Maya Ellison
Plastic is everywhere, from water bottles to spacecraft, and it's essential to recycle it properly to protect the planet. There are seven types of plastic, and they differ in chemical structure, appearance, and feel. Some are reusable, while others are toxic and require special disposal methods. To identify a plastic type, you can use the Resin Identification Code (RIC) system, which categorises plastic resins by number. You can also use the float test, burn test, or smell the plastic to identify it. Knowing the differences between plastic types helps consumers make informed decisions about the products they buy.
| Characteristics | Values |
|---|---|
| Appearance | Different colours, shapes, and textures |
| Chemical makeup | Different plastics have different chemical structures |
| Compliance | Some plastics comply with laws and restrictions |
| Density | Different plastics have different densities |
| Reaction to heat | Some plastics react to heat by changing appearance and smell |
| Recyclability | Some plastics are easier to recycle than others |
| Safety | Some plastics are toxic and hazardous |
| Buoyancy | Some plastics float, others sink |
| Flammability | Some plastics burn and produce smoke and soot |
| Smell | Different plastics have different smells when burnt |
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What You'll Learn
Look for the Resin Identification Code (RIC)
The Resin Identification Code (RIC) was developed in 1988 by the Plastics Industry Association to help workers in the plastic and recycling industries sort and recycle plastics more efficiently. The RIC is a numbered system that divides plastic resins into seven different categories, with each number corresponding to a specific type of resin.
The seven categories of the RIC are:
- Polyethylene terephthalate (PET): This type of plastic is known for being strong and lightweight, with high impact and chemical resistance. It is commonly used for food and drink packaging, as well as for personal care products such as shampoos, lotions, and other containers.
- High-Density Polyethylene (HDPE): HDPE is a strong and versatile plastic with good impact and chemical resistance. It is commonly used for liquid products in the food, chemical, and pharmaceutical industries, as well as for grocery bags, milk jugs, and recycling bins.
- Polyvinyl chloride (PVC): PVC is a versatile and flexible plastic that can be used for a variety of applications, including pipes, hoses, window frames, and flooring. It is the third most widely produced synthetic plastic polymer.
- Low-density polyethylene (LDPE): LDPE is a soft and flexible plastic commonly used for plastic bags, wraps, films, and containers. It has a simple structure, making it easy and cheap to produce.
- Polypropylene (PP): Polypropylene is a tough, heat-resistant plastic that is used for yogurt cups, margarine tubs, microwaveable containers, and automotive parts, among other things. It is the second most widely produced commodity plastic.
- Polystyrene (PS): Polystyrene is a hard and brittle plastic that is commonly used for disposable cups, plates, cutlery, egg cartons, and packing materials. It is also known by its commercial name, Styrofoam.
- Other: This category includes plastics that do not fit into the previous six categories, such as those made from multiple resins or newer, less common resins. These plastics may have different properties and uses depending on their composition.
The RIC is typically found on the bottom of plastic products and is surrounded by three arrows forming a triangle. While the RIC provides valuable information for the recycling industry, it can be challenging for consumers to understand. As a result, organisations like the Sustainable Packaging Coalition are advocating for a more consumer-friendly plastic recycling code system, such as the How2Recycle system, which provides clearer instructions on how to treat and recycle specific plastic items.
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Test density with the float test
One way to identify the type of plastic is to test its density with the float test. This test involves putting a sample of the plastic in water and observing its buoyancy. If the plastic floats, it has a lower density than water, and if it sinks, it has a higher density.
The float test can help distinguish between different types of plastics. For example, high-density plastics such as PET (or PETE), PVC, and PS (polystyrene) sink in water. On the other hand, LDPE, HDPE, and PP are examples of plastics with lower densities that float.
It is important to note that the density of plastics can vary during manufacturing, so there may be a range of density values for each type of plastic. Additionally, some plastics with the same density may be challenging to distinguish using only the float test, as they may have similar floating behaviour.
When performing the float test, it is essential to take safety precautions and avoid exposure to harmful chemicals that may be present in the plastic. It is also suggested to use this test in conjunction with other identification methods, such as observing the appearance and feel of the plastic, as well as checking for codes or labels that may indicate the specific type of plastic.
By understanding the density of plastics through the float test and combining it with other identification methods, individuals can make more informed decisions about plastic usage and recycling, contributing to the well-being of the planet.
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Identify by appearance and feel
One of the easiest ways to identify plastics is through their appearance and how they feel to the touch. LDPE (low-density polyethylene) is thin and flexible enough to be crumpled in the palm of your hand. It also makes a loud crackling noise when handled. LDPE has a soft and smooth texture, like a sandwich bag. It produces a soft swishing sound when rubbed together, unlike the harsher, crinklier sound of HDPE.
HDPE (high-density polyethylene) is tougher to deform and has a waxy appearance when uncoloured. It feels harder and crinklier than LDPE. Many plastic shopping bags are made from HDPE. PP (polypropylene) is used for food packaging and feels much firmer and stiffer than polyethylene. It does not stretch and will rip and tear when pressure is applied.
Polyvinyl chloride products feel soft, tough, and sometimes sticky. They have a glossy texture and often appear yellowish. Polystyrene is brittle and can be broken with little force. It is used for mass-produced disposable containers, lab bottles, and cutlery.
Another way to distinguish plastics is by their density. The floating test can be used to determine the weight of plastics by observing their buoyancy in water.
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Burn a sample and observe
Burning a sample of plastic and observing its reaction can help identify the type of plastic. This process, known as the burn test, is a fundamental method for distinguishing different plastics through their distinct combustion properties. While it does not provide conclusive identification, it offers initial information about the material. Here's a step-by-step guide to performing the burn test:
Prepare the Sample
Begin by heating a stirring rod, such as a metal or glass rod, to a temperature of approximately 500°F (260°C). This temperature is important, as it helps distinguish between thermoplastics and thermosets. Thermoplastics will generally soften and become pliable at this temperature, while thermosets will remain unchanged.
Apply Heat to the Sample
Once the rod is heated, press it against the plastic sample. If the sample softens, it is likely a thermoplastic. If it remains rigid, it may be a thermoset. To further confirm, hold the sample to a flame source, such as a lighter, torch, or bottled gas burner. Observe if the sample ignites immediately or takes a few seconds. Some plastics may require holding in the flame for about 10 seconds to ignite.
Observe the Combustion
As the sample burns, pay attention to the nature of the smoke and the presence of soot. Note whether the plastic drips during combustion. Thermoplastics, for example, tend to drip when heated due to their pliable nature. In contrast, thermosets typically maintain their form and do not drip.
Extinguish and Smell the Fumes
After extinguishing the flame, cautiously smell the resulting fumes. Different plastics produce unique odours when burned. For instance, PVC emits a sharp, acrid smell, while polyethylene releases a sweet and gentle odour. Comparison references can be helpful in determining the identity of the sample based on its odour.
Compare Observations
Finally, compare your observations with known characteristics of different plastics. While this test provides preliminary identification, it is not entirely reliable for complex plastic compounds. For conclusive identification, advanced techniques such as spectral analysis, infrared spectroscopy, or pyrolysis-gas chromatography may be required.
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Check for international plastic identification codes
Plastic products often feature a Plastics Identification Code (PIC), also known as a Resin Identification Code (RIC). This is a classification system created by plastic manufacturers to identify the type of plastic used to make a product. The codes are usually found stamped or printed on the bottom of products and show a number from 1 to 7 inside a triangle with chasing arrows. PICs always appear inside a triangle.
The RIC was developed in 1988 by the Society of the Plastics Industry (now the Plastics Industry Association) in the United States. Since 2008, it has been administered by ASTM International, an international standards organisation. The RIC was originally created to "provide a consistent national system to facilitate recycling of post-consumer plastics". However, the presence of a RIC on a plastic product does not mean that the product is recyclable or that there are recycling systems in place to process it.
The different types of plastics identified by the RIC include:
- Code 1: Polyethylene terephthalate (PET), a widely recycled plastic that is lightweight, cheap to produce, and commonly used in water and drinks bottles, as well as packaging for cooking oil.
- Code 2: High-density polyethylene (HDPE), another widely recycled plastic that is durable and hard, and commonly used for cleaning or personal care products.
- Code 3: Materials that are not often recycled and are rarely used with food products because they release toxins. They are commonly used to make pipes, detergent bottles, medical equipment, and shoe soles.
- Code 4: Low-density polyethylene (LDPE), a very flexible plastic with great sealing properties, commonly used in the food industry.
- Code 5: Polypropylene (PP), a durable plastic with many uses, including food packaging and fibres for clothing and upholstery.
- Code 6: Polystyrene (PS) or styrofoam, which is hard to recycle and has been known to leach chemicals when heated. It is commonly used in food trays, household appliance packaging, and cups for hot drinks.
- Code 7: A wide variety of plastics that are very difficult to recycle, commonly found in sunglasses, DVDs, water bottles, and food packaging.
It is important to note that the RIC only identifies the type of resin used in a plastic product and does not indicate its recyclability. The recyclability of a plastic product depends on various factors, including local recycling facilities and programs. Consumers should check with their local facilities to determine which plastics can be accepted for recycling.
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Frequently asked questions
By locating three arrows forming a triangle with a specific number in the middle. These international codes offer clarity on plastic identification based on chemical makeup and the grading for recycling. For example, Symbol 1 is for polyester and PET plastics, and Symbol 2 is for High-Density Polyethylene.
The floating method can be used to test the weight of plastics by observing their buoyancy in water. Different types of plastics have varying densities, and this test helps distinguish them.
Low-density polyethylene and polystyrene products will remain above water, whereas polyethylenes, polypropylene, and polyvinyl chloride will sink.
A burn test can be used to determine whether a material is thermoset or thermoplastic. Heat a stirring rod to about 500°F/260°C; if the material is a thermoplastic, it will melt. If not, it is likely a thermoset. Caution: Always perform such tests in a well-ventilated area.
Observe the nature of the smoke, the presence of soot, and if the sample drips. Then, extinguish the flame and cautiously smell the fumes. Different plastics have distinct odours. For example, PET smells like burnt sugar, while PVC has an acrid, chlorine-like odour.
