**Recycling of Polytetrafluoroethylene (PTFE) Scrap Materials**

Arunachalam Lakshmanan and S.K. Chakraborty

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/59599

**1. Introduction**

#### **1.1. Plastics**

Polymers are formed from *thermoplastic* and *thermosetting plastic* materials. The binding forces between polymer chains in thermoplastics such as polyethylene are the result of van der Walls forces between the molecules and mechanical entanglement between the chains as shown in Fig.1. Most of the thermoplastics can be reused after melting since the bonds between the molecules are easily broken on heating. However, in thermosetting plastics such as Bakelite various polymer chains are held together by strong covalent bond. They are rigid, strong and more brittle. Due to strong covalent bond and cross-link, they are insoluble in almost all organic solvents. They will not become plastic when heated.

#### **1.2. PTFE**

Polytetrafluoroethylene (PTFE) was discovered by a research chemist in DuPont in the year 1938. In 1941 it has been patented and got the first brand name as Teflon. It is a fluorinated polymer obtained from tetrafluroethylene (TFE) monomer through free radical vinyl poly‐ merization. Tetra means four carbon atoms are covalently bonded to carbon atoms. Fluro means bonded atoms are fluorine. Ethylene means carbon atoms are joined by a double bond as in the case of ethylene.

In PTFE, carbon to carbon atom double bond becomes a single bond and a linear chain of carbon atoms are formed with two fluorine atoms covalently bonded to each carbon atom. These fluorine atoms shield the carbon atoms and hence no solvent can attack the carbon atoms. As a result, PTFE exhibits extraordinary chemical resistance to acids and alkalis. Carbon to fluorine bonds have high dissociation energy. Due to the high electronegativity of fluorine,

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**Figure 1.** Typical interwinded PTFE polymer. Due to strong intermolecular forces, the polymer chains are tangled. Due to its chemical inertness, PTFE cannot be cross-linked.

**Figure 2.** The molecular structure of PTFE

PTFE repels everything and hence no molecules can stick to the PTFE surface which makes it slippery (Fig.2). Ice is the only material that is slicker than PTFE. A thin PTFE coating over metal cooking pans makes them nonsticky with food items. PTFE can withstand a wide range of temperature (-184°C to 260°C) and is used in cold as well hot environments. It is hydrophobic (water repellant) and hence is resistant to weathering. It has fantastic chemical resistance and superb electrical insulation properties. It is the only plastic which can withstand temperatures up to 300°C. On heating to temperatures above 400°C, PTFE disintegrates with the production of carbon. Above 500°C, when heated in air, PTFE disappears altogether due to the production and escape of carbon and fluorine in the form of CO2 and fluorine gases into the atmosphere [1]. PTFE is insoluble in common solvents and is resistant to nearly all acidic and alkaline materials. It has a high dielectric strength and low dielectric loss. Due to high melt viscosity, injection or blow molding is not possible with PTFE. Only hot sintering or ram extrusion manufacturing processes which are relatively expensive are being followed for making PTFE products. In rapidly growing economies like China, the demand for PTFE has grown 5 times over the past 5 years.
