From morning to night, you use things made from plastic – your toothbrush, milk, water and soda bottles, your computer, the phone. The list can go on and on. Plastic is everywhere!

Plastics are made from oil. Oil is a carbon-rich raw material, and plastics are large carbon-containing compounds. They're large molecules called polymers, which are composed of repeating units of shorter carbon-containing compounds called monomers. A polymer is like a chain in which each link is a monomer. Chemists combine various types of monomers in many different arrangements to make plastic. Most plastic is chemically inert -- it will not react chemically with other substances. This means that you can store alcohol, soap, water, acid or gasoline in a plastic container without dissolving the container itself. Plastic can be molded into an almost infinite variety of shapes, so you can find it in toys, wiring, cars, even in bubble gum.

Making Plastics
To make plastics, chemists and chemical engineers start with various raw materials that make up the monomers. Ethylene and propylene, for example, come from crude oil, which contains the hydrocarbons that make up the monomers. The hydrocarbon raw materials are obtained from the "cracking process" used in refining oil and natural gas. Once various hydrocarbons are obtained from cracking, they are chemically processed to make hydrocarbon monomers and other carbon monomers in plastics. Next, the monomers carry out polymerization reactions in large polymerization plants. The reactions produce polymer resins, which are collected and further processed. Processing can include the addition of plasticizers, dyes and flame-retardant chemicals. The final polymer resins are usually in the forms of pellets or beads. Finally, the polymer resins are processed into final plastic products. Generally, they are heated, molded and allowed to cool. There are several processes involved in this stage, depending upon the type of product.

Image © Creatas Images/Jupiter (http://www.jupiterimages.com Extruding plastic is a hot process.

During extrusion, pellets are heated and mechanically mixed in a long chamber, forced through a small opening and cooled with air or water. This method is used to make plastic films. For injection molding, the resin pellets are heated and mechanically mixed in a chamber and then forced under high pressure into a cooled mold. This process is used for containers like butter and yogurt tubs. Blow molding is used in conjunction with extrusion or injection molding. The resin pellets are heated and compressed into a liquid tube, like toothpaste. The resin goes into the chilled mold, and compressed air gets blown into the resin tube. The air expands the resin against the walls of the mold. This process is used to make plastic bottles. And in rotational molding, the resin pellets are heated and cooled in a mold that can be rotated in three dimensions. The rotation evenly distributes the plastic along the walls of the mold. This technique is used to make large, hollow plastic items like toys, furniture, sporting equipment, septic tanks, garbage cans and kayaks.

Bioplastics Because plastic doesn't react chemically with most other substances, it doesn't decay. Plastic hangs around in the environment for centuries, so recycling is the best method of disposal. However, new technologies are being developed to make plastic from biological substances. Naturally occurring or biopolymers, such as soy protein, vegetable oil and bacterial polyesters, can be extracted from crops and bacteria. Bioplastics made from these biopolymers are better for the environment. They're produced from renewable resources (bacteria, plants) rather than nonrenewable resources (oil, natural gas). And, they are biodegradable – meaning they can break down in the environment instead of overfilling our landfills.