What is Polymers | Thermosetting and Thermoplastic plastics

What is Polymers

• A polymer is a compound consisting of long-chain molecules, each molecule made up of repeating units connected together.
• There may be thousands, even millions of units in a single polymer molecule.
• The word is derived from the Greek words poly, meaning many, and meros (reduced to mer), meaning part.
• Most polymers are based on carbon and are therefore considered organic chemicals.
• Polymers can be separated into plastics and rubbers.
• As engineering materials, they are relatively new compared to metals and ceramics, dating only from around the mid-1800 s.
• It is appropriate to divide them into the following three categories

1. Thermoplastic polymers (thermoplastics/TP)
2. Thermosetting polymers (thermosets/TS)
3. Elastomers (rubbers/E)

Thermoplastic polymers (thermoplastics)

• TP Solid materials at room temperature, but they become viscous liquids when heated to temperatures of only a few hundred degrees.
• This characteristic allows them to be easily and economically shaped into products.
• They can be subjected to this heating and cooling cycle repeatedly without significant degradation of the polymer.

The most important thermoplastics are:

• Acrylics (Plexiglas) : lenses, window glazing
• Fluorocarbons (Teflon) : nonstick coatings, bearings, seals
• Polyamides (Nylons, Kevlar) : fibers
• Polycarbonates (Lexan) : helmets, bullet-resistance windows, wind-shields
• Polyesters (Dacron, Mylar, Kodel) : gears, cams, rollers
• Polyvinyl chloride (PVC) : pipes, cable insulation, packaging, flooring, toys
• Polyethylene : bottles, cans, packaging materials

Thermosetting polymers (Thermosets)

TS cannot tolerate repeated heating cycles as thermoplastics can. When initially heated, they soften and flow for molding, but the elevated temperatures also produce a chemical reaction.

The most important thermosets are:

1. Epoxies : fiber-reinforced materials
2. Phenolics (Bakelite) : knobs, handles, cases
3. Polyesters : fiber-reinforced materials
4. Silicones : waterproof and heat resistance materials

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