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 nan
INTRODUCTION
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/)
Hot (Thermal) Cold (Non thermal)
Sub–atmospheric pressure Atmospheric pressure
DBD (Dielectric Barrier Discharge) Glow discharge Plasma jet
During the 20 th century, science and technology together achieved many “magical” evolutions from materials, medicine, natural sciences, etc… and it is predicted that the 21 st 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 (TiO 2 ) is a solution TiO 2 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
4 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.
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
METHODOLOGY
The methodology chosen for the work can be considered in the following stages as below
The objectives were pointed out with the hope of improving the properties or more specific the adsorption characteristic of textile substrates and nanoparticles This feature lately hasn’t been noticed by most researchers and industrialists If this work gives positive outcomes, there will be a promising trend for a new type of nanocomposite which consists of three constituents: resin, a textile substrate and nanoparticles
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
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
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
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.
THESIS STRUCTURE
This thesis comprises of five chapters which are introduction, state of art, experimental work and conclusions and future work A brief summary of each chapter is expressed as below
This chapter introduces the general context of textile’s role in human routine and a general view of plasma techniques existing Besides, objectives of the research, working plan, selected methodologies, and the thesis structure are proposed.
STATE OF ART
POLYAMIDE
In the history of synthetic fibers, polyamide has a very interesting role Everything started from the basic research executed by Wallace Carothers to develop new product for DuPont at Wilmington in the USA starting in 1928 (McIntyre, 2004) The polyamide fibers include the nylon and the aramid fibers Both fiber types are formed from polymers of long–chain polyamides According to the definition of Federal Trade Commission (FTC) from the USA, in nylon fibers less than 85 % of the polyamide units are attached directly to two aromatic rings, whereas in aramid fibers more than 85 % of the amide groups are directly attached to aromatic rings (Needles, 1986) In fact, nylon is a generic word representing a class of polymers as polyamides This “nylon” term is more popular in UK and North American countries; meanwhile polyamide is more prevalent in European countries (Chawl, 1998) Among polyamides, nylon was the only synthetic fiber brought to a full–scale production and was kept so until prior to the World War
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 4.8×10 6 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 2×10 6 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
10 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)
H 2 N – (CH 2 ) X – NH 2 + HOOC – (CH 2 ) Y-2 – COOH (2.1)
⇌ –[– HN – (CH 2 ) X – NHOC – (CH 2 ) 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
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): nH 2 N – (CH 2 ) 6 – NH 2 + nHOOC – (CH 2 ) 4 – COOH Hexamethylene diamine Adipic acid
⇌ H –[– HN – (CH 2 ) 6 – NH – OC – (CH 2 ) 4 – CO –] n – OH + 2nH 2 O Nylon-6,6: poly(hexamethylene adipamide)
Hexamethylene diamine melts at 40.9 O C and is normally used in the form of a concentrated aqueous solution Adipic acid has a melting temperature of 152.1 O C 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 212 O C to 275 O C 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 200 O C, is minimal The resulting polymer is suitable for melt spinning or chip forming (Lewin, 2006)
Nylon–6 is the generic name for polycaprolactam It is almost exclusively synthesized from ε– caprolactam by a ring–opening reaction Equation (2.3):
HN – (CH2)5 – C = O ⇌ –[– HN – (CH2)5 – CO –]– ε–caprolactam Nylon 6: polycaprolactam
The reaction is essentially an addition polymerization, but can be considered to be the condensation polymerization of AB–type polyamide
Caprolactam melts at about 69 O C 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 [NH 2 ] 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 265 O C 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 [NH 2 ] 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 280 O C (Lewin, 2006)
Figure 2.2 – General production line of polyamide fiber
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)
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
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)
(http://www.tedpella.com/gold_html/Nanotubes.htm)
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
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
19 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
22 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
23 results between silk and nylon are not the same but in total, both final products presented good antimicrobial applications
EXPERIMENTAL PROCEDURE
MATERIALS
In order to implement the work, three types of silver nanoparticles were used Two commercially available silver nanoparticles of 10 and 20 nm in water–based colloidal solutions with a concentration of 0.02 mg L -1 were provided by Sigma–Aldrich, St Louis, MO, USA These two types of AgNPs will have the notations of “Sigma 10” and “Sigma 20”
A colloidal solution of 50 nm AgNPs with concentration of 0.02 g.L -1 was entirely synthetized in the chemical lab of Textile Engineering Department at University of Minho The synthesis process is described in the following stages Ag colloid nanoparticles were prepared by a modified stepwise method of the conventional reduction technique in order to improve the synthesis of spherical and size controlled nanoparticles (Dong et al., 2009; Turkevich, Stevenson, & Hillier, 1951) During the process, solution was boiled and mixed vigorously All solutions of reacting materials were prepared in distilled water A 100 ml of 1 mM silver nitrate (AgNO 3 ) was heated to boiling in a 250 mL flask To this solution 10 ml of 1 % trisodium citrate (Na3C6H5O7) was added drop by drop (3.8 mM final concentration) At the end of the citrate addition was suddenly added distilled water to restore the initial volume Solution was heated until color’s change became evident (pale yellow) Then it was removed from the heating element and stirred until cooled to room temperature This nanoparticle would be called “Synthetized” in this research and the average diameter of these AgNPs is 50nm
The textile substrate used for this work is a commercial plain–weave woven polyamide 66 fabrics with warp density of 40 threads/cm and weft density of 18 threads/cm The yarn count is 15 tex and 37 tex for warp and weft yarns respectively The specific weight of the fabric is 135 g/cm 2
RESULTS AND DISCUSSIONS
CONCLUSIONS AND FUTURE WORK
CONCLUSIONS
With the objective of improving the adsorption ability of textile substrate, especially here polyamide
66 fabric, in respect to nanoparticles (silver in this work) this research has been implemented in the three main following stages In each stage there will be some steps to fulfill the tasks
1 – Polyamide 66 fabric was processed with a DBD plasma machine with the optimal parameters proved in other work to modify the fabric surface
2 – After going through a plasma treatment, the textile substrate was examined by many techniques including physical and chemical analyses which are Scanning Electron Microscopy (SEM), static/dynamic contact angle, X–ray photoelectron spectroscopy (XPS)
The results obtained in this stage have shown big differences in both chemical and physical performance of polyamide 66 fabric before and after plasma treatment It was proved that the wettability (contact angle test) was highly increased after the fabric treated with plasma due to the etching effect leading to a greater roughness on the surface of the fabric Besides, the chemical composition on the surface was also modified with the creation of functional groups which also have a big influence on the wettability of liquids onto the substrate’s surface
1 – In addition to two commercial AgNPs with diameter of 10 and 20 nm respectively, synthetized AgNPs has been fabricated in lab with diameter of 50 nm
2 – These three AgNPs were characterized by UV–vis, Dynamic Light Scattering and Zeta potential
On one hand, the techniques used all showed that the two commercial AgNPs are monodisperse just as described by producer On the other hand, the synthetized AgNPs is proved to be polydisperse (a high polydispersity index was calculated) and have a quite spherical shape Generally, all three kinds of AgNPs are qualified in shape and dimension for a required thorough research
1 – The three kinds of AgNPs were applied onto original and plasma pretreated polyamide 66 samples by a dipping and then curing process, the procedure repeated once
2 – Again, these samples were then analyzed with several techniques consisting of SEM, reflectance spectrophotometer, static/dynamic contact angle and XPS
The SEM photos have shown the existence of AgNPs on the samples and clearly the amount of AgNPs on plasma pretreated samples is higher An analogous result also notified by XPS, this technique however has not only provided details about the amount of AgNPs present on virgin and plasma treated samples but also figured out that the diameter of AgNPs has a certain effect on the adsorption of fabric It was found that the smaller the AgNPs, the more they are adsorbed onto the fabric Data obtained from reflectance spectrophotometer are consistent to those of XPS and SEM
For static contact angle, although the plasma provides better wettability for the polyamide 66 fabric, it is the presence of AgNPs has reverse the effect by increasing the static contact angles up to the range of
94 0 –125 0 for all three types of AgNPs Within all, the synthetized AgNPs (50nm) have the lowest hydrophobic effect due to their low amount adsorbed onto the polyamide 66 fabric which proved by the XPS evaluation In respect to the dynamic contact angle, plasma processed samples have shown an interesting outcome Reversely to the hydrophobic behavior of static contact angles, these plasma treated samples showed a hydrophilic dynamic contact angles It is proposed that the electrostatic bonds between the silver ions on the surface of AgNPs (positive charge) and negative plasma species have attracted each other leading to the hydrophilicity of the AgNPs–deposited polyamide 66 fabric
In short, plasma treatment has improved threefold the adsorbed amount of AgNPs onto the polyamide 66 fabric with the diameter of AgNPs ranging from 10 to ~50 nm Besides, the AgNPs play an interesting role to the surface characteristic of textile substrate With original polyamide 66 fabric samples (no plasma), AgNPs will add more hydrophobic behavior to the surface which is inherently hydrophobic With polyamide 66 fabric samples pre–treated with plasma, at first the AgNPs still make the surface hydrophobic (high contact angles 90 0 –125 0 ) but this behavior is very constant Right after less than 1 second, all the drops are absorbed completely and very fast This is because AgNPs have preserved part of the plasma functional species from ageing as compared with the control samples of the same ageing due to electrostatic bonds
FUTURE WORK
For future work, it is necessary to study different plasma dosages, different type of nanoparticles (other metals like gold, copper or metal oxides like titanium dioxide) of more different diameters, different textile substrate (polyester, cotton, wool, acrylic…) in order to understand deeper the ability of plasma treatment for the improvement of nanoparticles adsorption As stated in the conclusions, it is necessary to find out the dependence of AgNPs size on the dynamic contact angle of plasma treated polyamide 66 fabric deposited with AgNPs
In this work, the cross–section view of the polyamide 66 fiber was implemented by using liquid nitrogen After being frozen, the fiber was then broken and had an evaluation by SEM – Figure 5.1
Figure 5.1 – Cross–section view of polyamide 66 fiber
From the Figure 5.1, it can be clearly seen that there are some particles inside the fiber Due to some limitations, these particles couldn’t have been figured out what materials they are However, this finding is very interesting because normally, many researches have confirmed that plasma treatment only has superficial effect and can’t have a deeper effect Therefore, a more ambitious purpose is that it is possible to use plasma treatment to make to nanoparticles go deeper into the fiber It is already known from many researches that plasma of different approaches altogether improved dyeability which means more dyestuff absorbed by textile materials Hence, if it is possible to make nanoparticles go deeper into fibers surface, it would promise a new generation of composite materials
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