Application of plasma treatment to textile substrates in order to enhance the adsorption of nanoparticles

Master in Advanced TextilesMultifunctional Textiles Trabalho efectuado sob a orientação do Professor Doutor António Pedro Garcia de Valadares Souto NGUYEN KHANH VU Application of plasma

Master in Advanced Textiles

Multifunctional Textiles

Trabalho efectuado sob a orientação do

Professor Doutor António Pedro Garcia de Valadares Souto

NGUYEN KHANH VU

Application of plasma treatment to textile substrates in order to enhance the adsorption

of nanoparticles

“Study, study more, study forever”

Vladimir Ilyich Lenin

ACKNOWLEDGEMENTS

In order to successfully fulfill my thesis, I had a lot of support and encouragements from people around

me I would like, hence, to express my gratitude to all those who contributed in certain ways to the completion of my work

First, I want to show my deep gracefulness to Professor Pedro Souto, who gave me a lot of invaluable knowledge as well as his orientations for the first fundamental steps of my career in science It is a big honor to be accepted as a master student under your supervision

Second, I would like to thank Mr Andrea Zille It is a sudden luck that I am able to work aside him, who has spent his precious time explaining doubts and wonderings of mine during the preparation of my thesis Furthermore, I want also to say thank to Professor Ana Rocha, my coordinator at University of Minho over the past two years, who also plays a very important role of my study during my course Master in High–tech Textiles (Multifunctional Textiles)

And for all Staff, Professors, I hope they can understand my appreciation of their support, help and friendly environment they created for me

Besides Professors, Counselors, everyone does have friends In my case, I want to send my love to Fernando, Fernanda, Marta, Angela, Juliana, Sandra, Heriberto and many others those I can’t name all, who shared their experiences with me during lab work, lunches Those times were very fantastic for me Some people I am not allowed to forget are Staff from EM–EuroAsia 2010–2012 project, whom I just can narrate here as representatives, they are Ms Mette Svensson from Boras University (the Host of this project), Ms Andriana Carvalho from University of Minho and Mr Nguyen Hoang Nam from Ho Chi Minh City University of Technology Thanks to their kindness, I was able to implement my dream of studying and researching

Moreover, I want to say thank to all of my friends who made my experiences in Portugal become unforgettable in my life time

Finally, there are people whom anyone must miss are his/her family members I just don’t know phrases

or sentences which I can use to depict my profound emotions to them I want to say thousands of thanks

to my own parents (bố Minh, mẹ Trúc), my parents–in–law (ba Khánh, mẹ Tuyết), my aunts (dì Nguyệt, dì Thủy, dì Tư Thủy), my uncles (bác Ba, bác Tư Tuyết), my sister (bé Ngọc) and my cousins (Bu, Tí, Khoa) These people are my motivations, my hope that encourages me not only my study here in Portugal but for the rest of my life Last but not least, the most important person, my dearest wife, Phan Xuân Khánh Yên, who sacrificed here career so as she can come to stay with me, take care of

me when I study in Guimarães She shared with me both sadness and happiness She is one of the most paramount key factors affecting my thesis I want to show you my endless love to her and our going–to–be–born kid in her

This master thesis has been finished thanks to the sponsorship of an Erasmus project called EM–EuroAsia which is under the auspices of The European Commission

RESUMO

A tecnologia plasmática de dupla barreira dieléctrica (DBD) pertence à classe de plasma a frio de baixa frequência utilizado a pressão atmosférica Deve ser alimentado por uma corrente alternada e accionado por uma energia de alta tensão que pode variar entre 1–100kHz Este método é especialmente utilizado

em aplicações com sistemas roll–to–roll que são termicamente sensíveis, por exemplo, películas, folhas

de papel para impressão gráfica, membranas poliméricas e materiais têxteis Para além destes produtos, a tecnologia DBD pode ser aplicada a outros tipos de materiais, tais como madeira, cabos isoladores ou até mesmo em unhas humanas A aplicação mais comum em substratos têxteis tem como objetivo melhorar

a molhabilidade e aumentar determinados grupos polares na superfície do material No entanto, outras diversas propriedades podem também ser modificadas, nomeadamente; a energia de superfície, o coeficiente de atrito, o comportamento anti–estático, dentre outros Desta forma, a modificação via descarga DBD é a técnica mais aplicada quando se pretende alterar superficialmente diversos tipos de materiais Por ser tratar de uma tecnologia de facil implementação industrial, este equipamento tem um grande potencial para ser adaptado a muitas indústrias, incluindo a têxtil

Na última década, a utilização de nanopartículas tornou–se uma das áreas científicas mais atraentes a serem exploradas No entanto, a aplicação de nanopartículas em substratos têxteis possui a limitação da aderência ao substrato, com solidezes à lavagem ou fricção mais baixas do que o desejado Portanto, a melhoria desta ligação interfacial é uma necessidade presente

Este trabalho utilizou um protótipo semi–industrial de plasma DBD, com o intuito de modificar superficialmente as propriedades físico–químicas de um tecido de poliamida 66, com a finalidade de melhorar a adsorção e adesão de nanopartículas de prata Para estudar as modificacões superficiais do substrato foram utilizadas as seguintes técnicas de caracterização: ângulo de contato, microscopia electrónica de varrimento (SEM), espectroscopia fotoeletronica de raios–X (XPS) e a espectroscopia de energia dispersiva de raios X (EDX) Os resultados mostraram que a quantidade de nanopartículas de prata adsorvidas teve um aumento significativo no tecido de poliamida previamente tratado com plasma

ABSTRACT

Plasma Dielectric Barrier Discharge (DBD) technology belongs to the class of cold plasma with low frequency used at atmospheric pressure It must be powered by an A.C current and driven by a high voltage power running at 1–100 kHz frequency This approach is specially used on applications with roll–to–roll systems which are thermally sensitive, for instance, foils, photo–graphic print paper, polymeric membranes and textiles Besides those products, nevertheless, the DBD technology can be also applied to some various materials such as, wood, insulated cable or even to human nails (fingers’ or toes’) The most common application of textile is to enhance the wettability and polar groups on the material surface However, there are more properties which can also be modified as surface energy, friction coefficient, and antistatic behaviour, among others Thus, the DBD plasma modification is the most applied technique when it is intended to modify several types of materials Because this technology is an easy industrial implementation, this device has great potential to be adapted to many industries, including textiles

In the last decade, the use of nanoparticles has become one of the most attractive scientific areas to be explored However, the application of nanoparticles on textile substrates is limited due to its adherence to the substrate with the washing or rubbing fastness than expected Therefore, the enhancement of interfacial bonding is a present necessity

This study used a semi–industrial DBD plasma prototype to modify the surface of physic–chemical properties of polyamide 66, in order to improve the adherence and adsorption of silver nanoparticles To study surface modifications of the substrate, several techniques were used namely, contact angle measurement, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) The results showed that the amount of adsorbed silver nanoparticles had a significant increase in polyamide fabric pre–treated with DBD plasma

CONTENT

Acknowledgement iv

Resumo vii

Abstract viii

Abbreviations xii

List of figures xiii

List of tables xv

CHAPTER 1 – INTRODUCTION 1

1.1 GENERAL CONTEXT 1

1.2 OBJECTIVES 5

1.3 METHODOLOGY 6

1.4 THESIS STRUCTURE 7

CHAPTER 2 – STATE OF ART 9

2.1 POLYAMIDE 9

2.1.1 HISTORY 9

2.1.2 CHEMICAL STRUCTURE AND SYNTHETIC PROCEDURE 10

2.1.3 PHYSICAL AND CHEMICAL PROPERTIES 14

2.1.4 APPLICATIONS OF POLYAMIDE 14

2.2 NANOPARTICLES AND APPLICATIONS 16

2.3 PLASMA TECHNOLOGY 26

2.3.1 WHAT IS PLASMA? 26

2.3.2 PLASMA – SURFACE COLLISION 28

2.3.3 ATMOSPHERIC PRESSURE PLASMA 29

2.3.4 TYPICAL APPLICATIONS OF PLASMA TECHNOLOGIES IN TEXTILE AREA 31

CHAPTER 3 – EXPERIMENTAL PROCEDURE 38

3.1 MATERIALS 38

3.1.1 SILVER NANOPARTICLES 38

3.1.2 FABRIC 38

3.2 METHODOLOGY 39

3.2.1 PLASMA TREATMENT 39

3.2.2 SAMPLE PREPARATION 40

3.2.3 EVALUATION TECHNIQUES 40

3.2.3.1 SPECTROPHOTOMETER 40

3.2.3.2 DYNAMIC LIGHT SCATTERING 41

3.2.3.3 ZETA POTENTIAL MEASUREMENT 41

3.2.3.4 GONIOMETER 41

3.2.3.5 CHEMICAL COMPOSITION ANALYSIS 42

3.2.3.6 SURFACE ANALYSIS 42

3.2.3.7 SPECTROPHOTOMETER 43

CHAPTER 4 – RESULTS AND DISCUSSIONS 44

4.1 PLASMA CHARACTERIZATION 44

4.1.1 CONTACT ANGLE 44

4.1.2 EDS AND XPS 46

4.1.3 SCANNING ELECTRON MICROSCOPY (SEM) 48

4.2 SILVER NANOPARTICLES CHARACTERIZATION 50

4.2.1 SEM & STEM 50

4.2.2 UV–VIS ABSORPTION SPECTRA 51

4.2.3 DYNAMIC LIGHT SCATTERING 53

4.2.4 CONTACT ANGLE 54

4.2.5 X–RAY PHOTOELECTRON SCANNING (XPS) 57

4.2.6 SEM – EDS 59

4.2.6 ABSORBANCE PERCENTAGE 61

CHAPTER 5 – CONCLUSIONS AND FUTURE WORK 62

5.1 CONCLUSIONS 62

5.2 FUTURE WORK 64

BIBLIOGRAPHY 65

ABBREVIATIONS AgNPs  Silver nanoparticles

APPJ  Atmospheric Pressure Plasma Jet

At(%)  Atomic percentage

AuNPs  Gold nanoparticles

CNTs  Carbon nanotubes

DBD  Dielectric Barrier Discharge

DLS  Dynamic Light Scattering

EDX/EDS  Energy Dispersive X–ray Spectroscopy

FTC  Federal Trade Commission

ILSS  inter–laminar shear strength

LTCC  Low–temperature Co–fired Ceramic

PAN  Polyacrylonitrile

PDI  Polydispersity Index

SEM  Scanning Electron Microscopy

STEM  Scanning Transmission Electron Microscopy

UV–vis  Ultra violet–visible

XPS  X–ray Photoelectron Spectroscopy

LIST OF FIGURES

Figure 2.8 – Schematic representation of the bottom–up and top–down approaches for the

Figure 2.9 – SEM photo of cotton fiber impregnated with AgNPs for antimicrobial property 22 Figure 2.10 – SEM photo of super–hydrophobic textile material created using nanotechnology 24 Figure 2.11 – UV transmittance characteristics of textile materials 25 Figure 2.12 – Lotus Effect® removing dirt particles from super–hydrophobic surface 26 Figure 2.13 – Advantages of plasma treatment over traditional wet chemistry 27

Figure 2.17 – Untreated fiber (left) and plasma treated fiber (right) for the improving pilling property

Figure 2.18 – Wettability of untreated grey cotton fabric (left) and plasma treated grey cotton fabric 33 Figure 2.19 – Exhaustion of Sirius dyes (Orange, Violet, and Blue), in “control” samples and after

Figure 2.20 – Images of polyester fabrics which were taken by DZ3–video focus–exchanged microscope at 75 multiple after inkjet printing with pigment inks 35 Figure 2.21 – Adhesive joint strength of as received titanium and surface modified titanium 37 Figure 3.1 – Semi–industrial prototype of the plasma machine Softal [Pat PCT/PT 2004/

Figure 3.2 – The aligned polyamide 66 samples in covered boxes for silver nanoparticles imbue

Figure 4.2 – SEM image of polyamides untreated (a, c) and treated with dosage of 2.5 kW min m–2 (b,

Figure 4.3 – Sphericalish AgNPs obtained via citrate reduction method captured by SEM and STEM 50 Figure 4.4 – UV–vis spectra of commercial (Sigma 10 and 20) and synthetized AgNPs with

corresponding maximum wavelength of absorbance band Commercial samples diluted 3 times before recording the spectra The synthetized AgNPs were also diluted accordingly to the absorption of

Figure 4.5 – Dynamic contact angles of non–plasma and plasma treated with AgNPs of different sizes 55 Figure 4.6 – XPS spectra of silver on the surface of silver deposited polyamide 66 fabric 58 Figure 4.7 – SEM images of PA fabrics loaded with AgNPs (20 ppm) with magnification of 13000X 60 Figure 4.8 – Increase in Absorption at 400 (Sigma10 and 20) and 430 nm (Synthetized) of untreated and plasma treated polyamide after silver nanoparticle adsorption 61

LIST OF TABLES

Table 4.1 – Static contact angle of non–plasma and plasma treated samples (0) 44

Table 4.6 – Atomic percentage of origin and plasma treated samples loaded with AgNPs of different

INTRODUCTION

1.1 GENERAL CONTEXT

Together with food, clothes have a very important role to human beings Obviously, since the primitive time, mankind has been trying hard to make new things in order to satisfy its own demanding ambitions including clothes As the most fundamental part, fibre is the first focus According to Engelhardt (Sangwatanaroj, 2011), in The Fibre Year report for fibre production of 2010, the world total production volumes of both natural and man–made fibres increased 8.6% (6.4 million tons) to the total of 80.8 million tons For annual growth rate, the fibre growth in the last decade was at 3.4% meanwhile the world population’s growth was 1.2% In the total world fibre production of 2010, synthetic fibre shared for 56% (about 45.25 million tons) while natural fibres were accounted for 39% (31.51 million tons) and the rest 5%

is the cellulose fibre segment (accounting about 4.04 million tons)

The world population has increased at an incredible speed in the last few decades More people means there will be more requirements to satisfy their desires There is a saying that “many men, many minds” So far, human doesn’t only want to stay warm but they want to feel more comfortable; and for that purpose, it is important to finish by functionalization clothing and apparel articles With that requirement, plenty of finishing techniques have been developed till now such as lamination, coating, water–based finishing and others which basically create more novel functions for clothes Among those methods, wet finishing is the most dominant; however it has many drawbacks such as the necessity of waste water treatment which costs more money, drying processes to remove water which spend energy intensively, etc

Lately, to satisfy the call of environmentalists over the world, scientists and textile industrialists have created new clean technologies One important technique growing in relevance is the so–called “Plasma Technology” There are many kinds of plasma techniques being used, for instance, hot (thermal) plasma, cold (non–thermal) plasma, reactive plasma, elementary plasma (Rauscher et al., 2010) Nevertheless, cold plasma is the most common technique of plasma technologies employed for textile industry A general viewpoint of classification of plasma technologies used in many industries is depicted in Figure 1.1

Figure 1.1 – General characterization of plasma techniques (Rauscher, 2010, pp 138–142)

Among those plasma treatment technologies, atmospheric Dielectric Barrier Discharge (DBD) has shown some advantages as compared to the others It can be conveniently in–line applied on a production, doesn’t require low–pressure (vacuum) generating machines, which are costly More importantly, DBD provides more homogeneous and higher fluxes of active species and it is much less prone to cause surface damage as compared to corona discharges (Borcia et al., 2006) With this development, less costly paradigm of DBD, there will be a lot of properties of textile products improved, modified more thoroughly, economically and safely

Figure 1.2 – Nanocoating, an example of nanofinishing techniques

(Source: http://oecotextiles.wordpress.com/2010/09/01/silver-and-other-nanoparticles-in-fabrics/)

Plasma technologies

Hot (Thermal) Cold (Non thermal)

(used for textile industry)

Reactive Elementary

Low pressure

Sub–atmospheric pressure Atmospheric pressure

Corona discharge

DBD (Dielectric Barrier Discharge) Glow discharge Plasma jet

During the 20th century, science and technology together achieved many “magical” evolutions from materials, medicine, natural sciences, etc… and it is predicted that the 21st century will be the domain of nanotechnology As part of this newly born technology, nanoparticle incrementally creates its huge influence on the stage of science This nanoscale finishing brings many desirable properties and especially, when applied on textiles, the finishing doesn’t affect much fabric’s weight, thickness, stiffness as compared with previously used techniques According to Lisa et al (2006), gold nanoparticles supported by alumina were employed to improve the removal of Mercury (Hg) in drinking water, meanwhile, in medical area, gold nanoparticles are used very commonly in various applications, one of the examples is from Cai et al (2008), this research has shown that gold nanoparticles can be used to improve the treatment of cancer and to be vehicles for drug delivery Alongside with gold, many alternative metals such as zinc, copper and silver nanoparticles also gain attractions from scientists With the ability of killing microorganisms even at a low concentration whilst it doesn’t cause habituation in microorganism, the most prevalent application of AgNPs is to be used as an antimicrobial agent for textiles (Wasif, and Laga, 2009; Filipowska et al., 2011; Tang et al., 2011) An application which takes advantage of nanoscale particles is self–cleaning In order to apply this function to products, titanium dioxide (TiO2) is a solution TiO2 particles under daylight or UV radiation in the presence of water vapour and oxygen will lead to the formation of free radical These radical are very powerful oxidizing species leading to the destruction of organic substances or microbial structures on the surface of treated materials (Budde, 2010; Rahal, 2011) Although there are many promising merits with nanoparticles but the long term effect of this lately–born materials on human health, especially the absorption via skin of people and living things, still requires more thorough researches From a long time ago the finding of new materials has been conducted by people In ancient time, people knew to mix straw and mud to build walls for their houses The straw can provide the structure meanwhile the mud acts as a binder, maintaining the straws together in place This new type of material is called composite materials or in shorter term “composites” The correct definition of composite is below (Source: http://metals.about.com/library/bldef-Composite-Material.htm)

“Composite materials is a combination of two or more materials (reinforcing elements, fillers, and composite matrix binder), differing in form or composition on a macroscale The constituents retain their

identities, that is, they do not dissolve or merge completely into one another although they act in concert Normally, the components can be physically identified and exhibit an interface between one another.” Nowadays, thanks to the support of high technological apparatuses, researchers day by day are trying to find better raw materials in place of straws, which can be narrated as steel (civil engineering) and more prominently textile fibres in many applications (ceramic, aeronautics, army, sports equipment …) In comparison to other materials, textile fibre have certain superior advantages of which the two most important are structural behaviour and weight (Miravete, 1999) There are many methods in textile technology which can fabricate a lot of types of preforms subsequently used in myriad of applications Those approaches are woven, knitted, braided and non–woven fabrics and even raw continuous fibrous materials can be an option as well

Figure 1.3 – Examples of yarn–to–fabric preforms (Miravete, 1999)

In composites, nonetheless, the connection between fibre and matrices will have a huge influence

on mechanical and chemical behaviours The better the bonds are, the higher the level of the properties According to many other publications, plasma treatment can improve inter–laminar shear strength (ILSS)

of composite materials, their fatigue resistance, delamination and corrosion All of those improvements are thanks to the enhancement of interaction at interfaces (micropitting, mechanical interlocking) and changes

in surface chemistry If the parameters are suitably selected, the fibre strength will be minimum lost (1–2%) though in some cases even improved (Morent, 2008) With the recent appearance of nanotechnology, which has a very long arm reaching nearly almost every corner in science and industry, a new potential material is born and named “nanocomposite” This new generation of materials has been taking care of by scientists throughout the world in order to perfect this infant material

Generally, in this work, the focused object needs an enhancement is nanoparticles’ adsorption onto textile substrates which hasn’t been paid much attention during the past few years Therefore, it is worth studying the changes in adsorption of nanoparticles by textile substrate with DBD plasma treatment

1.2 OBJECTIVES

 Dosage optimization of the plasma treatment to textile substrates: cotton, polyamide

 Study of physical and chemical modification after plasma treatment

 Implementation of the most appropriate application of nanoparticles on textile substrates Some techniques will be considered to find the solution for example: sol–gel, padding, coating, layer–by–layer…

 Study of an application for a functionalized material: characterization, development and evaluation Techniques intended to be used: Energy–dispersive X–ray spectroscopy (EDX/EDS), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM)

 Study of washing and rubbing fastness of nanoparticles prior to and after plasma treatments of different dosages, materials feeding rate, power

a new type of nanocomposite which consists of three constituents: resin, a textile substrate and nanoparticles

Literature survey

The literature research has been carried out in order to understand knowledge about the application

of nanoparticles onto substrates Furthermore, surface roughness and surface energy that have a great influence to the adsorption between interfaces are investigated as well Finally, chemical functional groups which play important roles for the bonding/linkage between materials are also considered carefully

After the objectives are clearly stated, the articles finding will aid to establish “STATE of ART” for the work as well Finally, the working plan is developed to execute all the steps of this work

Working plan

a Theoretical concepts: contact angle, adsorption, nanocomposite, nanoparticles, functional chemical groups as well as finding suppliers of raw materials

b Searching for references to develop the “State of Art”

c Optimizing the application of DBD plasma treatment on textile substrates:

Study the topographical/morphological alterations;

Study physical and chemical alterations;

Study the mechanism of nanoparticles adsorption onto textile substrates

d Final draft of dissertation

Experimental work

The experimental work includes the following steps

- The synthesis of silver nanoparticles;

- The treatment of polyamide 66 fabric with Dielectric Barrier Discharge plasma technique;

- Application of silver nanoparticles of different diameters onto polyamide 66 fabrics;

- Evaluation of physical and chemical modifications of treated and virgin samples

Results analysis

The results at each stage in this work were analyzed so that they could satisfy the level of the objectives proposed at the beginning of the study

Conclusion and future work

The conclusions were withdrawn thanks to the results obtained during the work Experiences acquired from this study would be used as the basis for the future researches in this perspective

Chapter 2 – State of Art

Chapter two discusses about the latest achievements relating to polyamide fabrics, plasma technologies

and nanoparticles

Chapter 3 – Experimental Procedure

This current chapter describes the experimental steps carried out in order to obtain the scopes proposed at the beginning of the study Evaluation techniques are also shortly depicted in this part

Chapter 4 – Results and Discussions

Here, all the results gained during experimental work will be expressed and discussions are talked about in order to evaluate the outcomes

Chapter 5 – Conclusions and Future Work

Final conclusions of the research were concluded and orientations for future studies suggested in this chapter

Bibliography

A full list of references utilized for this work

II During the World War II, nylon was used in many applications, for instance, waterproof tents, lightweight parachutes and many others Nylon was marketed for the production of women’s hosiery in 1938 by E.I

du Pont de Nemours & Company Follow the instantaneous success (since 4 million pairs of nylon stockings were sold in the first few hours of sale on 15 May, 1940 (Deopura, 2008), nylon had brought Dupont consecutive 50 years of gigantic income and it also became the household name globally

In 1950 the total world production of synthetic fibers was only 69,000 tonnes, and almost all of this was nylon Over the next 20 years production of polyester, acrylic and polypropylene fibers started, and the volume produced increased to 4.8×106 tonnes Nylon remained the most important synthetic fiber in volume terms In 1970 nylon accounted for 40 % of the total synthetic fiber production with just less than 2×106 tonnes The applications also expanded from the initial hosiery market to reinforcement of rubber in tyres and belts, and to carpets, often in blends with wool (McIntyre, 2004)

The name “nylon” was chosen in order to signify the fineness of the manufactured filament The reason was that a pound of nylon could be converted into the length which is equal to the distance from New York to London In reality, there is a variety of polyamides have been fabricated and introduced to the

market under many different commercial names like Antron, Tactel, Tactesse, Anso, Cadon, Cantrece, Cordura, Caprolan, duPont nylon, and Enkalure It is because in the commerce, nylon and polyamide are not used prominently

Figure 2.1 – Several examples of polyamide fibers (Lewin, 2006)

Although “nylon” represents the whole family of polyamides, there are, nevertheless, two major important types of nylon which have the notations of Nylon XY and Nylon Z Polyamide 6 and polyamide 66 are the two typical examples of these two types respectively The above nomenclature of Nylon XY and Nylon Z can be explained as follows The four fundamental constituents of nylon are C, H, N and O that are combined to form adipic acid hexamethylene diamine and caprolactam In nylon XY type, the X refers to the number of carbon atoms in the diamine monomer, whereas, Y represents the number of carbon atoms

in diacid monomer, i.e both diamine and dibasic acid contain 6 carbon atoms each in the case of Nylon

66 In nylon Z type, Z refers to the number of carbon atoms in the monomer In the case of Nylon 6, Z = 6

is the number of carbon atoms in an amino acid (Deopura et al., 2008, page 41 and Chawl, 1998)

2.1.2 CHEMICAL STRUCTURE AND SYNTHETIC PROCEDURE

Nylon fibers consist of linear macromolecules whose structural units are connected by the –NHCO– groups which are called amide linkages Thus, the term polyamide has been used more popularly Practically, nylon polymers can be formed via a plenty of ways wherein there are four most important for industrial process are (McIntyre, 2004):

1 The condensation of diamines with diacids;

2 The self–condensation of amino acids;

3 The hydrolytic polymerization of lactams, which involves partial hydrolysis of the lactam to an amino acid; and

4 The anhydrous addition polymerization of lactams

Among the above four methods, the first and the third ones are widely used in fiber manufacture whilst the second one is used for the production of specially–used nylon and the fourth one is for reaction molding Carother’s approach relates to the first method which is a condensation of two difunctional monomers, a carboxylic acid and an amine Polyamides originate from diacids and diamines are generally referred to as the AABB type As mentioned before, these polyamides are assigned as Nylon XY where X and Y correspond to the numbers of carbon atoms in the diamine and the diacid respectively Although this process is capable of creating many kinds of Nylon XY, only nylon 66 has a commercially important meaning Another process is involved in the condensation of an ω–amino acid with the amine and the carboxylic acid groups on opposite ends of the molecule And nylons produced from amino acids will be called the AB type This polyamide group refers to Nylon Z where Z is the number of carbon atoms in the monomer And nylon 6 is the prominent member of this group which has the best commercial potential Polyamides are macromolecules which contain recurring amide groups as integral parts of the polymer backbone And nylons are polyamides with structural units derived predominantly from aliphatic monomers Although many reactions are known that are suitable for polyamide formation, commercially important nylons have been obtained by either of two basic approaches (poly–condensation and ring opening polymerization) as represented by the following general equations (Deopura et al., 2008)

H2N – (CH2)X – NH2 + HOOC – (CH2)Y-2 – COOH (2.1)

⇌ –[– HN – (CH2)X – NHOC – (CH2)Y-2 – CO –]n– OH Equation (2.1) refers to the synthesis of AABB–type nylons through poly–condensation of bifunctional monomers utilizing stoichiometric pairs of dicarboxylic acids and diamines,

H2N – (CH2)Z-1 – COOH ⇌ –[– HN – (CH2)Z-1 –CO –]– + H2O (2.2)

HN – (CH2)Z-1 – C = O ⇌ –[– HN – (CH2)Z-1 – CO –]– (2.3) Equations (2.2) and (2.3) pertain to the synthesis of AB–type nylons entailing respectively the polycondensation of amino acids and the ring–opening polymerization of lactams

Polyamide 66

Nylon–66 is the generic term for poly(hexamethylene adipamide) It is commercially synthesized by polycondensation from hexamethylene diamine and adipic acid according to the amidation reaction of Equation (2.1):

nH2N – (CH2)6 – NH2 + nHOOC – (CH2)4 – COOH Hexamethylene diamine Adipic acid

⇌ H –[– HN – (CH2)6 – NH – OC – (CH2)4 – CO –]n– OH + 2nH2O Nylon-6,6: poly(hexamethylene adipamide)

(Lewin, 2006)

Hexamethylene diamine melts at 40.9OC and is normally used in the form of a concentrated aqueous solution Adipic acid has a melting temperature of 152.1OC and is used in its pure solid form A salt solution of about 50% concentration containing precisely stoichiometric quantities of the two intermediates is first prepared In a typical polymerization reaction, the salt solution is heated to boiling to evaporate water, possibly at elevated pressure, until its salt content reaches ≥ 60% The concentrated salt solution is then heated gradually in a reactor as water is evaporated, typically from 212OC to 275OC at 1.73 MPa (250 psi) The polymer molecular weight will reach about 4400 at this point The pressure is then gradually reduced to atmospheric to allow further reaction for about an hour The polymer molecular weight is now in the range of 15000 to 17000, but is not quite equilibrated All of the liquid water in the salt solution and nearly all of the potential water of reaction in the form of amine and carboxyl end groups are removed at this point The loss of hexamethylene diamine, which boils at 200OC, is minimal The resulting polymer is suitable for melt spinning or chip forming (Lewin, 2006)

The reaction is essentially an addition polymerization, but can be considered to be the condensation polymerization of AB–type polyamide

(Lewin, 2006)

Caprolactam melts at about 69OC It does not polymerize upon heating to elevated temperatures However, shortly after Carothers developed nylon–66, Schlack of I.G Farben discovered that the ring–opening reaction occurs readily in the presence of amine and carboxyl groups Thus, ε–aminocaproic acid, nylon–66 salt, or simply water, is employed to hydrolyze lactam to form [COOH] and [NH2] end groups The [COOH] group catalyzes the addition of [NH2] to the caprolactam ring This discovery led to the polymerization of caprolactam for nylon–6 The polymerization of caprolactam is carried out initially in the presence of water at 265OC under pressure It is generally characterized by an induction period to build up the hydrolyzed products As the end group concentrations increase, the carboxyl–catalyzed amine addition proceeds at an increasing rate and the polymer chain grows This reaction also produces cyclic oligomers The [COOH] and [NH2] end groups reach a maximum concentration with time and then decrease as the monomer content depletes to equilibrium The equilibrium constants for the end groups in nylon–6 is reportedly in the range from about the same as nylon–66 to somewhat above, e.g., 428 at 280OC (Lewin, 2006)

Figure 2.2 – General production line of polyamide fiber

2.1.3 PHYSICAL AND CHEMICAL PROPERTIES

Nylon 6 and 66 fibers are strong, with a dry tenacity of 4–9 g/d (36–81 g/tex) and a wet tenacity of 2.5–8 g/d (23–72 g/tex) These nylons have elongations at break of 15%–50% dry, which increase somewhat on wetting Recovery from stretch deformation is very good, with 99% recovery from elongations

up to 10% The nylons are stiff fibers with excellent resiliency and recovery from bending deformation They are of low density, with a specific gravity of 1.14 They are moderately hydrophilic with a moisture regain of 4%–5% under standard conditions and a regain of 9% at 100% relative humidity Nylon 6 and 66 are soluble in hydrogen bond breaking solvents such as phenols, 90% formic acid, and benzyl alcohol They have moderate heat conductivity properties and are unaffected by heating below 150°C The nylons have

a high resistivity and readily build up static charge (Needles, 1986)

The nylons are fairly resistant to chemical attack They are attacked by acids, bases, and reducing and oxidizing agents only under extreme conditions They are unaffected by biological agents, but at elevated temperatures or in the presence of sunlight they will undergo oxidative degradation with yellowing and loss of strength (Needles, 1986)

2.1.4 APPLICATIONS OF POLYAMIDE

Practically, polyamide fiber is chosen for numerous applications in both apparel and industry sectors The reasons lie in their good elastic recovery, low initial modulus, excellent abrasion resistance and high resistance to rupture (Deopura et al., 2008) Polyamide is often a good option for garment where low modulus, high strength and good abrasion are not required Besides, wool is also blended with polyamide in order to enhance the durability of products made of wool

For technical textiles, there is a number of applications need polyamide’s behavior The first example is carpet Polyamide is one of the best fibers utilized in tapestry because of its good resilience, perfect deformation resistance and the most important thing is that polyamide is very useful in heavy traffic Other examples are safety belts for cars, hoses, etc…Polyurethane coated polyamide is used for the production of hot balloons as well In automotive engineering, polyamide is used as reinforcement for car tires Fishing nets are also products fabricated from polyamide More specially, cloth made of polyamide permits deformation under high wind speed and it can recover as the wind speed reduces thus the cloth

can take optimal advantage of the wind’s velocity With this performance, polyamide is frequently the core material for boats’ sail Civil engineering is also interested in polyamide In many types of synthetic fibers, polyamide is also an option for fiber–reinforced concrete (Figure 2.3)

Figure 2.3 – Synthetic fiber–reinforced concrete (Deopura, 2008)

Besides being used as raw materials, polyamide is also functionalized in many researches with expectation of producing polyamide fabrics with specific properties Several experiments have been done in order to confer certain functions onto polyamide fabrics Bessada et al., 2011 have used DBD plasma to functionalized polyamide 66 fabric and they proved an improvement in wettability of the material In another work, Zhang and Yang (2012) deposited a membrane of TiO2 nanoparticles onto polyamide fabric

so that the fabric is photocatalytic On the other hand, Zhang and Zhu (2012) created magnetic polyamide fabric by immobilization of Fe3O4 onto polyamide 6 fibre and last but not least Glampedaki et al 2011 increased the absorption ability of polyamide 66 fabrics by chitosa–based hydrogel finishing Those are just typical examples for the functionalization of polyamide in order to depict a general look at how polyamide is being utilized so far

Figure 2.4 – Sail cloth made of polyamide

(Source: http://www.sailmakerint.com/hexagon_en.php)

2.2 NANOPARTICLES AND APPLICATIONS

It is well–known that one nanometer equals one billionth of a meter which is the size of atoms and molecules “Nano” originates from a Greek word which means “dwarf” Nanotechnology, therefore, is a novel technology that deals with materials consisting of at least one dimension in nanometer scale They can be nanoparticles, nanorods, nanowires, thin films and bulk materials made of nanoscale building blocks or possessing nanoscale structures (Cao, 2004) Nevertheless, nanotechnology is not merely a physically dimensional descent from microscale to nanoscale but it promises to propose totally new and enhanced functions for materials (Wei, 2009) It is, although, entirely agreed that nanotechnology is new, nanotechnology is not a brand new scientific aspect; it provides a new way of looking and studying phenomena more scientifically and thoroughly

Medicine is a field wherein nanotechnology has been applied widely One of the applications is the utilization of nanorobots as a drug delivery agent (Freitas, 2006) This nanosystem is capable of transporting, timing, targeting and releasing curing chemicals digitally accurately onto particular infected area Another industry in which nanotechnology has created a gigantic advance is semiconductor industry

In 2007, Intel has announced their first 45nm chips for their processor production (Gasman 2006) Thus

at the moment, the size must be shrunk to a smaller size due to the development of technology in 5 years,

a long enough period in regarding technological innovation

Together with medicine and semiconductor industry, there are many other areas which nanotechnology has more or less its influence For instance, several types of automobile paints, developed from nanotechnology, have improved the scratch–resistant ability as compared with normal paints (Mongillo, 2007) Furthermore, regarding of nanoscale materials, one member cannot be ignored is nanotube, especially carbon nanotubes First discovered in 1991 by Iijima, so far, carbon nanotubes (CNTs) have shown its wide domain of applications (Meyyappan, 2005)

Figure 2.5 – Carbon nanotubes structures

(http://www.tedpella.com/gold_html/Nanotubes.htm)

 Materials

 Chemical and biological separation, purification, and catalysis

 Energy storage such as hydrogen storage, fuel cells, and the lithium battery

 Composites for coating, filling, and structural materials

 Devices

 Probes, sensors, and actuators for molecular imaging, sensing, and manipulation

 Transistors, memories, logic devices, and other nanoelectronic devices

 Field emission devices for x–ray instruments, flat panel display, and other vacuum nanoelectronic applications

Carbon has the outstanding ability to adsorb various inorganic and organic substances, particularly when it is oxidized or activated, therefore, CNTs has been used as a useful utensil to aid the water purification processes and desalination of salted water Because CNTs has nearly smooth (nonfrictional) wall whereon exist nanopores, they offer superior merits to traditional materials (Nasrabadi, and Foroutan 2011)

Figure 2.6 – Applications of carbon nanotubes (Hsieh, 2006)

With oxidized CNTs, they can be exploited in form of sheets (Tofighy, and Mohammadi, 2010), membranes (Tofighy, 2011) in order to remove dissolved mineral in seawater Although CNTs can allow the high efficiency, they are still quite expensive New Jersey Institute of Technology, thus, tried to develop

a new faster, better, and cheaper approach for the desalination process Professor Mitra’s new method creates a better membrane by immobilizing carbon nanotubes in the pores The novel architecture not only eases vapor permeation, but also prevents liquid water from clogging the membrane pores Test outcomes show dramatic increases in both reductions in salt and water production (Mitra, 2011)

Sensors can also be enhanced their performance with the utilization of CNTs Many researches have been done so far so as to find out the optimal solution for the usage of CNTs for sensing gases like hydrogen (Wong at el., 2003; I Sayago et al., 2007), ozone (Park et al., 2009), CO and NO (Li, Wang, and Cao, 2011) and even small molecules (Wang, and Li, 2011) At the moment, there are still lots of work need being done in order to maximize the prominent properties of CNTs

Figure 2.7 – Scale of things (Mongillo, 2007)

Among various industrial fields, textile is also another huge industry cannot be out of affecting domain of nanotechnology which will lead to the addition of new functions or enhancement of inherent properties Nanoparticles are one of prevalent favorite products which are used in textile applications As a typical example of nanomaterials, the synthesis procedure of nanoparticles, hence, can be classified as two main categories, which are top–down and bottom–up

Milling and colloidal dispersion are typical examples of top–down and bottom–up methods, respectively The bottom–up approach promises a better chance of obtaining nanostructures with fewer defects and more homogeneous chemical composition, as it is mainly driven by the reduction of Gibbs free energy leading to a state closer to thermodynamic equilibrium In contrast, the top–down approach is more likely to introduce internal stress, in addition to surface defects and contaminations A schematic representation of the top–down and bottom–up approaches for the synthesis of nanomaterials is given in Figure 2.8

Figure 2.8 – Schematic representation of the bottom–up and top–down approaches for the

synthesis of nanomaterials (Wei, 2009)

Many researches have been studied with metal nanoparticles While Platinum and Palladium nanoparticles are attractive with their catalytic activities (Mei et al., 2005 and Mei et al 2007), gold nanoparticles (AuNPs) are fond of in food technology, biology and medicine The AuNPs is used in pharmaceuticals delivery (Ghosh et al., 2008) This is due to their inert and non–toxic core and their ease

of synthesis Furthermore, AuNPs can create molecular ligands which are very essential in detection of chemicals in the surrounding environment promptly Some typical examples as the detection of mercury, lead and copper (Guo at el., 2011), detection of melamine (Li et al., 2011) and the detection of cholesterol (Raj et al., 2011)

Being one of precious metals, which is also utilized in a wide spectrum of applications, is AgNPs Practically, AgNPs are used in many other areas as well; one of which is printing Due to their good electrical and thermal conductivity, AgNPs were selected for the production of printed circuits This is manifested in so–called Ink–jet printing technology A research made by Shim et al (2008) has shown that AgNPs are very useful as ink–jettable materials when they are formulated into inks Another work executed by Kosmala, Wright and Zhang (2011) gives another positive result from the integration of AgNPs into inks The process was considered cost–effective, eco–friendly and simple With AgNPs of 50nm in size, the ink produced was successfully printed on Al2O3 and on low–temperature co–fired ceramic (LTCC) and the printed films show low resistivity

Due to a special optical property, AgNPs have been openly investigated in order to take advantage of this property and they all gave positive outcomes as expected (Karimzadeh, and Mansour, 2010; Andrade, Fan, and Brolo, 2010; Angelescu et al., 2010; Zhang, 2011)

Metal nanoparticles are well known to display characteristic size dependent properties different from those of their bulk counterparts and the most significant effects occur in the 1–10 nm range These nanoparticles elicit considerable interest due to their high dispersion and the manifestation of quantum effects For example, AgNPs with spherical shape and nanometer size exhibit a very intense absorption band in the visible region due to the surface plasmon resonance These plasmons have strong optical extinctions that can be tuned to different colours by varying their size and shape In order to create a red and yellow color for glass, Gila and Villegas (2004), used AgNPs based on the Ag+ ion exchange process They concluded that this process is under control and reproducible and the color obtained has satisfied the

decorative requirement Also with the purpose of fabricating expected colors for decorative purposes, some other studies have been carried out for ceramic wares (S Mestre, 2011 and M Blosi et al., 2012)

Figure 2.9 – SEM photo of cotton fiber impregnated with AgNPs for antimicrobial property (Wei, 2009)

One of the most important properties of AgNPs is their antimicrobial ability This feature has been discovered and applied by our ancestors since the old days Moreover, silver is non–toxic to humans, doesn’t cause habituation, and can affect a wide spectrum of microorganisms Therefore silver and nanosilver antimicrobial agents are commonly used in hospitals, particularly medical textiles Silver will bind to the inter–molecular proteins making the microbes inactive One more advantageous attribute of AgNPs is there high surface to volume ratio, which provides a high efficiency in the inhibition of bacterial and fungal proliferation Radetić et al (2008) exploited corona plasma treatment on polyamide and polyester fabrics with the expectation of activation the fibers’ surface in order to increase the amount of AgNPs applied via colloids This combination has shown a fabulous antibacterial capacity and also meets the requirements of laundering durability

Some other investigators have tried utilizing some various techniques in order to deposit AgNPs onto fabrics for the antimicrobial goal, for example by ultrasound (Perelshtein et al., 2008), ion beam (Klueh et al., 2000) The energy radiated fiber surface during treatments led to the appearance of free radicals which are attributed being involved in formations of covalent bonds with AgNPs and thus making an antibacterial surface Or with the layer–by–layer method (Dubas et al., 2006), one natural fiber and one synthetic fiber, which are silk and nylon respectively, are the two raw materials chosen Although the final

results between silk and nylon are not the same but in total, both final products presented good antimicrobial applications

Polyamide is a rather popular object of research for the functionalization of antimicrobial Perkas et

al (2006) took use of ultrasound coating method to coat AgNPs onto nylon 66 fabrics and the coating was stable and still had effect even after 10 washing cycles Damm (2008) and his colleagues had done another experiment with polyamide6/AgNPs for filtration and made a comparison with the polyamide/Ag microcomposite The result retained from nanocomposite had superior ability of killing Escherichia coli to that of microcomposite This is due to the higher surface specific area of AgNPs than that of Ag micro particles Textor et al (2010) chose another method to produce a thin layer of silver under the heterogeneous Tollen’s reaction onto polyamide fabrics The coating not only showed a great antimicrobial activity but also had a high durability The efficacy had been the same although the treated sample underwent 30 washing cycles One similar work was done by Sedaghat and Nasseri (2011), however, this time AgNPs were synthesized by the controlled reduction of Ag+ ions with sodium borohydride at room temperature The treated polyamide 66 was intended to use for antiseptic bandage owing to a good effect

on E.Coli

Another fiber also attracting for the application of AgNPs is cotton There were studies implemented with the goal of fabricating cotton fabric with the antimicrobial functions which will be used for biomedical aims (Alay et al, 2007) Several typical tries can be found from other documents like Lee et al (2007), Khalil–Abad et al (2009), Ilić et al (2009)

One group from Korea of Hanyang University padded colloidal silver solution onto fabrics made of cotton, polyester, cotton/polyester and cotton/spandex The results expressed an affective annihilation against both Staphylococcus aureus and Klebsiella pneumonia (Lee and Jeong, 2005) with a good laundering durability (Lee, Yeo, and Jeong, 2003) Meanwhile, Jiang et al (2006) have metallized cotton and polyester fabrics on which a nano–layer of silver was coated by plating technique Many improved properties have been observed along with antimicrobial like ultra violet (UV) light absorption, antistatic, and light–fastness abilities The reasons proposed are because basic AgNPs have a better shielding property and better conductivity than the original fabrics

Figure 2.10 – SEM photo of super–hydrophobic textile material created using nanotechnology (Wei, 2009).

One of recently attractive technologies, which so–called plasma treatment, plays a supporting tool in modifying textile substrates as well With the bombardment of electrical charged particles (ions, photons, electrons), researchers want to find out how the etching of plasmatic treatment will affect the surface of substrates which subsequently, in turn, exert the AgNPs coated on the surfaces Ilić et al (2010) chose to work with radio frequency plasma to modify polyester fabrics It was found that treated polyester sample showed excellent action upon gram–negative bacterium E coli and gram–positive bacterium S.aureus until

5 washes Another favorite plasma technique is corona treatment that was deeply investigated

A lot of documents can be found to provide an overview of the potential outcomes with plasma treatment (Radetić et al., 2008; Saponjić, 2008; Ilić, 2009; Gorensek et al., 2009; Ilić et al., 2009) Actually, the core reason for the better antibacterial activities is due to the rough surface created by plasma treatment With more channels, or valleys appear on the surface, there are more AgNPs can adhere and consequently leading to a better ability of inhibition fungal/bacterial development

Metal oxides are also a popular option for textile applications One of which is ultraviolet (UV) radiation absorption It is all clear that the solar radiation consists of UV light which causes skin cancer in humans In fact, the less time of exposure to sunlight is the better for the formation of cancer cells For outdoor workers, however, this condition is impractical and, clothes with UV–block protection, therefore, are the best solution As the UV light approaches textiles, there are many phenomena will occur, which can

be seen in Figure 2.11 Only the transmitted and scattered rays are concentrated for the treatment of UV protection because they are the main factor exerting cancer disease

Figure 2.11 – UV transmittance characteristics of textile materials (Wei, 2009)

For the commercial element, zinc oxide (ZnO) is the first priority Besides, ZnO is more steady as a

UV blocker when compared to organic blockers With the high surface area to volume ration, nano sized ZnO will improve the UV–blocking ability of fabrics Several works have been performed on cotton fabrics such as (Vigneshwaran et al., 2006; Yadav et al., 2006 and Becheri et al., 2007) The data retained from these studies altogether represented not only a good antimicrobial ability but also rendered treated cotton

a high efficiency of UV protection as compared with original cotton

The capability of being water and oil repellent can be obtained by creating roughness on the surface

of substrates This is so–called biomimetic because researchers try to imitate a very famous plant in nature, Lotus leaf In fact, on the lotus leaf, it has many miniscule ridges protruding on the leaf surface leading to low surface tension Consequently, when a water drop is dripped on the leaf, it just can roll on those spiky arrows due to very low adhesion This phenomenon is patented as Lotus Effect® Hsieh (2005), together with his companies, has proved this theory by applying TiO2 nanoparticles onto substrates

to find out the influence of roughness to water and oil repellency Another research also concluded that due to the roughness alteration on the substrate surface caused by nanoparticles, the wettability can be controllable (Soeno et al, 2004)

Figure 2.12 – Lotus Effect® removing dirt particles from super–hydrophobic surface (Wei, 2009)

2.3 PLASMA TECHNOLOGY

2.3.1 WHAT IS PLASMA?

The term plasma was first used by Lewi Tonks and Irving Langmuir in 1929 to describe a collection

of charged particles in their studies of oscillations in the inner region of an electrical discharge Later, the definition was broadened to define a state of matter (‘the fourth state of matter’) in which a significant number of atoms and/or molecules are electrically charged or ionized with the fundamental characteristic

of exhibiting a collective behavior due to the long–range Coulomb interactions (Rauscher, Perucca, and Buyle, 2010)

Plasma processing is a technology used in a large number of industries, and whilst semiconductor device fabrication for computers is perhaps the best known, it is equally important in other sectors such as automotive, textile, food packaging, biomedical, polymers, and solar energy A common theme in the applications is plasma treatment of surfaces Plasma is an environmentally friendly process technology, producing an extremely low level of industrial by–products, especially when compared to more traditional wet chemical treatments (Shishoo, 2007)