Chloe Zhang
Plastic is everywhere, but it's not all the same. There are several ways to identify different types of plastic, such as the float test, burn test, or simply looking for the plastic identification code. For example, a blue flame with yellow tips indicates burning polyethylene, while PVC produces a yellow flame with green tips. However, burning plastic is not recommended due to the release of harmful chemicals. PVC, or Polyvinyl Chloride, is a hazardous plastic known to cause various health issues, including cancer and birth defects. Polyethylene, on the other hand, is a common type of plastic with high flexibility and resistance to chemicals. It is often used in textiles and food storage.
| Characteristics | Values |
|---|---|
| Identification code | Polyethylene is identified by the number 2, 4, or 5, while PVC is identified by the number 3. |
| Float test | Polyolefins, including polyethylene, generally float in water, while other plastics generally sink. |
| Burn test | Polyethylene burns with a blue flame and yellow tips, while PVC burns with yellow flames and green tips. |
| Smoke test | PVC smoke should not be smelled, but other plastics may be identified by carefully wafting smoke towards the nose. For example, PET smells like burnt sugar. |
| Flexibility | Low-density polyethylene is flexible and can change shape without damage, while PVC comes in both rigid and flexible forms. |
| Applications | Polyethylene is used in plumbing pipes, electrical insulation, and upholstery coverings. PVC is used in sneakers, soles of shoes, windows and doors, and plumbing pipes. |
| Health effects | PVC is one of the most hazardous plastics and can cause cancer, birth defects, genetic changes, and other health issues. |
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Float test
The float test is a simple way to help identify different types of plastics. It is based on the fact that plastics have different densities, which determine whether they float or sink in water. While it is a good test for ruling out certain plastics, it is difficult to use it to specifically identify a plastic.
The polyolefins, which include high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP), generally float in water. So, if a piece of plastic floats, it is likely one of these three types. On the other hand, plastics with a higher density, such as PET (polyethylene terephthalate), PVC (polyvinyl chloride), and PS (polystyrene), tend to sink.
To perform the float test, you can cut or break off a small piece of the plastic you want to identify. Place the piece of plastic in a container of water and observe whether it floats or sinks. For example, if you try this with a milk bottle made of HDPE, it will float, while a piece from a single-use plastic drink bottle made of PET will sink.
It is important to note that the density of plastics can vary during manufacturing, resulting in a range of values for each type of plastic. Therefore, while the float test can provide a general indication, it may not always give a definitive answer. Additionally, the float test should be used with caution, as it may not be safe for certain types of plastics or applications, especially if the plastic has come into contact with toxic substances.
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Burn test
The float test and burn test are traditional methods used to identify plastics. While these tests are good for ruling out certain plastics, they are not very effective in specifically identifying a plastic.
The burn test is performed as follows:
- First, ensure that you are wearing the proper safety equipment, including safety goggles, a lab coat, and gloves.
- Using a pair of scissors, cut a small piece of the plastic you want to identify. Make sure the piece is small enough to melt quickly.
- Hold the plastic sample with a pair of tongs or heat-resistant gloves and ignite it with a burner.
- Observe the colour and behaviour of the flame. Different plastics will produce different flame colours and behaviours. For example, PVC (polyvinyl chloride) typically produces a yellow flame with green hues and emits a chlorine-like odour.
- Note the behaviour of the plastic after it has been burned. Some plastics may self-extinguish, while others may continue to burn.
- Examine the residue left after the burn test. The type of ash and the presence of any unburned plastic can provide additional clues about the plastic's identity.
It is important to perform the burn test in a well-ventilated area or under a fume hood to ensure the safe disposal of any harmful gases produced during the test. Additionally, it is recommended to have a fire extinguisher or a bucket of water nearby in case of any accidental fires.
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International recycling codes
Recycling codes are used to identify the materials used in an item's manufacture, facilitating a more efficient recycling process. The presence of a recycling code, chasing arrows logo, or resin code does not guarantee recyclability; it merely explains the item's composition. Codes have been developed for batteries, biomatter/organic material, glass, metals, paper, and plastics.
Different countries have adopted different recycling codes. For example, China has a polymer identification system with seven plastic classifications, five post-consumer path symbols, and 140 identification codes. In contrast, the United States has fewer codes, grouping ABS with "others" in group seven.
The Standardization Administration of the People's Republic of China (SAC) has defined material codes for plastics consistent with RIC up to #6. ASTM International has replaced the three-arrow symbol with a solid, equilateral triangle for resin codes, clarifying that the code identifies the resin rather than recyclability.
To identify PVC and polyethylene, you can perform a float test or burn test, though these methods may not always provide specific identification. PVC, or polyvinyl chloride, is used in garden hosepipes and household plumbing pipes but is falling out of favour due to health concerns. Polyethylene, specifically low-density polyethylene (LDPE), is one of the polyolefins that generally float in water.
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Appearance and feel
Polyethylene is flexible and soft to the touch, and it crinkles, making a crackling sound. It usually appears translucent or opaque and has a waxy surface. It is also possible to identify polyethylene by its density in water—it floats. Polyethylene is the second most common plastic and is used in shopping bags, beverage bottles, and water pipes.
Polypropylene is stiffer and harder than polyethylene, making it suitable for automotive components and textiles. It is bendable but does not break easily. It has a high melting point, which contributes to its strength and chemical resistance. Polypropylene tends to be more opaque with a waxy surface. It sinks in water. Polypropylene is generally safer and is often used for food packaging and medical supplies.
PVC (Polyvinyl Chloride) products feel soft, tough, and sometimes sticky. They are flexible and have higher transparency than other plastics, with a glossy texture and a yellowish appearance. PVC is one of the most hazardous plastics and is used in toys, blood bags, detergent bottles, and plumbing pipes.
Polystyrene is smooth, brittle, and easy to break. It is impact-resistant and has a transparent appearance that resembles uncolored glass. It sinks in water and is commonly used for stationery, cups, food containers, and kitchen appliances.
It is important to note that burning plastic is harmful to health and the environment and is not recommended as a method of identification.
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Use case
Plastic is everywhere in our daily lives, but it's important to be able to identify different types of plastic to understand their use cases and potential health and environmental impacts.
Polyvinyl Chloride (PVC) is one of the most common types of plastic and is used in a wide range of applications, from construction to clothing. PVC is known for its durability and flexibility, making it ideal for products such as plumbing pipes, electrical insulation, window frames, and even footwear. However, PVC is also one of the most hazardous kinds of plastic, with potential health risks including cancer, birth defects, and respiratory issues when burned in the open air.
High-Density Polyethylene (HDPE) is another commonly used plastic, known for its strength and resistance to chemicals. HDPE is often used for containers that require strong and durable packaging, such as fuel tanks, bleach bottles, and shampoo containers. It is also one of the polyolefins, which generally float in water, making it easily identifiable.
Low-Density Polyethylene (LDPE) is a branch of the polyethylene family, known for its flexibility and ability to change shape without damage. LDPE is commonly used in packaging, especially for food and liquids, due to its wrinkle-free and durable nature. It is also a polyolefin and will float in water.
To identify these types of plastic, there are a few simple tests that can be performed. The float test is a good indicator, as polyolefins like HDPE and LDPE will float, while PVC will generally sink. Additionally, the burn test can be used, where a blue flame with yellow tips indicates burning polyethylene, and yellow flames with green tips point towards PVC. However, it is important to note that burning plastic is harmful to health and the environment, and there are other identification methods that can be used, such as locating the international recycling codes, which are usually embossed on plastic products.
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Frequently asked questions
The easiest way to identify plastic is by locating three arrows forming a triangle with a specific number in the middle. These international codes offer clarity based on chemical makeup and recycling grading. For example, Symbol 1 is for polyester and PET plastics, while Symbol 2 is for High-Density Polyethylene.
A blue flame with yellow tips indicates burning Polyethylene, while PVC plastic produces yellow flames with green tips. However, it is advised against using this method due to the harmful health and environmental impacts of burning plastic.
The float test is a simple way to rule out certain plastics. Generally, polyolefins, including High-Density Polyethylene (HDPE) and Low-Density Polyethylene (LDPE), float in water, while other plastics tend to sink.
PVC, or Polyvinyl Chloride, is used in plumbing pipes, electrical insulation, footwear, and window frames. Polyethylene, on the other hand, is commonly used in food storage, textiles, and electrical insulation.
