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What is Plastic?

Plastic bag

There are thousands of different kinds of plastic, from shopping bags to Fisher-Price toys to photographic film, CD's, and plumbing pipes. Some plastics, like chewing gum or rubber, grow as part of plants, but people make most of the different kinds of plastic. We call them "plastics" because they are plastic, which means easy to bend or mold into different shapes.

All plastics are groups of hydrocarbon molecules. Each of these molecules is very large with tens of thousands of carbon atoms and hydrogen atoms in it. Most plastic molecules are just hydrogen and carbon atoms, or mostly hydrogen and carbon with some oxygen, sulfur, nitrogen or chlorine atoms as well. They take advantage of the ability of carbon atoms to bond their electrons together in long flexible chains in order to create long flexible molecules.

When a number of these huge plastic molecules join together, they attract each other. They don't attract the way water does, because plastic molecules are not polar - that's why plastics don't dissolve in water the way sugar does, even though both sugar and plastic are hydrocarbons. Instead,

How do people make plastic out of wood or oil?

People make cellulose plastics out of wood; they include rayon, cellophane, ping-pong balls, and celluloid film. We make most of the other kinds of plastic out of oil (the same stuff people use to heat their house or run their car). Polystyrene plastics, made from oil, include Styrofoam. Polyvinyl chloride, or PVC, is also made from oil, but with the addition of chlorine atoms, so it forms strong, stiff bonds to make a stiffer plastic we use for pipes, the boxes around computers and VCRs, and siding for houses. Nylon is another kind of plastic made from oil. We use it to make nylon stockings (pantyhose), and also other cloth things like windbreakers and parachutes and, because it lasts a long time without wearing out, gears and car parts. Acrylics are a kind of plastic that we use to make paint, and also fabrics that imitate fur and wool. Polypropylene is what we make plastic bottles, carpets, and plastic furniture out of; there's also a lot of polypropylene in cars. Polyethylene terephthalate, or PET, becomes soda pop bottles. Polyurethane is what we make into foam rubber mattresses and insulation. Finally, Kevlar is a kind of plastic that we make into bullet-proof vests and helmets. There are more plastics, too, but these are the most important kinds.

Bibliography and further reading:

Organic molecules
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Professor Carr

Karen Eva Carr, PhD.
Assoc. Professor Emerita, History
Portland State University

Professor Carr holds a B.A. with high honors from Cornell University in classics and archaeology, and her M.A. and PhD. from the University of Michigan in Classical Art and Archaeology. She has excavated in Scotland, Cyprus, Greece, Israel, and Tunisia, and she has been teaching history to university students for a very long time.

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