Wonder Plastic- Teflon

Teflon is the very important commercial polymer formed by the repeated union of tetrafluoro ethylene monomer unit. The emulsion polymerisation method is generally employed to synthesise teflon in presence of dibenzoyl peroxide initiator.

Teflon is the most important plastic because of its extremely good properties. Teflon is the trade name for polytetrafluoroethylene. It has the linear structure (-CF2-CF2-) .The monomer used is tetrafluoro ethylene which is a non-toxic gas with boiling point -76 degree Celsius. The monomer TFE is obtained by the reaction of chloroform and hydrogen fluoride.

CHCL3 + 2HF --------CHClF2 + 2HCl

chloroform chlorodifluoro methane

2CHClF3---pyrolysis---- C2F4 +2HCl

Teflon is essentially a linear polymer without branching. It is an example for a thermoplastic that is softens on heating and hardens on cooling. Teflon is the synthetic macro molecule which plays vital role in our every day life. It shows the following unique properties:

• High degree of crystallinity.
• melting point (327 degree Celsius).
• High density.
• Practically insoluble in any solvent.
• High resistance to corrosive chemicals, oxidising and reducing agents and strong mineral acids including concentrated nitric acid.
• It is not wetted by either oil or water.
• Remains slippery over a wide range of temperature( -40 to 300 degree Celsius)
• Teflon has low coefficient of friction
• High thermal stability and good mechanical strength.
• Excellent electrical insulating properties.

Teflon is therefore rightly called as a "Wonder Plastic"

Applications of Teflon:

1. Insulating material: Because Teflon is a good electrical insulator, it has been used in wire and cable insulation, insulation of motors generators, transformers and high frequency electronic equipments.


2. Antistic applications: It is not wetted by oil or water. Teflon is coated on articles such as bakery trays, frying pans and food processing equipments.


3. Industrial filters, gaskets and belts of Teflon are used,where resistance to chemical and high temperature are required.
4. Anti corrosive coating: Teflon can be coated on metal surfaces just like paints and then heat fused. These coatings offer permanent protection against corrosion. This technique is widely used fr army weapons.

5. As a dry Lubricant : It is the ideal lubricant because it stays slippery a wide range of temperature. Teflon does not collect dust and sand. Therefore teflon is used for non lubricated bearings as a dry lubricant.

Polymers-Basic Concept

Polymer: A Polymer is a macro molecule(high molecular weight) formed by the repeated union of simple, small chemical unit called monomer. The monomer units are linked together in a macro molecule by a covalent bond. The physical and chemical nature (properties) of macromolecules are totally different from which it is formed (monomers). In general the molecular weight of macromolecules varies from 1000 to 10000000.

Eg. 1. Polythene is the addition polymer formed by the repeated union of simple unit ethene

Eg. 2. Nylon 6,6 is an example for condensation polymer formed by the condensation reaction between adipic acid and hexamethylene diamine.

Monomer: Monomer is defined as a small unit which has two or more bonding sites through which it forms a covalent bonds with the other monomer units to form a giant molecule with high molecular mass. All chemical simple units cannot act as a monomers but only those simple units with minimum two bonding sites can behave as monomers. Example for simple units which behaves as monomers are alkenes (ethene), vinyl chloride, adipic acid, glycol, hexamethylene diamine etc.

Eg. Vinyl chloride(chloroethene) is the monomer having two bonding sites. Two functionality results in the formation of giant molecule of poly vinyl chloride (PVC).

Polymerization: The chemical reaction of obtaining high molecular weight macro molecule(polymer) from a low molecular weight, simple molecule (monomer) in presence of initiator is called polymerization.

Monomer ---- Polymer

Eg1. Vinyl chloride----PVC

Eg2. Styrene ----Polystyrene

Functionality: It is the number of bonding sites present in a molecule of the monomer. Compounds containing double bonds like ethene, propene,vinyl chloride etc have two bonding sites. Therefore their functionality is two or bifunctional. Phenol has three active centres at 2,4 and 6 positions. There fore its functionality is three.

Polymer Composites

Composites are combinations of two materials, containing 'reinforcing phase' and 'matrix phase'. The reinforcing material and the matrix can be metal, ceramic, or polymer. The first phase made of materials which are strong with low densities while the matrix phase is usually a ductile or tough material. Concrete is an example for a composite, which is formed by mixing sand and rocks in a paste of cement. Concrete shows best compressive nature but less tensile strength unless supported with steel. Concrete is used in infrastructure and construction bodies like, bridges, roads etc. Polymer composites are made up of at least two distinct materials. For example, a plastic composite consists of a combination of polymer resin matrix and fibrous material. The combination of materials having different properties yields a unique classs of materials which provide a user with the tailerability, which can be used to fulfill specific requirements. Polymer composites are known for higher strength per unit weight, so it can be translated directly into light weight materials (weight savings). Reduction in weight results in more efficient structures, which also reduces the energy cost and hence the material cost. Polymer composites offer many advantages such as resistance to fatigue and corrosion, low cost of fabrication etc.

Polymer composites are synthesized by mixing fiber materials with polymer resin matrix and curing the same under high pressure and heat. The resin matrix used in polymer composites are polyesters, epoxy resins, phenol-formaldehyde resin, silicone resins, vinyl derivatives and polyamides. Resistance to high temperature is induced by using phenolic resins.The fibre is embedded in the matrix in order to result the stronger matrix. Fibre reinforced composites are stronger and light. They are four to five times stronger than steel. Use of this composites makes the automobiles lighter, and hence increases the fuel effieciency.

Today polymer composites are very much required which can stand up to the torture in various applications and they are more preferred to many metals and materails for having following advantages.

• Polymer composites are very light in weight.
• They have high strength to weight ratio.
• Composite polymers are very strong and are more durable than ordinary conventional metals like steel and aluminium.
• Polymer composites are most convenienty used for aerospace applications due to its inherent properties.
• They are known for very good corrosion resistance and temperature resistance and also cutting resistance.