-100 Plasma Ireland machine is described in the reference material. The

gas flows, exhaust system, and monitoring systems are all shown, along with the

necessary plasma generation components.

There are only a few more devices being used for atmospheric plasma treatments.

One study shows treatments performed with two devices, one manufactured by Hirano

Kohon, Ltd and the other built experimentally [41]. These machines can be seen in

Figure I-10 and Figure I-11. They are very similar in principle to the other devices

mentioned, as well as to each other. Differences lie in the presence or absence of a

dielectric, floating or grounded electrodes, the type of material used for dielectrics, and

the cooling system used.

Figure I-10: Hirano Kohon, Ltd Atmospheric Plasma Device [41]


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Figure I-11: Atmospheric Device Built Experimentally by the Technology ResearchInstitute of Osaka Prefecture in Japan [41]

The following chart displays the similarites and differences in all of the

atmospheric devices mentioned, including the previous two from Japan and excluding the

preliminary bell-jar apparatus.

Table I-1: Characteristic Operating Parameters of Atmospheric Plasma Machines

OAUGDP PALADIN AP-100 Hirano-Kohon Experimental/JapanFrequency 1-20 kHz 1-12 kHz 50-350 kHz 20.4 kHz 20 kHz

Voltage 1.5-9.5 kVrms up to 7.8 kVrms 0-25 kV 2.5 kV

Electrode gap,d 0.8-2.5 cm 0.8-3.0 cm 0.8-3.0 cm 0.25 cm 0.5 cm

rms Power 1-150 W 1-250W 0-3 kVA 1 kW

Pressure 760+15,-5 Torr 760+15,-5 Torr 760 Torr 760 Torr

Plasma Volume 700-2,400 cm3 Avg. 774 cm3 75 cm3 14 cm3

ReferenceNumber 11 40 9 41 41

The uses of an atmospheric glow discharge device are numerous. It can be used

for the surface treatment and activation of metals and polymers, including textile fabrics.

The textile industry does not need sterile environments for their treatments and vacuum

processes would be too expensive and slow to meet desired production rates. Some

companies (Plasma Ireland, iplas Cyrannus) have already started to manufacture and

market machines for plasma use in a continuous (textile) processes. Studies are still

needed to evaluate the durability of the treatments on these types of materials. These

plasmas can also be used for sterilization, such as those used for the biomedical and food

industry [42]. Atmospheric plasma will aid in making the sterilization process faster

(continuous) and less expensive. Depending on the gas used, oxidation, reduction, and

other chemical treatments can be done with this device mainly to cause cleaning, ashing


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or etching of a material. There is still much work and experimentation to be done on

these devices in order to understand their mechanisms of operation and the differences

between them and the plasmas in the vacuum environment. Once understanding is more

clear, particular industrial applications for these devices can be optimized.

C. Plasma Treatments: Previous Research Findings

C.1 Traditional Fabric Processing

In order to understand why plasma treatments are important, it is necessary for

reviewing the normal processing of fibers. Below is a chart that shows the main

processes that most fabrics go through, but each step tends to differ as per fiber. Figure

I-12 applies only to fabrics not yarns before they are dyed and made into fabric.

Figure I-12: Process Flow of Fabric Preparation

Singeing Desizing Scouring Bleaching

Mercerizing / Caustisizing Heat Setting / Carbonizing

Singeing describes the burning off of protruding fibers, loose fuzz, or lint on the

fabric surface. It gives the fabric a clean look. Cotton and cotton blends are the most

common fabrics to be singed. Size is typically added to yarns either when in filament

form, as in the case of synthetics, or once they are spun into yarns (like cotton and wool).

Once in fabric form, it is customary to remove the size from the fabric in order to make

the fabric softer through desizing. Not all fabrics are desized; it depends on the type of

fabric and the type of size used. Scouring takes place in order to remove all impurities,

mainly oils, waxes, dirt, minerals, and other material. Bleaching helps to get the fabric a

uniform shade of white by destroying the color bodies in the fabric. Sometimes, after

bleaching, fabrics will be treated with an optical brightener. This chemical will assist the

fabric in obtaining extremely bright colors, such as neons. Mercerizing is a step, mainly

used with cotton that improves its luster, strength, water absorbency, and dye yield. This

step will also help destroy dead or immature cotton fibers and stabilize the shrinkage.

Mercerizing the fiber causes the fiber to swell. Since cotton is normally ribbon-like in


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structure, the swelling action results in an increased luster (more uniform light reflection)

and the swollen fiber form does not allow for as much shrinkage. Caustisizing is

conducted to improve all of the properties mentioned for mercerizing except for luster.

Heat-Setting is common to most thermoplastic fibers, mainly polyester and nylon. By

heating the fabric to above the glass transition temperature but below the melting

temperature, forming it (or applying tension), then cooling the fabric, dimensional

stability of the fabric can be obtained. Carbonizing is a similar process, mainly done for

wool, but is conducted for removing the remaining impurities in the fabric. These

processes do not involve any chemicals [43,44].

After the main processing of the fabric is completed, the fabric is normally dyed

with the chemical dye best suited for the particular fiber or blend. After dying, other

specialty processes may be added in order to obtain particular properties. For instance,

anti-soil and soil release finishes can be, and normally are, applied. Finishes for flame

retardancy, water-repellency, durable press, anti-pill, and anti-static can all be applied

after processing [43,44].

As mentioned earlier, most of the data available for plasma treatments on textile

materials involve vacuum plasma processing. In order to compare results between

vacuum plasma effects and atmospheric plasma effects in the future, it is necessary to

explore all that vacuum plasma has succeeded in accomplishing in the field of textiles.

For each fiber, a brief summary of work done with plasma treatments on that particular

fiber will be given.

C.2 Cotton

Cotton is a natural fiber, however it is very different in structure from other

natural fibers like wool or silk. Because of the chemical and physical structure, many of

the processes and chemicals used in regular treatments are unique. In Figure I-13, the

typical cotton fiber and its structure are shown.


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Figure I-13: Chemical Structure of Cotton and a Picture of the Morphology ofCotton [45]

C.2.1 Main Problems

Cotton is a very intensively processed fiber. It is sent through all of the processes

mentioned above, with the exception of heat-setting. However, some cotton blends may

have to be heat-set. Cotton fabric normally has many finishes applied, as well. Because

of the variability of color in baled cotton, it must be bleached before being dyed a color,

except for black. Hypochlorite or hydrogen peroxide is normally used for the bleaching

of cotton. Desizing the fabric requires enzymes, acid hydrolysis, or oxidation. For

scouring, sodium hydroxide is used. Mercerization normally requires caustic soda, but

sometimes uses sodium hydroxide. If a durable press finish is applied to the fabric,

formaldehyde or DMDHEU (dimethylol-4,5-dihydroxyethylene urea) has been used in

the process [43]. The high crystallinity of cotton makes it difficult to dye; however, the

water resistance or repellency of the fiber is very low. Cotton yarns usually go through a

sizing process where starch is added to the yarn to give it strength and lower friction to

ease the yarn through weaving. This size is later removed through desizing once the yarn

is in fabric form.

There is a lot of pre-treatment for cotton materials today, therefore, the potential

for plasmas in the treatment of cotton are large. Most of these processes are very

chemically intensive, which can be harmful to both the fiber and the environment. All of

the mentioned processes are targeted areas that could benefit greatly in any further

development. For instance, partial replacement of the desizing process would be a huge

improvement. Completely replacing the scouring, bleaching, and mercerization process


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are other opportunities for plasmas that would set new standards for the industry. In

potentially achieving these goals, costs in the following areas would be greatly reduced:

- Water consumption

- Labor costs (increased productivity)

- Chemicals and auxiliaries

- Amortization costs [6]

C.2.2 Plasma Treatments

C.2.2.1 Desizing

In 1995 there was an attempt to desize cotton with plasma treatments, however

the treatments did damage to the cotton. This is the only documented attempt to desize

cotton that was found. The gas used is not mentioned so air plasma is assumed. The

deterioration of the fiber was seen largely through discoloration of the fiber, a loss of

mass, and a loss of strength (both tensile and tear) [1].

C.2.2.2 Dyeability

In a 1998 study, plasma etching with O2 gas, was found to result in no

improvement of dyeability. In fact, the cellulosic fibers tend to have less dye affinity

than untreated fibers. A reason given for this event is that the plasma induces etching onthe non-crystalline (i.e. amorphous) regions of the fiber. These regions are the ones

inherently responsible for the dyeing of cotton or any other cellulosic fiber [7].

C.2.2.3 Water Repellency

By using unsaturated hydrocarbons (CH3) or unsaturated fluorocarbons (CF3),

water repellent properties can be achieved. Other research groups document achieving

water and oil repellency in cotton through fluorination, as well [46]. Also, ethene plasma

treatment can yield more hydrophobic cotton. Through plasma polymerization, ethene

forms a polymer film on the material. It also increases the proportions of aliphatic carbon

on the fiber surface while reducing the hydrophilic carbon components on the fiber

surface [7]. On cotton materials, Ar plasma has been shown to improve the water

absorption [8].


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C.2.3 Summary

Table I-2 and Table I-3 shows the highlights of the discussed research on cotton. To

add to Table I-2, the scouring and mercerizing process are thought to be possible

processes that plasma treatments can replace, however little work has been done to

investigate it.

Table I-2: Regular Treatments on Cotton and the Possible Plasma TreatmentReplacement

Process Regular Chemical Treatment Plasma Treatment Reference

Bleaching Hydrogen Peroxide, Sodium

Hypochlorite, Sodium Hydrosulfite,Sulfur Dioxide

Argon-Helium 6

Desizing Water, caustic soda Air 1

Table I-3: Plasma Treatments and the Resulting Property Effects for Cotton

Property Plasma Treatment Treatment Outcome Reference

Hydrophobicity UnsaturatedFluorocarbons

UnsaturatedHydrocarbons

Ethene

Fluoromonomer

Increase

Increase

Increase

Increase

7

7

7

6

Oleophilicity Fluorination Decrease 46Dye Penetration & Rateof Dyeing

Oxygen No effect 7

Standard Dye Affinity Oxygen Decrease slightly 7

C.3 Nylons and Polyamides

Nylon fibers are of a very different nature than cotton. Being man-made, their outer

morphology is typically more uniform and the basic molecule of nylon is smaller in

weight. It also has different side groups that result; nylon has oxygen, cotton has CH2OHand OH groups. The following, Figure I-14 is a view of the fiber morphology and

chemical structure of common nylon fibers.


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Figure I-14: Chemical Structures of Nylon 6 and Nylon 6,6 [45]

Nylon 6 Nylon 6,6

C.3.1 Main Problems

Nylon is a synthetic fiber and shares their common characteristics. Synthetic

fibers, many times, do not require as much processing as natural fibers due to their

filamentary form and specific end uses. Polyester, aramid fibers, polyethylene,

polypropylene, and polyamides have wonderful properties of high strength, high stability

in various conditions, and high modulus. However, synthetics still have much room forimprovement. Their chemical structure usually does not allow for them to be dyed easily.

Also their wettability is usually poor due to a lack of hydrophilic groups and a negative

charge on the surface. Many synthetics are now being used in composite materials,

requiring excellent adhesion properties. Adhesion can be improved by changing the

surface tension or surface energy. Most synthetic fibers, especially nylon, all have low

surface energies that result in bad adhesion properties, presenting difficulty when

bonding, coating, printing, and dyeing. Instead of using solvents like chromic acid or

others that can be poisonous or abrasive, a variety of plasma treatments can be used to

increase the surface energy of these polymers [13]. Plasma treatments could also assist in

bleaching, sizing, and desizing synthetics. In bleaching, hydrogen peroxide is commonly

used, however peracetic acid can be used for nylon and acetate. Polyvinyl alcohol (PVA)

is used as a size for most synthetic fibers. PVA is water soluble, but desizing just

requires the aid of a wetting agent. Even in this circumstance, water used for desizing

must be cleaned. The utilization of plasma treatments would eliminate this necessity.

C.3.2 Plasma Treatments

C.3.2.1 Dyeability

In 1996, a study out of Japan researched the penetration of acid and basic dyes

into nylon 6 after the fibers were treated with a low temperature O2 plasma. Both the


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saturation dye exhaustion and the rate of dyeing were investigated. The nitrogen content

in the nylon remained unchanged with the O2 plasma treatment. From ESCA analysis, it

was concluded that there was a large increase the intensity of oxygen on the fiber surface.

Most of the oxygen was found in hydroxy or carboxylic acid groups on the surface of the

fiber. This result leads to an increase in surface energy of the fiber and wettability. The

zeta-potential of the fiber increased, which means that the apparent negative surface

charge increased. With this increase, it would be suspected that the rate of dyeing and the

saturation of dye exhaustion would increase with basic dyes and decrease with acid dyes

due to their anionic nature. For the case of nylon 6, this conclusion is true. Since the

structure of nylon is very homogeneous physically and chemically, the electronegativity

of the fiber plays a prominent role in its dyeing behavior [47].

An interesting study from Japan in 1992 attempted to find the relationship

between plasma etching and fiber crystallinity for PET and nylon 6,6 fibers spun over a

range of temperatures. The dyeability of these fibers was also examined. The

experiment was arranged so that PET and nylon 6,6 fibers, of varying crystallinity, were

treated with air plasma only and then tested for weight loss of the sample, referred to as

plasma susceptibility. The crystallinity was found to increase continuously over the

temperature range provided, for both fibers. The fibers were then Air-plasma treated. It

was found that the plasma susceptibility decreased when treating the fibers that were

made at temperatures below 180C. The plasma treatment increased the susceptibility

slightly in the fibers prepared at temperatures above 180C. This phenomenon was

explained by a theoretical model of three-phase semi crystalline polymers. The model

relies on the assumption that plasma will preferentially treat dyeable amorphous regions

of a polymer [48]. A conceptual diagram of this model can be seen below in Figure I-15.


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Figure I-15: Three-Phase Model Schematic Diagram of PET or Nylon 66 Fibers [48]

The three-phase model describes dyeable and non-dyeable amorphous regions in

synthetic fiber, along with crystalline areas. These non-dyeable amorphous regions

consist of polymer chains that have a high degree of order, but are not crystalline (as

defined as detectable with x-ray analysis). The dyeable amorphous regions are those

commonly associated with amorphous, having very little order or orientation of thechains. With low heat treatments, non-dyeable amorphous regions remain relatively

constant (as compared with an untreated polymer), while the dyeable amorphous regions

decrease. This decrease would result in the apparent increase in crystallinity that was

observed. At higher heat treatment temperatures, however, partial melting could result in

both increased crystalline regions as well as increased dyeable amorphous regions,

leaving a dramatic decrease in the non-dyeable amorphous areas. If the model holds true,

then the trends noted in the plasma susceptibility can be explained and the dye diffusion,

or dyeability, of the fiber should decrease. According to the experimental results, the

plasma treated fibers all had reduced dyeability, with the reduction being more

pronounced at the lower heat treatment temperatures and less pronounced at the higher

heat treatment temperatures. The results support the model given [48].


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C.3.2.2 Filtration

In a 1997 study from China, plasma was used to modify an aromatic polyamide

reverse osmosis composite membrane. Currently these membranes are used in the

desalination of seawater and for ultrapure water preparation. However, the water

permeability and the chlorine resistance of the membrane limit the market and application

of this product. The actual composite was made of a polysulphone substrate with a thin

film of poly (-1,3-phenylene terephthalamide) polymerized on the surface through

interfacial condensation. The membrane was treated with both O2 and Ar plasmas and

was evaluated through ATR-FTIR spectroscopy, X-ray photoelectron spectroscopy, and

the contact angle of the composite. Water permeability increased with exposure time

when the membrane was treated with O2 plasma, but decreased slightly when treated with

Ar plasma. This was explained by the observation of carboxylic groups that form on the

surface of the membrane when treated with O2 plasma. These groups do not appear when

treated with argon. The chlorine resistance greatly increased with Ar plasma exposure,

and only slightly increased with O2 plasma. This occurrence was thought to be the result

of an increase in the crosslinking of the polyamide. Therefore, it is assumed that the

crosslinking degree of Ar plasma is greater than that of O2 plasma [49].

The contact angle decreased with longer exposure to O2 plasma. With Ar the

contact angle decreased, but less dramatically than in O2 plasma. A decrease in thecontact angle implies an increase in the hydrophilicity of the material. Again, this result

was explained by the introduction of carboxylic groups when in oxygen plasma. Through

ATR-FTIR and XPS spectra, reasonable explanations were made of the above results. In

the O2 plasma, it can be concluded that the polyamide chain cleaves during treatment,

leaving -COOH groups in abundance throughout the surface of the fiber. A cleaving

mechanism can be modeled as seen in Figure I-16. The figure shows where the chain

could possibly separate, leaving room for -OH attachment to make unstable ester groups

on the end of a chain [49].


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Figure I-16: Possible Cleaving Mechanism of Polyamide Chain [49]

For Ar plasma treatments, spectra showed a change in the environment of

nitrogen within the polyamide. The most reasonable and possible change to be concluded

was that the hydrogen in the -CONH groups was substituted by another atom or group.

Due to the increase in chlorine resistance, it was also concluded that crosslinking at the

nitrogen atom between chains occur [49]. The theoretical crosslinking mechanism used

in this paper is shown in Figure I-17. Here, the hydrogen atom leaves the nitrogen on the

chain. The nitrogen atom then bonds with another unstable nitrogen atom on the

backbone of another polymer chain. Thus, a crosslinking situation is formed.

Figure I-17: Possible Crosslinking Mechanism of Polyamide Chain [49]


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Table I-4 gives an overview of the property changes in nylon and polyamides that

have been explored with plasma treatments. The property, plasma gas, treatment

outcome (how the plasma gas effects the fiber), and the reference number are all given.

Table I-4: Plasma Treatments and Resulting Property Effects for Nylon andPolyamides

Property Plasma Treatment Treatment Outcome Reference

Hydrophobicity OxygenArgon

DecreaseDecrease (less)

47,491,49

Dye Penetration &Rate of Dyeing

Oxygen Increase (basic dyes)Decrease (acid dyes)

4747

Surface Tension Oxygen Increase 47

Crystallinity Air Increase 48

Chlorine Resistance OxygenArgon

Increase slightlyIncrease

4948

Electronegativity Oxygen Increase 47

C.4 Other Plasma Treatments of Interest

There have been many plasma treatments performed on other fibers. Relative to

the focus of this project (cotton and nylon), there are only a few fibers that would allow a

treatment comparison based on their closeness in structure to cotton or nylon. There are

really no polymers similar in structure to cotton that have been a documented substrate in

plasma research. However, nylon is a polyamide material, containing similar structures

to that of wool and silk, which are both natural fibers that also contain amide linkages.

Both of these fibers have unique morphologies and surfaces that add different processing

necessities to their manufacture, but the effects of plasma treatment on them should still

be reviewed for comparison. Also, for comparative purposes, the basic synthetic

polymer, polypropylene, should be reviewed to determine effects that would be

significant only to synthetic materials, which also includes nylon. The chemical structure

of these three polymers can be seen in Figure I-18. Wool and silk have the same basicchemical composition, but they differ in the amino acid groups that are attached to the

chain.


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Figure I-18: Chemical Structures of Wool, Silk, and Polypropylene [45,50]

Wool & Silk Polypropylene

C.4.1 Wool Fiber

Wool fibers have been the subject of many plasma treatment studies because it is

a fiber that normally undergoes a lot of chemical processing. There are three main

problem areas in wool manufacturing that could always use improvement: bleaching,

dyeing, and shrink resistance. It has been proven that Ar-He plasma can effectively

improve the whiteness of wool, possibly replacing the bleaching process. Currently

bleaching uses chemicals such as hydrogen peroxide, sodium hypochlorite, sodium

hydrosulfite, and sulfur dioxide. An increase in dyeing (dye affinity and rate of dyeing)

can be associated with the fiber hydrophobicity, or hydrophilicity. An increase in fiber

hydrophilicity, or decrease in the hydrophobicity, means an increase in the dyeing

properties. O2, N2, and air plasmas have all been proven to increase the hydrophilicity ofwool [7,51,52]. Likewise, studies conducted directly on the dye properties have shown

that all of these plasmas (O2, N2, and air) have increased the dye affinity, dye penetration,

and dyeing rate [13,47,53]. All three of these plasmas have also shown to increase the

surface roughness of the fiber [51,54]. Fluoromonomer plasmas decrease the

hydrophilicity of wool, making the surface more hydrophobic than it normally is [55].

Shrink resistance treatments have been successfully conducted with Acetone-Ar, He-Ar,

O2, N2, and air plasmas [41,51,54]. All treatments have improved the shrink resistance,

however none have done as well as the regular chemical treatment, which consists of

chemicals such as dichloroisocyanuric acid (DCCA), persulfuric acid, and NaDCCA,

followed by a polymer application. The plasma treatments were all greatly improved if a

polymer or collagen application were still used [51,54]. These are not the only properties


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of wool to have been analyzed after plasma treatment, but they are the main and most

prominent ones.

C.4.2 Silk Fiber

Silk fiber has not been studied as much as wool with regards to plasma, however,

some work has been done. As in wool, O2, N2, and air plasmas have been found to

increase the hydrophilicity of the fiber [8]. Treatments with fluoromonomer plasma

improve the hydrophobicity of the fiber [8]. It has also been found that N2 plasma has

no effect on the degree of crystallinity of silk, however the surface crystallinity somewhat

decreases [56]. N2 plasma has also been found to improve the drying rate of silk and

decrease its wrinkle recovery, however some weight loss does occur with treatment [8].

C.4.3 Polypropylene

Hydrophobicity, oleophobicity, and dyeing properties have been explored using

plasma treatments on polypropylene. As in the case of wool and silk, O2 and N2 plasmas

decrease the hydrophobicity and tetrafluoromethane (a fluoromonomer) plasma increases

the hydrophobicity [1,2,46,57,58]. Tetrafluoromethane also increases the oleophobicity

of polypropylene [46,58]. O2 plasma was found to increase the dye affinity, dye

penetration, and the rate of dyeing, as well [14].

C.4.4 Other Fibers

It is also worthy to note that high performance fibers, such as Kevlar and

Nomex have been the subject of many plasma treatment studies. The main concern for

these fibers is the improvement of their adhesion properties without affecting their

strength. High performance fibers are largely used in composites so adhesion between

the fiber and matrix is very important. This is so that the total composite strength will be

that of the materials used not the strength of the bond that holds them together. The

fibers mentioned both have amide linkages within their basic repeat structure so

similarities in treatment may be found between them and nylon materials. Ar plasma has

been used on these fibers, as well as Conex and Technora, in order to improve the dye

shade depth. All fibers increased the dye shade with the exception of Conex (due to its

chemical structure) [59,60]. Ammonia, O2, and Ar have all been used to successfully


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increase adhesion properties of high performance aramid fibers and ultra-high molecular

weight polyethylene (UHMWPE) [13,61,62].

C.5 Fabric Treatments with Atmospheric Plasma

C.5.1 Cotton Fiber

There have not been many treatments on textile materials utilizing atmospheric

plasma. One of the primary studies conducted with plasma treatments on textiles was a

1977 experiment that used a corona glow discharge treatment using air on cotton sliver.

The treatment was conducted in a continuous process at atmospheric pressure. The

cohesion of the fibers was evaluated after different treatment times and various power

levels. For staple fibers, such as cotton, greater fiber cohesion means an increase in yarn

strength. Also, different gases (CO2, N2, and Ar) were exposed to the system to observe

fiber changes that may occur in different surrounding atmospheres. The different gases

used all yielded the same treatment effects. With plasma treatment, the fiber cohesion

increased with an increase in treatment time and power. However, the treatment was

most efficient (in terms of cohesion per watt or per treatment time) at lower powers and

treatment times. From this finding it was concluded that the most efficient methods of

plasma treating the cotton was to use multiple passes through the plasma zone or have

separate sequenced treatment points [63].

C.5.2 Polypropylene

After building their atmospheric device at the University of Tennessee, Roth et al.

treated polypropylene meltblown webs with different gases and under various conditions

in order to improve the materials affinity towards water. The critical surface tension was

measured over time (days) and chemical analysis (ESCA) of the treated surface was done

before and after treatments. The gases used were CO2, O2, H2, and combinations of the

three. It was found that, although there are critical voltages, power driving frequencies,

and temperatures that cause wettability, treatments using these gases can be successful in

causing hydrophilicity. The wettability was found to decay, but leveled off after three

days. This phenomena is attributed to the fact that the polarization induced by the plasma


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treatment with decays over time but the polar groups stay attached to the material since

the reaction that converts hydrocarbon to polar groups is irreversible. There were some

samples treated for only 30 seconds that maintained good wettability after a year [21].

Experiments were conducted on the PALADIN device when it was first built.

Non-woven polypropylene fabric was treated under different helium plasma levels.

Tensile tests and absorption tests were performed for fabric characterization. It was

noticed that the tears in the fabric looked different from those in the untreated fabrics.

This is attributed to the formation of cross-links on the fiber surface during the treatment.

However, the strength was dramatically decreased after treatment. Also, the fabric had a

greater elongation at break. After treatment, the absorption of the fabric decreased with

time. This is believed to be the result of a decrease in polarity after the fabric had been

exposed to air [40].

C.5.3 Polyethylene terephthalate

Surface fluorination of PET films have been carried out under atmospheric

conditions. A Pyrex glass reactor was used for these treatments at atmospheric pressure

[39]. The results of the fluorination treatment, using CF4 and O2 gas mixtures, was

compared with treatments done in low pressure plasmas. The atmospheric discharge

actually yielded higher contact angles (fluorination increases hydrophobicity) than that of

the lower pressure discharge. The effect of aging was studied but not reviewed in this

source. However, the treatments remained effective after washing with Daiflon solvent

(C2Cl3F3), although a decrease in fluorination after washing was observed [39].

C.5.4 Wool

In 1993, plasma treatments were successfully applied to increase the shrink

resistance of two wool fabrics using acetone-argon plasma and helium-argon plasma.

Both treatments were conducted in low temperature plasma at atmospheric pressure. Theshrinkage over twenty laundering cycles for untreated fabric were 39.4% and 14.1%. The

acetone-argon treatment showed the best improvement with a resulting shrinkage of

10.6% and 6.8%, respectively, while the helium-argon plasma resulted in shrinkage of

13.1% and 9.1% over twenty laundering cycles. No explanation for the difference is

given [64].


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Recently, a group out of Japan has experimented with wool treated with various

glow discharges at atmospheric pressures. In the described experiment, the surfaces of

the fibers were studied after oxygen plasma treatments in two different atmospheric

plasma chambers. It was found that both chambers produced similar granular and

porous structures on the surfaces of the fibers. After long treatment times (over 25

minutes) large circular granules begin to form. This can be seen in Figure I-19. It is

presumed that these surface structures grow or aggregate from smaller ones that are

formed during plasma treatment [41].

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