Previously, we learned about why plastic is so useful and how it is made. Now it's time to learn about the chemical makeup of plastic. Why is some plastic rigid, while other plastic is flexible? It is because of the chemical makeup of each kind of plastic. We are going to examine plastics 1-6. We will skip type 7 (Other) because it covers all of the remaining plastics.

Hydrocarbons: the Building Blocks of Plastic

Remember that plastics have one thing in common: hydrocarbons. The hydrocarbons are extracted from crude oil by distillation. They come from natural gas through condensation. Once they are cracked, they can be combined with other elements to create polymers. Polymers are links of monomers, which are molecules that bind together. A polymer is like a chain, and the links are made up of monomers. Let’s look at the six main types of plastic:

Resin code #1: Polyethylene terephthalate (PET/PETE)

PET is a polymer chain of carbon, hydrogen, and oxygen molecules. It is made up of repeating (C10H8O4) units (ten carbon, eight hydrogen, and four oxygen). PET is commonly used for food and beverage containers.

Resin codes #2 and #4: High Density Polyethylene (HDPE) and Low Density Polyethylene (LDPE)

These two plastics are made up of ethylene (C2H4) molecules (two carbon and four hydrogen). HDPE polymers link together tightly. LDPE polymers have branches and don’t stack as snugly. HDPE is used for milk containers, lotion bottles, and bleach containers. LDPE is found in plastic bags and squeezable containers.

Resin code #3: Polyvinyl Chloride (PVC)

PVC is made up of ethylene (containing hydrogen and carbon) and chlorine. The monomers of PVC are made up of (C2H3Cl) chains (two carbon, three hydrogen, and one chlorine). PVC can be combined with many different additives, giving it different properties. It can be plasticized to make it flexible or unplasticized to make it rigid. It is used for pipes, wire insulation, flooring, and windows.

Resin code #5: Polypropylene (PP)

Polypropylene is created by joining chains of propene, or propylene, together. Its chemical makeup is (C3H6) monomers (three carbon and six hydrogen) linked together. PP is commonly found in automotive parts, bottle caps, and drinking straws.

Resin code #6: Polystyrene (PS)

Polystyrene is made up of styrene (C8H8) monomers (eight carbon and eight hydrogen) linked together. It is widely found in food containers, insulation, Styrofoam, and disposable utensils.

 At Container & Packaging Supply, we offer plastics in lots of shapes and sizes, made out of all sorts of kinds of plastic. Now that you know where plastic comes from, you may never look at plastic the same way again.