From nylon shirts to the white pipes in your home, plastics are an inescapable fact of our world. When you watch television, use a computer, or text on your phone, you are using plastics. But did you know that not all plastics are created equal? So where do plastics come from and what exactly are they?
Plastics are derived from materials found in nature, such as natural gas, oil, coal, minerals and plants. The very first plastics were made by nature. Did you know that rubber from a rubber tree is actually a plastic? In the 1800s when some materials like ivory or tortoise shell started to become scarce the interest to find and make replacement materials began. The first synthetic plastics were derived from a substance found in plants and trees – cellulose. Heated with chemicals, cellulose resulted in a new material that was extremely durable. The raw materials for the plastics we know today come from many places, but most plastics are made from the hydrocarbons that are readily available in natural gas, oil and coal.
The chemistry of plastics can be complex, but the basics are straightforward. With few exceptions, plastics are organic polymers, formed through polymerization of petrochemical monomers. This is why many plastics begin with “poly,” such as polyethylene, polystyrene, and polypropylene. The word polymer comes from two Greek words: poly, meaning many, and meros, meaning parts or units. Polyvinyl chloride (PVC), for instance, is a plastic formed from the polymerization of vinyl chloride. To understand polymerization, imagine that you have several small ropes that you want connected. You decide to tie the ends together in order to form a longer rope. Each small rope is a monomer, the final long rope is a polymer, and the process of making the long rope is polymerization. At least 1,000 of these “small ropes” need to be connected to form a long rope. Applying this to PVC, vinyl chloride is the monomer, PVC is the polymer, and the chemical process to make the PVC is polymerization. The specific chemical/monomer used determines the characteristics of the corresponding plastic created. Polymers often are made of carbon and hydrogen and sometimes oxygen, nitrogen, sulfur, chlorine, fluorine, phosphorous, or silicon. The term “plastics” encompasses all these various polymers. Although there are many polymers, plastics in general are lightweight with significant degrees of strength. They can be molded, extruded, cast and blown into shapes and films or foams or even drawn into fibers for textiles. Many types of coatings, sealants and glues are actually plastics, too.
The different plastics are categorized according to the 1988 system created by The Society of the Plastics Industry (SPI), which remains one of the most popular systems used today. The system numbers can be found on most plastic containers worldwide.
Type 1: polyethylene terephthalate (PET/PETE/polyester) is used for most food jars and bottles, as well as for cleaning product containers. It can also be used as a wood finish on pianos, guitars, and vehicle interiors.
Type 2: high density polyethylene (HDPE) is used most notably in plastic grocery bags, as well as in food containers, garbage bags, and even some types of insulation and piping.
Type 3: polyvinyl chloride (PVC) is found in two forms. Soft PVC is used in toys, take-out boxes, squeeze bottles, shower curtains, medical tubing, and wire insulation. Rigid PVC is used for credit cards, piping, window frames, and for other construction materials.
Type 4: low density polyethylene (LDPE) is used most commonly in plastic grocery and trash bags, plastic wraps, milk carton coatings, food storage containers, lids, and in wire/cable coverings.
Type 5: polypropylene (PP) is used for food containers, medicine containers, bottle caps, baby bottles, thermal vests, appliance and car parts, and for several other items.
Type 6: polystyrene (PS) has three forms. Expanded PS is made into food containers and packing peanuts. Harder/Clear PS is made into plastic utensils, razors, and CD/DVD cases. Finally, high impact PS is made into things like hangers, license plate frames, and test tubes.
Type 7: All other plastics fall into this category; Nylon, polycarbonate (PC), and acrylic are just a few. Each have numerous applications, but properties vary between them. If you are curious, look for the numbers!
Types 2, 4, and 5 are the best for holding food, as they do not readily leach chemicals into food. Type 5, PP, is especially good for microwavable containers, due to its rigidity and heat resistance. Although PS, PET, PVC, and PC have been shown to leach chemicals into food, they are still commonly used for food. It is recommended to only use types 2, 4, and 5 for food. Although types 1, 2, and 4 are frequently recycled, all plastics are very difficult to break down completely, which has resulted in the excessive plastic waste that we see around the world.
This realization was the driving factor behind the first ever “Plastic Free Week” held at USAG Ansbach back in September 2018 and why it has now been turned into an annual month long event each April. This garrison-wide event demonstrates how we can drastically reduce our plastic consumption and waste. Look and listen for more details and daily tips on AFN and the Garrison’s Facebook page. We hope that this event will show that reducing use of all plastics, especially single use plastics is doable for everyone. We are doing our part to preserve our home, the Earth.