Welcome to You Ask Andy

Bobby Pace, age 11, of Charlotte, North Carolina, for his question:

How are plastics made?

The dozens of plastics of our modern age are chemical success stories. Each requires its own ingredients and its own recipe. And for every plastic material that serves a useful purpose, dozens of others turned out to be useless    at least for the present. Enormous amounts of cash are spent on research to discover new marketable man made plastics. So naturally, details of the recipe often are kept secret. However, we know the basic ingredients and also the general methods used to transform them into synthetic plastic materials.

As the world population increased, there were shortages of natural fibers such as wool and linen, leather, wood, metals and other materials to fill our everyday needs. About this time, our clever chemists invented plastics    and saved the day with synthetic substitutes. Many proved superior to natural substances and most of them are cheaper to buy. Basically, they are made from an assortment of plentiful, inexpensive ingredients. However, many of the recipes require lots of power and costly equipment.

The basic ingredients in most plastics are hydrocarbons extracted from coal, petroleum and natural gas. The five major ones are benzene, methane, ethylene, propylene and butylene. These basic raw materials are light gases made of small molecules.

The trick is to remodel these tiny units into large, more complex molecules. In some cases, the rings and other basic structures of the small molecular units are broken apart and reassembled to form links in long chains. Giant molecules made from smaller ones are called polymers and many of the man made polymers used to make plastics are not found in nature.

Each recipe requires a precise series of intricate stages, using controlled heat and pressure. The chemical equipment uses enormous power and looks like an assortment of giant gadgets from some other world. Small molecules of benzene gas are tortured through chemical processes to become polystyrene or synthetic rubber, fibers of nylon or colorful dyes, detergents or fibrous glass resins, aspirins or cleaning fluids. Plexiglass and acrylic, antifreeze and dozens of other synthetics may be made from methane. Ethylene may be processed to create explosives or sulfa drugs, dacron or vinyl, cleaning fluids or polythylene. The finished plastics are the result of variations  in the chemical processes. At a precise moment, many of them require the addition of other ingredients such as acetic acid, carbon monoxide or alcohol.

In the nylon polymer, about 1,700 atoms are packaged in about 45 units and the units linked together in a long chain. The small gas molecules in the raw ingredients were broken apart and synthesized, or put together, to create those durable, elastic fibers that do not dissolve in water. Nature creates the basic ingredients, but never uses them to create miraculous nylon fibers.

 

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