This is an informative post that will explain the different types of plastics and the implications of recycling them. Before we dive in, please consider the lifespan of some typical plastic products before they actually begin to biodegrade:
- Plastic Water Bottle – 450 years
- Disposable Diapers – 500 years
- Plastic 6-Pack Collar – 450 Years
- Extruded Polystyrene Foam – over 5,000 years
Approximately , eight million metric tons of wasted plastic enter the earth’s ocean every year.
Plastics are typically “organic high polymers”, meaning they consist of large chain-like molecules containing carbon, and are formed into a plastic either during or after their transition from a small-molecule chemical to a solid material. The large chain-like molecules are formed by hooking together short-chain molecules of chemicals in a reaction known as polymerization (many molecules hooked together which make a 3D network). The best way I can explain it is that each type of plastic has a different molecular network, which defines its polymer type, and the type of plastic.
Recycling involves sorting the plastics into different polymer types, and then melting them down into pellets. Soft plastics, such as polyethylene film and bags, can also be recycled. When different types of plastics are melted together, they tend to phase-separate, like oil and water, and set into separate layers. This causes structural weakness in the resulting material, which doesn’t make for good re-use.
Another difficulty with recycling plastic is the common use of dyes, fillers, and a mix of other materials included with the plastic, otherwise called “additives”. The polymer is generally too viscous (measure of its resistance to gradual deformation by stress) to economically remove fillers, and would be damaged by many of the processes that could cheaply remove it. Additives are less widely used in beverage containers and plastic bags, allowing them to be recycled more often. Yet another obstacle to removing large quantities of plastic from the waste stream is the fact that many common but small plastic items lack the universal triangle recycling symbol and accompanying number. An example is the billions of plastic utensils commonly distributed at fast food restaurants or sold for use at picnics.
In 1988, the plastics industry was under pressure from environmentalists for producing more and more plastic, which was consistently ending up in landfills or the ocean. Instead, of reducing the amount of plastic being manufactured, the Society of the Plastics Industry (SPI) released a system for manufacturers to classify each resin polymer type of plastic so it could inform consumers how to recycle the material better. (This is the triangle recycle symbol with the corresponding SPI code in the middle). This brought more transparency to the different types of plastics that are recyclable, but, in my opinion, shows how some plastics are almost better off just thrown in the trash to prevent cross-contamination…which is sad. Below you can find the 7 SPI classifications, which fall under thermoplastics. Not mentioned are thermosets, which are products such as car tires that can’t be recycled due to their polymer chain structure. See glossary for details.
1. Polyethylene terephthalate, also known as PETE or PET. These are the plastic beverage bottles, peanut butter jars, combs, and mushroom containers commonly found at your local grocery store. PET tends to get recycled the most out of all other types, because it’s one of the most common consumer plastics used. Still, there is a lot of controversy surrounding PET recycling, since PET bottles often get recycled into goods like polyester textiles, which aren’t very recyclable. So, you could say that recycling PET bottles delays plastic from going to the landfill, but may not prevent it from ending up there eventually.
2. High-density polyethylene, or HDPE. These plastics are also more commonly recycled than others, and come in the form of gallon milk jugs, shampoo and conditioner bottles, motor oil containers, and laundry detergent bottles. It is typically downcycled into plastic lumber, tables, roadside curbs, benches, truck cargo liners, trash receptacles, stationery (e.g. rulers) and other durable plastic products and is usually in demand. HDPE products are very safe and aren’t known to leach any chemicals into foods or drinks.
3. Polyvinyl chloride, or PVC. PVC isn’t often recycled and can be extremely harmful if ingested. PVC is used for all kinds of plastic pipes and tiles, but it’s most commonly found in plumbing pipes. Recycled PVC is used to make flooring, mobile home skirting, and other industrial-grade items.
4. Low-density polyethylene (LDPE). Commonly found in the form of plastic grocery bags, plastic cling wrap, sandwich bags, and squeezable bottles. LDPE is not often recycled, but certain places have the capacity to recycle it. It’s material is both durable and flexible, and isn’t known to release harmful chemicals into objects in contact with it. Thus it is a safe choice for food storage. Recycled LDPE is used to make garbage cans, plastic lumber, furniture, and many other products seen around the house.
5. The SPI code 5 is for items made of polypropylene, or PP. Once again, this is not commonly accepted for recycling in most places. This type of plastic is strong and can usually withstand higher temperatures. Among other products, it is used to make plastic diapers, Tupperware, margarine containers, yogurt boxes, syrup bottles, prescription bottles, and some stadium cups. Plastic bottle caps often are made from PP as well. Recycled PP is used to make ice scrapers, rakes, battery cables, and similar items that need to be durable. I just learned today that thanks to the Preserve’s Gimme 5 program you are allowed to drop off these #5 plastics at Whole Foods Market locations. Preserve then uses the recycled material to create their toothbrushes, razors, food storage containers and more.
6. Plastic marked with an SPI code 6 is made with polystyrene (PS) or most commonly known as Styrofoam. It can be recycled, but not efficiently; recycling it takes a lot of energy, which means that few places are willing to accept it. For example, at the Watertown Recycle Center, where I volunteer, we only designate special days a couple times a year for people to bring in Styrofoam. Recycled PS is used to make many different kinds of products, including insulation for walls, license plate frames, and rulers.
7. Last, and most depressingly, SPI code 7 is used to designate miscellaneous types of plastic that are not defined by the previous six codes. It’s very hard to find someone willing to invest in recycling this type of plastic, because there’s the risk of creating a structurally weak product. Polycarbonate and polylactide are included in this category. Polycarbonate, or PC, is used in baby bottles, large water bottles (multiple-gallon jugs), compact discs, and medical storage containers. Recycled plastics in this category are used to make plastic lumber.
Moral of the story… DON’T USE PLASTIC!
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“The Different Types Of Plastics And Their Classifications.” How Stuff Works – Science. Quality Logo Products, <https://www.qualitylogoproducts.com/lib/different-types-of-plastic.htm>.
Strickland, Jonathan. “Are some things we recycle better off in landfill.” How Stuff Works – Science. <http://science.howstuffworks.com/environmental/green-science/recycle-better-in-landfill.htm>.
“Plastics Additives.” British Plastics Federation. <http://www.bpf.co.uk/plastipedia/additives/default.aspx>.
Clark Howard, Brian. “Recycling Symbols on Plastics – What Do Recycling Codes on Plastics Mean”. The Daily Green (Good Housekeeping).