Sofia Martinez
Plastic is everywhere, from water bottles to shopping bags, and it's essential to know what type of plastic you're dealing with for recycling and safety purposes. Each type of plastic has unique characteristics, such as flexibility or durability, that make it suitable for specific uses. For instance, some plastics are safe for food contact, while others may contain toxic chemicals. There are several methods to identify plastics, including international codes based on chemical composition, visual symbols like the three arrows forming a triangle, and even sound and float tests. Knowing how to identify different types of plastics empowers individuals to make informed decisions about their health and the environment.
| Characteristics | Values |
|---|---|
| Identification | Locating three arrows forming a triangle with a specific number in the middle |
| Float test | Nylon sinks, Polyolefins float |
| Burn test | Polyolefins and nylon produce a blue flame with a yellow tip |
| Sound | LDPE makes a soft, swishing sound; HDPE makes a crisper, crinklier sound |
| Feel | PP (polypropylene) feels firm and stiff but does not stretch |
| Heat resistance | Styrofoam is stiff and works well against heat |
| Toxicity | Polycarbonate (PC) contains traces of Bisphenol A (BPA) and is very toxic |
| Common uses | Polyester and PET plastics are commonly found in clothing, plastic bottles, and insulation |
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What You'll Learn
Float test and burn test
One way to identify the type of plastic is by performing a float test. Plastics all have a particular density, and not all plastics float on water. If the density of the material is greater than water, it will sink, and if it is less dense, it will float. For example, plastics such as PET (polyethylene terephthalate), PVC (polyvinyl chloride), and PS (polystyrene) sink in water. On the other hand, HDPE, LDPE, and PP float.
Another method to identify the type of plastic is by performing a burn test. It is important to note that this test should be performed in an industrial setting with the correct equipment as some burning plastics can release carcinogens. Heat the plastic with a lighter until it burns, ensuring proper ventilation. Different plastics will have distinct burning behaviours and smells. For example, nylon will smell like burnt wool, have a flame that is blue with a yellow tip, and will not continue to burn when the flame source is removed.
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Chemical makeup and SPI codes
The Society of the Plastics Industry (SPI) created the Resin Identification Code (RIC) system in 1988 to help sorting line workers identify post-consumer packaging types using the six basic packaging resin classes. The SPI code segments the different plastics on the market based on their materials and how they should be recycled. Polyethylene terephthalate (PETE or PET), for example, is a common plastic material used for water bottles and jars for kitchen goods. When recycled, it's used to make textiles and fabrics. High-density polyethylene (HDPE) plastic is safe and doesn't give off harmful chemicals. It's often used for containers for shampoo, detergents, and motor oil, and when recycled, it can be used for plastic lumber, fencing, or bathroom partitions. Polyvinyl chloride (PVC) is primarily used for pipes and tiles. Polystyrene (Styrofoam) is difficult to recycle efficiently, requiring a lot of energy. Recycled Styrofoam can be used for insulation, license plate frames, and rulers.
SPI Code 7 materials include plastics that don't fall into the previous six categories, such as polycarbonates and polylactides, which are challenging to recycle. These materials are often seen as compact discs, storage containers, and baby bottles. The "How2Recycle" labels indicate the recyclability of a plastic product: "Widely Recycled" means more than 60% of the US can recycle it; "Limited" means 20-60% can recycle it; "Not Yet Recycled" means less than 20% can recycle it; and "Store Drop-Off" means it can be recycled at participating stores.
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Sound and feel
When it comes to sound, LDPE and HDPE plastics tend to make a crinkling, harsher sound, whereas LDPE rubbed together will make a soft swishing sound. Polypropylene (PP) sounds similar to HDPE and is crinkly. LDPE is often used for sandwich bags, and PP is used for food packaging like chocolate wrappers.
PVC, or Polyvinyl Chloride, is one of the more hazardous plastics and has an acrid smell, similar to chlorine. LDPE and HDPE smell like candle wax, while polypropylene has a similar scent but with a hint of paraffin. ABS and polystyrene smell like styrene, and ABS also has a faint rubbery scent.
The density of plastics also helps distinguish them. Polyvinyl Chloride, for example, is heavy and will sink in water. LDPE, on the other hand, can remain above water.
In terms of feel, LDPE feels soft and smooth, like a sandwich bag. Polypropylene feels much firmer and stiffer, and it does not stretch. If pulled, it will simply rip and tear. Polyvinyl Chloride products feel soft, tough, and sometimes sticky. They have a glossy texture and often appear yellowish.
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Flame colour
The colour of a flame when a plastic is burned can be used to identify the type of plastic. This is a common process in recycling companies to identify different types of polymers in a shipment. The flame colour, as well as the smoke odour, can be used to distinguish the type of plastic.
For example, when Polyethylene (PE) is burned, the upper end of the flame is slightly yellow, and the lower end is blue. Polypropylene (PP) also burns with a yellow and blue flame, but the upper end is yellow, and there is dripping. Polyvinyl is non-flammable, but when heated, it releases an irritating stench of chlorine. Polystyrene (PS) is highly flammable and produces a strong burnt styrene smell. When Polyvinyl Chloride (PVC) is burned, the upper part of the flame is yellow, the lower part is green, and it emits black smoke. Polyurethane (PU) has a yellow flame with smoke and a slight flower and fruit odour.
Other plastics have distinct flame colours and odours, such as SAN, which burns with a yellow flame and black smoke, and POM, which has a pure blue flame and a pungent formaldehyde smell.
It is important to note that burning plastics can release toxic chemicals, so caution should be exercised when performing any tests involving flames.
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Symbols and triangle markings
Plastic products often have a triangle with a number inside, ranging from 1 to 7. These symbols are part of the Resin Identification Coding system, implemented by the Society of the Plastics Industry in 1988. The triangle symbols are meant to indicate the type of plastic used in the product, and how the containers may be used for recycling.
Symbol 1 with the acronym PETE or PETG plastic, also known as polyethylene terephthalate, is represented by a triangle with the number one inside. This plastic is commonly used for soft drink bottles, mineral water containers, fruit juice containers, and cooking oil containers. It is easily recyclable and is often part of curbside recycling programs. Recycled PETE can be reused to make new containers, carpets, and furniture.
Symbol 2 stands for HDPE or high-density polyethylene. This is a commonly used plastic in the United States and is often used for containers for cleaning agents, milk, detergents, and washing soap. It is also used for butter/yogurt containers, milk jugs, and juice bottles.
Symbol 3 with the letter "V" represents PVC or polyvinyl chloride. PVC is used in bubble foils, trays for sweets and fruit, and expanded PVC foam boards for commercial applications. PVC is rarely recycled and is not usually part of curbside recycling programs. However, in rare instances, it can be recycled for speed bumps, roadway gutters, and cables.
Symbol 4 stands for LDPE or low-density polyethylene. LDPE is commonly found in shopping bags, highly resistant sacks, crushed bottles, and soft plastics like cling film. LDPE is not usually recycled through curbside programs but can be converted into floor tiles, shipping envelopes, compost bins, paneling, trash can liners, and decking.
Symbol 5 stands for PP or polypropylene. This plastic is known for its durability, strength, and low weight. PP is used in furniture, luggage, toys, car parts, bottle tops, kitchen containers, straws, carpets, rope, and medicine and ketchup bottles. It is increasingly being accepted in curbside recycling programs.
Symbol 6 stands for PS or polystyrene. This plastic is commonly found in toys, hard packing, refrigerator trays, cosmetic bags, CD cases, vending cups, disposable cups, meat trays, and packaging for electronics. Polystyrene is not widely accepted in curbside recycling programs but can be recycled to make egg cartons, takeout containers, and rulers.
Symbol 7 is a miscellaneous category that includes "other plastics" that do not fall into the previous categories. This can include acrylic plastic, polycarbonate plastic, polylactic fibers, nylon, fiberglass, polyurethane, and polyvinyl chloride. Code 7 plastics are rarely recycled and are often burned instead.
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Frequently asked questions
LDPE plastic bags make a soft, swishing sound when crinkled, whereas HDPE plastic bags make a crisper, crinklier sound.
PVC items can be identified by a flame test, which will produce a yellow flame with a green tip. PVC is also a hard, stiff plastic that can be both rigid and flexible. It is used for door and window frames, sporting balls, and electrical wire insulation.
LDPE is flexible and can change its shape without damage. It is commonly used for grocery bags, shrink wrap, and juice and milk cartons.
Styrofoam, or polystyrene, is a common plastic used for food and drink packaging. It is stiff, heat-resistant, and often used for food containers, egg cartons, and disposable cups.
