Table of Contents
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
- Thermoplastic polymers (thermoplastics/TP)
- Thermosetting polymers (thermosets/TS)
- 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:
- Epoxies : fiber-reinforced materials
- Phenolics (Bakelite) : knobs, handles, cases
- Polyesters : fiber-reinforced materials
- Silicones : waterproof and heat resistance materials
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