Coating of Yarns with Electro-active Layers

Contents

Chapter I Literature Study
1.1 Coating
1.2 Polypyrrole (PPy)
1.3 Coating of Yarns with Polypyrrole (PPy)
1.4 Carbon
1.5 Graphite
1.5.1 Properties
1.5.2 Applications Carbon (Graphite) Coated Yarns
1.6 Dip Coating
1.7 Electrical Conductivity
1.8 Electrical Resistance
1.9 Plasma Treatment
1.10 Materials Used

Chapter II Coating of Yarns with Polypyrrole
2.1 Polypyrrole (PPy) Coating Procedure
2.1.1 Plasma Treatment
2.1.2 Rinsing
2.1.3 Polymerization
2.1.4 Rinsing
2.1.5 Drying
2.2 Resistance Measurement at different lengths for coating with Polypyrrole
2.3 Resistance Measurement at different lengths for coating with Polypyrrole(PPy)
2.4 Resistance Measurement at different lengths for coating with Polypyrrole(PPy)
2.5 Resistance Measurement at different lengths for coating with Polypyrrole (PPy)
2.6 Optical Microscopic Views
2.7 Electron Microscopic Views

Chapter III Dip Coating of Yarns with Carbon (Graphite)
3.1 Carbon (Graphite) Dip Coating Procedure
3.1.1 Plasma Treatment
3.1.2 Preparation of Solution
3.1.3 Machine Operation:
3.2 Resistance Measurement at different speeds for Dip Coating with Carbon (Graphite)
3.3 Dip Coating of Yarns with Carbon (Graphite)

Chapter IV Characterization of Yarns
4.1 Comparison of Coated and Uncoated Yarns after Polypyrrole Coating
4.2 Comparison of Uncoated and Coated Diameters after Coating with Carbon (Graphite)
4.3 Comparison of Diameters among Yarns after Coating with Carbon (Graphite)
4.4 Comparison of Different Yarn Resistances after Polypyrrole Coating
4.5 Comparison of Different Yarn Resistances after Carbon (Graphite) Dip Coating

Chapter V Results and Discussions
5.1 Conductivity
5.1.1 For Polypyrrole Coating
5.1.2 For Carbon (Graphite) Coating
5.2 Yarn Diameter
5.2.1 For Polypyrrole Coating
5.2.2 For Carbon (Graphite) Coating

Chapter VI Drawbacks
6.1 Limitations of Project Work

Chapter VII Conclusions
7.1 Conclusions

Bibliography

Abstract

Recently electrically conductive textiles have been of increasing research interest due to their numerous possibilities for application in various fields of activity. These conductive textiles in future will be used in clothing to measure body parameters or in textiles used to protect against electromagnetic shielding. As this is an emerging field, there is still a lack of characterizing and evaluating the performance of these conductive materials. In the scope of this project work, different yarn materials are coated with Polypyrrole and Carbon (Graphite). These layers are applied to realize textile humidity and temperature sensors. Coated yarns are characterized in order to evaluate their behavior when being worn in every-day life. So, Literature study on electro-less coating of textile structures with Polypyrrole and Carbon (Graphite) coating of different yarn materials and Characterization of coated yarns is presented in this project work.

Keywords: Coating, polypyrrole, Carbon (Graphite), dip coating, diameter, resistance, conductivity.

Chapter I Literature Study

1.1 Coating

A layer of a substance spread over a surface for protection or decoration; a covering layer. Fabrics made of conventional textile materials generally have high electrical resistivity

(> 1010 Ω). Treatment with a conducting polymer lowers the surface resistivity to (1–104 Ω). Unfortunately, conducting polymers have a poor level of process ability because of their mechanical and physical properties (e.g. fragility, infusibility and insolubility). These problems have been overcome by deposition of conducting polymer. [11]

1.2 Polypyrrole (PPy)

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Figure 1: Polypyrrole Chemical Structure [10]

Polypyrrole (PPy) is a type of organic polymer formed from by polymerization of Pyrrole.

- Among the many electrically conductive polymers that have been given attention to over the last decade, Polypyrrole (PPy), which consists of five membered heterocyclic rings, has become especially important because of it exhibits high conductivity, low resistivity, redox properties, easy preparation with low cost and environmental stability. [10]

1.3 Coating of Yarns with Polypyrrole (PPy)

There are different possible ways or methods available to coat the yarns with Polypyrrole. Like:

Cotton yarn can be coated with Polypyrrole by the

- Vapor Phase Polymerization Technique

- Synthesized via Chemical Processing Route

Wool yarns can be coated with Conducting Polypyrrole by the

- Chemical Synthesis Method

- Vapor Polymerization

Nylon yarns can be coated with Polypyrrole by the

- Chemical Polymerization

- Vapor Polymerization

Polyester yarns can be coated with Polypyrrole by the

- Chemical Synthesis Method [11] [8]

1.3.1 Applications of Polypyrrole Coated Yarns

Since Polypyrrole shows extremely low thermal diffusivities regardless of the electrical conductivity, the low thermal conductivity gives significant advantage.

- These textiles are suitable for several applications from antistatic films to electromagnetic interference shielding devices and sensors.
- The usage of conductive polymers in electromagnetic shielding applications is widespread.

Other applications are:

- Antibacterial fabrics
- Wearable sensors in Biomechanical monitoring. [11] [7]

1.4 Carbon

Carbon has a symbol C and atomic number 6. It is nonmetallic and tetravalent — making four electrons available to form covalent chemical bonds. There are three isotropic forms of carbon as 12C and 13C being stable, while 14C is radioactive, decaying with a half-life of about 5,730 years.

There are several allotropes of carbon of which the best known are graphite, diamond, and amorphous carbon. [5]

1.5 Graphite

Graphite is made almost entirely of carbon atoms. Graphite is the most stable form of carbon under standard conditions. Therefore, it is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds. Graphite may be considered the highest grade of coal, just above anthracite and alternatively called meta-anthracite, although it is not normally used as fuel because it is difficult to ignite. [6]

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Figure 2: Microscope Image of Graphite Surface Atom [6]

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Figure 3: Graphite's Unit Cell [6]

Graphite has a layered, planar structure. In each layer, the carbon atoms are arranged in a honeycomb lattice with separation of 0.142 nm, and the distance between planes is 0.335 nm. The two known forms of graphite, alpha (hexagonal) and beta (rhombohedral), have very similar physical properties, except the graphene layers stack slightly differently. The hexagonal graphite may be either flat or buckled. The alpha form can be converted to the beta form through mechanical treatment and the beta form reverts to the alpha form when it is heated above 1300 °C. [6]

1.5.1 Properties

Graphite and graphite powder are valued in industrial applications for their self-lubricating and dry lubricating properties. There is a common belief that graphite's lubricating properties are solely due to the loose interlamellar coupling between sheets in the structure. However, it has been shown that in a vacuum environment (such as in technologies for use in space), graphite is a very poor lubricant.

The electrical properties of these conductive materials are influenced by different factors such as the carbon black concentration, and the insertion of conductive yarns in the fabric. An increase in CB particle concentration from 10.41% to 15.96% causes a decrease in electrical resistivity we can say that increasing the CB particle concentration causes a decrease in electrical resistivity; the concentration of the other components of the coating material have less of an influence on the electrical properties of the conductive fabric obtained. [17]

1.5.2 Applications Carbon (Graphite) Coated Yarns

Conductive fabrics represent potential applications for instance;

- In clothing
- In the medical and military fields as
- Sensors
- Actuators
- Electromagnetic shields etc.

Conductive textiles obtained using conductive materials can be used in

- Heating applications where parts of the body can be heated
- In health care and
- Military applications. [11]

1.6 Dip Coating

Dip coating refers to the immersing of a substrate into a tank containing coating material, removing the piece from the tank, and allowing it to drain. The coated piece can then be dried by force-drying or baking. It is a popular way of creating thin film coated materials along with the spin coating procedure.

Stages of Dip Coating

The dip coating process can be, generally, separated into 3 stages:

- Immersion: the substrate is immersed in the solution of the coating material at a constant speed preferably judder free.

- Dwell time: the substrate remains fully immersed and motionless to allow for the coating material to apply itself to the substrate.

- Withdrawal: the substrate is withdrawn, again at a constant speed to avoid any judders. The faster the substrate is withdrawn from the tank the thicker the coating material that will be applied to the board. [1]

1.7 Electrical Conductivity

It is the degree to which a specified material conducts electricity, calculated as the ratio of the current density in the material to the electric field which causes the flow of current. Electrical conductivity is the ability of a material to carry the flow of an electric current (a flow of electrons). [2]

1.8 Electrical Resistance
Another way of describing the conductivity of a material is through resistance. Resistance can be defined as the extent to which a material prevents the flow of electricity. Silver, aluminum, iron and other metals have a low resistance (and a high conductivity). Wood, paper, and most plastics have a high resistance (and a low conductivity).

The unit of measurement for electrical resistance is called the ohm (abbreviation: Ω). The ohm was named for German physicist Georg Simon Ohm (1789–1854), who first expressed the mathematical laws of electrical conductance and resistance in detail. This choice of units clearly illustrates the reciprocal (opposite) relationship between electrical resistance and conductivity. [2]

1.9 Plasma Treatment

If a substrate has a low surface energy, its wettability is poor and coating adhesion very scarce, and then needs a surface treatment to increase energy. The surface energies of the treated materials increased substantially, thereby enhancing wettability, printability, and adhesion properties.

The Plasma Treatment Process consists of exposing a polymer to a low-temperature, high density glow discharge. Primarily, a plasma treatment provides manifold possibilities to refine a polymer surface, enabled by the adjustment of parameters like gas flows, power, and pressure and treatment time.

The resulting plasma is a partially ionised gas consisting of large concentrations of excited atomic, molecular, ionic, and free-radical species which force themselves into the polymer and roughens the surface of the polymer (yarn). Plasma treatment of polymer surfaces causes not only a modification during the plasma exposure, but also leaves active sites at the surfaces which are subject to post-reactions. [16]

1.10 Materials Used

In the scope of this project we have used four different types of yarns manufactured from synthetic materials. Such as:

- Polyamide 6.10; Diameter: 0.220 mm

- Polyester PET 930C; Diameter: 0.550 mm

- Polyester PETP Monofilament; Diameter: 0.650 mm

- Polyester PET 930R Monofilament; Diameter: 0.650 mm

Chapter II Coating of Yarns with Polypyrrole

2.1 Polypyrrole (PPy) Coating Procedure

2.1.1 Plasma Treatment

As yarns used for this project work are synthetic and have low coating adhesion so plasma treatment has done.

The Plasma Treatment Process consists of exposing a polymer to a low-temperature, high density glow discharge. Primarily, a plasma treatment provides manifold possibilities to refine a polymer surface, enabled by the adjustment of parameters like

- Gas flows (50%),
- Power (50%),
- Pressure (starting from 886 pa to 50 pa)
- Treatment time (30 seconds).

2.1.2 Rinsing

After the washing step, the yarns have been rinsed with distilled water and dried (wih a hair dryer).

2.1.3 Polymerization

2.1.3.1 Preparation of Polypyrrole (PPy) solution

For the polymerization reaction, first a 0.04M PPy solution has been used.

- 0.71 ml/250 ml of PPy

It was necessary to use 0.71 ml of PPy and filled up with distilled water till we had 250 ml in the slops(PPy was well mixed with water). After that the yarn were placed in the solution for 1 hour at room temperature.

2.1.3.2 Preparation of FeCl3 –BSA (Benzene Sulphonic Acid) solution

The solution contains:

- FeCl3 -- 6.43 g/250 ml
- BSA-- 0.54 g/250 ml

It was weighed out 6.43 g/250 ml of FeCl3 and 0.54 g/250 ml of BSA and dissolved them in 250 ml of distilled water. This solution was added to the yarn in the Pyrrole solution and the polymerization was carried out at least 1 hour at 50 C.

The polymerization was stopped when the color of the solution and the yarn changed into a very dark greenish color.

2.1.4 Rinsing

The Polypyrrole coated yarn was rinsed with distilled water until no coating residues are visible on the yarn and rinsing water appeared clear in color.

2.1.5 Drying

The yarns were dried by using a hair dryer.

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