Maya Ellison
Plastic hardware encompasses a wide range of products, from buckles and rings to computer components and industrial cases. With so many varieties of plastic available, each with unique properties, identifying an unknown plastic item can be challenging. However, several methods can assist in determining the type of plastic, such as examining its appearance characteristics (e.g., colour, transparency, and hardness), referring to recycling symbols, observing its behaviour in different solutions, and applying heat to observe its response. These techniques can help distinguish between commonly used plastics like polyethylene, polypropylene, polycarbonate, PVC, and acrylic, each of which has distinct features and applications.
| Characteristics | Values |
|---|---|
| Identification | Refer to recycling symbols, usually found at the bottom of the container |
| Identify by appearance characteristics such as shape, transparency, colour, gloss, hardness, and elasticity | |
| Polypropylene (PP) is white, semi-transparent, waxy, and smooth to the touch | |
| Polymethyl Methacrylate (PMMA) looks like clear glass, can be bent when heated, is hard and not easily shattered | |
| Polycarbonate is transparent, stable, tough, and 250 times stronger than glass | |
| Polyethylene can be manufactured in varying densities, resulting in unique physical properties | |
| Acrylic is a lightweight, shatter-resistant alternative to glass, and can be made in different colours and with different properties | |
| PVC can be made rigid or flexible, and is often used in construction materials, bottles, and clothing | |
| Polypropylene (PP) is stronger and more flexible than PE | |
| PET is shatterproof and has a high strength-to-weight ratio | |
| Thermoplastic materials soften when heated, melt easily, and become transparent when molten | |
| Thermosetting plastics do not dissolve in solvents and typically do not swell | |
| Uses | Apparel, bags, backpacks, organisation, high-security environments, laboratory equipment, automotive parts, medical devices, food containers, optical devices, DVDs, sunglasses, riot gear, kiosks, store displays, plumbing products, electrical cable insulation, and more |
| Advantages | Less expensive, lightweight, rot and rust-resistant, durable |
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What You'll Learn
Check the recycling symbol
When it comes to recycling plastic, it is important to understand the different symbols and their respective meanings. This knowledge will enable you to effectively separate plastics according to their specific processing criteria. Different plastics have varying requirements, such as different melting temperatures, and they are ultimately recycled into distinct products.
The seven plastic recycling symbols, ranging from numbers one to seven, represent different types of plastic with unique recycling instructions. These symbols are known as the Resin Identification Coding system, implemented by the Society of the Plastics Industry in 1988. The number enclosed within the triangular "chasing arrows" symbol helps identify the type of plastic used, which, in turn, guides its appropriate disposal route.
- PETE/PET/PETG: This symbol stands for polyethylene terephthalate, a clear, strong, and lightweight plastic. It is commonly used for single-use food and drink packaging, like soda and water bottles, salad dressing bottles, and peanut butter containers. It is easily recyclable and often part of curbside recycling programs.
- HDPE: This acronym indicates high-density polyethylene, one of the most commonly used plastics in the United States. It is widely used for containers such as milk cartons, detergents, and cleaning agents due to its low weight and high strength. HDPE is easily recyclable and commonly accepted in curbside recycling.
- PVC: Polyvinyl chloride is represented by the number three and the letter "V". PVC is lightweight, rigid, and durable. It is commonly found in bubble foils, trays for sweets and fruit, and expanded PVC foam boards for commercial applications. PVC is rarely recycled and is typically not included in curbside recycling programs.
- LDPE: Low-density polyethylene, or LDPE, is denoted by the number four. It is used for shopping bags, highly-resistant sacks, and crushed bottles. LDPE is challenging to recycle at most facilities due to its flexibility and low weight. However, when recycled, it can be converted into floor tiles, shipping envelopes, and other products.
- PP: Polypropylene, or PP, is marked by the number five and the acronym PP. It is known for its durability, strength, and low weight, making it ideal for furniture, luggage, toys, and the automotive industry. PP is increasingly accepted in curbside recycling programs.
- PS: The number six symbol represents polystyrene, also known as styrene plastic.
- "Other": The number seven symbol is a miscellaneous category for plastics that don't fit into the previous six categories. This includes materials such as fiberglass, polycarbonate, plexiglass, nylon, and acrylic fabrics. Products under this category should not be disposed of curbside but may be accepted by drop-off centres or mail-in programs.
To ensure proper recycling, it is essential to check your municipality's recycling guidelines and confirm which symbols and plastics are accepted by your local waste hauler or recycling centre.
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Identify by touch and appearance
There are several ways to identify plastic types by touch and appearance. Firstly, different plastics have different colours, lustres, transparencies, and hardness, which can be used to distinguish them. For example, polypropylene (PP) is white and semi-transparent when uncoloured, with a waxy, smooth feel, while polyethylene (PE) is a white powder or transparent resin, with a wax-like texture that shows scratch marks. Nylon (PA) has a milky white, gel-like appearance, with a hard surface that feels warm to the touch. Polyvinyl Chloride (PVC) often appears yellowish and has a glossy texture.
Secondly, plastics can be differentiated by their density, as some are denser and sink in water, while others are less dense and float. For example, polyolefins generally float, while nylon (PA) sinks.
Thirdly, the appearance of plastics when heated can be indicative of their type. Thermoplastic materials soften and melt when heated, becoming transparent, while thermosetting plastics maintain their hardness and do not soften. When heated, different plastics can also produce distinct smells. For example, polyethylene and polypropylene smell like burning wax, while polyvinyl gives off an irritated smell of chlorine.
Lastly, the recycling symbols on plastics are a simple and effective way to identify them. These symbols are usually found at the bottom of containers and can accurately determine the specific type of plastic.
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Burn test
While burn tests can be useful for identifying unknown plastics, they should be performed with caution due to the toxicity of plastic combustion products. Before attempting a burn test, check for a label on the plastic item, as most plastic manufacturers use the SPI resin identification coding system to label their products.
If your plastic item doesn't have a label, you can try the burn test. First, heat a stirring rod to about 500°F/260°C. If the plastic melts, it's a thermoplastic; if it doesn't melt, it's probably a thermoset. Next, hold the sample to the edge of a flame until it ignites (if no flame is produced, hold the sample in the flame for about 10 seconds). Observe the nature of the smoke, the presence of soot, and whether the sample drips while burning.
After extinguishing the flame, cautiously smell the fumes and compare the odour with that of a known sample, if possible. Finally, check your observations against the known characteristics of each plastic. For example, PVC contains chlorine and will turn white when bent, whereas PET does not. Most plastics, except polyethylene and polypropylene, will become tacky when exposed to acetone.
It's important to note that some complex plastic compounds require rigorous analysis for accurate identification. Therefore, a burn test may only provide tentative results, and additional tests may be necessary to confirm the type of plastic.
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Float test
To identify an unknown plastic item, one of the tests you can perform is the float test. This test is based on the fact that plastics have different densities, which determine whether they float or sink when submerged in water.
The float test is simple and safe to perform at home. First, fill a container with water. Then, gently place the plastic item into the water and observe whether it floats or sinks. If the item floats, the plastic likely has a density lower than that of water. Conversely, if the item sinks, its density is higher than that of water.
It's important to note that not all plastics float on water. Only three commonly used plastics have densities lower than water, causing them to float: HDPE, LDPE, and PP. These plastics are often used in items like plastic bags, containers, and packaging.
On the other hand, plastics with higher densities, such as PET (or PETE, commonly used in drink bottles), PVC (used in construction, packaging, and medical tubing), and PS (used in disposable cups and food packaging), will sink in the float test.
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Apply heat
Applying heat is a common method used to identify plastics. One of the simplest methods is the float test, which involves placing the plastic in water to observe whether it floats or sinks. While there are exceptions, this test can help identify the type of plastic. For example, polypropylene, ABS, high-density polyethylene, and low-density polyethylene tend to float, while polycarbonate, PTFE, Polyester, and PVC tend to sink.
Another method is to heat a stirring rod to about 500°F/260°C. If the plastic melts, it is a thermoplastic; if not, it is likely a thermoset. Additionally, holding a plastic sample to a flame can provide further identification clues. Observe the nature of the smoke, the presence of soot, and whether the sample drips. After extinguishing the flame, cautiously smell the fumes to identify any distinctive odours. For example, PVC emits a distinct odour when heated.
It is important to note that these tests only provide tentative identification, and complex plastic compounds may require more rigorous analysis. Burn tests, colour-coding, and flexibility checks can also aid in identifying plastics. Consulting material data sheets and professionals in the field can provide valuable insights into plastic identification and ensure the selection of appropriate welding rods for specific plastics.
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Frequently asked questions
The six most commonly used types of plastics can be identified by their recycling symbols, which are usually found at the bottom of the container.
Different types of plastics have varying ranges of temperature tolerance, and their characteristics when heated also differ. By applying heat, we can discern the types of plastics. Thermoplastic materials, for example, soften when heated and melt easily.
Polypropylene (PP) is a widely used synthetic plastic that is strong, flexible, durable, heat resistant, acid resistant, and cheap. Polyethylene Terephthalate (PET) is another common plastic that is easily recyclable, practically shatterproof, and has a high strength-to-weight ratio.
Online retailers like Strapworks offer a wide range of plastic hardware, including buckles, rings, locks, adjusters, and slides in various shapes, sizes, colours, and styles.
