Ethan Clarke
Plastic is everywhere, from food containers to clothing, and it's important to understand the different types and their potential impact on our health and the environment. The easiest way to identify the type of plastic is by locating the recycling symbol, which usually consists of three arrows forming a triangle with a number in the middle, known as the Resin Identification Code (RIC). This international coding system provides information about the chemical makeup and recyclability of the plastic item. However, it's important to note that the presence of a code does not guarantee recyclability, and it also does not indicate the toxicity or safety of the plastic. To further identify the type of plastic, one can also consider its density, appearance, and other physical characteristics.
| Characteristics | Values |
|---|---|
| Plastic Identification | Look for the Resin Identification Code (RIC), a symbol of three arrows forming a triangle with a number in the middle, usually at the bottom of the container. |
| Number 1 | Polyester and PET plastics. Includes plastic bottles, clothing, and insulation. |
| Number 2 | High-Density Polyethylene (HDPE). Strong and resistant to acidic chemicals. Includes bleach bottles, fuel tanks, and storage containers. |
| Number 3 | PVC (Polyvinyl Chloride). Can be rigid or flexible. Includes door and window frames, sporting balls, and electrical wire insulation. |
| Number 4 | Low-Density Polyethylene (LDPE). Flexible and shape-retaining. Includes grocery bags, shrink wrap, and cartons. |
| Number 5 | Polypropylene. Tough and flexible, resistant to acids and solvents. |
| Number 6 | Polystyrene (PS). Stiff, rigid, and clear. Includes CD cases, pens, and kitchen appliances. |
| Number 7 | Acrylic, Nylon, Polycarbonate, and other mixed plastics. Often non-recyclable. |
| Density | Float test to determine density and identify plastic types. |
| Texture | PE feels smooth, soft, and tough. MDPE and HDPE are hard and rigid. PP feels smooth and is bendable. |
| Appearance | LDPE is thin and crumbles easily. HDPE is tougher and harder to deform. PVC is yellowish and translucent. |
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What You'll Learn
Look for a recycling symbol, usually on the bottom of the container
The most common and simplest method to identify the type of plastic used in a container is to look for a recycling symbol, usually on the bottom of the container. This symbol typically consists of three arrows forming a triangle with a number in the middle, ranging from one to seven. Known as the Resin Identification Code (RIC), these international codes offer clarity on plastic identification based on chemical makeup and recycling potential.
The RIC system was developed in 1988 by the U.S.-based Society of the Plastics Industry to facilitate the recycling of post-consumer plastics. It is not mandatory for manufacturers, but it has become a standard practice for many plastic products sold globally. It's important to note that the presence of a code does not guarantee recyclability. The code simply identifies the type of plastic resin, and plastic manufacturers are not required to disclose additional chemicals added to the plastic polymer.
Here's what each of the numbers means:
- Polyester and PET plastics, including plastic bottles, clothing, and insulation materials. PET plastics are clear, lightweight, strong, and have high impact and chemical resistance.
- High-Density Polyethylene (HDPE), which is strong and resistant to acidic chemicals. This category includes bleach bottles, fuel tanks, and motor oil containers.
- PVC, which can be both rigid and flexible. PVC is used in door and window frames, sporting balls, water pipes, and electrical wire insulation.
- Low-Density Polyethylene (LDPE), which is flexible and can change shape without damage. LDPE is commonly found in grocery bags, shrink wrap, and juice and milk cartons.
- Polypropylene, a tough and flexible plastic that can resist most acids and solvents.
- Polystyrene, a stiff, rigid, and clear plastic. Polystyrene is used in CD cases, ballpoint pens, kitchen appliances, and electronics casings.
- Other plastic types, including acrylic, nylon, and polycarbonate. Most plastics in this category are not recyclable and are combined with other polymers.
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Identify the plastic by its density, using the floating method
One way to identify the type of plastic used in a container is by its density, using the floating method. This method involves placing the plastic in water and observing whether it sinks or floats. The buoyancy of the plastic will indicate its density in relation to water.
Density is a property of a substance that relates to how heavy it is relative to its size. If a substance is denser than water, it will sink when placed in water, and if it is less dense than water, it will float. This characteristic is independent of the amount of the substance. For example, a large ball of clay will sink in water because clay is denser than water, regardless of the size of the clay ball.
The floating method can be used to test the density of various plastics. For instance, low-density polyethylene and polystyrene products will float in water due to their lower density. On the other hand, polyethylenes, polypropylene, and polyvinyl chloride are denser than water and will sink when placed in it.
It is important to note that the appearance and texture of plastics can also provide clues about their type. Polyethylene, for example, has a smooth texture and is flexible, while low-density polyethylene is thin and crumbly. Additionally, manufacturers often include symbols or Resin Identification Codes (RICs) on plastic containers to facilitate identification. These symbols typically consist of a triangle of three arrows with a number in the centre, which corresponds to a specific type of plastic.
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Identify the plastic by its appearance
The appearance of plastic can be a good indicator of its type. However, it is important to note that some types of plastics may have similar appearances, so other tests may be required for definitive identification.
One of the most common types of plastic is polyethylene, which has two main varieties: Low-Density Polyethylene (LDPE) and High-Density Polyethylene (HDPE). LDPE is thin and flexible, often used in plastic bags, and can be identified by its translucent, waxy appearance. On the other hand, HDPE is tougher and more rigid, commonly found in containers like juice or shampoo bottles, and usually has a milky white or waxy appearance.
Polypropylene (PP) is another type of plastic that is bendable and challenging to break. It is often used for product containers due to its resistance to fatigue. Polypropylene typically has a smooth, waxy, and translucent appearance, and it is white when uncolored.
PVC, or Polyvinyl Chloride, is a hazardous type of plastic that was once commonly used. It has a soft, sticky texture and a yellowish, translucent, and glossy appearance.
Polystyrene is a well-known type of plastic that is easily recognisable by its brittleness and tendency to break easily. It often has a cloudy, translucent appearance.
ABS, or Acrylonitrile Butadiene Styrene, is a hard, rigid, and durable plastic used in products like appliance casings and suitcases. It typically appears milky white or beige, with an opaque and dull finish.
Another way to identify plastics by appearance is to observe whether they float or sink in water. Polyolefins, which include LDPE, HDPE, and Polypropylene, generally float, while other types of plastics tend to sink.
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Identify the plastic by its feel
One way to identify plastic is by the number inside the recycling symbol, which denotes the type of plastic. However, another easy method to identify plastics is through appearance and feeling the material in your hands.
PE, or polyethylene, feels smooth, soft and tough, is extensible and bendable, and has obvious marks when scratched. MDPE and HDPE are hard and possess great rigidity and toughness. The appearance is milky white, translucent and waxy when uncolored. LDPE, or low-density polyethylene, feels soft and smooth. It is flexible and can change its shape without damage. PP, or polypropylene, feels smooth, without marks when scratched. It is bendable, tough, and not easy to break. When uncolored, the appearance is white, waxy and translucent.
PS, or polystyrene, feels smooth, is brittle and easy to break. It is impact-resistant and dull, and sinks in water. It has a metallic sound when flicked with a fingernail. Pure PS is a transparent plastic. PVC, or polyvinyl chloride, feels soft, and the product is tough and feels sticky. The hardness of a hard product is higher than that of LDPE, but lower than polypropylene. Bending marks tend to occur. The appearance is yellowish, translucent and glossy. The transparency is higher than that of polyethylene and polypropylene, but lower than that of polystyrene.
ABS is an engineering plastic that is ivory yellow and opaque. It has a rough texture and poor gloss. POM is a very rigid engineering plastic, similar to metals, and has a greasy feeling when touched.
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Identify the plastic by its chemical reaction to heat
Different types of plastics exhibit distinct combustion characteristics when exposed to heat. This can be leveraged to identify the type of plastic based on its behaviour during combustion.
Thermoplastic materials, for instance, soften when heated, melt easily, and become transparent when molten. They can be easily drawn into threads from the melt and typically leave a unique smell. Thermoplastics also swell when exposed to solvents but generally do not dissolve in cold solvents. On the other hand, thermosetting plastics, when heated to just below the point of chemical decomposition, maintain their original hardness and do not soften. They are dimensionally stable and only carbonize at decomposition temperatures. Elastomers, meanwhile, do not flow until they reach the temperature of chemical decomposition, at which point they decompose and carbonize.
The pyrolysis test is another method of identification that involves heating the plastic to its pyrolysis temperature and then using litmus paper or pH test paper to test the pH of the evolved gases.
The combustion method, however, is primarily based on the ease of burning, odour, flame characteristics, and changes in the state of the plastic during combustion. For instance, polystyrene is highly flammable and produces a strong odour of burnt styrene that lingers even after the fire is extinguished. Polyvinyl is non-flammable and produces an irritating chlorine smell when heated.
It is important to note that these tests should only be used for tentative identification as some complex plastic compounds require rigorous analysis for accurate identification. Additionally, burning plastic can be harmful to both health and the environment, so it is recommended to use other methods of identification whenever possible.
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Frequently asked questions
The simplest way to identify the type of plastic is by locating a symbol of three arrows forming a triangle with a number in the middle. This is known as the Resin Identification Code (RIC). Each number coincides with a certain plastic. For example, Symbol 1 refers to polyester and PET plastics, while Symbol 2 covers High-Density Polyethylene.
The RIC ranges from 1 to 7, with each number representing a different type of plastic. For instance, plastic #1 or PET plastic is one of the most commonly used thermoplastic polymer resins, often used in water bottles, food containers, and clothing fibres. Plastic #2 can be easily recycled up to 10 times, while plastic #3 or PVC is known to be dangerous and difficult to recycle.
Yes, another method is to distinguish plastics based on their density or weight. The floating method involves placing the plastic in water to observe its buoyancy. For example, low-density polyethylene can remain above water. Additionally, plastics can be identified by their appearance, texture, and flexibility.
Some common plastics include PET (polyethylene terephthalate), HDPE (high-density polyethylene), LDPE (low-density polyethylene), and PP (polypropylene). PET is often used in food and beverage packaging due to its strength and ability to create a liquid and gas barrier. HDPE is known for its strength and resistance to chemicals, making it suitable for bleach bottles and fuel tanks. LDPE is squeezable and malleable, commonly used for droppers and dispensing applications like honey and shampoo. PP is versatile, featuring excellent chemical resistance and impact resistance, making it suitable for various industries.
