Plastics are made from petrochemical monomers extracted from crude oil or natural gas, which are polymerized to form thermosets or thermoplastics. The molding process involves superheating and pressurizing the monomer soup to ensure a solid, uniform product. Plastic’s disadvantage is its environmental impact, as it takes many years to biodegrade and only 5% is currently recycled.
Plastic is the most versatile and widely used synthetic material on the market today. They are polymers, i.e. large molecules (molecular weight ~10,000+) that consist of long repeating chains of smaller molecules (molecular weight ~100) known as monomers. Common monomers used in the manufacture of plastics, such as vinyl acetate, styrene, butadiene and vinyl chloride, are extracted from crude oil or natural gas. Monomers fall into the class of chemicals known as petrochemicals.
Plastics are made using a process called polymerization, in which many thousands of monomers are joined together to form a polymer chain. Monomers are made up of atoms such as chlorine, nitrogen, oxygen, hydrogen and sulfur. Monomers are easily extracted from abundant organic sources, although as the price of crude oil rises, so does the price of plastic.
There are two main types of plastics; thermosets and thermoplastics. Both are produced by pouring liquid monomers into a mold where they undergo polymerization. Thermosetting plastics are permanent once printed: they do not deform with heat. Thermoplastics melt under heat and can be re-formed repeatedly. The polymerization process increases the molecular weight of the constituent molecules, transforming liquid monomers into solid polymers. (The increase in molecular weight causes the substance to undergo a phase change.)
During the molding process, the monomer soup is superheated and condensed under many atmospheres of pressure. This causes curing and ensures that the plastic is solid and uniform, free from internal air bubbles (a major problem that had to be worked around in the early days of plastic). The result is a finished plastic product. Well known plastics include Bakelite®, nylon, PVC, synthetic rubber, acrylic, polyethylene (Tupperware®), Formica® and Teflon®. The disadvantage of plastic is its impact on the environment. They take many thousands (or even millions) of years to biodegrade. In recent decades, plastic recycling has been encouraged, although only about 5 percent of plastic in the United States today is actually recycled.
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