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A plastic is a material that can change its shape. Many things are made of plastics, usually because making them the right shape is easy. There are many types of plastic. Some can be shaped only when they are freshly made; then they become hard. Others are thermoplastic and can be softened by heating them.
Most plastics are man-made; they do not occur in nature. The process of making plastics is usually quite complicated. Most of the materials that are called plastic are polymers. Polymers are long chains of atoms bonded to each other. In most plastics, the long chain is a chain of carbon atoms.
People experimented with plastics based on natural polymers for a very long time. Alexander Parkes, an English inventor (1813-1890), created early form of plastic in 1855. It was hard but flexible and transparent. He called it "Parkesine" but now it is called "Celluloid."
Plastics are mostly petrochemicals, made from natural gas or from petroleum, a type of oil. Chemical engineers refine the petroleum which goes through a heating process. It develops ethylene and propylene, which are the chemical building blocks for many plastics. These chemicals are then combined with other chemicals to produce a polymer.
Well-known plastics, and their use[change | change source]
- Polyamide (usually called nylon) – Women's stockings.
- Polycarbonate – bulletproof glass, compact discs, DVDs.
- Polyethylene – tubes, bottles, shopping bags
- Polyethylene terephtalate (called PET when used for bottles, and polyester when used for clothes or other materials)
- Polyvinyl chloride (called PVC, usually).